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| author | Franklin Schmidt <fschmidt@gmail.com> |
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| date | Fri, 17 Apr 2015 07:25:51 -0600 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/website/src/manual.html Fri Apr 17 07:25:51 2015 -0600 @@ -0,0 +1,10791 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<html> + +<head> +<title>Lua 5.3 Reference Manual</title> +<link rel="stylesheet" type="text/css" href="../../lua.css"> +<link rel="stylesheet" type="text/css" href="../manual.css"> +<META HTTP-EQUIV="content-type" CONTENT="text/html; charset=iso-8859-1"> +</head> + +<body> + +<hr> +<h1> +<a href="../../home.html"><img src="../../images/logo.gif" alt="" border="0"></a> +Lua 5.3 Reference Manual +</h1> + +by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes +<p> +<small> +Copyright © 2015 Lua.org, PUC-Rio. +Freely available under the terms of the +<a href="../../license.html">Lua license</a>. +</small> +<hr> +<p> + +<a href="contents.html#contents">contents</A> +· +<a href="contents.html#index">index</A> +· +<a href="../">other versions</A> + +<!-- ====================================================================== --> +<p> + +<!-- $Id: manual.of,v 1.146 2015/01/06 11:23:01 roberto Exp $ --> + + + + +<h1>1 – <a name="1">Introduction</a></h1> + +<p> +Lua is an extension programming language designed to support +general procedural programming with data description +facilities. +Lua also offers good support for object-oriented programming, +functional programming, and data-driven programming. +Lua is intended to be used as a powerful, lightweight, +embeddable scripting language for any program that needs one. +Lua is implemented as a library, written in <em>clean C</em>, +the common subset of Standard C and C++. + + +<p> +As an extension language, Lua has no notion of a "main" program: +it only works <em>embedded</em> in a host client, +called the <em>embedding program</em> or simply the <em>host</em>. +The host program can invoke functions to execute a piece of Lua code, +can write and read Lua variables, +and can register C functions to be called by Lua code. +Through the use of C functions, Lua can be augmented to cope with +a wide range of different domains, +thus creating customized programming languages sharing a syntactical framework. +The Lua distribution includes a sample host program called <code>lua</code>, +which uses the Lua library to offer a complete, standalone Lua interpreter, +for interactive or batch use. + + +<p> +Lua is free software, +and is provided as usual with no guarantees, +as stated in its license. +The implementation described in this manual is available +at Lua's official web site, <code>www.lua.org</code>. + + +<p> +Like any other reference manual, +this document is dry in places. +For a discussion of the decisions behind the design of Lua, +see the technical papers available at Lua's web site. +For a detailed introduction to programming in Lua, +see Roberto's book, <em>Programming in Lua</em>. + + + +<h1>2 – <a name="2">Basic Concepts</a></h1> + +<p> +This section describes the basic concepts of the language. + + + +<h2>2.1 – <a name="2.1">Values and Types</a></h2> + +<p> +Lua is a <em>dynamically typed language</em>. +This means that +variables do not have types; only values do. +There are no type definitions in the language. +All values carry their own type. + + +<p> +All values in Lua are <em>first-class values</em>. +This means that all values can be stored in variables, +passed as arguments to other functions, and returned as results. + + +<p> +There are eight basic types in Lua: +<em>nil</em>, <em>boolean</em>, <em>number</em>, +<em>string</em>, <em>function</em>, <em>userdata</em>, +<em>thread</em>, and <em>table</em>. +<em>Nil</em> is the type of the value <b>nil</b>, +whose main property is to be different from any other value; +it usually represents the absence of a useful value. +<em>Boolean</em> is the type of the values <b>false</b> and <b>true</b>. +Both <b>nil</b> and <b>false</b> make a condition false; +any other value makes it true. +<em>Number</em> represents both +integer numbers and real (floating-point) numbers. +<em>String</em> represents immutable sequences of bytes. + +Lua is 8-bit clean: +strings can contain any 8-bit value, +including embedded zeros ('<code>\0</code>'). +Lua is also encoding-agnostic; +it makes no assumptions about the contents of a string. + + +<p> +The type <em>number</em> uses two internal representations, +one called <em>integer</em> and the other called <em>float</em>. +Lua has explicit rules about when each representation is used, +but it also converts between them automatically as needed (see <a href="#3.4.3">§3.4.3</a>). +Therefore, +the programmer may choose to mostly ignore the difference +between integers and floats +or to assume complete control over the representation of each number. +Standard Lua uses 64-bit integers and double-precision (64-bit) floats, +but you can also compile Lua so that it +uses 32-bit integers and/or single-precision (32-bit) floats. +The option with 32 bits for both integers and floats +is particularly attractive +for small machines and embedded systems. +(See macro <code>LUA_32BITS</code> in file <code>luaconf.h</code>.) + + +<p> +Lua can call (and manipulate) functions written in Lua and +functions written in C (see <a href="#3.4.10">§3.4.10</a>). +Both are represented by the type <em>function</em>. + + +<p> +The type <em>userdata</em> is provided to allow arbitrary C data to +be stored in Lua variables. +A userdata value represents a block of raw memory. +There are two kinds of userdata: +<em>full userdata</em>, +which is an object with a block of memory managed by Lua, +and <em>light userdata</em>, +which is simply a C pointer value. +Userdata has no predefined operations in Lua, +except assignment and identity test. +By using <em>metatables</em>, +the programmer can define operations for full userdata values +(see <a href="#2.4">§2.4</a>). +Userdata values cannot be created or modified in Lua, +only through the C API. +This guarantees the integrity of data owned by the host program. + + +<p> +The type <em>thread</em> represents independent threads of execution +and it is used to implement coroutines (see <a href="#2.6">§2.6</a>). +Lua threads are not related to operating-system threads. +Lua supports coroutines on all systems, +even those that do not support threads natively. + + +<p> +The type <em>table</em> implements associative arrays, +that is, arrays that can be indexed not only with numbers, +but with any Lua value except <b>nil</b> and NaN. +(<em>Not a Number</em> is a special numeric value used to represent +undefined or unrepresentable results, such as <code>0/0</code>.) +Tables can be <em>heterogeneous</em>; +that is, they can contain values of all types (except <b>nil</b>). +Any key with value <b>nil</b> is not considered part of the table. +Conversely, any key that is not part of a table has +an associated value <b>nil</b>. + + +<p> +Tables are the sole data-structuring mechanism in Lua; +they can be used to represent ordinary arrays, sequences, +symbol tables, sets, records, graphs, trees, etc. +To represent records, Lua uses the field name as an index. +The language supports this representation by +providing <code>a.name</code> as syntactic sugar for <code>a["name"]</code>. +There are several convenient ways to create tables in Lua +(see <a href="#3.4.9">§3.4.9</a>). + + +<p> +We use the term <em>sequence</em> to denote a table where +the set of all positive numeric keys is equal to {1..<em>n</em>} +for some non-negative integer <em>n</em>, +which is called the length of the sequence (see <a href="#3.4.7">§3.4.7</a>). + + +<p> +Like indices, +the values of table fields can be of any type. +In particular, +because functions are first-class values, +table fields can contain functions. +Thus tables can also carry <em>methods</em> (see <a href="#3.4.11">§3.4.11</a>). + + +<p> +The indexing of tables follows +the definition of raw equality in the language. +The expressions <code>a[i]</code> and <code>a[j]</code> +denote the same table element +if and only if <code>i</code> and <code>j</code> are raw equal +(that is, equal without metamethods). +In particular, floats with integral values +are equal to their respective integers +(e.g., <code>1.0 == 1</code>). +To avoid ambiguities, +any float with integral value used as a key +is converted to its respective integer. +For instance, if you write <code>a[2.0] = true</code>, +the actual key inserted into the table will be the +integer <code>2</code>. +(On the other hand, +2 and "<code>2</code>" are different Lua values and therefore +denote different table entries.) + + +<p> +Tables, functions, threads, and (full) userdata values are <em>objects</em>: +variables do not actually <em>contain</em> these values, +only <em>references</em> to them. +Assignment, parameter passing, and function returns +always manipulate references to such values; +these operations do not imply any kind of copy. + + +<p> +The library function <a href="#pdf-type"><code>type</code></a> returns a string describing the type +of a given value (see <a href="#6.1">§6.1</a>). + + + + + +<h2>2.2 – <a name="2.2">Environments and the Global Environment</a></h2> + +<p> +As will be discussed in <a href="#3.2">§3.2</a> and <a href="#3.3.3">§3.3.3</a>, +any reference to a free name +(that is, a name not bound to any declaration) <code>var</code> +is syntactically translated to <code>_ENV.var</code>. +Moreover, every chunk is compiled in the scope of +an external local variable named <code>_ENV</code> (see <a href="#3.3.2">§3.3.2</a>), +so <code>_ENV</code> itself is never a free name in a chunk. + + +<p> +Despite the existence of this external <code>_ENV</code> variable and +the translation of free names, +<code>_ENV</code> is a completely regular name. +In particular, +you can define new variables and parameters with that name. +Each reference to a free name uses the <code>_ENV</code> that is +visible at that point in the program, +following the usual visibility rules of Lua (see <a href="#3.5">§3.5</a>). + + +<p> +Any table used as the value of <code>_ENV</code> is called an <em>environment</em>. + + +<p> +Lua keeps a distinguished environment called the <em>global environment</em>. +This value is kept at a special index in the C registry (see <a href="#4.5">§4.5</a>). +In Lua, the global variable <a href="#pdf-_G"><code>_G</code></a> is initialized with this same value. +(<a href="#pdf-_G"><code>_G</code></a> is never used internally.) + + +<p> +When Lua loads a chunk, +the default value for its <code>_ENV</code> upvalue +is the global environment (see <a href="#pdf-load"><code>load</code></a>). +Therefore, by default, +free names in Lua code refer to entries in the global environment +(and, therefore, they are also called <em>global variables</em>). +Moreover, all standard libraries are loaded in the global environment +and some functions there operate on that environment. +You can use <a href="#pdf-load"><code>load</code></a> (or <a href="#pdf-loadfile"><code>loadfile</code></a>) +to load a chunk with a different environment. +(In C, you have to load the chunk and then change the value +of its first upvalue.) + + + + + +<h2>2.3 – <a name="2.3">Error Handling</a></h2> + +<p> +Because Lua is an embedded extension language, +all Lua actions start from C code in the host program +calling a function from the Lua library. +(When you use Lua standalone, +the <code>lua</code> application is the host program.) +Whenever an error occurs during +the compilation or execution of a Lua chunk, +control returns to the host, +which can take appropriate measures +(such as printing an error message). + + +<p> +Lua code can explicitly generate an error by calling the +<a href="#pdf-error"><code>error</code></a> function. +If you need to catch errors in Lua, +you can use <a href="#pdf-pcall"><code>pcall</code></a> or <a href="#pdf-xpcall"><code>xpcall</code></a> +to call a given function in <em>protected mode</em>. + + +<p> +Whenever there is an error, +an <em>error object</em> (also called an <em>error message</em>) +is propagated with information about the error. +Lua itself only generates errors whose error object is a string, +but programs may generate errors with +any value as the error object. +It is up to the Lua program or its host to handle such error objects. + + +<p> +When you use <a href="#pdf-xpcall"><code>xpcall</code></a> or <a href="#lua_pcall"><code>lua_pcall</code></a>, +you may give a <em>message handler</em> +to be called in case of errors. +This function is called with the original error message +and returns a new error message. +It is called before the error unwinds the stack, +so that it can gather more information about the error, +for instance by inspecting the stack and creating a stack traceback. +This message handler is still protected by the protected call; +so, an error inside the message handler +will call the message handler again. +If this loop goes on for too long, +Lua breaks it and returns an appropriate message. + + + + + +<h2>2.4 – <a name="2.4">Metatables and Metamethods</a></h2> + +<p> +Every value in Lua can have a <em>metatable</em>. +This <em>metatable</em> is an ordinary Lua table +that defines the behavior of the original value +under certain special operations. +You can change several aspects of the behavior +of operations over a value by setting specific fields in its metatable. +For instance, when a non-numeric value is the operand of an addition, +Lua checks for a function in the field "<code>__add</code>" of the value's metatable. +If it finds one, +Lua calls this function to perform the addition. + + +<p> +The keys in a metatable are derived from the <em>event</em> names; +the corresponding values are called <em>metamethods</em>. +In the previous example, the event is <code>"add"</code> +and the metamethod is the function that performs the addition. + + +<p> +You can query the metatable of any value +using the <a href="#pdf-getmetatable"><code>getmetatable</code></a> function. + + +<p> +You can replace the metatable of tables +using the <a href="#pdf-setmetatable"><code>setmetatable</code></a> function. +You cannot change the metatable of other types from Lua +(except by using the debug library (<a href="#6.10">§6.10</a>)); +you must use the C API for that. + + +<p> +Tables and full userdata have individual metatables +(although multiple tables and userdata can share their metatables). +Values of all other types share one single metatable per type; +that is, there is one single metatable for all numbers, +one for all strings, etc. +By default, a value has no metatable, +but the string library sets a metatable for the string type (see <a href="#6.4">§6.4</a>). + + +<p> +A metatable controls how an object behaves in +arithmetic operations, bitwise operations, +order comparisons, concatenation, length operation, calls, and indexing. +A metatable also can define a function to be called +when a userdata or a table is garbage collected (<a href="#2.5">§2.5</a>). + + +<p> +A detailed list of events controlled by metatables is given next. +Each operation is identified by its corresponding event name. +The key for each event is a string with its name prefixed by +two underscores, '<code>__</code>'; +for instance, the key for operation "add" is the +string "<code>__add</code>". +Note that queries for metamethods are always raw; +the access to a metamethod does not invoke other metamethods. +You can emulate how Lua queries a metamethod for an object <code>obj</code> +with the following code: + +<pre> + rawget(getmetatable(obj) or {}, "__" .. event_name) +</pre> + +<p> +For the unary operators (negation, length, and bitwise not), +the metamethod is computed and called with a dummy second operand, +equal to the first one. +This extra operand is only to simplify Lua's internals +(by making these operators behave like a binary operation) +and may be removed in future versions. +(For most uses this extra operand is irrelevant.) + + + +<ul> + +<li><b>"add": </b> +the <code>+</code> operation. + +If any operand for an addition is not a number +(nor a string coercible to a number), +Lua will try to call a metamethod. +First, Lua will check the first operand (even if it is valid). +If that operand does not define a metamethod for the "<code>__add</code>" event, +then Lua will check the second operand. +If Lua can find a metamethod, +it calls the metamethod with the two operands as arguments, +and the result of the call +(adjusted to one value) +is the result of the operation. +Otherwise, +it raises an error. +</li> + +<li><b>"sub": </b> +the <code>-</code> operation. + +Behavior similar to the "add" operation. +</li> + +<li><b>"mul": </b> +the <code>*</code> operation. + +Behavior similar to the "add" operation. +</li> + +<li><b>"div": </b> +the <code>/</code> operation. + +Behavior similar to the "add" operation. +</li> + +<li><b>"mod": </b> +the <code>%</code> operation. + +Behavior similar to the "add" operation. +</li> + +<li><b>"pow": </b> +the <code>^</code> (exponentiation) operation. + +Behavior similar to the "add" operation. +</li> + +<li><b>"unm": </b> +the <code>-</code> (unary minus) operation. + +Behavior similar to the "add" operation. +</li> + +<li><b>"idiv": </b> +the <code>//</code> (floor division) operation. + +Behavior similar to the "add" operation. +</li> + +<li><b>"band": </b> +the <code>&</code> (bitwise and) operation. + +Behavior similar to the "add" operation, +except that Lua will try a metamethod +if any operator is neither an integer +nor a value coercible to an integer (see <a href="#3.4.3">§3.4.3</a>). +</li> + +<li><b>"bor": </b> +the <code>|</code> (bitwise or) operation. + +Behavior similar to the "band" operation. +</li> + +<li><b>"bxor": </b> +the <code>~</code> (bitwise exclusive or) operation. + +Behavior similar to the "band" operation. +</li> + +<li><b>"bnot": </b> +the <code>~</code> (bitwise unary not) operation. + +Behavior similar to the "band" operation. +</li> + +<li><b>"shl": </b> +the <code><<</code> (bitwise left shift) operation. + +Behavior similar to the "band" operation. +</li> + +<li><b>"shr": </b> +the <code>>></code> (bitwise right shift) operation. + +Behavior similar to the "band" operation. +</li> + +<li><b>"concat": </b> +the <code>..</code> (concatenation) operation. + +Behavior similar to the "add" operation, +except that Lua will try a metamethod +if any operator is neither a string nor a number +(which is always coercible to a string). +</li> + +<li><b>"len": </b> +the <code>#</code> (length) operation. + +If the object is not a string, +Lua will try its metamethod. +If there is a metamethod, +Lua calls it with the object as argument, +and the result of the call +(always adjusted to one value) +is the result of the operation. +If there is no metamethod but the object is a table, +then Lua uses the table length operation (see <a href="#3.4.7">§3.4.7</a>). +Otherwise, Lua raises an error. +</li> + +<li><b>"eq": </b> +the <code>==</code> (equal) operation. + +Behavior similar to the "add" operation, +except that Lua will try a metamethod only when the values +being compared are either both tables or both full userdata +and they are not primitively equal. +The result of the call is always converted to a boolean. +</li> + +<li><b>"lt": </b> +the <code><</code> (less than) operation. + +Behavior similar to the "add" operation, +except that Lua will try a metamethod only when the values +being compared are neither both numbers nor both strings. +The result of the call is always converted to a boolean. +</li> + +<li><b>"le": </b> +the <code><=</code> (less equal) operation. + +Unlike other operations, +The less-equal operation can use two different events. +First, Lua looks for the "<code>__le</code>" metamethod in both operands, +like in the "lt" operation. +If it cannot find such a metamethod, +then it will try the "<code>__lt</code>" event, +assuming that <code>a <= b</code> is equivalent to <code>not (b < a)</code>. +As with the other comparison operators, +the result is always a boolean. +</li> + +<li><b>"index": </b> +The indexing access <code>table[key]</code>. + +This event happens when <code>table</code> is not a table or +when <code>key</code> is not present in <code>table</code>. +The metamethod is looked up in <code>table</code>. + + +<p> +Despite the name, +the metamethod for this event can be either a function or a table. +If it is a function, +it is called with <code>table</code> and <code>key</code> as arguments. +If it is a table, +the final result is the result of indexing this table with <code>key</code>. +(This indexing is regular, not raw, +and therefore can trigger another metamethod.) +</li> + +<li><b>"newindex": </b> +The indexing assignment <code>table[key] = value</code>. + +Like the index event, +this event happens when <code>table</code> is not a table or +when <code>key</code> is not present in <code>table</code>. +The metamethod is looked up in <code>table</code>. + + +<p> +Like with indexing, +the metamethod for this event can be either a function or a table. +If it is a function, +it is called with <code>table</code>, <code>key</code>, and <code>value</code> as arguments. +If it is a table, +Lua does an indexing assignment to this table with the same key and value. +(This assignment is regular, not raw, +and therefore can trigger another metamethod.) + + +<p> +Whenever there is a "newindex" metamethod, +Lua does not perform the primitive assignment. +(If necessary, +the metamethod itself can call <a href="#pdf-rawset"><code>rawset</code></a> +to do the assignment.) +</li> + +<li><b>"call": </b> +The call operation <code>func(args)</code>. + +This event happens when Lua tries to call a non-function value +(that is, <code>func</code> is not a function). +The metamethod is looked up in <code>func</code>. +If present, +the metamethod is called with <code>func</code> as its first argument, +followed by the arguments of the original call (<code>args</code>). +</li> + +</ul> + + + + +<h2>2.5 – <a name="2.5">Garbage Collection</a></h2> + +<p> +Lua performs automatic memory management. +This means that +you do not have to worry about allocating memory for new objects +or freeing it when the objects are no longer needed. +Lua manages memory automatically by running +a <em>garbage collector</em> to collect all <em>dead objects</em> +(that is, objects that are no longer accessible from Lua). +All memory used by Lua is subject to automatic management: +strings, tables, userdata, functions, threads, internal structures, etc. + + +<p> +Lua implements an incremental mark-and-sweep collector. +It uses two numbers to control its garbage-collection cycles: +the <em>garbage-collector pause</em> and +the <em>garbage-collector step multiplier</em>. +Both use percentage points as units +(e.g., a value of 100 means an internal value of 1). + + +<p> +The garbage-collector pause +controls how long the collector waits before starting a new cycle. +Larger values make the collector less aggressive. +Values smaller than 100 mean the collector will not wait to +start a new cycle. +A value of 200 means that the collector waits for the total memory in use +to double before starting a new cycle. + + +<p> +The garbage-collector step multiplier +controls the relative speed of the collector relative to +memory allocation. +Larger values make the collector more aggressive but also increase +the size of each incremental step. +You should not use values smaller than 100, +because they make the collector too slow and +can result in the collector never finishing a cycle. +The default is 200, +which means that the collector runs at "twice" +the speed of memory allocation. + + +<p> +If you set the step multiplier to a very large number +(larger than 10% of the maximum number of +bytes that the program may use), +the collector behaves like a stop-the-world collector. +If you then set the pause to 200, +the collector behaves as in old Lua versions, +doing a complete collection every time Lua doubles its +memory usage. + + +<p> +You can change these numbers by calling <a href="#lua_gc"><code>lua_gc</code></a> in C +or <a href="#pdf-collectgarbage"><code>collectgarbage</code></a> in Lua. +You can also use these functions to control +the collector directly (e.g., stop and restart it). + + + +<h3>2.5.1 – <a name="2.5.1">Garbage-Collection Metamethods</a></h3> + +<p> +You can set garbage-collector metamethods for tables +and, using the C API, +for full userdata (see <a href="#2.4">§2.4</a>). +These metamethods are also called <em>finalizers</em>. +Finalizers allow you to coordinate Lua's garbage collection +with external resource management +(such as closing files, network or database connections, +or freeing your own memory). + + +<p> +For an object (table or userdata) to be finalized when collected, +you must <em>mark</em> it for finalization. + +You mark an object for finalization when you set its metatable +and the metatable has a field indexed by the string "<code>__gc</code>". +Note that if you set a metatable without a <code>__gc</code> field +and later create that field in the metatable, +the object will not be marked for finalization. +However, after an object has been marked, +you can freely change the <code>__gc</code> field of its metatable. + + +<p> +When a marked object becomes garbage, +it is not collected immediately by the garbage collector. +Instead, Lua puts it in a list. +After the collection, +Lua goes through that list. +For each object in the list, +it checks the object's <code>__gc</code> metamethod: +If it is a function, +Lua calls it with the object as its single argument; +if the metamethod is not a function, +Lua simply ignores it. + + +<p> +At the end of each garbage-collection cycle, +the finalizers for objects are called in +the reverse order that the objects were marked for finalization, +among those collected in that cycle; +that is, the first finalizer to be called is the one associated +with the object marked last in the program. +The execution of each finalizer may occur at any point during +the execution of the regular code. + + +<p> +Because the object being collected must still be used by the finalizer, +that object (and other objects accessible only through it) +must be <em>resurrected</em> by Lua. +Usually, this resurrection is transient, +and the object memory is freed in the next garbage-collection cycle. +However, if the finalizer stores the object in some global place +(e.g., a global variable), +then the resurrection is permanent. +Moreover, if the finalizer marks a finalizing object for finalization again, +its finalizer will be called again in the next cycle where the +object is unreachable. +In any case, +the object memory is freed only in the GC cycle where +the object is unreachable and not marked for finalization. + + +<p> +When you close a state (see <a href="#lua_close"><code>lua_close</code></a>), +Lua calls the finalizers of all objects marked for finalization, +following the reverse order that they were marked. +If any finalizer marks objects for collection during that phase, +these marks have no effect. + + + + + +<h3>2.5.2 – <a name="2.5.2">Weak Tables</a></h3> + +<p> +A <em>weak table</em> is a table whose elements are +<em>weak references</em>. +A weak reference is ignored by the garbage collector. +In other words, +if the only references to an object are weak references, +then the garbage collector will collect that object. + + +<p> +A weak table can have weak keys, weak values, or both. +A table with weak keys allows the collection of its keys, +but prevents the collection of its values. +A table with both weak keys and weak values allows the collection of +both keys and values. +In any case, if either the key or the value is collected, +the whole pair is removed from the table. +The weakness of a table is controlled by the +<code>__mode</code> field of its metatable. +If the <code>__mode</code> field is a string containing the character '<code>k</code>', +the keys in the table are weak. +If <code>__mode</code> contains '<code>v</code>', +the values in the table are weak. + + +<p> +A table with weak keys and strong values +is also called an <em>ephemeron table</em>. +In an ephemeron table, +a value is considered reachable only if its key is reachable. +In particular, +if the only reference to a key comes through its value, +the pair is removed. + + +<p> +Any change in the weakness of a table may take effect only +at the next collect cycle. +In particular, if you change the weakness to a stronger mode, +Lua may still collect some items from that table +before the change takes effect. + + +<p> +Only objects that have an explicit construction +are removed from weak tables. +Values, such as numbers and light C functions, +are not subject to garbage collection, +and therefore are not removed from weak tables +(unless their associated values are collected). +Although strings are subject to garbage collection, +they do not have an explicit construction, +and therefore are not removed from weak tables. + + +<p> +Resurrected objects +(that is, objects being finalized +and objects accessible only through objects being finalized) +have a special behavior in weak tables. +They are removed from weak values before running their finalizers, +but are removed from weak keys only in the next collection +after running their finalizers, when such objects are actually freed. +This behavior allows the finalizer to access properties +associated with the object through weak tables. + + +<p> +If a weak table is among the resurrected objects in a collection cycle, +it may not be properly cleared until the next cycle. + + + + + + + +<h2>2.6 – <a name="2.6">Coroutines</a></h2> + +<p> +Lua supports coroutines, +also called <em>collaborative multithreading</em>. +A coroutine in Lua represents an independent thread of execution. +Unlike threads in multithread systems, however, +a coroutine only suspends its execution by explicitly calling +a yield function. + + +<p> +You create a coroutine by calling <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>. +Its sole argument is a function +that is the main function of the coroutine. +The <code>create</code> function only creates a new coroutine and +returns a handle to it (an object of type <em>thread</em>); +it does not start the coroutine. + + +<p> +You execute a coroutine by calling <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>. +When you first call <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>, +passing as its first argument +a thread returned by <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>, +the coroutine starts its execution, +at the first line of its main function. +Extra arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> are passed +as arguments to the coroutine's main function. +After the coroutine starts running, +it runs until it terminates or <em>yields</em>. + + +<p> +A coroutine can terminate its execution in two ways: +normally, when its main function returns +(explicitly or implicitly, after the last instruction); +and abnormally, if there is an unprotected error. +In case of normal termination, +<a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>true</b>, +plus any values returned by the coroutine main function. +In case of errors, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>false</b> +plus an error message. + + +<p> +A coroutine yields by calling <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>. +When a coroutine yields, +the corresponding <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns immediately, +even if the yield happens inside nested function calls +(that is, not in the main function, +but in a function directly or indirectly called by the main function). +In the case of a yield, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> also returns <b>true</b>, +plus any values passed to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>. +The next time you resume the same coroutine, +it continues its execution from the point where it yielded, +with the call to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a> returning any extra +arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>. + + +<p> +Like <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>, +the <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> function also creates a coroutine, +but instead of returning the coroutine itself, +it returns a function that, when called, resumes the coroutine. +Any arguments passed to this function +go as extra arguments to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>. +<a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> returns all the values returned by <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>, +except the first one (the boolean error code). +Unlike <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>, +<a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> does not catch errors; +any error is propagated to the caller. + + +<p> +As an example of how coroutines work, +consider the following code: + +<pre> + function foo (a) + print("foo", a) + return coroutine.yield(2*a) + end + + co = coroutine.create(function (a,b) + print("co-body", a, b) + local r = foo(a+1) + print("co-body", r) + local r, s = coroutine.yield(a+b, a-b) + print("co-body", r, s) + return b, "end" + end) + + print("main", coroutine.resume(co, 1, 10)) + print("main", coroutine.resume(co, "r")) + print("main", coroutine.resume(co, "x", "y")) + print("main", coroutine.resume(co, "x", "y")) +</pre><p> +When you run it, it produces the following output: + +<pre> + co-body 1 10 + foo 2 + main true 4 + co-body r + main true 11 -9 + co-body x y + main true 10 end + main false cannot resume dead coroutine +</pre> + +<p> +You can also create and manipulate coroutines through the C API: +see functions <a href="#lua_newthread"><code>lua_newthread</code></a>, <a href="#lua_resume"><code>lua_resume</code></a>, +and <a href="#lua_yield"><code>lua_yield</code></a>. + + + + + +<h1>3 – <a name="3">The Language</a></h1> + +<p> +This section describes the lexis, the syntax, and the semantics of Lua. +In other words, +this section describes +which tokens are valid, +how they can be combined, +and what their combinations mean. + + +<p> +Language constructs will be explained using the usual extended BNF notation, +in which +{<em>a</em>} means 0 or more <em>a</em>'s, and +[<em>a</em>] means an optional <em>a</em>. +Non-terminals are shown like non-terminal, +keywords are shown like <b>kword</b>, +and other terminal symbols are shown like ‘<b>=</b>’. +The complete syntax of Lua can be found in <a href="#9">§9</a> +at the end of this manual. + + + +<h2>3.1 – <a name="3.1">Lexical Conventions</a></h2> + +<p> +Lua is a free-form language. +It ignores spaces (including new lines) and comments +between lexical elements (tokens), +except as delimiters between names and keywords. + + +<p> +<em>Names</em> +(also called <em>identifiers</em>) +in Lua can be any string of letters, +digits, and underscores, +not beginning with a digit. +Identifiers are used to name variables, table fields, and labels. + + +<p> +The following <em>keywords</em> are reserved +and cannot be used as names: + + +<pre> + and break do else elseif end + false for function goto if in + local nil not or repeat return + then true until while +</pre> + +<p> +Lua is a case-sensitive language: +<code>and</code> is a reserved word, but <code>And</code> and <code>AND</code> +are two different, valid names. +As a convention, +programs should avoid creating +names that start with an underscore followed by +one or more uppercase letters (such as <a href="#pdf-_VERSION"><code>_VERSION</code></a>). + + +<p> +The following strings denote other tokens: + +<pre> + + - * / % ^ # + & ~ | << >> // + == ~= <= >= < > = + ( ) { } [ ] :: + ; : , . .. ... +</pre> + +<p> +<em>Literal strings</em> +can be delimited by matching single or double quotes, +and can contain the following C-like escape sequences: +'<code>\a</code>' (bell), +'<code>\b</code>' (backspace), +'<code>\f</code>' (form feed), +'<code>\n</code>' (newline), +'<code>\r</code>' (carriage return), +'<code>\t</code>' (horizontal tab), +'<code>\v</code>' (vertical tab), +'<code>\\</code>' (backslash), +'<code>\"</code>' (quotation mark [double quote]), +and '<code>\'</code>' (apostrophe [single quote]). +A backslash followed by a real newline +results in a newline in the string. +The escape sequence '<code>\z</code>' skips the following span +of white-space characters, +including line breaks; +it is particularly useful to break and indent a long literal string +into multiple lines without adding the newlines and spaces +into the string contents. + + +<p> +Strings in Lua can contain any 8-bit value, including embedded zeros, +which can be specified as '<code>\0</code>'. +More generally, +we can specify any byte in a literal string by its numerical value. +This can be done +with the escape sequence <code>\x<em>XX</em></code>, +where <em>XX</em> is a sequence of exactly two hexadecimal digits, +or with the escape sequence <code>\<em>ddd</em></code>, +where <em>ddd</em> is a sequence of up to three decimal digits. +(Note that if a decimal escape sequence is to be followed by a digit, +it must be expressed using exactly three digits.) + + +<p> +The UTF-8 encoding of a Unicode character +can be inserted in a literal string with +the escape sequence <code>\u{<em>XXX</em>}</code> +(note the mandatory enclosing brackets), +where <em>XXX</em> is a sequence of one or more hexadecimal digits +representing the character code point. + + +<p> +Literal strings can also be defined using a long format +enclosed by <em>long brackets</em>. +We define an <em>opening long bracket of level <em>n</em></em> as an opening +square bracket followed by <em>n</em> equal signs followed by another +opening square bracket. +So, an opening long bracket of level 0 is written as <code>[[</code>, +an opening long bracket of level 1 is written as <code>[=[</code>, +and so on. +A <em>closing long bracket</em> is defined similarly; +for instance, +a closing long bracket of level 4 is written as <code>]====]</code>. +A <em>long literal</em> starts with an opening long bracket of any level and +ends at the first closing long bracket of the same level. +It can contain any text except a closing bracket of the same level. +Literals in this bracketed form can run for several lines, +do not interpret any escape sequences, +and ignore long brackets of any other level. +Any kind of end-of-line sequence +(carriage return, newline, carriage return followed by newline, +or newline followed by carriage return) +is converted to a simple newline. + + +<p> +Any byte in a literal string not +explicitly affected by the previous rules represents itself. +However, Lua opens files for parsing in text mode, +and the system file functions may have problems with +some control characters. +So, it is safer to represent +non-text data as a quoted literal with +explicit escape sequences for non-text characters. + + +<p> +For convenience, +when the opening long bracket is immediately followed by a newline, +the newline is not included in the string. +As an example, in a system using ASCII +(in which '<code>a</code>' is coded as 97, +newline is coded as 10, and '<code>1</code>' is coded as 49), +the five literal strings below denote the same string: + +<pre> + a = 'alo\n123"' + a = "alo\n123\"" + a = '\97lo\10\04923"' + a = [[alo + 123"]] + a = [==[ + alo + 123"]==] +</pre> + +<p> +A <em>numerical constant</em> (or <em>numeral</em>) +can be written with an optional fractional part +and an optional decimal exponent, +marked by a letter '<code>e</code>' or '<code>E</code>'. +Lua also accepts hexadecimal constants, +which start with <code>0x</code> or <code>0X</code>. +Hexadecimal constants also accept an optional fractional part +plus an optional binary exponent, +marked by a letter '<code>p</code>' or '<code>P</code>'. +A numeric constant with a fractional dot or an exponent +denotes a float; +otherwise it denotes an integer. +Examples of valid integer constants are + +<pre> + 3 345 0xff 0xBEBADA +</pre><p> +Examples of valid float constants are + +<pre> + 3.0 3.1416 314.16e-2 0.31416E1 34e1 + 0x0.1E 0xA23p-4 0X1.921FB54442D18P+1 +</pre> + +<p> +A <em>comment</em> starts with a double hyphen (<code>--</code>) +anywhere outside a string. +If the text immediately after <code>--</code> is not an opening long bracket, +the comment is a <em>short comment</em>, +which runs until the end of the line. +Otherwise, it is a <em>long comment</em>, +which runs until the corresponding closing long bracket. +Long comments are frequently used to disable code temporarily. + + + + + +<h2>3.2 – <a name="3.2">Variables</a></h2> + +<p> +Variables are places that store values. +There are three kinds of variables in Lua: +global variables, local variables, and table fields. + + +<p> +A single name can denote a global variable or a local variable +(or a function's formal parameter, +which is a particular kind of local variable): + +<pre> + var ::= Name +</pre><p> +Name denotes identifiers, as defined in <a href="#3.1">§3.1</a>. + + +<p> +Any variable name is assumed to be global unless explicitly declared +as a local (see <a href="#3.3.7">§3.3.7</a>). +Local variables are <em>lexically scoped</em>: +local variables can be freely accessed by functions +defined inside their scope (see <a href="#3.5">§3.5</a>). + + +<p> +Before the first assignment to a variable, its value is <b>nil</b>. + + +<p> +Square brackets are used to index a table: + +<pre> + var ::= prefixexp ‘<b>[</b>’ exp ‘<b>]</b>’ +</pre><p> +The meaning of accesses to table fields can be changed via metatables. +An access to an indexed variable <code>t[i]</code> is equivalent to +a call <code>gettable_event(t,i)</code>. +(See <a href="#2.4">§2.4</a> for a complete description of the +<code>gettable_event</code> function. +This function is not defined or callable in Lua. +We use it here only for explanatory purposes.) + + +<p> +The syntax <code>var.Name</code> is just syntactic sugar for +<code>var["Name"]</code>: + +<pre> + var ::= prefixexp ‘<b>.</b>’ Name +</pre> + +<p> +An access to a global variable <code>x</code> +is equivalent to <code>_ENV.x</code>. +Due to the way that chunks are compiled, +<code>_ENV</code> is never a global name (see <a href="#2.2">§2.2</a>). + + + + + +<h2>3.3 – <a name="3.3">Statements</a></h2> + +<p> +Lua supports an almost conventional set of statements, +similar to those in Pascal or C. +This set includes +assignments, control structures, function calls, +and variable declarations. + + + +<h3>3.3.1 – <a name="3.3.1">Blocks</a></h3> + +<p> +A block is a list of statements, +which are executed sequentially: + +<pre> + block ::= {stat} +</pre><p> +Lua has <em>empty statements</em> +that allow you to separate statements with semicolons, +start a block with a semicolon +or write two semicolons in sequence: + +<pre> + stat ::= ‘<b>;</b>’ +</pre> + +<p> +Function calls and assignments +can start with an open parenthesis. +This possibility leads to an ambiguity in Lua's grammar. +Consider the following fragment: + +<pre> + a = b + c + (print or io.write)('done') +</pre><p> +The grammar could see it in two ways: + +<pre> + a = b + c(print or io.write)('done') + + a = b + c; (print or io.write)('done') +</pre><p> +The current parser always sees such constructions +in the first way, +interpreting the open parenthesis +as the start of the arguments to a call. +To avoid this ambiguity, +it is a good practice to always precede with a semicolon +statements that start with a parenthesis: + +<pre> + ;(print or io.write)('done') +</pre> + +<p> +A block can be explicitly delimited to produce a single statement: + +<pre> + stat ::= <b>do</b> block <b>end</b> +</pre><p> +Explicit blocks are useful +to control the scope of variable declarations. +Explicit blocks are also sometimes used to +add a <b>return</b> statement in the middle +of another block (see <a href="#3.3.4">§3.3.4</a>). + + + + + +<h3>3.3.2 – <a name="3.3.2">Chunks</a></h3> + +<p> +The unit of compilation of Lua is called a <em>chunk</em>. +Syntactically, +a chunk is simply a block: + +<pre> + chunk ::= block +</pre> + +<p> +Lua handles a chunk as the body of an anonymous function +with a variable number of arguments +(see <a href="#3.4.11">§3.4.11</a>). +As such, chunks can define local variables, +receive arguments, and return values. +Moreover, such anonymous function is compiled as in the +scope of an external local variable called <code>_ENV</code> (see <a href="#2.2">§2.2</a>). +The resulting function always has <code>_ENV</code> as its only upvalue, +even if it does not use that variable. + + +<p> +A chunk can be stored in a file or in a string inside the host program. +To execute a chunk, +Lua first <em>loads</em> it, +precompiling the chunk's code into instructions for a virtual machine, +and then Lua executes the compiled code +with an interpreter for the virtual machine. + + +<p> +Chunks can also be precompiled into binary form; +see program <code>luac</code> and function <a href="#pdf-string.dump"><code>string.dump</code></a> for details. +Programs in source and compiled forms are interchangeable; +Lua automatically detects the file type and acts accordingly (see <a href="#pdf-load"><code>load</code></a>). + + + + + +<h3>3.3.3 – <a name="3.3.3">Assignment</a></h3> + +<p> +Lua allows multiple assignments. +Therefore, the syntax for assignment +defines a list of variables on the left side +and a list of expressions on the right side. +The elements in both lists are separated by commas: + +<pre> + stat ::= varlist ‘<b>=</b>’ explist + varlist ::= var {‘<b>,</b>’ var} + explist ::= exp {‘<b>,</b>’ exp} +</pre><p> +Expressions are discussed in <a href="#3.4">§3.4</a>. + + +<p> +Before the assignment, +the list of values is <em>adjusted</em> to the length of +the list of variables. +If there are more values than needed, +the excess values are thrown away. +If there are fewer values than needed, +the list is extended with as many <b>nil</b>'s as needed. +If the list of expressions ends with a function call, +then all values returned by that call enter the list of values, +before the adjustment +(except when the call is enclosed in parentheses; see <a href="#3.4">§3.4</a>). + + +<p> +The assignment statement first evaluates all its expressions +and only then the assignments are performed. +Thus the code + +<pre> + i = 3 + i, a[i] = i+1, 20 +</pre><p> +sets <code>a[3]</code> to 20, without affecting <code>a[4]</code> +because the <code>i</code> in <code>a[i]</code> is evaluated (to 3) +before it is assigned 4. +Similarly, the line + +<pre> + x, y = y, x +</pre><p> +exchanges the values of <code>x</code> and <code>y</code>, +and + +<pre> + x, y, z = y, z, x +</pre><p> +cyclically permutes the values of <code>x</code>, <code>y</code>, and <code>z</code>. + + +<p> +The meaning of assignments to global variables +and table fields can be changed via metatables. +An assignment to an indexed variable <code>t[i] = val</code> is equivalent to +<code>settable_event(t,i,val)</code>. +(See <a href="#2.4">§2.4</a> for a complete description of the +<code>settable_event</code> function. +This function is not defined or callable in Lua. +We use it here only for explanatory purposes.) + + +<p> +An assignment to a global name <code>x = val</code> +is equivalent to the assignment +<code>_ENV.x = val</code> (see <a href="#2.2">§2.2</a>). + + + + + +<h3>3.3.4 – <a name="3.3.4">Control Structures</a></h3><p> +The control structures +<b>if</b>, <b>while</b>, and <b>repeat</b> have the usual meaning and +familiar syntax: + + + + +<pre> + stat ::= <b>while</b> exp <b>do</b> block <b>end</b> + stat ::= <b>repeat</b> block <b>until</b> exp + stat ::= <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b> +</pre><p> +Lua also has a <b>for</b> statement, in two flavors (see <a href="#3.3.5">§3.3.5</a>). + + +<p> +The condition expression of a +control structure can return any value. +Both <b>false</b> and <b>nil</b> are considered false. +All values different from <b>nil</b> and <b>false</b> are considered true +(in particular, the number 0 and the empty string are also true). + + +<p> +In the <b>repeat</b>–<b>until</b> loop, +the inner block does not end at the <b>until</b> keyword, +but only after the condition. +So, the condition can refer to local variables +declared inside the loop block. + + +<p> +The <b>goto</b> statement transfers the program control to a label. +For syntactical reasons, +labels in Lua are considered statements too: + + + +<pre> + stat ::= <b>goto</b> Name + stat ::= label + label ::= ‘<b>::</b>’ Name ‘<b>::</b>’ +</pre> + +<p> +A label is visible in the entire block where it is defined, +except +inside nested blocks where a label with the same name is defined and +inside nested functions. +A goto may jump to any visible label as long as it does not +enter into the scope of a local variable. + + +<p> +Labels and empty statements are called <em>void statements</em>, +as they perform no actions. + + +<p> +The <b>break</b> statement terminates the execution of a +<b>while</b>, <b>repeat</b>, or <b>for</b> loop, +skipping to the next statement after the loop: + + +<pre> + stat ::= <b>break</b> +</pre><p> +A <b>break</b> ends the innermost enclosing loop. + + +<p> +The <b>return</b> statement is used to return values +from a function or a chunk +(which is an anonymous function). + +Functions can return more than one value, +so the syntax for the <b>return</b> statement is + +<pre> + stat ::= <b>return</b> [explist] [‘<b>;</b>’] +</pre> + +<p> +The <b>return</b> statement can only be written +as the last statement of a block. +If it is really necessary to <b>return</b> in the middle of a block, +then an explicit inner block can be used, +as in the idiom <code>do return end</code>, +because now <b>return</b> is the last statement in its (inner) block. + + + + + +<h3>3.3.5 – <a name="3.3.5">For Statement</a></h3> + +<p> + +The <b>for</b> statement has two forms: +one numeric and one generic. + + +<p> +The numeric <b>for</b> loop repeats a block of code while a +control variable runs through an arithmetic progression. +It has the following syntax: + +<pre> + stat ::= <b>for</b> Name ‘<b>=</b>’ exp ‘<b>,</b>’ exp [‘<b>,</b>’ exp] <b>do</b> block <b>end</b> +</pre><p> +The <em>block</em> is repeated for <em>name</em> starting at the value of +the first <em>exp</em>, until it passes the second <em>exp</em> by steps of the +third <em>exp</em>. +More precisely, a <b>for</b> statement like + +<pre> + for v = <em>e1</em>, <em>e2</em>, <em>e3</em> do <em>block</em> end +</pre><p> +is equivalent to the code: + +<pre> + do + local <em>var</em>, <em>limit</em>, <em>step</em> = tonumber(<em>e1</em>), tonumber(<em>e2</em>), tonumber(<em>e3</em>) + if not (<em>var</em> and <em>limit</em> and <em>step</em>) then error() end + <em>var</em> = <em>var</em> - <em>step</em> + while true do + <em>var</em> = <em>var</em> + <em>step</em> + if (<em>step</em> >= 0 and <em>var</em> > <em>limit</em>) or (<em>step</em> < 0 and <em>var</em> < <em>limit</em>) then + break + end + local v = <em>var</em> + <em>block</em> + end + end +</pre> + +<p> +Note the following: + +<ul> + +<li> +All three control expressions are evaluated only once, +before the loop starts. +They must all result in numbers. +</li> + +<li> +<code><em>var</em></code>, <code><em>limit</em></code>, and <code><em>step</em></code> are invisible variables. +The names shown here are for explanatory purposes only. +</li> + +<li> +If the third expression (the step) is absent, +then a step of 1 is used. +</li> + +<li> +You can use <b>break</b> and <b>goto</b> to exit a <b>for</b> loop. +</li> + +<li> +The loop variable <code>v</code> is local to the loop body. +If you need its value after the loop, +assign it to another variable before exiting the loop. +</li> + +</ul> + +<p> +The generic <b>for</b> statement works over functions, +called <em>iterators</em>. +On each iteration, the iterator function is called to produce a new value, +stopping when this new value is <b>nil</b>. +The generic <b>for</b> loop has the following syntax: + +<pre> + stat ::= <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b> + namelist ::= Name {‘<b>,</b>’ Name} +</pre><p> +A <b>for</b> statement like + +<pre> + for <em>var_1</em>, ···, <em>var_n</em> in <em>explist</em> do <em>block</em> end +</pre><p> +is equivalent to the code: + +<pre> + do + local <em>f</em>, <em>s</em>, <em>var</em> = <em>explist</em> + while true do + local <em>var_1</em>, ···, <em>var_n</em> = <em>f</em>(<em>s</em>, <em>var</em>) + if <em>var_1</em> == nil then break end + <em>var</em> = <em>var_1</em> + <em>block</em> + end + end +</pre><p> +Note the following: + +<ul> + +<li> +<code><em>explist</em></code> is evaluated only once. +Its results are an <em>iterator</em> function, +a <em>state</em>, +and an initial value for the first <em>iterator variable</em>. +</li> + +<li> +<code><em>f</em></code>, <code><em>s</em></code>, and <code><em>var</em></code> are invisible variables. +The names are here for explanatory purposes only. +</li> + +<li> +You can use <b>break</b> to exit a <b>for</b> loop. +</li> + +<li> +The loop variables <code><em>var_i</em></code> are local to the loop; +you cannot use their values after the <b>for</b> ends. +If you need these values, +then assign them to other variables before breaking or exiting the loop. +</li> + +</ul> + + + + +<h3>3.3.6 – <a name="3.3.6">Function Calls as Statements</a></h3><p> +To allow possible side-effects, +function calls can be executed as statements: + +<pre> + stat ::= functioncall +</pre><p> +In this case, all returned values are thrown away. +Function calls are explained in <a href="#3.4.10">§3.4.10</a>. + + + + + +<h3>3.3.7 – <a name="3.3.7">Local Declarations</a></h3><p> +Local variables can be declared anywhere inside a block. +The declaration can include an initial assignment: + +<pre> + stat ::= <b>local</b> namelist [‘<b>=</b>’ explist] +</pre><p> +If present, an initial assignment has the same semantics +of a multiple assignment (see <a href="#3.3.3">§3.3.3</a>). +Otherwise, all variables are initialized with <b>nil</b>. + + +<p> +A chunk is also a block (see <a href="#3.3.2">§3.3.2</a>), +and so local variables can be declared in a chunk outside any explicit block. + + +<p> +The visibility rules for local variables are explained in <a href="#3.5">§3.5</a>. + + + + + + + +<h2>3.4 – <a name="3.4">Expressions</a></h2> + +<p> +The basic expressions in Lua are the following: + +<pre> + exp ::= prefixexp + exp ::= <b>nil</b> | <b>false</b> | <b>true</b> + exp ::= Numeral + exp ::= LiteralString + exp ::= functiondef + exp ::= tableconstructor + exp ::= ‘<b>...</b>’ + exp ::= exp binop exp + exp ::= unop exp + prefixexp ::= var | functioncall | ‘<b>(</b>’ exp ‘<b>)</b>’ +</pre> + +<p> +Numerals and literal strings are explained in <a href="#3.1">§3.1</a>; +variables are explained in <a href="#3.2">§3.2</a>; +function definitions are explained in <a href="#3.4.11">§3.4.11</a>; +function calls are explained in <a href="#3.4.10">§3.4.10</a>; +table constructors are explained in <a href="#3.4.9">§3.4.9</a>. +Vararg expressions, +denoted by three dots ('<code>...</code>'), can only be used when +directly inside a vararg function; +they are explained in <a href="#3.4.11">§3.4.11</a>. + + +<p> +Binary operators comprise arithmetic operators (see <a href="#3.4.1">§3.4.1</a>), +bitwise operators (see <a href="#3.4.2">§3.4.2</a>), +relational operators (see <a href="#3.4.4">§3.4.4</a>), logical operators (see <a href="#3.4.5">§3.4.5</a>), +and the concatenation operator (see <a href="#3.4.6">§3.4.6</a>). +Unary operators comprise the unary minus (see <a href="#3.4.1">§3.4.1</a>), +the unary bitwise not (see <a href="#3.4.2">§3.4.2</a>), +the unary logical <b>not</b> (see <a href="#3.4.5">§3.4.5</a>), +and the unary <em>length operator</em> (see <a href="#3.4.7">§3.4.7</a>). + + +<p> +Both function calls and vararg expressions can result in multiple values. +If a function call is used as a statement (see <a href="#3.3.6">§3.3.6</a>), +then its return list is adjusted to zero elements, +thus discarding all returned values. +If an expression is used as the last (or the only) element +of a list of expressions, +then no adjustment is made +(unless the expression is enclosed in parentheses). +In all other contexts, +Lua adjusts the result list to one element, +either discarding all values except the first one +or adding a single <b>nil</b> if there are no values. + + +<p> +Here are some examples: + +<pre> + f() -- adjusted to 0 results + g(f(), x) -- f() is adjusted to 1 result + g(x, f()) -- g gets x plus all results from f() + a,b,c = f(), x -- f() is adjusted to 1 result (c gets nil) + a,b = ... -- a gets the first vararg parameter, b gets + -- the second (both a and b can get nil if there + -- is no corresponding vararg parameter) + + a,b,c = x, f() -- f() is adjusted to 2 results + a,b,c = f() -- f() is adjusted to 3 results + return f() -- returns all results from f() + return ... -- returns all received vararg parameters + return x,y,f() -- returns x, y, and all results from f() + {f()} -- creates a list with all results from f() + {...} -- creates a list with all vararg parameters + {f(), nil} -- f() is adjusted to 1 result +</pre> + +<p> +Any expression enclosed in parentheses always results in only one value. +Thus, +<code>(f(x,y,z))</code> is always a single value, +even if <code>f</code> returns several values. +(The value of <code>(f(x,y,z))</code> is the first value returned by <code>f</code> +or <b>nil</b> if <code>f</code> does not return any values.) + + + +<h3>3.4.1 – <a name="3.4.1">Arithmetic Operators</a></h3><p> +Lua supports the following arithmetic operators: + +<ul> +<li><b><code>+</code>: </b>addition</li> +<li><b><code>-</code>: </b>subtraction</li> +<li><b><code>*</code>: </b>multiplication</li> +<li><b><code>/</code>: </b>float division</li> +<li><b><code>//</code>: </b>floor division</li> +<li><b><code>%</code>: </b>modulo</li> +<li><b><code>^</code>: </b>exponentiation</li> +<li><b><code>-</code>: </b>unary minus</li> +</ul> + +<p> +With the exception of exponentiation and float division, +the arithmetic operators work as follows: +If both operands are integers, +the operation is performed over integers and the result is an integer. +Otherwise, if both operands are numbers +or strings that can be converted to +numbers (see <a href="#3.4.3">§3.4.3</a>), +then they are converted to floats, +the operation is performed following the usual rules +for floating-point arithmetic +(usually the IEEE 754 standard), +and the result is a float. + + +<p> +Exponentiation and float division (<code>/</code>) +always convert their operands to floats +and the result is always a float. +Exponentiation uses the ISO C function <code>pow</code>, +so that it works for non-integer exponents too. + + +<p> +Floor division (<code>//</code>) is a division +that rounds the quotient towards minus infinite, +that is, the floor of the division of its operands. + + +<p> +Modulo is defined as the remainder of a division +that rounds the quotient towards minus infinite (floor division). + + +<p> +In case of overflows in integer arithmetic, +all operations <em>wrap around</em>, +according to the usual rules of two-complement arithmetic. +(In other words, +they return the unique representable integer +that is equal modulo <em>2<sup>64</sup></em> to the mathematical result.) + + + +<h3>3.4.2 – <a name="3.4.2">Bitwise Operators</a></h3><p> +Lua supports the following bitwise operators: + +<ul> +<li><b><code>&</code>: </b>bitwise and</li> +<li><b><code>|</code>: </b>bitwise or</li> +<li><b><code>~</code>: </b>bitwise exclusive or</li> +<li><b><code>>></code>: </b>right shift</li> +<li><b><code><<</code>: </b>left shift</li> +<li><b><code>~</code>: </b>unary bitwise not</li> +</ul> + +<p> +All bitwise operations convert its operands to integers +(see <a href="#3.4.3">§3.4.3</a>), +operate on all bits of those integers, +and result in an integer. + + +<p> +Both right and left shifts fill the vacant bits with zeros. +Negative displacements shift to the other direction; +displacements with absolute values equal to or higher than +the number of bits in an integer +result in zero (as all bits are shifted out). + + + + + +<h3>3.4.3 – <a name="3.4.3">Coercions and Conversions</a></h3><p> +Lua provides some automatic conversions between some +types and representations at run time. +Bitwise operators always convert float operands to integers. +Exponentiation and float division +always convert integer operands to floats. +All other arithmetic operations applied to mixed numbers +(integers and floats) convert the integer operand to a float; +this is called the <em>usual rule</em>. +The C API also converts both integers to floats and +floats to integers, as needed. +Moreover, string concatenation accepts numbers as arguments, +besides strings. + + +<p> +Lua also converts strings to numbers, +whenever a number is expected. + + +<p> +In a conversion from integer to float, +if the integer value has an exact representation as a float, +that is the result. +Otherwise, +the conversion gets the nearest higher or +the nearest lower representable value. +This kind of conversion never fails. + + +<p> +The conversion from float to integer +checks whether the float has an exact representation as an integer +(that is, the float has an integral value and +it is in the range of integer representation). +If it does, that representation is the result. +Otherwise, the conversion fails. + + +<p> +The conversion from strings to numbers goes as follows: +First, the string is converted to an integer or a float, +following its syntax and the rules of the Lua lexer. +(The string may have also leading and trailing spaces and a sign.) +Then, the resulting number is converted to the required type +(float or integer) according to the previous rules. + + +<p> +The conversion from numbers to strings uses a +non-specified human-readable format. +For complete control over how numbers are converted to strings, +use the <code>format</code> function from the string library +(see <a href="#pdf-string.format"><code>string.format</code></a>). + + + + + +<h3>3.4.4 – <a name="3.4.4">Relational Operators</a></h3><p> +Lua supports the following relational operators: + +<ul> +<li><b><code>==</code>: </b>equality</li> +<li><b><code>~=</code>: </b>inequality</li> +<li><b><code><</code>: </b>less than</li> +<li><b><code>></code>: </b>greater than</li> +<li><b><code><=</code>: </b>less or equal</li> +<li><b><code>>=</code>: </b>greater or equal</li> +</ul><p> +These operators always result in <b>false</b> or <b>true</b>. + + +<p> +Equality (<code>==</code>) first compares the type of its operands. +If the types are different, then the result is <b>false</b>. +Otherwise, the values of the operands are compared. +Strings are compared in the obvious way. +Numbers follow the usual rule for binary operations: +if both operands are integers, +they are compared as integers; +otherwise, they are converted to floats +and compared as such. + + +<p> +Tables, userdata, and threads +are compared by reference: +two objects are considered equal only if they are the same object. +Every time you create a new object +(a table, userdata, or thread), +this new object is different from any previously existing object. +Closures with the same reference are always equal. +Closures with any detectable difference +(different behavior, different definition) are always different. + + +<p> +You can change the way that Lua compares tables and userdata +by using the "eq" metamethod (see <a href="#2.4">§2.4</a>). + + +<p> +Equality comparisons do not convert strings to numbers +or vice versa. +Thus, <code>"0"==0</code> evaluates to <b>false</b>, +and <code>t[0]</code> and <code>t["0"]</code> denote different +entries in a table. + + +<p> +The operator <code>~=</code> is exactly the negation of equality (<code>==</code>). + + +<p> +The order operators work as follows. +If both arguments are numbers, +then they are compared following +the usual rule for binary operations. +Otherwise, if both arguments are strings, +then their values are compared according to the current locale. +Otherwise, Lua tries to call the "lt" or the "le" +metamethod (see <a href="#2.4">§2.4</a>). +A comparison <code>a > b</code> is translated to <code>b < a</code> +and <code>a >= b</code> is translated to <code>b <= a</code>. + + + + + +<h3>3.4.5 – <a name="3.4.5">Logical Operators</a></h3><p> +The logical operators in Lua are +<b>and</b>, <b>or</b>, and <b>not</b>. +Like the control structures (see <a href="#3.3.4">§3.3.4</a>), +all logical operators consider both <b>false</b> and <b>nil</b> as false +and anything else as true. + + +<p> +The negation operator <b>not</b> always returns <b>false</b> or <b>true</b>. +The conjunction operator <b>and</b> returns its first argument +if this value is <b>false</b> or <b>nil</b>; +otherwise, <b>and</b> returns its second argument. +The disjunction operator <b>or</b> returns its first argument +if this value is different from <b>nil</b> and <b>false</b>; +otherwise, <b>or</b> returns its second argument. +Both <b>and</b> and <b>or</b> use short-circuit evaluation; +that is, +the second operand is evaluated only if necessary. +Here are some examples: + +<pre> + 10 or 20 --> 10 + 10 or error() --> 10 + nil or "a" --> "a" + nil and 10 --> nil + false and error() --> false + false and nil --> false + false or nil --> nil + 10 and 20 --> 20 +</pre><p> +(In this manual, +<code>--></code> indicates the result of the preceding expression.) + + + + + +<h3>3.4.6 – <a name="3.4.6">Concatenation</a></h3><p> +The string concatenation operator in Lua is +denoted by two dots ('<code>..</code>'). +If both operands are strings or numbers, then they are converted to +strings according to the rules described in <a href="#3.4.3">§3.4.3</a>. +Otherwise, the <code>__concat</code> metamethod is called (see <a href="#2.4">§2.4</a>). + + + + + +<h3>3.4.7 – <a name="3.4.7">The Length Operator</a></h3> + +<p> +The length operator is denoted by the unary prefix operator <code>#</code>. +The length of a string is its number of bytes +(that is, the usual meaning of string length when each +character is one byte). + + +<p> +A program can modify the behavior of the length operator for +any value but strings through the <code>__len</code> metamethod (see <a href="#2.4">§2.4</a>). + + +<p> +Unless a <code>__len</code> metamethod is given, +the length of a table <code>t</code> is only defined if the +table is a <em>sequence</em>, +that is, +the set of its positive numeric keys is equal to <em>{1..n}</em> +for some non-negative integer <em>n</em>. +In that case, <em>n</em> is its length. +Note that a table like + +<pre> + {10, 20, nil, 40} +</pre><p> +is not a sequence, because it has the key <code>4</code> +but does not have the key <code>3</code>. +(So, there is no <em>n</em> such that the set <em>{1..n}</em> is equal +to the set of positive numeric keys of that table.) +Note, however, that non-numeric keys do not interfere +with whether a table is a sequence. + + + + + +<h3>3.4.8 – <a name="3.4.8">Precedence</a></h3><p> +Operator precedence in Lua follows the table below, +from lower to higher priority: + +<pre> + or + and + < > <= >= ~= == + | + ~ + & + << >> + .. + + - + * / // % + unary operators (not # - ~) + ^ +</pre><p> +As usual, +you can use parentheses to change the precedences of an expression. +The concatenation ('<code>..</code>') and exponentiation ('<code>^</code>') +operators are right associative. +All other binary operators are left associative. + + + + + +<h3>3.4.9 – <a name="3.4.9">Table Constructors</a></h3><p> +Table constructors are expressions that create tables. +Every time a constructor is evaluated, a new table is created. +A constructor can be used to create an empty table +or to create a table and initialize some of its fields. +The general syntax for constructors is + +<pre> + tableconstructor ::= ‘<b>{</b>’ [fieldlist] ‘<b>}</b>’ + fieldlist ::= field {fieldsep field} [fieldsep] + field ::= ‘<b>[</b>’ exp ‘<b>]</b>’ ‘<b>=</b>’ exp | Name ‘<b>=</b>’ exp | exp + fieldsep ::= ‘<b>,</b>’ | ‘<b>;</b>’ +</pre> + +<p> +Each field of the form <code>[exp1] = exp2</code> adds to the new table an entry +with key <code>exp1</code> and value <code>exp2</code>. +A field of the form <code>name = exp</code> is equivalent to +<code>["name"] = exp</code>. +Finally, fields of the form <code>exp</code> are equivalent to +<code>[i] = exp</code>, where <code>i</code> are consecutive integers +starting with 1. +Fields in the other formats do not affect this counting. +For example, + +<pre> + a = { [f(1)] = g; "x", "y"; x = 1, f(x), [30] = 23; 45 } +</pre><p> +is equivalent to + +<pre> + do + local t = {} + t[f(1)] = g + t[1] = "x" -- 1st exp + t[2] = "y" -- 2nd exp + t.x = 1 -- t["x"] = 1 + t[3] = f(x) -- 3rd exp + t[30] = 23 + t[4] = 45 -- 4th exp + a = t + end +</pre> + +<p> +The order of the assignments in a constructor is undefined. +(This order would be relevant only when there are repeated keys.) + + +<p> +If the last field in the list has the form <code>exp</code> +and the expression is a function call or a vararg expression, +then all values returned by this expression enter the list consecutively +(see <a href="#3.4.10">§3.4.10</a>). + + +<p> +The field list can have an optional trailing separator, +as a convenience for machine-generated code. + + + + + +<h3>3.4.10 – <a name="3.4.10">Function Calls</a></h3><p> +A function call in Lua has the following syntax: + +<pre> + functioncall ::= prefixexp args +</pre><p> +In a function call, +first prefixexp and args are evaluated. +If the value of prefixexp has type <em>function</em>, +then this function is called +with the given arguments. +Otherwise, the prefixexp "call" metamethod is called, +having as first parameter the value of prefixexp, +followed by the original call arguments +(see <a href="#2.4">§2.4</a>). + + +<p> +The form + +<pre> + functioncall ::= prefixexp ‘<b>:</b>’ Name args +</pre><p> +can be used to call "methods". +A call <code>v:name(<em>args</em>)</code> +is syntactic sugar for <code>v.name(v,<em>args</em>)</code>, +except that <code>v</code> is evaluated only once. + + +<p> +Arguments have the following syntax: + +<pre> + args ::= ‘<b>(</b>’ [explist] ‘<b>)</b>’ + args ::= tableconstructor + args ::= LiteralString +</pre><p> +All argument expressions are evaluated before the call. +A call of the form <code>f{<em>fields</em>}</code> is +syntactic sugar for <code>f({<em>fields</em>})</code>; +that is, the argument list is a single new table. +A call of the form <code>f'<em>string</em>'</code> +(or <code>f"<em>string</em>"</code> or <code>f[[<em>string</em>]]</code>) +is syntactic sugar for <code>f('<em>string</em>')</code>; +that is, the argument list is a single literal string. + + +<p> +A call of the form <code>return <em>functioncall</em></code> is called +a <em>tail call</em>. +Lua implements <em>proper tail calls</em> +(or <em>proper tail recursion</em>): +in a tail call, +the called function reuses the stack entry of the calling function. +Therefore, there is no limit on the number of nested tail calls that +a program can execute. +However, a tail call erases any debug information about the +calling function. +Note that a tail call only happens with a particular syntax, +where the <b>return</b> has one single function call as argument; +this syntax makes the calling function return exactly +the returns of the called function. +So, none of the following examples are tail calls: + +<pre> + return (f(x)) -- results adjusted to 1 + return 2 * f(x) + return x, f(x) -- additional results + f(x); return -- results discarded + return x or f(x) -- results adjusted to 1 +</pre> + + + + +<h3>3.4.11 – <a name="3.4.11">Function Definitions</a></h3> + +<p> +The syntax for function definition is + +<pre> + functiondef ::= <b>function</b> funcbody + funcbody ::= ‘<b>(</b>’ [parlist] ‘<b>)</b>’ block <b>end</b> +</pre> + +<p> +The following syntactic sugar simplifies function definitions: + +<pre> + stat ::= <b>function</b> funcname funcbody + stat ::= <b>local</b> <b>function</b> Name funcbody + funcname ::= Name {‘<b>.</b>’ Name} [‘<b>:</b>’ Name] +</pre><p> +The statement + +<pre> + function f () <em>body</em> end +</pre><p> +translates to + +<pre> + f = function () <em>body</em> end +</pre><p> +The statement + +<pre> + function t.a.b.c.f () <em>body</em> end +</pre><p> +translates to + +<pre> + t.a.b.c.f = function () <em>body</em> end +</pre><p> +The statement + +<pre> + local function f () <em>body</em> end +</pre><p> +translates to + +<pre> + local f; f = function () <em>body</em> end +</pre><p> +not to + +<pre> + local f = function () <em>body</em> end +</pre><p> +(This only makes a difference when the body of the function +contains references to <code>f</code>.) + + +<p> +A function definition is an executable expression, +whose value has type <em>function</em>. +When Lua precompiles a chunk, +all its function bodies are precompiled too. +Then, whenever Lua executes the function definition, +the function is <em>instantiated</em> (or <em>closed</em>). +This function instance (or <em>closure</em>) +is the final value of the expression. + + +<p> +Parameters act as local variables that are +initialized with the argument values: + +<pre> + parlist ::= namelist [‘<b>,</b>’ ‘<b>...</b>’] | ‘<b>...</b>’ +</pre><p> +When a function is called, +the list of arguments is adjusted to +the length of the list of parameters, +unless the function is a <em>vararg function</em>, +which is indicated by three dots ('<code>...</code>') +at the end of its parameter list. +A vararg function does not adjust its argument list; +instead, it collects all extra arguments and supplies them +to the function through a <em>vararg expression</em>, +which is also written as three dots. +The value of this expression is a list of all actual extra arguments, +similar to a function with multiple results. +If a vararg expression is used inside another expression +or in the middle of a list of expressions, +then its return list is adjusted to one element. +If the expression is used as the last element of a list of expressions, +then no adjustment is made +(unless that last expression is enclosed in parentheses). + + +<p> +As an example, consider the following definitions: + +<pre> + function f(a, b) end + function g(a, b, ...) end + function r() return 1,2,3 end +</pre><p> +Then, we have the following mapping from arguments to parameters and +to the vararg expression: + +<pre> + CALL PARAMETERS + + f(3) a=3, b=nil + f(3, 4) a=3, b=4 + f(3, 4, 5) a=3, b=4 + f(r(), 10) a=1, b=10 + f(r()) a=1, b=2 + + g(3) a=3, b=nil, ... --> (nothing) + g(3, 4) a=3, b=4, ... --> (nothing) + g(3, 4, 5, 8) a=3, b=4, ... --> 5 8 + g(5, r()) a=5, b=1, ... --> 2 3 +</pre> + +<p> +Results are returned using the <b>return</b> statement (see <a href="#3.3.4">§3.3.4</a>). +If control reaches the end of a function +without encountering a <b>return</b> statement, +then the function returns with no results. + + +<p> + +There is a system-dependent limit on the number of values +that a function may return. +This limit is guaranteed to be larger than 1000. + + +<p> +The <em>colon</em> syntax +is used for defining <em>methods</em>, +that is, functions that have an implicit extra parameter <code>self</code>. +Thus, the statement + +<pre> + function t.a.b.c:f (<em>params</em>) <em>body</em> end +</pre><p> +is syntactic sugar for + +<pre> + t.a.b.c.f = function (self, <em>params</em>) <em>body</em> end +</pre> + + + + + + +<h2>3.5 – <a name="3.5">Visibility Rules</a></h2> + +<p> + +Lua is a lexically scoped language. +The scope of a local variable begins at the first statement after +its declaration and lasts until the last non-void statement +of the innermost block that includes the declaration. +Consider the following example: + +<pre> + x = 10 -- global variable + do -- new block + local x = x -- new 'x', with value 10 + print(x) --> 10 + x = x+1 + do -- another block + local x = x+1 -- another 'x' + print(x) --> 12 + end + print(x) --> 11 + end + print(x) --> 10 (the global one) +</pre> + +<p> +Notice that, in a declaration like <code>local x = x</code>, +the new <code>x</code> being declared is not in scope yet, +and so the second <code>x</code> refers to the outside variable. + + +<p> +Because of the lexical scoping rules, +local variables can be freely accessed by functions +defined inside their scope. +A local variable used by an inner function is called +an <em>upvalue</em>, or <em>external local variable</em>, +inside the inner function. + + +<p> +Notice that each execution of a <b>local</b> statement +defines new local variables. +Consider the following example: + +<pre> + a = {} + local x = 20 + for i=1,10 do + local y = 0 + a[i] = function () y=y+1; return x+y end + end +</pre><p> +The loop creates ten closures +(that is, ten instances of the anonymous function). +Each of these closures uses a different <code>y</code> variable, +while all of them share the same <code>x</code>. + + + + + +<h1>4 – <a name="4">The Application Program Interface</a></h1> + +<p> + +This section describes the C API for Lua, that is, +the set of C functions available to the host program to communicate +with Lua. +All API functions and related types and constants +are declared in the header file <a name="pdf-lua.h"><code>lua.h</code></a>. + + +<p> +Even when we use the term "function", +any facility in the API may be provided as a macro instead. +Except where stated otherwise, +all such macros use each of their arguments exactly once +(except for the first argument, which is always a Lua state), +and so do not generate any hidden side-effects. + + +<p> +As in most C libraries, +the Lua API functions do not check their arguments for validity or consistency. +However, you can change this behavior by compiling Lua +with the macro <a name="pdf-LUA_USE_APICHECK"><code>LUA_USE_APICHECK</code></a> defined. + + + +<h2>4.1 – <a name="4.1">The Stack</a></h2> + +<p> +Lua uses a <em>virtual stack</em> to pass values to and from C. +Each element in this stack represents a Lua value +(<b>nil</b>, number, string, etc.). + + +<p> +Whenever Lua calls C, the called function gets a new stack, +which is independent of previous stacks and of stacks of +C functions that are still active. +This stack initially contains any arguments to the C function +and it is where the C function pushes its results +to be returned to the caller (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>). + + +<p> +For convenience, +most query operations in the API do not follow a strict stack discipline. +Instead, they can refer to any element in the stack +by using an <em>index</em>: +A positive index represents an absolute stack position +(starting at 1); +a negative index represents an offset relative to the top of the stack. +More specifically, if the stack has <em>n</em> elements, +then index 1 represents the first element +(that is, the element that was pushed onto the stack first) +and +index <em>n</em> represents the last element; +index -1 also represents the last element +(that is, the element at the top) +and index <em>-n</em> represents the first element. + + + + + +<h2>4.2 – <a name="4.2">Stack Size</a></h2> + +<p> +When you interact with the Lua API, +you are responsible for ensuring consistency. +In particular, +<em>you are responsible for controlling stack overflow</em>. +You can use the function <a href="#lua_checkstack"><code>lua_checkstack</code></a> +to ensure that the stack has enough space for pushing new elements. + + +<p> +Whenever Lua calls C, +it ensures that the stack has space for +at least <a name="pdf-LUA_MINSTACK"><code>LUA_MINSTACK</code></a> extra slots. +<code>LUA_MINSTACK</code> is defined as 20, +so that usually you do not have to worry about stack space +unless your code has loops pushing elements onto the stack. + + +<p> +When you call a Lua function +without a fixed number of results (see <a href="#lua_call"><code>lua_call</code></a>), +Lua ensures that the stack has enough space for all results, +but it does not ensure any extra space. +So, before pushing anything in the stack after such a call +you should use <a href="#lua_checkstack"><code>lua_checkstack</code></a>. + + + + + +<h2>4.3 – <a name="4.3">Valid and Acceptable Indices</a></h2> + +<p> +Any function in the API that receives stack indices +works only with <em>valid indices</em> or <em>acceptable indices</em>. + + +<p> +A <em>valid index</em> is an index that refers to a +real position within the stack, that is, +its position lies between 1 and the stack top +(<code>1 ≤ abs(index) ≤ top</code>). + +Usually, functions that can modify the value at an index +require valid indices. + + +<p> +Unless otherwise noted, +any function that accepts valid indices also accepts <em>pseudo-indices</em>, +which represent some Lua values that are accessible to C code +but which are not in the stack. +Pseudo-indices are used to access the registry +and the upvalues of a C function (see <a href="#4.4">§4.4</a>). + + +<p> +Functions that do not need a specific stack position, +but only a value in the stack (e.g., query functions), +can be called with acceptable indices. +An <em>acceptable index</em> can be any valid index, +including the pseudo-indices, +but it also can be any positive index after the stack top +within the space allocated for the stack, +that is, indices up to the stack size. +(Note that 0 is never an acceptable index.) +Except when noted otherwise, +functions in the API work with acceptable indices. + + +<p> +Acceptable indices serve to avoid extra tests +against the stack top when querying the stack. +For instance, a C function can query its third argument +without the need to first check whether there is a third argument, +that is, without the need to check whether 3 is a valid index. + + +<p> +For functions that can be called with acceptable indices, +any non-valid index is treated as if it +contains a value of a virtual type <a name="pdf-LUA_TNONE"><code>LUA_TNONE</code></a>, +which behaves like a nil value. + + + + + +<h2>4.4 – <a name="4.4">C Closures</a></h2> + +<p> +When a C function is created, +it is possible to associate some values with it, +thus creating a <em>C closure</em> +(see <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a>); +these values are called <em>upvalues</em> and are +accessible to the function whenever it is called. + + +<p> +Whenever a C function is called, +its upvalues are located at specific pseudo-indices. +These pseudo-indices are produced by the macro +<a href="#lua_upvalueindex"><code>lua_upvalueindex</code></a>. +The first value associated with a function is at position +<code>lua_upvalueindex(1)</code>, and so on. +Any access to <code>lua_upvalueindex(<em>n</em>)</code>, +where <em>n</em> is greater than the number of upvalues of the +current function (but not greater than 256), +produces an acceptable but invalid index. + + + + + +<h2>4.5 – <a name="4.5">Registry</a></h2> + +<p> +Lua provides a <em>registry</em>, +a predefined table that can be used by any C code to +store whatever Lua values it needs to store. +The registry table is always located at pseudo-index +<a name="pdf-LUA_REGISTRYINDEX"><code>LUA_REGISTRYINDEX</code></a>, +which is a valid index. +Any C library can store data into this table, +but it must take care to choose keys +that are different from those used +by other libraries, to avoid collisions. +Typically, you should use as key a string containing your library name, +or a light userdata with the address of a C object in your code, +or any Lua object created by your code. +As with variable names, +string keys starting with an underscore followed by +uppercase letters are reserved for Lua. + + +<p> +The integer keys in the registry are used +by the reference mechanism (see <a href="#luaL_ref"><code>luaL_ref</code></a>) +and by some predefined values. +Therefore, integer keys must not be used for other purposes. + + +<p> +When you create a new Lua state, +its registry comes with some predefined values. +These predefined values are indexed with integer keys +defined as constants in <code>lua.h</code>. +The following constants are defined: + +<ul> +<li><b><a name="pdf-LUA_RIDX_MAINTHREAD"><code>LUA_RIDX_MAINTHREAD</code></a>: </b> At this index the registry has +the main thread of the state. +(The main thread is the one created together with the state.) +</li> + +<li><b><a name="pdf-LUA_RIDX_GLOBALS"><code>LUA_RIDX_GLOBALS</code></a>: </b> At this index the registry has +the global environment. +</li> +</ul> + + + + +<h2>4.6 – <a name="4.6">Error Handling in C</a></h2> + +<p> +Internally, Lua uses the C <code>longjmp</code> facility to handle errors. +(Lua will use exceptions if you compile it as C++; +search for <code>LUAI_THROW</code> in the source code for details.) +When Lua faces any error +(such as a memory allocation error, type errors, syntax errors, +and runtime errors) +it <em>raises</em> an error; +that is, it does a long jump. +A <em>protected environment</em> uses <code>setjmp</code> +to set a recovery point; +any error jumps to the most recent active recovery point. + + +<p> +If an error happens outside any protected environment, +Lua calls a <em>panic function</em> (see <a href="#lua_atpanic"><code>lua_atpanic</code></a>) +and then calls <code>abort</code>, +thus exiting the host application. +Your panic function can avoid this exit by +never returning +(e.g., doing a long jump to your own recovery point outside Lua). + + +<p> +The panic function runs as if it were a message handler (see <a href="#2.3">§2.3</a>); +in particular, the error message is at the top of the stack. +However, there is no guarantee about stack space. +To push anything on the stack, +the panic function must first check the available space (see <a href="#4.2">§4.2</a>). + + +<p> +Most functions in the API can raise an error, +for instance due to a memory allocation error. +The documentation for each function indicates whether +it can raise errors. + + +<p> +Inside a C function you can raise an error by calling <a href="#lua_error"><code>lua_error</code></a>. + + + + + +<h2>4.7 – <a name="4.7">Handling Yields in C</a></h2> + +<p> +Internally, Lua uses the C <code>longjmp</code> facility to yield a coroutine. +Therefore, if a C function <code>foo</code> calls an API function +and this API function yields +(directly or indirectly by calling another function that yields), +Lua cannot return to <code>foo</code> any more, +because the <code>longjmp</code> removes its frame from the C stack. + + +<p> +To avoid this kind of problem, +Lua raises an error whenever it tries to yield across an API call, +except for three functions: +<a href="#lua_yieldk"><code>lua_yieldk</code></a>, <a href="#lua_callk"><code>lua_callk</code></a>, and <a href="#lua_pcallk"><code>lua_pcallk</code></a>. +All those functions receive a <em>continuation function</em> +(as a parameter named <code>k</code>) to continue execution after a yield. + + +<p> +We need to set some terminology to explain continuations. +We have a C function called from Lua which we will call +the <em>original function</em>. +This original function then calls one of those three functions in the C API, +which we will call the <em>callee function</em>, +that then yields the current thread. +(This can happen when the callee function is <a href="#lua_yieldk"><code>lua_yieldk</code></a>, +or when the callee function is either <a href="#lua_callk"><code>lua_callk</code></a> or <a href="#lua_pcallk"><code>lua_pcallk</code></a> +and the function called by them yields.) + + +<p> +Suppose the running thread yields while executing the callee function. +After the thread resumes, +it eventually will finish running the callee function. +However, +the callee function cannot return to the original function, +because its frame in the C stack was destroyed by the yield. +Instead, Lua calls a <em>continuation function</em>, +which was given as an argument to the callee function. +As the name implies, +the continuation function should continue the task +of the original function. + + +<p> +As an illustration, consider the following function: + +<pre> + int original_function (lua_State *L) { + ... /* code 1 */ + status = lua_pcall(L, n, m, h); /* calls Lua */ + ... /* code 2 */ + } +</pre><p> +Now we want to allow +the Lua code being run by <a href="#lua_pcall"><code>lua_pcall</code></a> to yield. +First, we can rewrite our function like here: + +<pre> + int k (lua_State *L, int status, lua_KContext ctx) { + ... /* code 2 */ + } + + int original_function (lua_State *L) { + ... /* code 1 */ + return k(L, lua_pcall(L, n, m, h), ctx); + } +</pre><p> +In the above code, +the new function <code>k</code> is a +<em>continuation function</em> (with type <a href="#lua_KFunction"><code>lua_KFunction</code></a>), +which should do all the work that the original function +was doing after calling <a href="#lua_pcall"><code>lua_pcall</code></a>. +Now, we must inform Lua that it must call <code>k</code> if the Lua code +being executed by <a href="#lua_pcall"><code>lua_pcall</code></a> gets interrupted in some way +(errors or yielding), +so we rewrite the code as here, +replacing <a href="#lua_pcall"><code>lua_pcall</code></a> by <a href="#lua_pcallk"><code>lua_pcallk</code></a>: + +<pre> + int original_function (lua_State *L) { + ... /* code 1 */ + return k(L, lua_pcallk(L, n, m, h, ctx2, k), ctx1); + } +</pre><p> +Note the external, explicit call to the continuation: +Lua will call the continuation only if needed, that is, +in case of errors or resuming after a yield. +If the called function returns normally without ever yielding, +<a href="#lua_pcallk"><code>lua_pcallk</code></a> (and <a href="#lua_callk"><code>lua_callk</code></a>) will also return normally. +(Of course, instead of calling the continuation in that case, +you can do the equivalent work directly inside the original function.) + + +<p> +Besides the Lua state, +the continuation function has two other parameters: +the final status of the call plus the context value (<code>ctx</code>) that +was passed originally to <a href="#lua_pcallk"><code>lua_pcallk</code></a>. +(Lua does not use this context value; +it only passes this value from the original function to the +continuation function.) +For <a href="#lua_pcallk"><code>lua_pcallk</code></a>, +the status is the same value that would be returned by <a href="#lua_pcallk"><code>lua_pcallk</code></a>, +except that it is <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> when being executed after a yield +(instead of <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>). +For <a href="#lua_yieldk"><code>lua_yieldk</code></a> and <a href="#lua_callk"><code>lua_callk</code></a>, +the status is always <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> when Lua calls the continuation. +(For these two functions, +Lua will not call the continuation in case of errors, +because they do not handle errors.) +Similarly, when using <a href="#lua_callk"><code>lua_callk</code></a>, +you should call the continuation function +with <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> as the status. +(For <a href="#lua_yieldk"><code>lua_yieldk</code></a>, there is not much point in calling +directly the continuation function, +because <a href="#lua_yieldk"><code>lua_yieldk</code></a> usually does not return.) + + +<p> +Lua treats the continuation function as if it were the original function. +The continuation function receives the same Lua stack +from the original function, +in the same state it would be if the callee function had returned. +(For instance, +after a <a href="#lua_callk"><code>lua_callk</code></a> the function and its arguments are +removed from the stack and replaced by the results from the call.) +It also has the same upvalues. +Whatever it returns is handled by Lua as if it were the return +of the original function. + + + + + +<h2>4.8 – <a name="4.8">Functions and Types</a></h2> + +<p> +Here we list all functions and types from the C API in +alphabetical order. +Each function has an indicator like this: +<span class="apii">[-o, +p, <em>x</em>]</span> + + +<p> +The first field, <code>o</code>, +is how many elements the function pops from the stack. +The second field, <code>p</code>, +is how many elements the function pushes onto the stack. +(Any function always pushes its results after popping its arguments.) +A field in the form <code>x|y</code> means the function can push (or pop) +<code>x</code> or <code>y</code> elements, +depending on the situation; +an interrogation mark '<code>?</code>' means that +we cannot know how many elements the function pops/pushes +by looking only at its arguments +(e.g., they may depend on what is on the stack). +The third field, <code>x</code>, +tells whether the function may raise errors: +'<code>-</code>' means the function never raises any error; +'<code>e</code>' means the function may raise errors; +'<code>v</code>' means the function may raise an error on purpose. + + + +<hr><h3><a name="lua_absindex"><code>lua_absindex</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_absindex (lua_State *L, int idx);</pre> + +<p> +Converts the acceptable index <code>idx</code> into an absolute index +(that is, one that does not depend on the stack top). + + + + + +<hr><h3><a name="lua_Alloc"><code>lua_Alloc</code></a></h3> +<pre>typedef void * (*lua_Alloc) (void *ud, + void *ptr, + size_t osize, + size_t nsize);</pre> + +<p> +The type of the memory-allocation function used by Lua states. +The allocator function must provide a +functionality similar to <code>realloc</code>, +but not exactly the same. +Its arguments are +<code>ud</code>, an opaque pointer passed to <a href="#lua_newstate"><code>lua_newstate</code></a>; +<code>ptr</code>, a pointer to the block being allocated/reallocated/freed; +<code>osize</code>, the original size of the block or some code about what +is being allocated; +and <code>nsize</code>, the new size of the block. + + +<p> +When <code>ptr</code> is not <code>NULL</code>, +<code>osize</code> is the size of the block pointed by <code>ptr</code>, +that is, the size given when it was allocated or reallocated. + + +<p> +When <code>ptr</code> is <code>NULL</code>, +<code>osize</code> encodes the kind of object that Lua is allocating. +<code>osize</code> is any of +<a href="#pdf-LUA_TSTRING"><code>LUA_TSTRING</code></a>, <a href="#pdf-LUA_TTABLE"><code>LUA_TTABLE</code></a>, <a href="#pdf-LUA_TFUNCTION"><code>LUA_TFUNCTION</code></a>, +<a href="#pdf-LUA_TUSERDATA"><code>LUA_TUSERDATA</code></a>, or <a href="#pdf-LUA_TTHREAD"><code>LUA_TTHREAD</code></a> when (and only when) +Lua is creating a new object of that type. +When <code>osize</code> is some other value, +Lua is allocating memory for something else. + + +<p> +Lua assumes the following behavior from the allocator function: + + +<p> +When <code>nsize</code> is zero, +the allocator must behave like <code>free</code> +and return <code>NULL</code>. + + +<p> +When <code>nsize</code> is not zero, +the allocator must behave like <code>realloc</code>. +The allocator returns <code>NULL</code> +if and only if it cannot fulfill the request. +Lua assumes that the allocator never fails when +<code>osize >= nsize</code>. + + +<p> +Here is a simple implementation for the allocator function. +It is used in the auxiliary library by <a href="#luaL_newstate"><code>luaL_newstate</code></a>. + +<pre> + static void *l_alloc (void *ud, void *ptr, size_t osize, + size_t nsize) { + (void)ud; (void)osize; /* not used */ + if (nsize == 0) { + free(ptr); + return NULL; + } + else + return realloc(ptr, nsize); + } +</pre><p> +Note that Standard C ensures +that <code>free(NULL)</code> has no effect and that +<code>realloc(NULL,size)</code> is equivalent to <code>malloc(size)</code>. +This code assumes that <code>realloc</code> does not fail when shrinking a block. +(Although Standard C does not ensure this behavior, +it seems to be a safe assumption.) + + + + + +<hr><h3><a name="lua_arith"><code>lua_arith</code></a></h3><p> +<span class="apii">[-(2|1), +1, <em>e</em>]</span> +<pre>void lua_arith (lua_State *L, int op);</pre> + +<p> +Performs an arithmetic or bitwise operation over the two values +(or one, in the case of negations) +at the top of the stack, +with the value at the top being the second operand, +pops these values, and pushes the result of the operation. +The function follows the semantics of the corresponding Lua operator +(that is, it may call metamethods). + + +<p> +The value of <code>op</code> must be one of the following constants: + +<ul> + +<li><b><a name="pdf-LUA_OPADD"><code>LUA_OPADD</code></a>: </b> performs addition (<code>+</code>)</li> +<li><b><a name="pdf-LUA_OPSUB"><code>LUA_OPSUB</code></a>: </b> performs subtraction (<code>-</code>)</li> +<li><b><a name="pdf-LUA_OPMUL"><code>LUA_OPMUL</code></a>: </b> performs multiplication (<code>*</code>)</li> +<li><b><a name="pdf-LUA_OPDIV"><code>LUA_OPDIV</code></a>: </b> performs float division (<code>/</code>)</li> +<li><b><a name="pdf-LUA_OPIDIV"><code>LUA_OPIDIV</code></a>: </b> performs floor division (<code>//</code>)</li> +<li><b><a name="pdf-LUA_OPMOD"><code>LUA_OPMOD</code></a>: </b> performs modulo (<code>%</code>)</li> +<li><b><a name="pdf-LUA_OPPOW"><code>LUA_OPPOW</code></a>: </b> performs exponentiation (<code>^</code>)</li> +<li><b><a name="pdf-LUA_OPUNM"><code>LUA_OPUNM</code></a>: </b> performs mathematical negation (unary <code>-</code>)</li> +<li><b><a name="pdf-LUA_OPBNOT"><code>LUA_OPBNOT</code></a>: </b> performs bitwise negation (<code>~</code>)</li> +<li><b><a name="pdf-LUA_OPBAND"><code>LUA_OPBAND</code></a>: </b> performs bitwise and (<code>&</code>)</li> +<li><b><a name="pdf-LUA_OPBOR"><code>LUA_OPBOR</code></a>: </b> performs bitwise or (<code>|</code>)</li> +<li><b><a name="pdf-LUA_OPBXOR"><code>LUA_OPBXOR</code></a>: </b> performs bitwise exclusive or (<code>~</code>)</li> +<li><b><a name="pdf-LUA_OPSHL"><code>LUA_OPSHL</code></a>: </b> performs left shift (<code><<</code>)</li> +<li><b><a name="pdf-LUA_OPSHR"><code>LUA_OPSHR</code></a>: </b> performs right shift (<code>>></code>)</li> + +</ul> + + + + +<hr><h3><a name="lua_atpanic"><code>lua_atpanic</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>lua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf);</pre> + +<p> +Sets a new panic function and returns the old one (see <a href="#4.6">§4.6</a>). + + + + + +<hr><h3><a name="lua_call"><code>lua_call</code></a></h3><p> +<span class="apii">[-(nargs+1), +nresults, <em>e</em>]</span> +<pre>void lua_call (lua_State *L, int nargs, int nresults);</pre> + +<p> +Calls a function. + + +<p> +To call a function you must use the following protocol: +first, the function to be called is pushed onto the stack; +then, the arguments to the function are pushed +in direct order; +that is, the first argument is pushed first. +Finally you call <a href="#lua_call"><code>lua_call</code></a>; +<code>nargs</code> is the number of arguments that you pushed onto the stack. +All arguments and the function value are popped from the stack +when the function is called. +The function results are pushed onto the stack when the function returns. +The number of results is adjusted to <code>nresults</code>, +unless <code>nresults</code> is <a name="pdf-LUA_MULTRET"><code>LUA_MULTRET</code></a>. +In this case, all results from the function are pushed. +Lua takes care that the returned values fit into the stack space. +The function results are pushed onto the stack in direct order +(the first result is pushed first), +so that after the call the last result is on the top of the stack. + + +<p> +Any error inside the called function is propagated upwards +(with a <code>longjmp</code>). + + +<p> +The following example shows how the host program can do the +equivalent to this Lua code: + +<pre> + a = f("how", t.x, 14) +</pre><p> +Here it is in C: + +<pre> + lua_getglobal(L, "f"); /* function to be called */ + lua_pushliteral(L, "how"); /* 1st argument */ + lua_getglobal(L, "t"); /* table to be indexed */ + lua_getfield(L, -1, "x"); /* push result of t.x (2nd arg) */ + lua_remove(L, -2); /* remove 't' from the stack */ + lua_pushinteger(L, 14); /* 3rd argument */ + lua_call(L, 3, 1); /* call 'f' with 3 arguments and 1 result */ + lua_setglobal(L, "a"); /* set global 'a' */ +</pre><p> +Note that the code above is <em>balanced</em>: +at its end, the stack is back to its original configuration. +This is considered good programming practice. + + + + + +<hr><h3><a name="lua_callk"><code>lua_callk</code></a></h3><p> +<span class="apii">[-(nargs + 1), +nresults, <em>e</em>]</span> +<pre>void lua_callk (lua_State *L, + int nargs, + int nresults, + lua_KContext ctx, + lua_KFunction k);</pre> + +<p> +This function behaves exactly like <a href="#lua_call"><code>lua_call</code></a>, +but allows the called function to yield (see <a href="#4.7">§4.7</a>). + + + + + +<hr><h3><a name="lua_CFunction"><code>lua_CFunction</code></a></h3> +<pre>typedef int (*lua_CFunction) (lua_State *L);</pre> + +<p> +Type for C functions. + + +<p> +In order to communicate properly with Lua, +a C function must use the following protocol, +which defines the way parameters and results are passed: +a C function receives its arguments from Lua in its stack +in direct order (the first argument is pushed first). +So, when the function starts, +<code>lua_gettop(L)</code> returns the number of arguments received by the function. +The first argument (if any) is at index 1 +and its last argument is at index <code>lua_gettop(L)</code>. +To return values to Lua, a C function just pushes them onto the stack, +in direct order (the first result is pushed first), +and returns the number of results. +Any other value in the stack below the results will be properly +discarded by Lua. +Like a Lua function, a C function called by Lua can also return +many results. + + +<p> +As an example, the following function receives a variable number +of numerical arguments and returns their average and their sum: + +<pre> + static int foo (lua_State *L) { + int n = lua_gettop(L); /* number of arguments */ + lua_Number sum = 0.0; + int i; + for (i = 1; i <= n; i++) { + if (!lua_isnumber(L, i)) { + lua_pushliteral(L, "incorrect argument"); + lua_error(L); + } + sum += lua_tonumber(L, i); + } + lua_pushnumber(L, sum/n); /* first result */ + lua_pushnumber(L, sum); /* second result */ + return 2; /* number of results */ + } +</pre> + + + + +<hr><h3><a name="lua_checkstack"><code>lua_checkstack</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_checkstack (lua_State *L, int n);</pre> + +<p> +Ensures that the stack has space for at least <code>n</code> extra slots. +It returns false if it cannot fulfill the request, +either because it would cause the stack +to be larger than a fixed maximum size +(typically at least several thousand elements) or +because it cannot allocate memory for the extra space. +This function never shrinks the stack; +if the stack is already larger than the new size, +it is left unchanged. + + + + + +<hr><h3><a name="lua_close"><code>lua_close</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>void lua_close (lua_State *L);</pre> + +<p> +Destroys all objects in the given Lua state +(calling the corresponding garbage-collection metamethods, if any) +and frees all dynamic memory used by this state. +On several platforms, you may not need to call this function, +because all resources are naturally released when the host program ends. +On the other hand, long-running programs that create multiple states, +such as daemons or web servers, +will probably need to close states as soon as they are not needed. + + + + + +<hr><h3><a name="lua_compare"><code>lua_compare</code></a></h3><p> +<span class="apii">[-0, +0, <em>e</em>]</span> +<pre>int lua_compare (lua_State *L, int index1, int index2, int op);</pre> + +<p> +Compares two Lua values. +Returns 1 if the value at index <code>index1</code> satisfies <code>op</code> +when compared with the value at index <code>index2</code>, +following the semantics of the corresponding Lua operator +(that is, it may call metamethods). +Otherwise returns 0. +Also returns 0 if any of the indices is not valid. + + +<p> +The value of <code>op</code> must be one of the following constants: + +<ul> + +<li><b><a name="pdf-LUA_OPEQ"><code>LUA_OPEQ</code></a>: </b> compares for equality (<code>==</code>)</li> +<li><b><a name="pdf-LUA_OPLT"><code>LUA_OPLT</code></a>: </b> compares for less than (<code><</code>)</li> +<li><b><a name="pdf-LUA_OPLE"><code>LUA_OPLE</code></a>: </b> compares for less or equal (<code><=</code>)</li> + +</ul> + + + + +<hr><h3><a name="lua_concat"><code>lua_concat</code></a></h3><p> +<span class="apii">[-n, +1, <em>e</em>]</span> +<pre>void lua_concat (lua_State *L, int n);</pre> + +<p> +Concatenates the <code>n</code> values at the top of the stack, +pops them, and leaves the result at the top. +If <code>n</code> is 1, the result is the single value on the stack +(that is, the function does nothing); +if <code>n</code> is 0, the result is the empty string. +Concatenation is performed following the usual semantics of Lua +(see <a href="#3.4.6">§3.4.6</a>). + + + + + +<hr><h3><a name="lua_copy"><code>lua_copy</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>void lua_copy (lua_State *L, int fromidx, int toidx);</pre> + +<p> +Copies the element at index <code>fromidx</code> +into the valid index <code>toidx</code>, +replacing the value at that position. +Values at other positions are not affected. + + + + + +<hr><h3><a name="lua_createtable"><code>lua_createtable</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>void lua_createtable (lua_State *L, int narr, int nrec);</pre> + +<p> +Creates a new empty table and pushes it onto the stack. +Parameter <code>narr</code> is a hint for how many elements the table +will have as a sequence; +parameter <code>nrec</code> is a hint for how many other elements +the table will have. +Lua may use these hints to preallocate memory for the new table. +This pre-allocation is useful for performance when you know in advance +how many elements the table will have. +Otherwise you can use the function <a href="#lua_newtable"><code>lua_newtable</code></a>. + + + + + +<hr><h3><a name="lua_dump"><code>lua_dump</code></a></h3><p> +<span class="apii">[-0, +0, <em>e</em>]</span> +<pre>int lua_dump (lua_State *L, + lua_Writer writer, + void *data, + int strip);</pre> + +<p> +Dumps a function as a binary chunk. +Receives a Lua function on the top of the stack +and produces a binary chunk that, +if loaded again, +results in a function equivalent to the one dumped. +As it produces parts of the chunk, +<a href="#lua_dump"><code>lua_dump</code></a> calls function <code>writer</code> (see <a href="#lua_Writer"><code>lua_Writer</code></a>) +with the given <code>data</code> +to write them. + + +<p> +If <code>strip</code> is true, +the binary representation is created without debug information +about the function. + + +<p> +The value returned is the error code returned by the last +call to the writer; +0 means no errors. + + +<p> +This function does not pop the Lua function from the stack. + + + + + +<hr><h3><a name="lua_error"><code>lua_error</code></a></h3><p> +<span class="apii">[-1, +0, <em>v</em>]</span> +<pre>int lua_error (lua_State *L);</pre> + +<p> +Generates a Lua error, +using the value at the top of the stack as the error object. +This function does a long jump, +and therefore never returns +(see <a href="#luaL_error"><code>luaL_error</code></a>). + + + + + +<hr><h3><a name="lua_gc"><code>lua_gc</code></a></h3><p> +<span class="apii">[-0, +0, <em>e</em>]</span> +<pre>int lua_gc (lua_State *L, int what, int data);</pre> + +<p> +Controls the garbage collector. + + +<p> +This function performs several tasks, +according to the value of the parameter <code>what</code>: + +<ul> + +<li><b><code>LUA_GCSTOP</code>: </b> +stops the garbage collector. +</li> + +<li><b><code>LUA_GCRESTART</code>: </b> +restarts the garbage collector. +</li> + +<li><b><code>LUA_GCCOLLECT</code>: </b> +performs a full garbage-collection cycle. +</li> + +<li><b><code>LUA_GCCOUNT</code>: </b> +returns the current amount of memory (in Kbytes) in use by Lua. +</li> + +<li><b><code>LUA_GCCOUNTB</code>: </b> +returns the remainder of dividing the current amount of bytes of +memory in use by Lua by 1024. +</li> + +<li><b><code>LUA_GCSTEP</code>: </b> +performs an incremental step of garbage collection. +</li> + +<li><b><code>LUA_GCSETPAUSE</code>: </b> +sets <code>data</code> as the new value +for the <em>pause</em> of the collector (see <a href="#2.5">§2.5</a>) +and returns the previous value of the pause. +</li> + +<li><b><code>LUA_GCSETSTEPMUL</code>: </b> +sets <code>data</code> as the new value for the <em>step multiplier</em> of +the collector (see <a href="#2.5">§2.5</a>) +and returns the previous value of the step multiplier. +</li> + +<li><b><code>LUA_GCISRUNNING</code>: </b> +returns a boolean that tells whether the collector is running +(i.e., not stopped). +</li> + +</ul> + +<p> +For more details about these options, +see <a href="#pdf-collectgarbage"><code>collectgarbage</code></a>. + + + + + +<hr><h3><a name="lua_getallocf"><code>lua_getallocf</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>lua_Alloc lua_getallocf (lua_State *L, void **ud);</pre> + +<p> +Returns the memory-allocation function of a given state. +If <code>ud</code> is not <code>NULL</code>, Lua stores in <code>*ud</code> the +opaque pointer given when the memory-allocator function was set. + + + + + +<hr><h3><a name="lua_getfield"><code>lua_getfield</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>int lua_getfield (lua_State *L, int index, const char *k);</pre> + +<p> +Pushes onto the stack the value <code>t[k]</code>, +where <code>t</code> is the value at the given index. +As in Lua, this function may trigger a metamethod +for the "index" event (see <a href="#2.4">§2.4</a>). + + +<p> +Returns the type of the pushed value. + + + + + +<hr><h3><a name="lua_getextraspace"><code>lua_getextraspace</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>void *lua_getextraspace (lua_State *L);</pre> + +<p> +Returns a pointer to a raw memory area associated with the +given Lua state. +The application can use this area for any purpose; +Lua does not use it for anything. + + +<p> +Each new thread has this area initialized with a copy +of the area of the main thread. + + +<p> +By default, this area has the size of a pointer to void, +but you can recompile Lua with a different size for this area. +(See <code>LUA_EXTRASPACE</code> in <code>luaconf.h</code>.) + + + + + +<hr><h3><a name="lua_getglobal"><code>lua_getglobal</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>int lua_getglobal (lua_State *L, const char *name);</pre> + +<p> +Pushes onto the stack the value of the global <code>name</code>. +Returns the type of that value. + + + + + +<hr><h3><a name="lua_geti"><code>lua_geti</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>int lua_geti (lua_State *L, int index, lua_Integer i);</pre> + +<p> +Pushes onto the stack the value <code>t[i]</code>, +where <code>t</code> is the value at the given index. +As in Lua, this function may trigger a metamethod +for the "index" event (see <a href="#2.4">§2.4</a>). + + +<p> +Returns the type of the pushed value. + + + + + +<hr><h3><a name="lua_getmetatable"><code>lua_getmetatable</code></a></h3><p> +<span class="apii">[-0, +(0|1), –]</span> +<pre>int lua_getmetatable (lua_State *L, int index);</pre> + +<p> +If the value at the given index has a metatable, +the function pushes that metatable onto the stack and returns 1. +Otherwise, +the function returns 0 and pushes nothing on the stack. + + + + + +<hr><h3><a name="lua_gettable"><code>lua_gettable</code></a></h3><p> +<span class="apii">[-1, +1, <em>e</em>]</span> +<pre>int lua_gettable (lua_State *L, int index);</pre> + +<p> +Pushes onto the stack the value <code>t[k]</code>, +where <code>t</code> is the value at the given index +and <code>k</code> is the value at the top of the stack. + + +<p> +This function pops the key from the stack, +pushing the resulting value in its place. +As in Lua, this function may trigger a metamethod +for the "index" event (see <a href="#2.4">§2.4</a>). + + +<p> +Returns the type of the pushed value. + + + + + +<hr><h3><a name="lua_gettop"><code>lua_gettop</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_gettop (lua_State *L);</pre> + +<p> +Returns the index of the top element in the stack. +Because indices start at 1, +this result is equal to the number of elements in the stack; +in particular, 0 means an empty stack. + + + + + +<hr><h3><a name="lua_getuservalue"><code>lua_getuservalue</code></a></h3><p> +<span class="apii">[-0, +1, –]</span> +<pre>int lua_getuservalue (lua_State *L, int index);</pre> + +<p> +Pushes onto the stack the Lua value associated with the userdata +at the given index. + + +<p> +Returns the type of the pushed value. + + + + + +<hr><h3><a name="lua_insert"><code>lua_insert</code></a></h3><p> +<span class="apii">[-1, +1, –]</span> +<pre>void lua_insert (lua_State *L, int index);</pre> + +<p> +Moves the top element into the given valid index, +shifting up the elements above this index to open space. +This function cannot be called with a pseudo-index, +because a pseudo-index is not an actual stack position. + + + + + +<hr><h3><a name="lua_Integer"><code>lua_Integer</code></a></h3> +<pre>typedef ... lua_Integer;</pre> + +<p> +The type of integers in Lua. + + +<p> +By default this type is <code>long long</code>, +(usually a 64-bit two-complement integer), +but that can be changed to <code>long</code> or <code>int</code> +(usually a 32-bit two-complement integer). +(See <code>LUA_INT</code> in <code>luaconf.h</code>.) + + +<p> +Lua also defines the constants +<a name="pdf-LUA_MININTEGER"><code>LUA_MININTEGER</code></a> and <a name="pdf-LUA_MAXINTEGER"><code>LUA_MAXINTEGER</code></a>, +with the minimum and the maximum values that fit in this type. + + + + + +<hr><h3><a name="lua_isboolean"><code>lua_isboolean</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_isboolean (lua_State *L, int index);</pre> + +<p> +Returns 1 if the value at the given index is a boolean, +and 0 otherwise. + + + + + +<hr><h3><a name="lua_iscfunction"><code>lua_iscfunction</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_iscfunction (lua_State *L, int index);</pre> + +<p> +Returns 1 if the value at the given index is a C function, +and 0 otherwise. + + + + + +<hr><h3><a name="lua_isfunction"><code>lua_isfunction</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_isfunction (lua_State *L, int index);</pre> + +<p> +Returns 1 if the value at the given index is a function +(either C or Lua), and 0 otherwise. + + + + + +<hr><h3><a name="lua_isinteger"><code>lua_isinteger</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_isinteger (lua_State *L, int index);</pre> + +<p> +Returns 1 if the value at the given index is an integer +(that is, the value is a number and is represented as an integer), +and 0 otherwise. + + + + + +<hr><h3><a name="lua_islightuserdata"><code>lua_islightuserdata</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_islightuserdata (lua_State *L, int index);</pre> + +<p> +Returns 1 if the value at the given index is a light userdata, +and 0 otherwise. + + + + + +<hr><h3><a name="lua_isnil"><code>lua_isnil</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_isnil (lua_State *L, int index);</pre> + +<p> +Returns 1 if the value at the given index is <b>nil</b>, +and 0 otherwise. + + + + + +<hr><h3><a name="lua_isnone"><code>lua_isnone</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_isnone (lua_State *L, int index);</pre> + +<p> +Returns 1 if the given index is not valid, +and 0 otherwise. + + + + + +<hr><h3><a name="lua_isnoneornil"><code>lua_isnoneornil</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_isnoneornil (lua_State *L, int index);</pre> + +<p> +Returns 1 if the given index is not valid +or if the value at this index is <b>nil</b>, +and 0 otherwise. + + + + + +<hr><h3><a name="lua_isnumber"><code>lua_isnumber</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_isnumber (lua_State *L, int index);</pre> + +<p> +Returns 1 if the value at the given index is a number +or a string convertible to a number, +and 0 otherwise. + + + + + +<hr><h3><a name="lua_isstring"><code>lua_isstring</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_isstring (lua_State *L, int index);</pre> + +<p> +Returns 1 if the value at the given index is a string +or a number (which is always convertible to a string), +and 0 otherwise. + + + + + +<hr><h3><a name="lua_istable"><code>lua_istable</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_istable (lua_State *L, int index);</pre> + +<p> +Returns 1 if the value at the given index is a table, +and 0 otherwise. + + + + + +<hr><h3><a name="lua_isthread"><code>lua_isthread</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_isthread (lua_State *L, int index);</pre> + +<p> +Returns 1 if the value at the given index is a thread, +and 0 otherwise. + + + + + +<hr><h3><a name="lua_isuserdata"><code>lua_isuserdata</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_isuserdata (lua_State *L, int index);</pre> + +<p> +Returns 1 if the value at the given index is a userdata +(either full or light), and 0 otherwise. + + + + + +<hr><h3><a name="lua_isyieldable"><code>lua_isyieldable</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_isyieldable (lua_State *L);</pre> + +<p> +Returns 1 if the given coroutine can yield, +and 0 otherwise. + + + + + +<hr><h3><a name="lua_KContext"><code>lua_KContext</code></a></h3> +<pre>typedef ... lua_KContext;</pre> + +<p> +The type for continuation-function contexts. +It must be a numerical type. +This type is defined as <code>intptr_t</code> +when <code>intptr_t</code> is available, +so that it can store pointers too. +Otherwise, it is defined as <code>ptrdiff_t</code>. + + + + + +<hr><h3><a name="lua_KFunction"><code>lua_KFunction</code></a></h3> +<pre>typedef int (*lua_KFunction) (lua_State *L, int status, lua_KContext ctx);</pre> + +<p> +Type for continuation functions (see <a href="#4.7">§4.7</a>). + + + + + +<hr><h3><a name="lua_len"><code>lua_len</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>void lua_len (lua_State *L, int index);</pre> + +<p> +Returns the length of the value at the given index. +It is equivalent to the '<code>#</code>' operator in Lua (see <a href="#3.4.7">§3.4.7</a>) and +may trigger a metamethod for the "length" event (see <a href="#2.4">§2.4</a>). +The result is pushed on the stack. + + + + + +<hr><h3><a name="lua_load"><code>lua_load</code></a></h3><p> +<span class="apii">[-0, +1, –]</span> +<pre>int lua_load (lua_State *L, + lua_Reader reader, + void *data, + const char *chunkname, + const char *mode);</pre> + +<p> +Loads a Lua chunk without running it. +If there are no errors, +<code>lua_load</code> pushes the compiled chunk as a Lua +function on top of the stack. +Otherwise, it pushes an error message. + + +<p> +The return values of <code>lua_load</code> are: + +<ul> + +<li><b><a href="#pdf-LUA_OK"><code>LUA_OK</code></a>: </b> no errors;</li> + +<li><b><a name="pdf-LUA_ERRSYNTAX"><code>LUA_ERRSYNTAX</code></a>: </b> +syntax error during precompilation;</li> + +<li><b><a href="#pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>: </b> +memory allocation error;</li> + +<li><b><a href="#pdf-LUA_ERRGCMM"><code>LUA_ERRGCMM</code></a>: </b> +error while running a <code>__gc</code> metamethod. +(This error has no relation with the chunk being loaded. +It is generated by the garbage collector.) +</li> + +</ul> + +<p> +The <code>lua_load</code> function uses a user-supplied <code>reader</code> function +to read the chunk (see <a href="#lua_Reader"><code>lua_Reader</code></a>). +The <code>data</code> argument is an opaque value passed to the reader function. + + +<p> +The <code>chunkname</code> argument gives a name to the chunk, +which is used for error messages and in debug information (see <a href="#4.9">§4.9</a>). + + +<p> +<code>lua_load</code> automatically detects whether the chunk is text or binary +and loads it accordingly (see program <code>luac</code>). +The string <code>mode</code> works as in function <a href="#pdf-load"><code>load</code></a>, +with the addition that +a <code>NULL</code> value is equivalent to the string "<code>bt</code>". + + +<p> +<code>lua_load</code> uses the stack internally, +so the reader function must always leave the stack +unmodified when returning. + + +<p> +If the resulting function has upvalues, +its first upvalue is set to the value of the global environment +stored at index <code>LUA_RIDX_GLOBALS</code> in the registry (see <a href="#4.5">§4.5</a>). +When loading main chunks, +this upvalue will be the <code>_ENV</code> variable (see <a href="#2.2">§2.2</a>). +Other upvalues are initialized with <b>nil</b>. + + + + + +<hr><h3><a name="lua_newstate"><code>lua_newstate</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>lua_State *lua_newstate (lua_Alloc f, void *ud);</pre> + +<p> +Creates a new thread running in a new, independent state. +Returns <code>NULL</code> if it cannot create the thread or the state +(due to lack of memory). +The argument <code>f</code> is the allocator function; +Lua does all memory allocation for this state through this function. +The second argument, <code>ud</code>, is an opaque pointer that Lua +passes to the allocator in every call. + + + + + +<hr><h3><a name="lua_newtable"><code>lua_newtable</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>void lua_newtable (lua_State *L);</pre> + +<p> +Creates a new empty table and pushes it onto the stack. +It is equivalent to <code>lua_createtable(L, 0, 0)</code>. + + + + + +<hr><h3><a name="lua_newthread"><code>lua_newthread</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>lua_State *lua_newthread (lua_State *L);</pre> + +<p> +Creates a new thread, pushes it on the stack, +and returns a pointer to a <a href="#lua_State"><code>lua_State</code></a> that represents this new thread. +The new thread returned by this function shares with the original thread +its global environment, +but has an independent execution stack. + + +<p> +There is no explicit function to close or to destroy a thread. +Threads are subject to garbage collection, +like any Lua object. + + + + + +<hr><h3><a name="lua_newuserdata"><code>lua_newuserdata</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>void *lua_newuserdata (lua_State *L, size_t size);</pre> + +<p> +This function allocates a new block of memory with the given size, +pushes onto the stack a new full userdata with the block address, +and returns this address. +The host program can freely use this memory. + + + + + +<hr><h3><a name="lua_next"><code>lua_next</code></a></h3><p> +<span class="apii">[-1, +(2|0), <em>e</em>]</span> +<pre>int lua_next (lua_State *L, int index);</pre> + +<p> +Pops a key from the stack, +and pushes a key–value pair from the table at the given index +(the "next" pair after the given key). +If there are no more elements in the table, +then <a href="#lua_next"><code>lua_next</code></a> returns 0 (and pushes nothing). + + +<p> +A typical traversal looks like this: + +<pre> + /* table is in the stack at index 't' */ + lua_pushnil(L); /* first key */ + while (lua_next(L, t) != 0) { + /* uses 'key' (at index -2) and 'value' (at index -1) */ + printf("%s - %s\n", + lua_typename(L, lua_type(L, -2)), + lua_typename(L, lua_type(L, -1))); + /* removes 'value'; keeps 'key' for next iteration */ + lua_pop(L, 1); + } +</pre> + +<p> +While traversing a table, +do not call <a href="#lua_tolstring"><code>lua_tolstring</code></a> directly on a key, +unless you know that the key is actually a string. +Recall that <a href="#lua_tolstring"><code>lua_tolstring</code></a> may change +the value at the given index; +this confuses the next call to <a href="#lua_next"><code>lua_next</code></a>. + + +<p> +See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying +the table during its traversal. + + + + + +<hr><h3><a name="lua_Number"><code>lua_Number</code></a></h3> +<pre>typedef double lua_Number;</pre> + +<p> +The type of floats in Lua. + + +<p> +By default this type is double, +but that can be changed to a single float. +(See <code>LUA_REAL</code> in <code>luaconf.h</code>.) + + + + + +<hr><h3><a name="lua_numbertointeger"><code>lua_numbertointeger</code></a></h3> +<pre>int lua_numbertointeger (lua_Number n, lua_Integer *p);</pre> + +<p> +Converts a Lua float to a Lua integer. +This macro assumes that <code>n</code> has an integral value. +If that value is within the range of Lua integers, +it is converted to an integer and assigned to <code>*p</code>. +The macro results in a boolean indicating whether the +conversion was successful. +(Note that this range test can be tricky to do +correctly without this macro, +due to roundings.) + + +<p> +This macro may evaluate its arguments more than once. + + + + + +<hr><h3><a name="lua_pcall"><code>lua_pcall</code></a></h3><p> +<span class="apii">[-(nargs + 1), +(nresults|1), –]</span> +<pre>int lua_pcall (lua_State *L, int nargs, int nresults, int msgh);</pre> + +<p> +Calls a function in protected mode. + + +<p> +Both <code>nargs</code> and <code>nresults</code> have the same meaning as +in <a href="#lua_call"><code>lua_call</code></a>. +If there are no errors during the call, +<a href="#lua_pcall"><code>lua_pcall</code></a> behaves exactly like <a href="#lua_call"><code>lua_call</code></a>. +However, if there is any error, +<a href="#lua_pcall"><code>lua_pcall</code></a> catches it, +pushes a single value on the stack (the error message), +and returns an error code. +Like <a href="#lua_call"><code>lua_call</code></a>, +<a href="#lua_pcall"><code>lua_pcall</code></a> always removes the function +and its arguments from the stack. + + +<p> +If <code>msgh</code> is 0, +then the error message returned on the stack +is exactly the original error message. +Otherwise, <code>msgh</code> is the stack index of a +<em>message handler</em>. +(In the current implementation, this index cannot be a pseudo-index.) +In case of runtime errors, +this function will be called with the error message +and its return value will be the message +returned on the stack by <a href="#lua_pcall"><code>lua_pcall</code></a>. + + +<p> +Typically, the message handler is used to add more debug +information to the error message, such as a stack traceback. +Such information cannot be gathered after the return of <a href="#lua_pcall"><code>lua_pcall</code></a>, +since by then the stack has unwound. + + +<p> +The <a href="#lua_pcall"><code>lua_pcall</code></a> function returns one of the following constants +(defined in <code>lua.h</code>): + +<ul> + +<li><b><a name="pdf-LUA_OK"><code>LUA_OK</code></a> (0): </b> +success.</li> + +<li><b><a name="pdf-LUA_ERRRUN"><code>LUA_ERRRUN</code></a>: </b> +a runtime error. +</li> + +<li><b><a name="pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>: </b> +memory allocation error. +For such errors, Lua does not call the message handler. +</li> + +<li><b><a name="pdf-LUA_ERRERR"><code>LUA_ERRERR</code></a>: </b> +error while running the message handler. +</li> + +<li><b><a name="pdf-LUA_ERRGCMM"><code>LUA_ERRGCMM</code></a>: </b> +error while running a <code>__gc</code> metamethod. +(This error typically has no relation with the function being called.) +</li> + +</ul> + + + + +<hr><h3><a name="lua_pcallk"><code>lua_pcallk</code></a></h3><p> +<span class="apii">[-(nargs + 1), +(nresults|1), –]</span> +<pre>int lua_pcallk (lua_State *L, + int nargs, + int nresults, + int msgh, + lua_KContext ctx, + lua_KFunction k);</pre> + +<p> +This function behaves exactly like <a href="#lua_pcall"><code>lua_pcall</code></a>, +but allows the called function to yield (see <a href="#4.7">§4.7</a>). + + + + + +<hr><h3><a name="lua_pop"><code>lua_pop</code></a></h3><p> +<span class="apii">[-n, +0, –]</span> +<pre>void lua_pop (lua_State *L, int n);</pre> + +<p> +Pops <code>n</code> elements from the stack. + + + + + +<hr><h3><a name="lua_pushboolean"><code>lua_pushboolean</code></a></h3><p> +<span class="apii">[-0, +1, –]</span> +<pre>void lua_pushboolean (lua_State *L, int b);</pre> + +<p> +Pushes a boolean value with value <code>b</code> onto the stack. + + + + + +<hr><h3><a name="lua_pushcclosure"><code>lua_pushcclosure</code></a></h3><p> +<span class="apii">[-n, +1, <em>e</em>]</span> +<pre>void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);</pre> + +<p> +Pushes a new C closure onto the stack. + + +<p> +When a C function is created, +it is possible to associate some values with it, +thus creating a C closure (see <a href="#4.4">§4.4</a>); +these values are then accessible to the function whenever it is called. +To associate values with a C function, +first these values must be pushed onto the stack +(when there are multiple values, the first value is pushed first). +Then <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> +is called to create and push the C function onto the stack, +with the argument <code>n</code> telling how many values will be +associated with the function. +<a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> also pops these values from the stack. + + +<p> +The maximum value for <code>n</code> is 255. + + +<p> +When <code>n</code> is zero, +this function creates a <em>light C function</em>, +which is just a pointer to the C function. +In that case, it never raises a memory error. + + + + + +<hr><h3><a name="lua_pushcfunction"><code>lua_pushcfunction</code></a></h3><p> +<span class="apii">[-0, +1, –]</span> +<pre>void lua_pushcfunction (lua_State *L, lua_CFunction f);</pre> + +<p> +Pushes a C function onto the stack. +This function receives a pointer to a C function +and pushes onto the stack a Lua value of type <code>function</code> that, +when called, invokes the corresponding C function. + + +<p> +Any function to be registered in Lua must +follow the correct protocol to receive its parameters +and return its results (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>). + + +<p> +<code>lua_pushcfunction</code> is defined as a macro: + +<pre> + #define lua_pushcfunction(L,f) lua_pushcclosure(L,f,0) +</pre><p> +Note that <code>f</code> is used twice. + + + + + +<hr><h3><a name="lua_pushfstring"><code>lua_pushfstring</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>const char *lua_pushfstring (lua_State *L, const char *fmt, ...);</pre> + +<p> +Pushes onto the stack a formatted string +and returns a pointer to this string. +It is similar to the ISO C function <code>sprintf</code>, +but has some important differences: + +<ul> + +<li> +You do not have to allocate space for the result: +the result is a Lua string and Lua takes care of memory allocation +(and deallocation, through garbage collection). +</li> + +<li> +The conversion specifiers are quite restricted. +There are no flags, widths, or precisions. +The conversion specifiers can only be +'<code>%%</code>' (inserts the character '<code>%</code>'), +'<code>%s</code>' (inserts a zero-terminated string, with no size restrictions), +'<code>%f</code>' (inserts a <a href="#lua_Number"><code>lua_Number</code></a>), +'<code>%L</code>' (inserts a <a href="#lua_Integer"><code>lua_Integer</code></a>), +'<code>%p</code>' (inserts a pointer as a hexadecimal numeral), +'<code>%d</code>' (inserts an <code>int</code>), +'<code>%c</code>' (inserts an <code>int</code> as a one-byte character), and +'<code>%U</code>' (inserts a <code>long int</code> as a UTF-8 byte sequence). +</li> + +</ul> + + + + +<hr><h3><a name="lua_pushglobaltable"><code>lua_pushglobaltable</code></a></h3><p> +<span class="apii">[-0, +1, –]</span> +<pre>void lua_pushglobaltable (lua_State *L);</pre> + +<p> +Pushes the global environment onto the stack. + + + + + +<hr><h3><a name="lua_pushinteger"><code>lua_pushinteger</code></a></h3><p> +<span class="apii">[-0, +1, –]</span> +<pre>void lua_pushinteger (lua_State *L, lua_Integer n);</pre> + +<p> +Pushes an integer with value <code>n</code> onto the stack. + + + + + +<hr><h3><a name="lua_pushlightuserdata"><code>lua_pushlightuserdata</code></a></h3><p> +<span class="apii">[-0, +1, –]</span> +<pre>void lua_pushlightuserdata (lua_State *L, void *p);</pre> + +<p> +Pushes a light userdata onto the stack. + + +<p> +Userdata represent C values in Lua. +A <em>light userdata</em> represents a pointer, a <code>void*</code>. +It is a value (like a number): +you do not create it, it has no individual metatable, +and it is not collected (as it was never created). +A light userdata is equal to "any" +light userdata with the same C address. + + + + + +<hr><h3><a name="lua_pushliteral"><code>lua_pushliteral</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>const char *lua_pushliteral (lua_State *L, const char *s);</pre> + +<p> +This macro is equivalent to <a href="#lua_pushlstring"><code>lua_pushlstring</code></a>, +but can be used only when <code>s</code> is a literal string. +It automatically provides the string length. + + + + + +<hr><h3><a name="lua_pushlstring"><code>lua_pushlstring</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>const char *lua_pushlstring (lua_State *L, const char *s, size_t len);</pre> + +<p> +Pushes the string pointed to by <code>s</code> with size <code>len</code> +onto the stack. +Lua makes (or reuses) an internal copy of the given string, +so the memory at <code>s</code> can be freed or reused immediately after +the function returns. +The string can contain any binary data, +including embedded zeros. + + +<p> +Returns a pointer to the internal copy of the string. + + + + + +<hr><h3><a name="lua_pushnil"><code>lua_pushnil</code></a></h3><p> +<span class="apii">[-0, +1, –]</span> +<pre>void lua_pushnil (lua_State *L);</pre> + +<p> +Pushes a nil value onto the stack. + + + + + +<hr><h3><a name="lua_pushnumber"><code>lua_pushnumber</code></a></h3><p> +<span class="apii">[-0, +1, –]</span> +<pre>void lua_pushnumber (lua_State *L, lua_Number n);</pre> + +<p> +Pushes a float with value <code>n</code> onto the stack. + + + + + +<hr><h3><a name="lua_pushstring"><code>lua_pushstring</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>const char *lua_pushstring (lua_State *L, const char *s);</pre> + +<p> +Pushes the zero-terminated string pointed to by <code>s</code> +onto the stack. +Lua makes (or reuses) an internal copy of the given string, +so the memory at <code>s</code> can be freed or reused immediately after +the function returns. + + +<p> +Returns a pointer to the internal copy of the string. + + +<p> +If <code>s</code> is <code>NULL</code>, pushes <b>nil</b> and returns <code>NULL</code>. + + + + + +<hr><h3><a name="lua_pushthread"><code>lua_pushthread</code></a></h3><p> +<span class="apii">[-0, +1, –]</span> +<pre>int lua_pushthread (lua_State *L);</pre> + +<p> +Pushes the thread represented by <code>L</code> onto the stack. +Returns 1 if this thread is the main thread of its state. + + + + + +<hr><h3><a name="lua_pushvalue"><code>lua_pushvalue</code></a></h3><p> +<span class="apii">[-0, +1, –]</span> +<pre>void lua_pushvalue (lua_State *L, int index);</pre> + +<p> +Pushes a copy of the element at the given index +onto the stack. + + + + + +<hr><h3><a name="lua_pushvfstring"><code>lua_pushvfstring</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>const char *lua_pushvfstring (lua_State *L, + const char *fmt, + va_list argp);</pre> + +<p> +Equivalent to <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>, except that it receives a <code>va_list</code> +instead of a variable number of arguments. + + + + + +<hr><h3><a name="lua_rawequal"><code>lua_rawequal</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_rawequal (lua_State *L, int index1, int index2);</pre> + +<p> +Returns 1 if the two values in indices <code>index1</code> and +<code>index2</code> are primitively equal +(that is, without calling metamethods). +Otherwise returns 0. +Also returns 0 if any of the indices are not valid. + + + + + +<hr><h3><a name="lua_rawget"><code>lua_rawget</code></a></h3><p> +<span class="apii">[-1, +1, –]</span> +<pre>int lua_rawget (lua_State *L, int index);</pre> + +<p> +Similar to <a href="#lua_gettable"><code>lua_gettable</code></a>, but does a raw access +(i.e., without metamethods). + + + + + +<hr><h3><a name="lua_rawgeti"><code>lua_rawgeti</code></a></h3><p> +<span class="apii">[-0, +1, –]</span> +<pre>int lua_rawgeti (lua_State *L, int index, lua_Integer n);</pre> + +<p> +Pushes onto the stack the value <code>t[n]</code>, +where <code>t</code> is the table at the given index. +The access is raw; +that is, it does not invoke metamethods. + + +<p> +Returns the type of the pushed value. + + + + + +<hr><h3><a name="lua_rawgetp"><code>lua_rawgetp</code></a></h3><p> +<span class="apii">[-0, +1, –]</span> +<pre>int lua_rawgetp (lua_State *L, int index, const void *p);</pre> + +<p> +Pushes onto the stack the value <code>t[k]</code>, +where <code>t</code> is the table at the given index and +<code>k</code> is the pointer <code>p</code> represented as a light userdata. +The access is raw; +that is, it does not invoke metamethods. + + +<p> +Returns the type of the pushed value. + + + + + +<hr><h3><a name="lua_rawlen"><code>lua_rawlen</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>size_t lua_rawlen (lua_State *L, int index);</pre> + +<p> +Returns the raw "length" of the value at the given index: +for strings, this is the string length; +for tables, this is the result of the length operator ('<code>#</code>') +with no metamethods; +for userdata, this is the size of the block of memory allocated +for the userdata; +for other values, it is 0. + + + + + +<hr><h3><a name="lua_rawset"><code>lua_rawset</code></a></h3><p> +<span class="apii">[-2, +0, <em>e</em>]</span> +<pre>void lua_rawset (lua_State *L, int index);</pre> + +<p> +Similar to <a href="#lua_settable"><code>lua_settable</code></a>, but does a raw assignment +(i.e., without metamethods). + + + + + +<hr><h3><a name="lua_rawseti"><code>lua_rawseti</code></a></h3><p> +<span class="apii">[-1, +0, <em>e</em>]</span> +<pre>void lua_rawseti (lua_State *L, int index, lua_Integer i);</pre> + +<p> +Does the equivalent of <code>t[i] = v</code>, +where <code>t</code> is the table at the given index +and <code>v</code> is the value at the top of the stack. + + +<p> +This function pops the value from the stack. +The assignment is raw; +that is, it does not invoke metamethods. + + + + + +<hr><h3><a name="lua_rawsetp"><code>lua_rawsetp</code></a></h3><p> +<span class="apii">[-1, +0, <em>e</em>]</span> +<pre>void lua_rawsetp (lua_State *L, int index, const void *p);</pre> + +<p> +Does the equivalent of <code>t[k] = v</code>, +where <code>t</code> is the table at the given index, +<code>k</code> is the pointer <code>p</code> represented as a light userdata, +and <code>v</code> is the value at the top of the stack. + + +<p> +This function pops the value from the stack. +The assignment is raw; +that is, it does not invoke metamethods. + + + + + +<hr><h3><a name="lua_Reader"><code>lua_Reader</code></a></h3> +<pre>typedef const char * (*lua_Reader) (lua_State *L, + void *data, + size_t *size);</pre> + +<p> +The reader function used by <a href="#lua_load"><code>lua_load</code></a>. +Every time it needs another piece of the chunk, +<a href="#lua_load"><code>lua_load</code></a> calls the reader, +passing along its <code>data</code> parameter. +The reader must return a pointer to a block of memory +with a new piece of the chunk +and set <code>size</code> to the block size. +The block must exist until the reader function is called again. +To signal the end of the chunk, +the reader must return <code>NULL</code> or set <code>size</code> to zero. +The reader function may return pieces of any size greater than zero. + + + + + +<hr><h3><a name="lua_register"><code>lua_register</code></a></h3><p> +<span class="apii">[-0, +0, <em>e</em>]</span> +<pre>void lua_register (lua_State *L, const char *name, lua_CFunction f);</pre> + +<p> +Sets the C function <code>f</code> as the new value of global <code>name</code>. +It is defined as a macro: + +<pre> + #define lua_register(L,n,f) \ + (lua_pushcfunction(L, f), lua_setglobal(L, n)) +</pre> + + + + +<hr><h3><a name="lua_remove"><code>lua_remove</code></a></h3><p> +<span class="apii">[-1, +0, –]</span> +<pre>void lua_remove (lua_State *L, int index);</pre> + +<p> +Removes the element at the given valid index, +shifting down the elements above this index to fill the gap. +This function cannot be called with a pseudo-index, +because a pseudo-index is not an actual stack position. + + + + + +<hr><h3><a name="lua_replace"><code>lua_replace</code></a></h3><p> +<span class="apii">[-1, +0, –]</span> +<pre>void lua_replace (lua_State *L, int index);</pre> + +<p> +Moves the top element into the given valid index +without shifting any element +(therefore replacing the value at the given index), +and then pops the top element. + + + + + +<hr><h3><a name="lua_resume"><code>lua_resume</code></a></h3><p> +<span class="apii">[-?, +?, –]</span> +<pre>int lua_resume (lua_State *L, lua_State *from, int nargs);</pre> + +<p> +Starts and resumes a coroutine in a given thread. + + +<p> +To start a coroutine, +you push onto the thread stack the main function plus any arguments; +then you call <a href="#lua_resume"><code>lua_resume</code></a>, +with <code>nargs</code> being the number of arguments. +This call returns when the coroutine suspends or finishes its execution. +When it returns, the stack contains all values passed to <a href="#lua_yield"><code>lua_yield</code></a>, +or all values returned by the body function. +<a href="#lua_resume"><code>lua_resume</code></a> returns +<a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the coroutine yields, +<a href="#pdf-LUA_OK"><code>LUA_OK</code></a> if the coroutine finishes its execution +without errors, +or an error code in case of errors (see <a href="#lua_pcall"><code>lua_pcall</code></a>). + + +<p> +In case of errors, +the stack is not unwound, +so you can use the debug API over it. +The error message is on the top of the stack. + + +<p> +To resume a coroutine, +you remove any results from the last <a href="#lua_yield"><code>lua_yield</code></a>, +put on its stack only the values to +be passed as results from <code>yield</code>, +and then call <a href="#lua_resume"><code>lua_resume</code></a>. + + +<p> +The parameter <code>from</code> represents the coroutine that is resuming <code>L</code>. +If there is no such coroutine, +this parameter can be <code>NULL</code>. + + + + + +<hr><h3><a name="lua_rotate"><code>lua_rotate</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>void lua_rotate (lua_State *L, int idx, int n);</pre> + +<p> +Rotates the stack elements from <code>idx</code> to the top <code>n</code> positions +in the direction of the top, for a positive <code>n</code>, +or <code>-n</code> positions in the direction of the bottom, +for a negative <code>n</code>. +The absolute value of <code>n</code> must not be greater than the size +of the slice being rotated. + + + + + +<hr><h3><a name="lua_setallocf"><code>lua_setallocf</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>void lua_setallocf (lua_State *L, lua_Alloc f, void *ud);</pre> + +<p> +Changes the allocator function of a given state to <code>f</code> +with user data <code>ud</code>. + + + + + +<hr><h3><a name="lua_setfield"><code>lua_setfield</code></a></h3><p> +<span class="apii">[-1, +0, <em>e</em>]</span> +<pre>void lua_setfield (lua_State *L, int index, const char *k);</pre> + +<p> +Does the equivalent to <code>t[k] = v</code>, +where <code>t</code> is the value at the given index +and <code>v</code> is the value at the top of the stack. + + +<p> +This function pops the value from the stack. +As in Lua, this function may trigger a metamethod +for the "newindex" event (see <a href="#2.4">§2.4</a>). + + + + + +<hr><h3><a name="lua_setglobal"><code>lua_setglobal</code></a></h3><p> +<span class="apii">[-1, +0, <em>e</em>]</span> +<pre>void lua_setglobal (lua_State *L, const char *name);</pre> + +<p> +Pops a value from the stack and +sets it as the new value of global <code>name</code>. + + + + + +<hr><h3><a name="lua_seti"><code>lua_seti</code></a></h3><p> +<span class="apii">[-1, +0, <em>e</em>]</span> +<pre>void lua_seti (lua_State *L, int index, lua_Integer n);</pre> + +<p> +Does the equivalent to <code>t[n] = v</code>, +where <code>t</code> is the value at the given index +and <code>v</code> is the value at the top of the stack. + + +<p> +This function pops the value from the stack. +As in Lua, this function may trigger a metamethod +for the "newindex" event (see <a href="#2.4">§2.4</a>). + + + + + +<hr><h3><a name="lua_setmetatable"><code>lua_setmetatable</code></a></h3><p> +<span class="apii">[-1, +0, –]</span> +<pre>void lua_setmetatable (lua_State *L, int index);</pre> + +<p> +Pops a table from the stack and +sets it as the new metatable for the value at the given index. + + + + + +<hr><h3><a name="lua_settable"><code>lua_settable</code></a></h3><p> +<span class="apii">[-2, +0, <em>e</em>]</span> +<pre>void lua_settable (lua_State *L, int index);</pre> + +<p> +Does the equivalent to <code>t[k] = v</code>, +where <code>t</code> is the value at the given index, +<code>v</code> is the value at the top of the stack, +and <code>k</code> is the value just below the top. + + +<p> +This function pops both the key and the value from the stack. +As in Lua, this function may trigger a metamethod +for the "newindex" event (see <a href="#2.4">§2.4</a>). + + + + + +<hr><h3><a name="lua_settop"><code>lua_settop</code></a></h3><p> +<span class="apii">[-?, +?, –]</span> +<pre>void lua_settop (lua_State *L, int index);</pre> + +<p> +Accepts any index, or 0, +and sets the stack top to this index. +If the new top is larger than the old one, +then the new elements are filled with <b>nil</b>. +If <code>index</code> is 0, then all stack elements are removed. + + + + + +<hr><h3><a name="lua_setuservalue"><code>lua_setuservalue</code></a></h3><p> +<span class="apii">[-1, +0, –]</span> +<pre>void lua_setuservalue (lua_State *L, int index);</pre> + +<p> +Pops a value from the stack and sets it as +the new value associated to the userdata at the given index. + + + + + +<hr><h3><a name="lua_State"><code>lua_State</code></a></h3> +<pre>typedef struct lua_State lua_State;</pre> + +<p> +An opaque structure that points to a thread and indirectly +(through the thread) to the whole state of a Lua interpreter. +The Lua library is fully reentrant: +it has no global variables. +All information about a state is accessible through this structure. + + +<p> +A pointer to this structure must be passed as the first argument to +every function in the library, except to <a href="#lua_newstate"><code>lua_newstate</code></a>, +which creates a Lua state from scratch. + + + + + +<hr><h3><a name="lua_status"><code>lua_status</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_status (lua_State *L);</pre> + +<p> +Returns the status of the thread <code>L</code>. + + +<p> +The status can be 0 (<a href="#pdf-LUA_OK"><code>LUA_OK</code></a>) for a normal thread, +an error code if the thread finished the execution +of a <a href="#lua_resume"><code>lua_resume</code></a> with an error, +or <a name="pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the thread is suspended. + + +<p> +You can only call functions in threads with status <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>. +You can resume threads with status <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> +(to start a new coroutine) or <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> +(to resume a coroutine). + + + + + +<hr><h3><a name="lua_stringtonumber"><code>lua_stringtonumber</code></a></h3><p> +<span class="apii">[-0, +1, –]</span> +<pre>size_t lua_stringtonumber (lua_State *L, const char *s);</pre> + +<p> +Converts the zero-terminated string <code>s</code> to a number, +pushes that number into the stack, +and returns the total size of the string, +that is, its length plus one. +The conversion can result in an integer or a float, +according to the lexical conventions of Lua (see <a href="#3.1">§3.1</a>). +The string may have leading and trailing spaces and a sign. +If the string is not a valid numeral, +returns 0 and pushes nothing. +(Note that the result can be used as a boolean, +true if the conversion succeeds.) + + + + + +<hr><h3><a name="lua_toboolean"><code>lua_toboolean</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_toboolean (lua_State *L, int index);</pre> + +<p> +Converts the Lua value at the given index to a C boolean +value (0 or 1). +Like all tests in Lua, +<a href="#lua_toboolean"><code>lua_toboolean</code></a> returns true for any Lua value +different from <b>false</b> and <b>nil</b>; +otherwise it returns false. +(If you want to accept only actual boolean values, +use <a href="#lua_isboolean"><code>lua_isboolean</code></a> to test the value's type.) + + + + + +<hr><h3><a name="lua_tocfunction"><code>lua_tocfunction</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>lua_CFunction lua_tocfunction (lua_State *L, int index);</pre> + +<p> +Converts a value at the given index to a C function. +That value must be a C function; +otherwise, returns <code>NULL</code>. + + + + + +<hr><h3><a name="lua_tointeger"><code>lua_tointeger</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>lua_Integer lua_tointeger (lua_State *L, int index);</pre> + +<p> +Equivalent to <a href="#lua_tointegerx"><code>lua_tointegerx</code></a> with <code>isnum</code> equal to <code>NULL</code>. + + + + + +<hr><h3><a name="lua_tointegerx"><code>lua_tointegerx</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>lua_Integer lua_tointegerx (lua_State *L, int index, int *isnum);</pre> + +<p> +Converts the Lua value at the given index +to the signed integral type <a href="#lua_Integer"><code>lua_Integer</code></a>. +The Lua value must be an integer, +or a number or string convertible to an integer (see <a href="#3.4.3">§3.4.3</a>); +otherwise, <code>lua_tointegerx</code> returns 0. + + +<p> +If <code>isnum</code> is not <code>NULL</code>, +its referent is assigned a boolean value that +indicates whether the operation succeeded. + + + + + +<hr><h3><a name="lua_tolstring"><code>lua_tolstring</code></a></h3><p> +<span class="apii">[-0, +0, <em>e</em>]</span> +<pre>const char *lua_tolstring (lua_State *L, int index, size_t *len);</pre> + +<p> +Converts the Lua value at the given index to a C string. +If <code>len</code> is not <code>NULL</code>, +it also sets <code>*len</code> with the string length. +The Lua value must be a string or a number; +otherwise, the function returns <code>NULL</code>. +If the value is a number, +then <code>lua_tolstring</code> also +<em>changes the actual value in the stack to a string</em>. +(This change confuses <a href="#lua_next"><code>lua_next</code></a> +when <code>lua_tolstring</code> is applied to keys during a table traversal.) + + +<p> +<code>lua_tolstring</code> returns a fully aligned pointer +to a string inside the Lua state. +This string always has a zero ('<code>\0</code>') +after its last character (as in C), +but can contain other zeros in its body. + + +<p> +Because Lua has garbage collection, +there is no guarantee that the pointer returned by <code>lua_tolstring</code> +will be valid after the corresponding Lua value is removed from the stack. + + + + + +<hr><h3><a name="lua_tonumber"><code>lua_tonumber</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>lua_Number lua_tonumber (lua_State *L, int index);</pre> + +<p> +Equivalent to <a href="#lua_tonumberx"><code>lua_tonumberx</code></a> with <code>isnum</code> equal to <code>NULL</code>. + + + + + +<hr><h3><a name="lua_tonumberx"><code>lua_tonumberx</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>lua_Number lua_tonumberx (lua_State *L, int index, int *isnum);</pre> + +<p> +Converts the Lua value at the given index +to the C type <a href="#lua_Number"><code>lua_Number</code></a> (see <a href="#lua_Number"><code>lua_Number</code></a>). +The Lua value must be a number or a string convertible to a number +(see <a href="#3.4.3">§3.4.3</a>); +otherwise, <a href="#lua_tonumberx"><code>lua_tonumberx</code></a> returns 0. + + +<p> +If <code>isnum</code> is not <code>NULL</code>, +its referent is assigned a boolean value that +indicates whether the operation succeeded. + + + + + +<hr><h3><a name="lua_topointer"><code>lua_topointer</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>const void *lua_topointer (lua_State *L, int index);</pre> + +<p> +Converts the value at the given index to a generic +C pointer (<code>void*</code>). +The value can be a userdata, a table, a thread, or a function; +otherwise, <code>lua_topointer</code> returns <code>NULL</code>. +Different objects will give different pointers. +There is no way to convert the pointer back to its original value. + + +<p> +Typically this function is used only for debug information. + + + + + +<hr><h3><a name="lua_tostring"><code>lua_tostring</code></a></h3><p> +<span class="apii">[-0, +0, <em>e</em>]</span> +<pre>const char *lua_tostring (lua_State *L, int index);</pre> + +<p> +Equivalent to <a href="#lua_tolstring"><code>lua_tolstring</code></a> with <code>len</code> equal to <code>NULL</code>. + + + + + +<hr><h3><a name="lua_tothread"><code>lua_tothread</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>lua_State *lua_tothread (lua_State *L, int index);</pre> + +<p> +Converts the value at the given index to a Lua thread +(represented as <code>lua_State*</code>). +This value must be a thread; +otherwise, the function returns <code>NULL</code>. + + + + + +<hr><h3><a name="lua_touserdata"><code>lua_touserdata</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>void *lua_touserdata (lua_State *L, int index);</pre> + +<p> +If the value at the given index is a full userdata, +returns its block address. +If the value is a light userdata, +returns its pointer. +Otherwise, returns <code>NULL</code>. + + + + + +<hr><h3><a name="lua_type"><code>lua_type</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_type (lua_State *L, int index);</pre> + +<p> +Returns the type of the value in the given valid index, +or <code>LUA_TNONE</code> for a non-valid (but acceptable) index. +The types returned by <a href="#lua_type"><code>lua_type</code></a> are coded by the following constants +defined in <code>lua.h</code>: +<a name="pdf-LUA_TNIL"><code>LUA_TNIL</code></a>, +<a name="pdf-LUA_TNUMBER"><code>LUA_TNUMBER</code></a>, +<a name="pdf-LUA_TBOOLEAN"><code>LUA_TBOOLEAN</code></a>, +<a name="pdf-LUA_TSTRING"><code>LUA_TSTRING</code></a>, +<a name="pdf-LUA_TTABLE"><code>LUA_TTABLE</code></a>, +<a name="pdf-LUA_TFUNCTION"><code>LUA_TFUNCTION</code></a>, +<a name="pdf-LUA_TUSERDATA"><code>LUA_TUSERDATA</code></a>, +<a name="pdf-LUA_TTHREAD"><code>LUA_TTHREAD</code></a>, +and +<a name="pdf-LUA_TLIGHTUSERDATA"><code>LUA_TLIGHTUSERDATA</code></a>. + + + + + +<hr><h3><a name="lua_typename"><code>lua_typename</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>const char *lua_typename (lua_State *L, int tp);</pre> + +<p> +Returns the name of the type encoded by the value <code>tp</code>, +which must be one the values returned by <a href="#lua_type"><code>lua_type</code></a>. + + + + + +<hr><h3><a name="lua_Unsigned"><code>lua_Unsigned</code></a></h3> +<pre>typedef ... lua_Unsigned;</pre> + +<p> +The unsigned version of <a href="#lua_Integer"><code>lua_Integer</code></a>. + + + + + +<hr><h3><a name="lua_upvalueindex"><code>lua_upvalueindex</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_upvalueindex (int i);</pre> + +<p> +Returns the pseudo-index that represents the <code>i</code>-th upvalue of +the running function (see <a href="#4.4">§4.4</a>). + + + + + +<hr><h3><a name="lua_version"><code>lua_version</code></a></h3><p> +<span class="apii">[-0, +0, <em>v</em>]</span> +<pre>const lua_Number *lua_version (lua_State *L);</pre> + +<p> +Returns the address of the version number stored in the Lua core. +When called with a valid <a href="#lua_State"><code>lua_State</code></a>, +returns the address of the version used to create that state. +When called with <code>NULL</code>, +returns the address of the version running the call. + + + + + +<hr><h3><a name="lua_Writer"><code>lua_Writer</code></a></h3> +<pre>typedef int (*lua_Writer) (lua_State *L, + const void* p, + size_t sz, + void* ud);</pre> + +<p> +The type of the writer function used by <a href="#lua_dump"><code>lua_dump</code></a>. +Every time it produces another piece of chunk, +<a href="#lua_dump"><code>lua_dump</code></a> calls the writer, +passing along the buffer to be written (<code>p</code>), +its size (<code>sz</code>), +and the <code>data</code> parameter supplied to <a href="#lua_dump"><code>lua_dump</code></a>. + + +<p> +The writer returns an error code: +0 means no errors; +any other value means an error and stops <a href="#lua_dump"><code>lua_dump</code></a> from +calling the writer again. + + + + + +<hr><h3><a name="lua_xmove"><code>lua_xmove</code></a></h3><p> +<span class="apii">[-?, +?, –]</span> +<pre>void lua_xmove (lua_State *from, lua_State *to, int n);</pre> + +<p> +Exchange values between different threads of the same state. + + +<p> +This function pops <code>n</code> values from the stack <code>from</code>, +and pushes them onto the stack <code>to</code>. + + + + + +<hr><h3><a name="lua_yield"><code>lua_yield</code></a></h3><p> +<span class="apii">[-?, +?, <em>e</em>]</span> +<pre>int lua_yield (lua_State *L, int nresults);</pre> + +<p> +This function is equivalent to <a href="#lua_yieldk"><code>lua_yieldk</code></a>, +but it has no continuation (see <a href="#4.7">§4.7</a>). +Therefore, when the thread resumes, +it continues the function that called +the function calling <code>lua_yield</code>. + + + + + +<hr><h3><a name="lua_yieldk"><code>lua_yieldk</code></a></h3><p> +<span class="apii">[-?, +?, <em>e</em>]</span> +<pre>int lua_yieldk (lua_State *L, + int nresults, + lua_KContext ctx, + lua_KFunction k);</pre> + +<p> +Yields a coroutine (thread). + + +<p> +When a C function calls <a href="#lua_yieldk"><code>lua_yieldk</code></a>, +the running coroutine suspends its execution, +and the call to <a href="#lua_resume"><code>lua_resume</code></a> that started this coroutine returns. +The parameter <code>nresults</code> is the number of values from the stack +that will be passed as results to <a href="#lua_resume"><code>lua_resume</code></a>. + + +<p> +When the coroutine is resumed again, +Lua calls the given continuation function <code>k</code> to continue +the execution of the C function that yielded (see <a href="#4.7">§4.7</a>). +This continuation function receives the same stack +from the previous function, +with the <code>n</code> results removed and +replaced by the arguments passed to <a href="#lua_resume"><code>lua_resume</code></a>. +Moreover, +the continuation function receives the value <code>ctx</code> +that was passed to <a href="#lua_yieldk"><code>lua_yieldk</code></a>. + + +<p> +Usually, this function does not return; +when the coroutine eventually resumes, +it continues executing the continuation function. +However, there is one special case, +which is when this function is called +from inside a line hook (see <a href="#4.9">§4.9</a>). +In that case, <code>lua_yieldk</code> should be called with no continuation +(probably in the form of <a href="#lua_yield"><code>lua_yield</code></a>), +and the hook should return immediately after the call. +Lua will yield and, +when the coroutine resumes again, +it will continue the normal execution +of the (Lua) function that triggered the hook. + + +<p> +This function can raise an error if it is called from a thread +with a pending C call with no continuation function, +or it is called from a thread that is not running inside a resume +(e.g., the main thread). + + + + + + + +<h2>4.9 – <a name="4.9">The Debug Interface</a></h2> + +<p> +Lua has no built-in debugging facilities. +Instead, it offers a special interface +by means of functions and <em>hooks</em>. +This interface allows the construction of different +kinds of debuggers, profilers, and other tools +that need "inside information" from the interpreter. + + + +<hr><h3><a name="lua_Debug"><code>lua_Debug</code></a></h3> +<pre>typedef struct lua_Debug { + int event; + const char *name; /* (n) */ + const char *namewhat; /* (n) */ + const char *what; /* (S) */ + const char *source; /* (S) */ + int currentline; /* (l) */ + int linedefined; /* (S) */ + int lastlinedefined; /* (S) */ + unsigned char nups; /* (u) number of upvalues */ + unsigned char nparams; /* (u) number of parameters */ + char isvararg; /* (u) */ + char istailcall; /* (t) */ + char short_src[LUA_IDSIZE]; /* (S) */ + /* private part */ + <em>other fields</em> +} lua_Debug;</pre> + +<p> +A structure used to carry different pieces of +information about a function or an activation record. +<a href="#lua_getstack"><code>lua_getstack</code></a> fills only the private part +of this structure, for later use. +To fill the other fields of <a href="#lua_Debug"><code>lua_Debug</code></a> with useful information, +call <a href="#lua_getinfo"><code>lua_getinfo</code></a>. + + +<p> +The fields of <a href="#lua_Debug"><code>lua_Debug</code></a> have the following meaning: + +<ul> + +<li><b><code>source</code>: </b> +the name of the chunk that created the function. +If <code>source</code> starts with a '<code>@</code>', +it means that the function was defined in a file where +the file name follows the '<code>@</code>'. +If <code>source</code> starts with a '<code>=</code>', +the remainder of its contents describe the source in a user-dependent manner. +Otherwise, +the function was defined in a string where +<code>source</code> is that string. +</li> + +<li><b><code>short_src</code>: </b> +a "printable" version of <code>source</code>, to be used in error messages. +</li> + +<li><b><code>linedefined</code>: </b> +the line number where the definition of the function starts. +</li> + +<li><b><code>lastlinedefined</code>: </b> +the line number where the definition of the function ends. +</li> + +<li><b><code>what</code>: </b> +the string <code>"Lua"</code> if the function is a Lua function, +<code>"C"</code> if it is a C function, +<code>"main"</code> if it is the main part of a chunk. +</li> + +<li><b><code>currentline</code>: </b> +the current line where the given function is executing. +When no line information is available, +<code>currentline</code> is set to -1. +</li> + +<li><b><code>name</code>: </b> +a reasonable name for the given function. +Because functions in Lua are first-class values, +they do not have a fixed name: +some functions can be the value of multiple global variables, +while others can be stored only in a table field. +The <code>lua_getinfo</code> function checks how the function was +called to find a suitable name. +If it cannot find a name, +then <code>name</code> is set to <code>NULL</code>. +</li> + +<li><b><code>namewhat</code>: </b> +explains the <code>name</code> field. +The value of <code>namewhat</code> can be +<code>"global"</code>, <code>"local"</code>, <code>"method"</code>, +<code>"field"</code>, <code>"upvalue"</code>, or <code>""</code> (the empty string), +according to how the function was called. +(Lua uses the empty string when no other option seems to apply.) +</li> + +<li><b><code>istailcall</code>: </b> +true if this function invocation was called by a tail call. +In this case, the caller of this level is not in the stack. +</li> + +<li><b><code>nups</code>: </b> +the number of upvalues of the function. +</li> + +<li><b><code>nparams</code>: </b> +the number of fixed parameters of the function +(always 0 for C functions). +</li> + +<li><b><code>isvararg</code>: </b> +true if the function is a vararg function +(always true for C functions). +</li> + +</ul> + + + + +<hr><h3><a name="lua_gethook"><code>lua_gethook</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>lua_Hook lua_gethook (lua_State *L);</pre> + +<p> +Returns the current hook function. + + + + + +<hr><h3><a name="lua_gethookcount"><code>lua_gethookcount</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_gethookcount (lua_State *L);</pre> + +<p> +Returns the current hook count. + + + + + +<hr><h3><a name="lua_gethookmask"><code>lua_gethookmask</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_gethookmask (lua_State *L);</pre> + +<p> +Returns the current hook mask. + + + + + +<hr><h3><a name="lua_getinfo"><code>lua_getinfo</code></a></h3><p> +<span class="apii">[-(0|1), +(0|1|2), <em>e</em>]</span> +<pre>int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar);</pre> + +<p> +Gets information about a specific function or function invocation. + + +<p> +To get information about a function invocation, +the parameter <code>ar</code> must be a valid activation record that was +filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or +given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>). + + +<p> +To get information about a function you push it onto the stack +and start the <code>what</code> string with the character '<code>></code>'. +(In that case, +<code>lua_getinfo</code> pops the function from the top of the stack.) +For instance, to know in which line a function <code>f</code> was defined, +you can write the following code: + +<pre> + lua_Debug ar; + lua_getglobal(L, "f"); /* get global 'f' */ + lua_getinfo(L, ">S", &ar); + printf("%d\n", ar.linedefined); +</pre> + +<p> +Each character in the string <code>what</code> +selects some fields of the structure <code>ar</code> to be filled or +a value to be pushed on the stack: + +<ul> + +<li><b>'<code>n</code>': </b> fills in the field <code>name</code> and <code>namewhat</code>; +</li> + +<li><b>'<code>S</code>': </b> +fills in the fields <code>source</code>, <code>short_src</code>, +<code>linedefined</code>, <code>lastlinedefined</code>, and <code>what</code>; +</li> + +<li><b>'<code>l</code>': </b> fills in the field <code>currentline</code>; +</li> + +<li><b>'<code>t</code>': </b> fills in the field <code>istailcall</code>; +</li> + +<li><b>'<code>u</code>': </b> fills in the fields +<code>nups</code>, <code>nparams</code>, and <code>isvararg</code>; +</li> + +<li><b>'<code>f</code>': </b> +pushes onto the stack the function that is +running at the given level; +</li> + +<li><b>'<code>L</code>': </b> +pushes onto the stack a table whose indices are the +numbers of the lines that are valid on the function. +(A <em>valid line</em> is a line with some associated code, +that is, a line where you can put a break point. +Non-valid lines include empty lines and comments.) + + +<p> +If this option is given together with option '<code>f</code>', +its table is pushed after the function. +</li> + +</ul> + +<p> +This function returns 0 on error +(for instance, an invalid option in <code>what</code>). + + + + + +<hr><h3><a name="lua_getlocal"><code>lua_getlocal</code></a></h3><p> +<span class="apii">[-0, +(0|1), –]</span> +<pre>const char *lua_getlocal (lua_State *L, const lua_Debug *ar, int n);</pre> + +<p> +Gets information about a local variable of +a given activation record or a given function. + + +<p> +In the first case, +the parameter <code>ar</code> must be a valid activation record that was +filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or +given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>). +The index <code>n</code> selects which local variable to inspect; +see <a href="#pdf-debug.getlocal"><code>debug.getlocal</code></a> for details about variable indices +and names. + + +<p> +<a href="#lua_getlocal"><code>lua_getlocal</code></a> pushes the variable's value onto the stack +and returns its name. + + +<p> +In the second case, <code>ar</code> must be <code>NULL</code> and the function +to be inspected must be at the top of the stack. +In this case, only parameters of Lua functions are visible +(as there is no information about what variables are active) +and no values are pushed onto the stack. + + +<p> +Returns <code>NULL</code> (and pushes nothing) +when the index is greater than +the number of active local variables. + + + + + +<hr><h3><a name="lua_getstack"><code>lua_getstack</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>int lua_getstack (lua_State *L, int level, lua_Debug *ar);</pre> + +<p> +Gets information about the interpreter runtime stack. + + +<p> +This function fills parts of a <a href="#lua_Debug"><code>lua_Debug</code></a> structure with +an identification of the <em>activation record</em> +of the function executing at a given level. +Level 0 is the current running function, +whereas level <em>n+1</em> is the function that has called level <em>n</em> +(except for tail calls, which do not count on the stack). +When there are no errors, <a href="#lua_getstack"><code>lua_getstack</code></a> returns 1; +when called with a level greater than the stack depth, +it returns 0. + + + + + +<hr><h3><a name="lua_getupvalue"><code>lua_getupvalue</code></a></h3><p> +<span class="apii">[-0, +(0|1), –]</span> +<pre>const char *lua_getupvalue (lua_State *L, int funcindex, int n);</pre> + +<p> +Gets information about a closure's upvalue. +(For Lua functions, +upvalues are the external local variables that the function uses, +and that are consequently included in its closure.) +<a href="#lua_getupvalue"><code>lua_getupvalue</code></a> gets the index <code>n</code> of an upvalue, +pushes the upvalue's value onto the stack, +and returns its name. +<code>funcindex</code> points to the closure in the stack. +(Upvalues have no particular order, +as they are active through the whole function. +So, they are numbered in an arbitrary order.) + + +<p> +Returns <code>NULL</code> (and pushes nothing) +when the index is greater than the number of upvalues. +For C functions, this function uses the empty string <code>""</code> +as a name for all upvalues. + + + + + +<hr><h3><a name="lua_Hook"><code>lua_Hook</code></a></h3> +<pre>typedef void (*lua_Hook) (lua_State *L, lua_Debug *ar);</pre> + +<p> +Type for debugging hook functions. + + +<p> +Whenever a hook is called, its <code>ar</code> argument has its field +<code>event</code> set to the specific event that triggered the hook. +Lua identifies these events with the following constants: +<a name="pdf-LUA_HOOKCALL"><code>LUA_HOOKCALL</code></a>, <a name="pdf-LUA_HOOKRET"><code>LUA_HOOKRET</code></a>, +<a name="pdf-LUA_HOOKTAILCALL"><code>LUA_HOOKTAILCALL</code></a>, <a name="pdf-LUA_HOOKLINE"><code>LUA_HOOKLINE</code></a>, +and <a name="pdf-LUA_HOOKCOUNT"><code>LUA_HOOKCOUNT</code></a>. +Moreover, for line events, the field <code>currentline</code> is also set. +To get the value of any other field in <code>ar</code>, +the hook must call <a href="#lua_getinfo"><code>lua_getinfo</code></a>. + + +<p> +For call events, <code>event</code> can be <code>LUA_HOOKCALL</code>, +the normal value, or <code>LUA_HOOKTAILCALL</code>, for a tail call; +in this case, there will be no corresponding return event. + + +<p> +While Lua is running a hook, it disables other calls to hooks. +Therefore, if a hook calls back Lua to execute a function or a chunk, +this execution occurs without any calls to hooks. + + +<p> +Hook functions cannot have continuations, +that is, they cannot call <a href="#lua_yieldk"><code>lua_yieldk</code></a>, +<a href="#lua_pcallk"><code>lua_pcallk</code></a>, or <a href="#lua_callk"><code>lua_callk</code></a> with a non-null <code>k</code>. + + +<p> +Hook functions can yield under the following conditions: +Only count and line events can yield +and they cannot yield any value; +to yield a hook function must finish its execution +calling <a href="#lua_yield"><code>lua_yield</code></a> with <code>nresults</code> equal to zero. + + + + + +<hr><h3><a name="lua_sethook"><code>lua_sethook</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>void lua_sethook (lua_State *L, lua_Hook f, int mask, int count);</pre> + +<p> +Sets the debugging hook function. + + +<p> +Argument <code>f</code> is the hook function. +<code>mask</code> specifies on which events the hook will be called: +it is formed by a bitwise or of the constants +<a name="pdf-LUA_MASKCALL"><code>LUA_MASKCALL</code></a>, +<a name="pdf-LUA_MASKRET"><code>LUA_MASKRET</code></a>, +<a name="pdf-LUA_MASKLINE"><code>LUA_MASKLINE</code></a>, +and <a name="pdf-LUA_MASKCOUNT"><code>LUA_MASKCOUNT</code></a>. +The <code>count</code> argument is only meaningful when the mask +includes <code>LUA_MASKCOUNT</code>. +For each event, the hook is called as explained below: + +<ul> + +<li><b>The call hook: </b> is called when the interpreter calls a function. +The hook is called just after Lua enters the new function, +before the function gets its arguments. +</li> + +<li><b>The return hook: </b> is called when the interpreter returns from a function. +The hook is called just before Lua leaves the function. +There is no standard way to access the values +to be returned by the function. +</li> + +<li><b>The line hook: </b> is called when the interpreter is about to +start the execution of a new line of code, +or when it jumps back in the code (even to the same line). +(This event only happens while Lua is executing a Lua function.) +</li> + +<li><b>The count hook: </b> is called after the interpreter executes every +<code>count</code> instructions. +(This event only happens while Lua is executing a Lua function.) +</li> + +</ul> + +<p> +A hook is disabled by setting <code>mask</code> to zero. + + + + + +<hr><h3><a name="lua_setlocal"><code>lua_setlocal</code></a></h3><p> +<span class="apii">[-(0|1), +0, –]</span> +<pre>const char *lua_setlocal (lua_State *L, const lua_Debug *ar, int n);</pre> + +<p> +Sets the value of a local variable of a given activation record. +Parameters <code>ar</code> and <code>n</code> are as in <a href="#lua_getlocal"><code>lua_getlocal</code></a> +(see <a href="#lua_getlocal"><code>lua_getlocal</code></a>). +<a href="#lua_setlocal"><code>lua_setlocal</code></a> assigns the value at the top of the stack +to the variable and returns its name. +It also pops the value from the stack. + + +<p> +Returns <code>NULL</code> (and pops nothing) +when the index is greater than +the number of active local variables. + + + + + +<hr><h3><a name="lua_setupvalue"><code>lua_setupvalue</code></a></h3><p> +<span class="apii">[-(0|1), +0, –]</span> +<pre>const char *lua_setupvalue (lua_State *L, int funcindex, int n);</pre> + +<p> +Sets the value of a closure's upvalue. +It assigns the value at the top of the stack +to the upvalue and returns its name. +It also pops the value from the stack. +Parameters <code>funcindex</code> and <code>n</code> are as in the <a href="#lua_getupvalue"><code>lua_getupvalue</code></a> +(see <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>). + + +<p> +Returns <code>NULL</code> (and pops nothing) +when the index is greater than the number of upvalues. + + + + + +<hr><h3><a name="lua_upvalueid"><code>lua_upvalueid</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>void *lua_upvalueid (lua_State *L, int funcindex, int n);</pre> + +<p> +Returns a unique identifier for the upvalue numbered <code>n</code> +from the closure at index <code>funcindex</code>. +Parameters <code>funcindex</code> and <code>n</code> are as in the <a href="#lua_getupvalue"><code>lua_getupvalue</code></a> +(see <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>) +(but <code>n</code> cannot be greater than the number of upvalues). + + +<p> +These unique identifiers allow a program to check whether different +closures share upvalues. +Lua closures that share an upvalue +(that is, that access a same external local variable) +will return identical ids for those upvalue indices. + + + + + +<hr><h3><a name="lua_upvaluejoin"><code>lua_upvaluejoin</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>void lua_upvaluejoin (lua_State *L, int funcindex1, int n1, + int funcindex2, int n2);</pre> + +<p> +Make the <code>n1</code>-th upvalue of the Lua closure at index <code>funcindex1</code> +refer to the <code>n2</code>-th upvalue of the Lua closure at index <code>funcindex2</code>. + + + + + + + +<h1>5 – <a name="5">The Auxiliary Library</a></h1> + +<p> + +The <em>auxiliary library</em> provides several convenient functions +to interface C with Lua. +While the basic API provides the primitive functions for all +interactions between C and Lua, +the auxiliary library provides higher-level functions for some +common tasks. + + +<p> +All functions and types from the auxiliary library +are defined in header file <code>lauxlib.h</code> and +have a prefix <code>luaL_</code>. + + +<p> +All functions in the auxiliary library are built on +top of the basic API, +and so they provide nothing that cannot be done with that API. +Nevertheless, the use of the auxiliary library ensures +more consistency to your code. + + +<p> +Several functions in the auxiliary library use internally some +extra stack slots. +When a function in the auxiliary library uses less than five slots, +it does not check the stack size; +it simply assumes that there are enough slots. + + +<p> +Several functions in the auxiliary library are used to +check C function arguments. +Because the error message is formatted for arguments +(e.g., "<code>bad argument #1</code>"), +you should not use these functions for other stack values. + + +<p> +Functions called <code>luaL_check*</code> +always raise an error if the check is not satisfied. + + + +<h2>5.1 – <a name="5.1">Functions and Types</a></h2> + +<p> +Here we list all functions and types from the auxiliary library +in alphabetical order. + + + +<hr><h3><a name="luaL_addchar"><code>luaL_addchar</code></a></h3><p> +<span class="apii">[-?, +?, <em>e</em>]</span> +<pre>void luaL_addchar (luaL_Buffer *B, char c);</pre> + +<p> +Adds the byte <code>c</code> to the buffer <code>B</code> +(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). + + + + + +<hr><h3><a name="luaL_addlstring"><code>luaL_addlstring</code></a></h3><p> +<span class="apii">[-?, +?, <em>e</em>]</span> +<pre>void luaL_addlstring (luaL_Buffer *B, const char *s, size_t l);</pre> + +<p> +Adds the string pointed to by <code>s</code> with length <code>l</code> to +the buffer <code>B</code> +(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). +The string can contain embedded zeros. + + + + + +<hr><h3><a name="luaL_addsize"><code>luaL_addsize</code></a></h3><p> +<span class="apii">[-?, +?, <em>e</em>]</span> +<pre>void luaL_addsize (luaL_Buffer *B, size_t n);</pre> + +<p> +Adds to the buffer <code>B</code> (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>) +a string of length <code>n</code> previously copied to the +buffer area (see <a href="#luaL_prepbuffer"><code>luaL_prepbuffer</code></a>). + + + + + +<hr><h3><a name="luaL_addstring"><code>luaL_addstring</code></a></h3><p> +<span class="apii">[-?, +?, <em>e</em>]</span> +<pre>void luaL_addstring (luaL_Buffer *B, const char *s);</pre> + +<p> +Adds the zero-terminated string pointed to by <code>s</code> +to the buffer <code>B</code> +(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). + + + + + +<hr><h3><a name="luaL_addvalue"><code>luaL_addvalue</code></a></h3><p> +<span class="apii">[-1, +?, <em>e</em>]</span> +<pre>void luaL_addvalue (luaL_Buffer *B);</pre> + +<p> +Adds the value at the top of the stack +to the buffer <code>B</code> +(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). +Pops the value. + + +<p> +This is the only function on string buffers that can (and must) +be called with an extra element on the stack, +which is the value to be added to the buffer. + + + + + +<hr><h3><a name="luaL_argcheck"><code>luaL_argcheck</code></a></h3><p> +<span class="apii">[-0, +0, <em>v</em>]</span> +<pre>void luaL_argcheck (lua_State *L, + int cond, + int arg, + const char *extramsg);</pre> + +<p> +Checks whether <code>cond</code> is true. +If it is not, raises an error with a standard message (see <a href="#luaL_argerror"><code>luaL_argerror</code></a>). + + + + + +<hr><h3><a name="luaL_argerror"><code>luaL_argerror</code></a></h3><p> +<span class="apii">[-0, +0, <em>v</em>]</span> +<pre>int luaL_argerror (lua_State *L, int arg, const char *extramsg);</pre> + +<p> +Raises an error reporting a problem with argument <code>arg</code> +of the C function that called it, +using a standard message +that includes <code>extramsg</code> as a comment: + +<pre> + bad argument #<em>arg</em> to '<em>funcname</em>' (<em>extramsg</em>) +</pre><p> +This function never returns. + + + + + +<hr><h3><a name="luaL_Buffer"><code>luaL_Buffer</code></a></h3> +<pre>typedef struct luaL_Buffer luaL_Buffer;</pre> + +<p> +Type for a <em>string buffer</em>. + + +<p> +A string buffer allows C code to build Lua strings piecemeal. +Its pattern of use is as follows: + +<ul> + +<li>First declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li> + +<li>Then initialize it with a call <code>luaL_buffinit(L, &b)</code>.</li> + +<li> +Then add string pieces to the buffer calling any of +the <code>luaL_add*</code> functions. +</li> + +<li> +Finish by calling <code>luaL_pushresult(&b)</code>. +This call leaves the final string on the top of the stack. +</li> + +</ul> + +<p> +If you know beforehand the total size of the resulting string, +you can use the buffer like this: + +<ul> + +<li>First declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li> + +<li>Then initialize it and preallocate a space of +size <code>sz</code> with a call <code>luaL_buffinitsize(L, &b, sz)</code>.</li> + +<li>Then copy the string into that space.</li> + +<li> +Finish by calling <code>luaL_pushresultsize(&b, sz)</code>, +where <code>sz</code> is the total size of the resulting string +copied into that space. +</li> + +</ul> + +<p> +During its normal operation, +a string buffer uses a variable number of stack slots. +So, while using a buffer, you cannot assume that you know where +the top of the stack is. +You can use the stack between successive calls to buffer operations +as long as that use is balanced; +that is, +when you call a buffer operation, +the stack is at the same level +it was immediately after the previous buffer operation. +(The only exception to this rule is <a href="#luaL_addvalue"><code>luaL_addvalue</code></a>.) +After calling <a href="#luaL_pushresult"><code>luaL_pushresult</code></a> the stack is back to its +level when the buffer was initialized, +plus the final string on its top. + + + + + +<hr><h3><a name="luaL_buffinit"><code>luaL_buffinit</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>void luaL_buffinit (lua_State *L, luaL_Buffer *B);</pre> + +<p> +Initializes a buffer <code>B</code>. +This function does not allocate any space; +the buffer must be declared as a variable +(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). + + + + + +<hr><h3><a name="luaL_buffinitsize"><code>luaL_buffinitsize</code></a></h3><p> +<span class="apii">[-?, +?, <em>e</em>]</span> +<pre>char *luaL_buffinitsize (lua_State *L, luaL_Buffer *B, size_t sz);</pre> + +<p> +Equivalent to the sequence +<a href="#luaL_buffinit"><code>luaL_buffinit</code></a>, <a href="#luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a>. + + + + + +<hr><h3><a name="luaL_callmeta"><code>luaL_callmeta</code></a></h3><p> +<span class="apii">[-0, +(0|1), <em>e</em>]</span> +<pre>int luaL_callmeta (lua_State *L, int obj, const char *e);</pre> + +<p> +Calls a metamethod. + + +<p> +If the object at index <code>obj</code> has a metatable and this +metatable has a field <code>e</code>, +this function calls this field passing the object as its only argument. +In this case this function returns true and pushes onto the +stack the value returned by the call. +If there is no metatable or no metamethod, +this function returns false (without pushing any value on the stack). + + + + + +<hr><h3><a name="luaL_checkany"><code>luaL_checkany</code></a></h3><p> +<span class="apii">[-0, +0, <em>v</em>]</span> +<pre>void luaL_checkany (lua_State *L, int arg);</pre> + +<p> +Checks whether the function has an argument +of any type (including <b>nil</b>) at position <code>arg</code>. + + + + + +<hr><h3><a name="luaL_checkinteger"><code>luaL_checkinteger</code></a></h3><p> +<span class="apii">[-0, +0, <em>v</em>]</span> +<pre>lua_Integer luaL_checkinteger (lua_State *L, int arg);</pre> + +<p> +Checks whether the function argument <code>arg</code> is an integer +(or can be converted to an integer) +and returns this integer cast to a <a href="#lua_Integer"><code>lua_Integer</code></a>. + + + + + +<hr><h3><a name="luaL_checklstring"><code>luaL_checklstring</code></a></h3><p> +<span class="apii">[-0, +0, <em>v</em>]</span> +<pre>const char *luaL_checklstring (lua_State *L, int arg, size_t *l);</pre> + +<p> +Checks whether the function argument <code>arg</code> is a string +and returns this string; +if <code>l</code> is not <code>NULL</code> fills <code>*l</code> +with the string's length. + + +<p> +This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result, +so all conversions and caveats of that function apply here. + + + + + +<hr><h3><a name="luaL_checknumber"><code>luaL_checknumber</code></a></h3><p> +<span class="apii">[-0, +0, <em>v</em>]</span> +<pre>lua_Number luaL_checknumber (lua_State *L, int arg);</pre> + +<p> +Checks whether the function argument <code>arg</code> is a number +and returns this number. + + + + + +<hr><h3><a name="luaL_checkoption"><code>luaL_checkoption</code></a></h3><p> +<span class="apii">[-0, +0, <em>v</em>]</span> +<pre>int luaL_checkoption (lua_State *L, + int arg, + const char *def, + const char *const lst[]);</pre> + +<p> +Checks whether the function argument <code>arg</code> is a string and +searches for this string in the array <code>lst</code> +(which must be NULL-terminated). +Returns the index in the array where the string was found. +Raises an error if the argument is not a string or +if the string cannot be found. + + +<p> +If <code>def</code> is not <code>NULL</code>, +the function uses <code>def</code> as a default value when +there is no argument <code>arg</code> or when this argument is <b>nil</b>. + + +<p> +This is a useful function for mapping strings to C enums. +(The usual convention in Lua libraries is +to use strings instead of numbers to select options.) + + + + + +<hr><h3><a name="luaL_checkstack"><code>luaL_checkstack</code></a></h3><p> +<span class="apii">[-0, +0, <em>v</em>]</span> +<pre>void luaL_checkstack (lua_State *L, int sz, const char *msg);</pre> + +<p> +Grows the stack size to <code>top + sz</code> elements, +raising an error if the stack cannot grow to that size. +<code>msg</code> is an additional text to go into the error message +(or <code>NULL</code> for no additional text). + + + + + +<hr><h3><a name="luaL_checkstring"><code>luaL_checkstring</code></a></h3><p> +<span class="apii">[-0, +0, <em>v</em>]</span> +<pre>const char *luaL_checkstring (lua_State *L, int arg);</pre> + +<p> +Checks whether the function argument <code>arg</code> is a string +and returns this string. + + +<p> +This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result, +so all conversions and caveats of that function apply here. + + + + + +<hr><h3><a name="luaL_checktype"><code>luaL_checktype</code></a></h3><p> +<span class="apii">[-0, +0, <em>v</em>]</span> +<pre>void luaL_checktype (lua_State *L, int arg, int t);</pre> + +<p> +Checks whether the function argument <code>arg</code> has type <code>t</code>. +See <a href="#lua_type"><code>lua_type</code></a> for the encoding of types for <code>t</code>. + + + + + +<hr><h3><a name="luaL_checkudata"><code>luaL_checkudata</code></a></h3><p> +<span class="apii">[-0, +0, <em>v</em>]</span> +<pre>void *luaL_checkudata (lua_State *L, int arg, const char *tname);</pre> + +<p> +Checks whether the function argument <code>arg</code> is a userdata +of the type <code>tname</code> (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>) and +returns the userdata address (see <a href="#lua_touserdata"><code>lua_touserdata</code></a>). + + + + + +<hr><h3><a name="luaL_checkversion"><code>luaL_checkversion</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>void luaL_checkversion (lua_State *L);</pre> + +<p> +Checks whether the core running the call, +the core that created the Lua state, +and the code making the call are all using the same version of Lua. +Also checks whether the core running the call +and the core that created the Lua state +are using the same address space. + + + + + +<hr><h3><a name="luaL_dofile"><code>luaL_dofile</code></a></h3><p> +<span class="apii">[-0, +?, <em>e</em>]</span> +<pre>int luaL_dofile (lua_State *L, const char *filename);</pre> + +<p> +Loads and runs the given file. +It is defined as the following macro: + +<pre> + (luaL_loadfile(L, filename) || lua_pcall(L, 0, LUA_MULTRET, 0)) +</pre><p> +It returns false if there are no errors +or true in case of errors. + + + + + +<hr><h3><a name="luaL_dostring"><code>luaL_dostring</code></a></h3><p> +<span class="apii">[-0, +?, –]</span> +<pre>int luaL_dostring (lua_State *L, const char *str);</pre> + +<p> +Loads and runs the given string. +It is defined as the following macro: + +<pre> + (luaL_loadstring(L, str) || lua_pcall(L, 0, LUA_MULTRET, 0)) +</pre><p> +It returns false if there are no errors +or true in case of errors. + + + + + +<hr><h3><a name="luaL_error"><code>luaL_error</code></a></h3><p> +<span class="apii">[-0, +0, <em>v</em>]</span> +<pre>int luaL_error (lua_State *L, const char *fmt, ...);</pre> + +<p> +Raises an error. +The error message format is given by <code>fmt</code> +plus any extra arguments, +following the same rules of <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>. +It also adds at the beginning of the message the file name and +the line number where the error occurred, +if this information is available. + + +<p> +This function never returns, +but it is an idiom to use it in C functions +as <code>return luaL_error(<em>args</em>)</code>. + + + + + +<hr><h3><a name="luaL_execresult"><code>luaL_execresult</code></a></h3><p> +<span class="apii">[-0, +3, <em>e</em>]</span> +<pre>int luaL_execresult (lua_State *L, int stat);</pre> + +<p> +This function produces the return values for +process-related functions in the standard library +(<a href="#pdf-os.execute"><code>os.execute</code></a> and <a href="#pdf-io.close"><code>io.close</code></a>). + + + + + +<hr><h3><a name="luaL_fileresult"><code>luaL_fileresult</code></a></h3><p> +<span class="apii">[-0, +(1|3), <em>e</em>]</span> +<pre>int luaL_fileresult (lua_State *L, int stat, const char *fname);</pre> + +<p> +This function produces the return values for +file-related functions in the standard library +(<a href="#pdf-io.open"><code>io.open</code></a>, <a href="#pdf-os.rename"><code>os.rename</code></a>, <a href="#pdf-file:seek"><code>file:seek</code></a>, etc.). + + + + + +<hr><h3><a name="luaL_getmetafield"><code>luaL_getmetafield</code></a></h3><p> +<span class="apii">[-0, +(0|1), <em>e</em>]</span> +<pre>int luaL_getmetafield (lua_State *L, int obj, const char *e);</pre> + +<p> +Pushes onto the stack the field <code>e</code> from the metatable +of the object at index <code>obj</code> and returns the type of pushed value. +If the object does not have a metatable, +or if the metatable does not have this field, +pushes nothing and returns <code>LUA_TNIL</code>. + + + + + +<hr><h3><a name="luaL_getmetatable"><code>luaL_getmetatable</code></a></h3><p> +<span class="apii">[-0, +1, –]</span> +<pre>int luaL_getmetatable (lua_State *L, const char *tname);</pre> + +<p> +Pushes onto the stack the metatable associated with name <code>tname</code> +in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>). +If there is no metatable associated with <code>tname</code>, +returns false and pushes <b>nil</b>. + + + + + +<hr><h3><a name="luaL_getsubtable"><code>luaL_getsubtable</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>int luaL_getsubtable (lua_State *L, int idx, const char *fname);</pre> + +<p> +Ensures that the value <code>t[fname]</code>, +where <code>t</code> is the value at index <code>idx</code>, +is a table, +and pushes that table onto the stack. +Returns true if it finds a previous table there +and false if it creates a new table. + + + + + +<hr><h3><a name="luaL_gsub"><code>luaL_gsub</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>const char *luaL_gsub (lua_State *L, + const char *s, + const char *p, + const char *r);</pre> + +<p> +Creates a copy of string <code>s</code> by replacing +any occurrence of the string <code>p</code> +with the string <code>r</code>. +Pushes the resulting string on the stack and returns it. + + + + + +<hr><h3><a name="luaL_len"><code>luaL_len</code></a></h3><p> +<span class="apii">[-0, +0, <em>e</em>]</span> +<pre>lua_Integer luaL_len (lua_State *L, int index);</pre> + +<p> +Returns the "length" of the value at the given index +as a number; +it is equivalent to the '<code>#</code>' operator in Lua (see <a href="#3.4.7">§3.4.7</a>). +Raises an error if the result of the operation is not an integer. +(This case only can happen through metamethods.) + + + + + +<hr><h3><a name="luaL_loadbuffer"><code>luaL_loadbuffer</code></a></h3><p> +<span class="apii">[-0, +1, –]</span> +<pre>int luaL_loadbuffer (lua_State *L, + const char *buff, + size_t sz, + const char *name);</pre> + +<p> +Equivalent to <a href="#luaL_loadbufferx"><code>luaL_loadbufferx</code></a> with <code>mode</code> equal to <code>NULL</code>. + + + + + +<hr><h3><a name="luaL_loadbufferx"><code>luaL_loadbufferx</code></a></h3><p> +<span class="apii">[-0, +1, –]</span> +<pre>int luaL_loadbufferx (lua_State *L, + const char *buff, + size_t sz, + const char *name, + const char *mode);</pre> + +<p> +Loads a buffer as a Lua chunk. +This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the +buffer pointed to by <code>buff</code> with size <code>sz</code>. + + +<p> +This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>. +<code>name</code> is the chunk name, +used for debug information and error messages. +The string <code>mode</code> works as in function <a href="#lua_load"><code>lua_load</code></a>. + + + + + +<hr><h3><a name="luaL_loadfile"><code>luaL_loadfile</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>int luaL_loadfile (lua_State *L, const char *filename);</pre> + +<p> +Equivalent to <a href="#luaL_loadfilex"><code>luaL_loadfilex</code></a> with <code>mode</code> equal to <code>NULL</code>. + + + + + +<hr><h3><a name="luaL_loadfilex"><code>luaL_loadfilex</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>int luaL_loadfilex (lua_State *L, const char *filename, + const char *mode);</pre> + +<p> +Loads a file as a Lua chunk. +This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the file +named <code>filename</code>. +If <code>filename</code> is <code>NULL</code>, +then it loads from the standard input. +The first line in the file is ignored if it starts with a <code>#</code>. + + +<p> +The string <code>mode</code> works as in function <a href="#lua_load"><code>lua_load</code></a>. + + +<p> +This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>, +but it has an extra error code <a name="pdf-LUA_ERRFILE"><code>LUA_ERRFILE</code></a> +if it cannot open/read the file or the file has a wrong mode. + + +<p> +As <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk; +it does not run it. + + + + + +<hr><h3><a name="luaL_loadstring"><code>luaL_loadstring</code></a></h3><p> +<span class="apii">[-0, +1, –]</span> +<pre>int luaL_loadstring (lua_State *L, const char *s);</pre> + +<p> +Loads a string as a Lua chunk. +This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in +the zero-terminated string <code>s</code>. + + +<p> +This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>. + + +<p> +Also as <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk; +it does not run it. + + + + + +<hr><h3><a name="luaL_newlib"><code>luaL_newlib</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>void luaL_newlib (lua_State *L, const luaL_Reg l[]);</pre> + +<p> +Creates a new table and registers there +the functions in list <code>l</code>. + + +<p> +It is implemented as the following macro: + +<pre> + (luaL_newlibtable(L,l), luaL_setfuncs(L,l,0)) +</pre><p> +The array <code>l</code> must be the actual array, +not a pointer to it. + + + + + +<hr><h3><a name="luaL_newlibtable"><code>luaL_newlibtable</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>void luaL_newlibtable (lua_State *L, const luaL_Reg l[]);</pre> + +<p> +Creates a new table with a size optimized +to store all entries in the array <code>l</code> +(but does not actually store them). +It is intended to be used in conjunction with <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a> +(see <a href="#luaL_newlib"><code>luaL_newlib</code></a>). + + +<p> +It is implemented as a macro. +The array <code>l</code> must be the actual array, +not a pointer to it. + + + + + +<hr><h3><a name="luaL_newmetatable"><code>luaL_newmetatable</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>int luaL_newmetatable (lua_State *L, const char *tname);</pre> + +<p> +If the registry already has the key <code>tname</code>, +returns 0. +Otherwise, +creates a new table to be used as a metatable for userdata, +adds to this new table the pair <code>__name = tname</code>, +adds to the registry the pair <code>[tname] = new table</code>, +and returns 1. +(The entry <code>__name</code> is used by some error-reporting functions.) + + +<p> +In both cases pushes onto the stack the final value associated +with <code>tname</code> in the registry. + + + + + +<hr><h3><a name="luaL_newstate"><code>luaL_newstate</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>lua_State *luaL_newstate (void);</pre> + +<p> +Creates a new Lua state. +It calls <a href="#lua_newstate"><code>lua_newstate</code></a> with an +allocator based on the standard C <code>realloc</code> function +and then sets a panic function (see <a href="#4.6">§4.6</a>) that prints +an error message to the standard error output in case of fatal +errors. + + +<p> +Returns the new state, +or <code>NULL</code> if there is a memory allocation error. + + + + + +<hr><h3><a name="luaL_openlibs"><code>luaL_openlibs</code></a></h3><p> +<span class="apii">[-0, +0, <em>e</em>]</span> +<pre>void luaL_openlibs (lua_State *L);</pre> + +<p> +Opens all standard Lua libraries into the given state. + + + + + +<hr><h3><a name="luaL_optinteger"><code>luaL_optinteger</code></a></h3><p> +<span class="apii">[-0, +0, <em>v</em>]</span> +<pre>lua_Integer luaL_optinteger (lua_State *L, + int arg, + lua_Integer d);</pre> + +<p> +If the function argument <code>arg</code> is an integer +(or convertible to an integer), +returns this integer. +If this argument is absent or is <b>nil</b>, +returns <code>d</code>. +Otherwise, raises an error. + + + + + +<hr><h3><a name="luaL_optlstring"><code>luaL_optlstring</code></a></h3><p> +<span class="apii">[-0, +0, <em>v</em>]</span> +<pre>const char *luaL_optlstring (lua_State *L, + int arg, + const char *d, + size_t *l);</pre> + +<p> +If the function argument <code>arg</code> is a string, +returns this string. +If this argument is absent or is <b>nil</b>, +returns <code>d</code>. +Otherwise, raises an error. + + +<p> +If <code>l</code> is not <code>NULL</code>, +fills the position <code>*l</code> with the result's length. + + + + + +<hr><h3><a name="luaL_optnumber"><code>luaL_optnumber</code></a></h3><p> +<span class="apii">[-0, +0, <em>v</em>]</span> +<pre>lua_Number luaL_optnumber (lua_State *L, int arg, lua_Number d);</pre> + +<p> +If the function argument <code>arg</code> is a number, +returns this number. +If this argument is absent or is <b>nil</b>, +returns <code>d</code>. +Otherwise, raises an error. + + + + + +<hr><h3><a name="luaL_optstring"><code>luaL_optstring</code></a></h3><p> +<span class="apii">[-0, +0, <em>v</em>]</span> +<pre>const char *luaL_optstring (lua_State *L, + int arg, + const char *d);</pre> + +<p> +If the function argument <code>arg</code> is a string, +returns this string. +If this argument is absent or is <b>nil</b>, +returns <code>d</code>. +Otherwise, raises an error. + + + + + +<hr><h3><a name="luaL_prepbuffer"><code>luaL_prepbuffer</code></a></h3><p> +<span class="apii">[-?, +?, <em>e</em>]</span> +<pre>char *luaL_prepbuffer (luaL_Buffer *B);</pre> + +<p> +Equivalent to <a href="#luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a> +with the predefined size <a name="pdf-LUAL_BUFFERSIZE"><code>LUAL_BUFFERSIZE</code></a>. + + + + + +<hr><h3><a name="luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a></h3><p> +<span class="apii">[-?, +?, <em>e</em>]</span> +<pre>char *luaL_prepbuffsize (luaL_Buffer *B, size_t sz);</pre> + +<p> +Returns an address to a space of size <code>sz</code> +where you can copy a string to be added to buffer <code>B</code> +(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). +After copying the string into this space you must call +<a href="#luaL_addsize"><code>luaL_addsize</code></a> with the size of the string to actually add +it to the buffer. + + + + + +<hr><h3><a name="luaL_pushresult"><code>luaL_pushresult</code></a></h3><p> +<span class="apii">[-?, +1, <em>e</em>]</span> +<pre>void luaL_pushresult (luaL_Buffer *B);</pre> + +<p> +Finishes the use of buffer <code>B</code> leaving the final string on +the top of the stack. + + + + + +<hr><h3><a name="luaL_pushresultsize"><code>luaL_pushresultsize</code></a></h3><p> +<span class="apii">[-?, +1, <em>e</em>]</span> +<pre>void luaL_pushresultsize (luaL_Buffer *B, size_t sz);</pre> + +<p> +Equivalent to the sequence <a href="#luaL_addsize"><code>luaL_addsize</code></a>, <a href="#luaL_pushresult"><code>luaL_pushresult</code></a>. + + + + + +<hr><h3><a name="luaL_ref"><code>luaL_ref</code></a></h3><p> +<span class="apii">[-1, +0, <em>e</em>]</span> +<pre>int luaL_ref (lua_State *L, int t);</pre> + +<p> +Creates and returns a <em>reference</em>, +in the table at index <code>t</code>, +for the object at the top of the stack (and pops the object). + + +<p> +A reference is a unique integer key. +As long as you do not manually add integer keys into table <code>t</code>, +<a href="#luaL_ref"><code>luaL_ref</code></a> ensures the uniqueness of the key it returns. +You can retrieve an object referred by reference <code>r</code> +by calling <code>lua_rawgeti(L, t, r)</code>. +Function <a href="#luaL_unref"><code>luaL_unref</code></a> frees a reference and its associated object. + + +<p> +If the object at the top of the stack is <b>nil</b>, +<a href="#luaL_ref"><code>luaL_ref</code></a> returns the constant <a name="pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>. +The constant <a name="pdf-LUA_NOREF"><code>LUA_NOREF</code></a> is guaranteed to be different +from any reference returned by <a href="#luaL_ref"><code>luaL_ref</code></a>. + + + + + +<hr><h3><a name="luaL_Reg"><code>luaL_Reg</code></a></h3> +<pre>typedef struct luaL_Reg { + const char *name; + lua_CFunction func; +} luaL_Reg;</pre> + +<p> +Type for arrays of functions to be registered by +<a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a>. +<code>name</code> is the function name and <code>func</code> is a pointer to +the function. +Any array of <a href="#luaL_Reg"><code>luaL_Reg</code></a> must end with a sentinel entry +in which both <code>name</code> and <code>func</code> are <code>NULL</code>. + + + + + +<hr><h3><a name="luaL_requiref"><code>luaL_requiref</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>void luaL_requiref (lua_State *L, const char *modname, + lua_CFunction openf, int glb);</pre> + +<p> +If <code>modname</code> is not already present in <a href="#pdf-package.loaded"><code>package.loaded</code></a>, +calls function <code>openf</code> with string <code>modname</code> as an argument +and sets the call result in <code>package.loaded[modname]</code>, +as if that function has been called through <a href="#pdf-require"><code>require</code></a>. + + +<p> +If <code>glb</code> is true, +also stores the module into global <code>modname</code>. + + +<p> +Leaves a copy of the module on the stack. + + + + + +<hr><h3><a name="luaL_setfuncs"><code>luaL_setfuncs</code></a></h3><p> +<span class="apii">[-nup, +0, <em>e</em>]</span> +<pre>void luaL_setfuncs (lua_State *L, const luaL_Reg *l, int nup);</pre> + +<p> +Registers all functions in the array <code>l</code> +(see <a href="#luaL_Reg"><code>luaL_Reg</code></a>) into the table on the top of the stack +(below optional upvalues, see next). + + +<p> +When <code>nup</code> is not zero, +all functions are created sharing <code>nup</code> upvalues, +which must be previously pushed on the stack +on top of the library table. +These values are popped from the stack after the registration. + + + + + +<hr><h3><a name="luaL_setmetatable"><code>luaL_setmetatable</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>void luaL_setmetatable (lua_State *L, const char *tname);</pre> + +<p> +Sets the metatable of the object at the top of the stack +as the metatable associated with name <code>tname</code> +in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>). + + + + + +<hr><h3><a name="luaL_Stream"><code>luaL_Stream</code></a></h3> +<pre>typedef struct luaL_Stream { + FILE *f; + lua_CFunction closef; +} luaL_Stream;</pre> + +<p> +The standard representation for file handles, +which is used by the standard I/O library. + + +<p> +A file handle is implemented as a full userdata, +with a metatable called <code>LUA_FILEHANDLE</code> +(where <code>LUA_FILEHANDLE</code> is a macro with the actual metatable's name). +The metatable is created by the I/O library +(see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>). + + +<p> +This userdata must start with the structure <code>luaL_Stream</code>; +it can contain other data after this initial structure. +Field <code>f</code> points to the corresponding C stream +(or it can be <code>NULL</code> to indicate an incompletely created handle). +Field <code>closef</code> points to a Lua function +that will be called to close the stream +when the handle is closed or collected; +this function receives the file handle as its sole argument and +must return either <b>true</b> (in case of success) +or <b>nil</b> plus an error message (in case of error). +Once Lua calls this field, +the field value is changed to <code>NULL</code> +to signal that the handle is closed. + + + + + +<hr><h3><a name="luaL_testudata"><code>luaL_testudata</code></a></h3><p> +<span class="apii">[-0, +0, <em>e</em>]</span> +<pre>void *luaL_testudata (lua_State *L, int arg, const char *tname);</pre> + +<p> +This function works like <a href="#luaL_checkudata"><code>luaL_checkudata</code></a>, +except that, when the test fails, +it returns <code>NULL</code> instead of raising an error. + + + + + +<hr><h3><a name="luaL_tolstring"><code>luaL_tolstring</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>const char *luaL_tolstring (lua_State *L, int idx, size_t *len);</pre> + +<p> +Converts any Lua value at the given index to a C string +in a reasonable format. +The resulting string is pushed onto the stack and also +returned by the function. +If <code>len</code> is not <code>NULL</code>, +the function also sets <code>*len</code> with the string length. + + +<p> +If the value has a metatable with a <code>"__tostring"</code> field, +then <code>luaL_tolstring</code> calls the corresponding metamethod +with the value as argument, +and uses the result of the call as its result. + + + + + +<hr><h3><a name="luaL_traceback"><code>luaL_traceback</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>void luaL_traceback (lua_State *L, lua_State *L1, const char *msg, + int level);</pre> + +<p> +Creates and pushes a traceback of the stack <code>L1</code>. +If <code>msg</code> is not <code>NULL</code> it is appended +at the beginning of the traceback. +The <code>level</code> parameter tells at which level +to start the traceback. + + + + + +<hr><h3><a name="luaL_typename"><code>luaL_typename</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>const char *luaL_typename (lua_State *L, int index);</pre> + +<p> +Returns the name of the type of the value at the given index. + + + + + +<hr><h3><a name="luaL_unref"><code>luaL_unref</code></a></h3><p> +<span class="apii">[-0, +0, –]</span> +<pre>void luaL_unref (lua_State *L, int t, int ref);</pre> + +<p> +Releases reference <code>ref</code> from the table at index <code>t</code> +(see <a href="#luaL_ref"><code>luaL_ref</code></a>). +The entry is removed from the table, +so that the referred object can be collected. +The reference <code>ref</code> is also freed to be used again. + + +<p> +If <code>ref</code> is <a href="#pdf-LUA_NOREF"><code>LUA_NOREF</code></a> or <a href="#pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>, +<a href="#luaL_unref"><code>luaL_unref</code></a> does nothing. + + + + + +<hr><h3><a name="luaL_where"><code>luaL_where</code></a></h3><p> +<span class="apii">[-0, +1, <em>e</em>]</span> +<pre>void luaL_where (lua_State *L, int lvl);</pre> + +<p> +Pushes onto the stack a string identifying the current position +of the control at level <code>lvl</code> in the call stack. +Typically this string has the following format: + +<pre> + <em>chunkname</em>:<em>currentline</em>: +</pre><p> +Level 0 is the running function, +level 1 is the function that called the running function, +etc. + + +<p> +This function is used to build a prefix for error messages. + + + + + + + +<h1>6 – <a name="6">Standard Libraries</a></h1> + +<p> +The standard Lua libraries provide useful functions +that are implemented directly through the C API. +Some of these functions provide essential services to the language +(e.g., <a href="#pdf-type"><code>type</code></a> and <a href="#pdf-getmetatable"><code>getmetatable</code></a>); +others provide access to "outside" services (e.g., I/O); +and others could be implemented in Lua itself, +but are quite useful or have critical performance requirements that +deserve an implementation in C (e.g., <a href="#pdf-table.sort"><code>table.sort</code></a>). + + +<p> +All libraries are implemented through the official C API +and are provided as separate C modules. +Currently, Lua has the following standard libraries: + +<ul> + +<li>basic library (<a href="#6.1">§6.1</a>);</li> + +<li>coroutine library (<a href="#6.2">§6.2</a>);</li> + +<li>package library (<a href="#6.3">§6.3</a>);</li> + +<li>string manipulation (<a href="#6.4">§6.4</a>);</li> + +<li>basic UTF-8 support (<a href="#6.5">§6.5</a>);</li> + +<li>table manipulation (<a href="#6.6">§6.6</a>);</li> + +<li>mathematical functions (<a href="#6.7">§6.7</a>) (sin, log, etc.);</li> + +<li>input and output (<a href="#6.8">§6.8</a>);</li> + +<li>operating system facilities (<a href="#6.9">§6.9</a>);</li> + +<li>debug facilities (<a href="#6.10">§6.10</a>).</li> + +</ul><p> +Except for the basic and the package libraries, +each library provides all its functions as fields of a global table +or as methods of its objects. + + +<p> +To have access to these libraries, +the C host program should call the <a href="#luaL_openlibs"><code>luaL_openlibs</code></a> function, +which opens all standard libraries. +Alternatively, +the host program can open them individually by using +<a href="#luaL_requiref"><code>luaL_requiref</code></a> to call +<a name="pdf-luaopen_base"><code>luaopen_base</code></a> (for the basic library), +<a name="pdf-luaopen_package"><code>luaopen_package</code></a> (for the package library), +<a name="pdf-luaopen_coroutine"><code>luaopen_coroutine</code></a> (for the coroutine library), +<a name="pdf-luaopen_string"><code>luaopen_string</code></a> (for the string library), +<a name="pdf-luaopen_utf8"><code>luaopen_utf8</code></a> (for the UTF8 library), +<a name="pdf-luaopen_table"><code>luaopen_table</code></a> (for the table library), +<a name="pdf-luaopen_math"><code>luaopen_math</code></a> (for the mathematical library), +<a name="pdf-luaopen_io"><code>luaopen_io</code></a> (for the I/O library), +<a name="pdf-luaopen_os"><code>luaopen_os</code></a> (for the operating system library), +and <a name="pdf-luaopen_debug"><code>luaopen_debug</code></a> (for the debug library). +These functions are declared in <a name="pdf-lualib.h"><code>lualib.h</code></a>. + + + +<h2>6.1 – <a name="6.1">Basic Functions</a></h2> + +<p> +The basic library provides core functions to Lua. +If you do not include this library in your application, +you should check carefully whether you need to provide +implementations for some of its facilities. + + +<p> +<hr><h3><a name="pdf-assert"><code>assert (v [, message])</code></a></h3> + + +<p> +Calls <a href="#pdf-error"><code>error</code></a> if +the value of its argument <code>v</code> is false (i.e., <b>nil</b> or <b>false</b>); +otherwise, returns all its arguments. +In case of error, +<code>message</code> is the error object; +when absent, it defaults to "<code>assertion failed!</code>" + + + + +<p> +<hr><h3><a name="pdf-collectgarbage"><code>collectgarbage ([opt [, arg]])</code></a></h3> + + +<p> +This function is a generic interface to the garbage collector. +It performs different functions according to its first argument, <code>opt</code>: + +<ul> + +<li><b>"<code>collect</code>": </b> +performs a full garbage-collection cycle. +This is the default option. +</li> + +<li><b>"<code>stop</code>": </b> +stops automatic execution of the garbage collector. +The collector will run only when explicitly invoked, +until a call to restart it. +</li> + +<li><b>"<code>restart</code>": </b> +restarts automatic execution of the garbage collector. +</li> + +<li><b>"<code>count</code>": </b> +returns the total memory in use by Lua in Kbytes. +The value has a fractional part, +so that it multiplied by 1024 +gives the exact number of bytes in use by Lua +(except for overflows). +</li> + +<li><b>"<code>step</code>": </b> +performs a garbage-collection step. +The step "size" is controlled by <code>arg</code>. +With a zero value, +the collector will perform one basic (indivisible) step. +For non-zero values, +the collector will perform as if that amount of memory +(in KBytes) had been allocated by Lua. +Returns <b>true</b> if the step finished a collection cycle. +</li> + +<li><b>"<code>setpause</code>": </b> +sets <code>arg</code> as the new value for the <em>pause</em> of +the collector (see <a href="#2.5">§2.5</a>). +Returns the previous value for <em>pause</em>. +</li> + +<li><b>"<code>setstepmul</code>": </b> +sets <code>arg</code> as the new value for the <em>step multiplier</em> of +the collector (see <a href="#2.5">§2.5</a>). +Returns the previous value for <em>step</em>. +</li> + +<li><b>"<code>isrunning</code>": </b> +returns a boolean that tells whether the collector is running +(i.e., not stopped). +</li> + +</ul> + + + +<p> +<hr><h3><a name="pdf-dofile"><code>dofile ([filename])</code></a></h3> +Opens the named file and executes its contents as a Lua chunk. +When called without arguments, +<code>dofile</code> executes the contents of the standard input (<code>stdin</code>). +Returns all values returned by the chunk. +In case of errors, <code>dofile</code> propagates the error +to its caller (that is, <code>dofile</code> does not run in protected mode). + + + + +<p> +<hr><h3><a name="pdf-error"><code>error (message [, level])</code></a></h3> +Terminates the last protected function called +and returns <code>message</code> as the error object. +Function <code>error</code> never returns. + + +<p> +Usually, <code>error</code> adds some information about the error position +at the beginning of the message, if the message is a string. +The <code>level</code> argument specifies how to get the error position. +With level 1 (the default), the error position is where the +<code>error</code> function was called. +Level 2 points the error to where the function +that called <code>error</code> was called; and so on. +Passing a level 0 avoids the addition of error position information +to the message. + + + + +<p> +<hr><h3><a name="pdf-_G"><code>_G</code></a></h3> +A global variable (not a function) that +holds the global environment (see <a href="#2.2">§2.2</a>). +Lua itself does not use this variable; +changing its value does not affect any environment, +nor vice versa. + + + + +<p> +<hr><h3><a name="pdf-getmetatable"><code>getmetatable (object)</code></a></h3> + + +<p> +If <code>object</code> does not have a metatable, returns <b>nil</b>. +Otherwise, +if the object's metatable has a <code>"__metatable"</code> field, +returns the associated value. +Otherwise, returns the metatable of the given object. + + + + +<p> +<hr><h3><a name="pdf-ipairs"><code>ipairs (t)</code></a></h3> + + +<p> +Returns three values (an iterator function, the table <code>t</code>, and 0) +so that the construction + +<pre> + for i,v in ipairs(t) do <em>body</em> end +</pre><p> +will iterate over the key–value pairs +(<code>1,t[1]</code>), (<code>2,t[2]</code>), ..., +up to the first nil value. + + + + +<p> +<hr><h3><a name="pdf-load"><code>load (chunk [, chunkname [, mode [, env]]])</code></a></h3> + + +<p> +Loads a chunk. + + +<p> +If <code>chunk</code> is a string, the chunk is this string. +If <code>chunk</code> is a function, +<code>load</code> calls it repeatedly to get the chunk pieces. +Each call to <code>chunk</code> must return a string that concatenates +with previous results. +A return of an empty string, <b>nil</b>, or no value signals the end of the chunk. + + +<p> +If there are no syntactic errors, +returns the compiled chunk as a function; +otherwise, returns <b>nil</b> plus the error message. + + +<p> +If the resulting function has upvalues, +the first upvalue is set to the value of <code>env</code>, +if that parameter is given, +or to the value of the global environment. +Other upvalues are initialized with <b>nil</b>. +(When you load a main chunk, +the resulting function will always have exactly one upvalue, +the <code>_ENV</code> variable (see <a href="#2.2">§2.2</a>). +However, +when you load a binary chunk created from a function (see <a href="#pdf-string.dump"><code>string.dump</code></a>), +the resulting function can have an arbitrary number of upvalues.) +All upvalues are fresh, that is, +they are not shared with any other function. + + +<p> +<code>chunkname</code> is used as the name of the chunk for error messages +and debug information (see <a href="#4.9">§4.9</a>). +When absent, +it defaults to <code>chunk</code>, if <code>chunk</code> is a string, +or to "<code>=(load)</code>" otherwise. + + +<p> +The string <code>mode</code> controls whether the chunk can be text or binary +(that is, a precompiled chunk). +It may be the string "<code>b</code>" (only binary chunks), +"<code>t</code>" (only text chunks), +or "<code>bt</code>" (both binary and text). +The default is "<code>bt</code>". + + +<p> +Lua does not check the consistency of binary chunks. +Maliciously crafted binary chunks can crash +the interpreter. + + + + +<p> +<hr><h3><a name="pdf-loadfile"><code>loadfile ([filename [, mode [, env]]])</code></a></h3> + + +<p> +Similar to <a href="#pdf-load"><code>load</code></a>, +but gets the chunk from file <code>filename</code> +or from the standard input, +if no file name is given. + + + + +<p> +<hr><h3><a name="pdf-next"><code>next (table [, index])</code></a></h3> + + +<p> +Allows a program to traverse all fields of a table. +Its first argument is a table and its second argument +is an index in this table. +<code>next</code> returns the next index of the table +and its associated value. +When called with <b>nil</b> as its second argument, +<code>next</code> returns an initial index +and its associated value. +When called with the last index, +or with <b>nil</b> in an empty table, +<code>next</code> returns <b>nil</b>. +If the second argument is absent, then it is interpreted as <b>nil</b>. +In particular, +you can use <code>next(t)</code> to check whether a table is empty. + + +<p> +The order in which the indices are enumerated is not specified, +<em>even for numeric indices</em>. +(To traverse a table in numeric order, +use a numerical <b>for</b>.) + + +<p> +The behavior of <code>next</code> is undefined if, +during the traversal, +you assign any value to a non-existent field in the table. +You may however modify existing fields. +In particular, you may clear existing fields. + + + + +<p> +<hr><h3><a name="pdf-pairs"><code>pairs (t)</code></a></h3> + + +<p> +If <code>t</code> has a metamethod <code>__pairs</code>, +calls it with <code>t</code> as argument and returns the first three +results from the call. + + +<p> +Otherwise, +returns three values: the <a href="#pdf-next"><code>next</code></a> function, the table <code>t</code>, and <b>nil</b>, +so that the construction + +<pre> + for k,v in pairs(t) do <em>body</em> end +</pre><p> +will iterate over all key–value pairs of table <code>t</code>. + + +<p> +See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying +the table during its traversal. + + + + +<p> +<hr><h3><a name="pdf-pcall"><code>pcall (f [, arg1, ···])</code></a></h3> + + +<p> +Calls function <code>f</code> with +the given arguments in <em>protected mode</em>. +This means that any error inside <code>f</code> is not propagated; +instead, <code>pcall</code> catches the error +and returns a status code. +Its first result is the status code (a boolean), +which is true if the call succeeds without errors. +In such case, <code>pcall</code> also returns all results from the call, +after this first result. +In case of any error, <code>pcall</code> returns <b>false</b> plus the error message. + + + + +<p> +<hr><h3><a name="pdf-print"><code>print (···)</code></a></h3> +Receives any number of arguments +and prints their values to <code>stdout</code>, +using the <a href="#pdf-tostring"><code>tostring</code></a> function to convert each argument to a string. +<code>print</code> is not intended for formatted output, +but only as a quick way to show a value, +for instance for debugging. +For complete control over the output, +use <a href="#pdf-string.format"><code>string.format</code></a> and <a href="#pdf-io.write"><code>io.write</code></a>. + + + + +<p> +<hr><h3><a name="pdf-rawequal"><code>rawequal (v1, v2)</code></a></h3> +Checks whether <code>v1</code> is equal to <code>v2</code>, +without invoking any metamethod. +Returns a boolean. + + + + +<p> +<hr><h3><a name="pdf-rawget"><code>rawget (table, index)</code></a></h3> +Gets the real value of <code>table[index]</code>, +without invoking any metamethod. +<code>table</code> must be a table; +<code>index</code> may be any value. + + + + +<p> +<hr><h3><a name="pdf-rawlen"><code>rawlen (v)</code></a></h3> +Returns the length of the object <code>v</code>, +which must be a table or a string, +without invoking any metamethod. +Returns an integer. + + + + +<p> +<hr><h3><a name="pdf-rawset"><code>rawset (table, index, value)</code></a></h3> +Sets the real value of <code>table[index]</code> to <code>value</code>, +without invoking any metamethod. +<code>table</code> must be a table, +<code>index</code> any value different from <b>nil</b> and NaN, +and <code>value</code> any Lua value. + + +<p> +This function returns <code>table</code>. + + + + +<p> +<hr><h3><a name="pdf-select"><code>select (index, ···)</code></a></h3> + + +<p> +If <code>index</code> is a number, +returns all arguments after argument number <code>index</code>; +a negative number indexes from the end (-1 is the last argument). +Otherwise, <code>index</code> must be the string <code>"#"</code>, +and <code>select</code> returns the total number of extra arguments it received. + + + + +<p> +<hr><h3><a name="pdf-setmetatable"><code>setmetatable (table, metatable)</code></a></h3> + + +<p> +Sets the metatable for the given table. +(You cannot change the metatable of other types from Lua, only from C.) +If <code>metatable</code> is <b>nil</b>, +removes the metatable of the given table. +If the original metatable has a <code>"__metatable"</code> field, +raises an error. + + +<p> +This function returns <code>table</code>. + + + + +<p> +<hr><h3><a name="pdf-tonumber"><code>tonumber (e [, base])</code></a></h3> + + +<p> +When called with no <code>base</code>, +<code>tonumber</code> tries to convert its argument to a number. +If the argument is already a number or +a string convertible to a number, +then <code>tonumber</code> returns this number; +otherwise, it returns <b>nil</b>. + + +<p> +The conversion of strings can result in integers or floats, +according to the lexical conventions of Lua (see <a href="#3.1">§3.1</a>). +(The string may have leading and trailing spaces and a sign.) + + +<p> +When called with <code>base</code>, +then <code>e</code> must be a string to be interpreted as +an integer numeral in that base. +The base may be any integer between 2 and 36, inclusive. +In bases above 10, the letter '<code>A</code>' (in either upper or lower case) +represents 10, '<code>B</code>' represents 11, and so forth, +with '<code>Z</code>' representing 35. +If the string <code>e</code> is not a valid numeral in the given base, +the function returns <b>nil</b>. + + + + +<p> +<hr><h3><a name="pdf-tostring"><code>tostring (v)</code></a></h3> +Receives a value of any type and +converts it to a string in a human-readable format. +Floats always produce strings with some +floating-point indication (either a decimal dot or an exponent). +(For complete control of how numbers are converted, +use <a href="#pdf-string.format"><code>string.format</code></a>.) + + +<p> +If the metatable of <code>v</code> has a <code>"__tostring"</code> field, +then <code>tostring</code> calls the corresponding value +with <code>v</code> as argument, +and uses the result of the call as its result. + + + + +<p> +<hr><h3><a name="pdf-type"><code>type (v)</code></a></h3> +Returns the type of its only argument, coded as a string. +The possible results of this function are +"<code>nil</code>" (a string, not the value <b>nil</b>), +"<code>number</code>", +"<code>string</code>", +"<code>boolean</code>", +"<code>table</code>", +"<code>function</code>", +"<code>thread</code>", +and "<code>userdata</code>". + + + + +<p> +<hr><h3><a name="pdf-_VERSION"><code>_VERSION</code></a></h3> +A global variable (not a function) that +holds a string containing the current interpreter version. +The current value of this variable is "<code>Lua 5.3</code>". + + + + +<p> +<hr><h3><a name="pdf-xpcall"><code>xpcall (f, msgh [, arg1, ···])</code></a></h3> + + +<p> +This function is similar to <a href="#pdf-pcall"><code>pcall</code></a>, +except that it sets a new message handler <code>msgh</code>. + + + + + + + +<h2>6.2 – <a name="6.2">Coroutine Manipulation</a></h2> + +<p> +The operations related to coroutines comprise a sub-library of +the basic library and come inside the table <a name="pdf-coroutine"><code>coroutine</code></a>. +See <a href="#2.6">§2.6</a> for a general description of coroutines. + + +<p> +<hr><h3><a name="pdf-coroutine.create"><code>coroutine.create (f)</code></a></h3> + + +<p> +Creates a new coroutine, with body <code>f</code>. +<code>f</code> must be a Lua function. +Returns this new coroutine, +an object with type <code>"thread"</code>. + + + + +<p> +<hr><h3><a name="pdf-coroutine.isyieldable"><code>coroutine.isyieldable ()</code></a></h3> + + +<p> +Returns true when the running coroutine can yield. + + +<p> +A running coroutine is yieldable if it is not the main thread and +it is not inside a non-yieldable C function. + + + + +<p> +<hr><h3><a name="pdf-coroutine.resume"><code>coroutine.resume (co [, val1, ···])</code></a></h3> + + +<p> +Starts or continues the execution of coroutine <code>co</code>. +The first time you resume a coroutine, +it starts running its body. +The values <code>val1</code>, ... are passed +as the arguments to the body function. +If the coroutine has yielded, +<code>resume</code> restarts it; +the values <code>val1</code>, ... are passed +as the results from the yield. + + +<p> +If the coroutine runs without any errors, +<code>resume</code> returns <b>true</b> plus any values passed to <code>yield</code> +(when the coroutine yields) or any values returned by the body function +(when the coroutine terminates). +If there is any error, +<code>resume</code> returns <b>false</b> plus the error message. + + + + +<p> +<hr><h3><a name="pdf-coroutine.running"><code>coroutine.running ()</code></a></h3> + + +<p> +Returns the running coroutine plus a boolean, +true when the running coroutine is the main one. + + + + +<p> +<hr><h3><a name="pdf-coroutine.status"><code>coroutine.status (co)</code></a></h3> + + +<p> +Returns the status of coroutine <code>co</code>, as a string: +<code>"running"</code>, +if the coroutine is running (that is, it called <code>status</code>); +<code>"suspended"</code>, if the coroutine is suspended in a call to <code>yield</code>, +or if it has not started running yet; +<code>"normal"</code> if the coroutine is active but not running +(that is, it has resumed another coroutine); +and <code>"dead"</code> if the coroutine has finished its body function, +or if it has stopped with an error. + + + + +<p> +<hr><h3><a name="pdf-coroutine.wrap"><code>coroutine.wrap (f)</code></a></h3> + + +<p> +Creates a new coroutine, with body <code>f</code>. +<code>f</code> must be a Lua function. +Returns a function that resumes the coroutine each time it is called. +Any arguments passed to the function behave as the +extra arguments to <code>resume</code>. +Returns the same values returned by <code>resume</code>, +except the first boolean. +In case of error, propagates the error. + + + + +<p> +<hr><h3><a name="pdf-coroutine.yield"><code>coroutine.yield (···)</code></a></h3> + + +<p> +Suspends the execution of the calling coroutine. +Any arguments to <code>yield</code> are passed as extra results to <code>resume</code>. + + + + + + + +<h2>6.3 – <a name="6.3">Modules</a></h2> + +<p> +The package library provides basic +facilities for loading modules in Lua. +It exports one function directly in the global environment: +<a href="#pdf-require"><code>require</code></a>. +Everything else is exported in a table <a name="pdf-package"><code>package</code></a>. + + +<p> +<hr><h3><a name="pdf-require"><code>require (modname)</code></a></h3> + + +<p> +Loads the given module. +The function starts by looking into the <a href="#pdf-package.loaded"><code>package.loaded</code></a> table +to determine whether <code>modname</code> is already loaded. +If it is, then <code>require</code> returns the value stored +at <code>package.loaded[modname]</code>. +Otherwise, it tries to find a <em>loader</em> for the module. + + +<p> +To find a loader, +<code>require</code> is guided by the <a href="#pdf-package.searchers"><code>package.searchers</code></a> sequence. +By changing this sequence, +we can change how <code>require</code> looks for a module. +The following explanation is based on the default configuration +for <a href="#pdf-package.searchers"><code>package.searchers</code></a>. + + +<p> +First <code>require</code> queries <code>package.preload[modname]</code>. +If it has a value, +this value (which must be a function) is the loader. +Otherwise <code>require</code> searches for a Lua loader using the +path stored in <a href="#pdf-package.path"><code>package.path</code></a>. +If that also fails, it searches for a C loader using the +path stored in <a href="#pdf-package.cpath"><code>package.cpath</code></a>. +If that also fails, +it tries an <em>all-in-one</em> loader (see <a href="#pdf-package.searchers"><code>package.searchers</code></a>). + + +<p> +Once a loader is found, +<code>require</code> calls the loader with two arguments: +<code>modname</code> and an extra value dependent on how it got the loader. +(If the loader came from a file, +this extra value is the file name.) +If the loader returns any non-nil value, +<code>require</code> assigns the returned value to <code>package.loaded[modname]</code>. +If the loader does not return a non-nil value and +has not assigned any value to <code>package.loaded[modname]</code>, +then <code>require</code> assigns <b>true</b> to this entry. +In any case, <code>require</code> returns the +final value of <code>package.loaded[modname]</code>. + + +<p> +If there is any error loading or running the module, +or if it cannot find any loader for the module, +then <code>require</code> raises an error. + + + + +<p> +<hr><h3><a name="pdf-package.config"><code>package.config</code></a></h3> + + +<p> +A string describing some compile-time configurations for packages. +This string is a sequence of lines: + +<ul> + +<li>The first line is the directory separator string. +Default is '<code>\</code>' for Windows and '<code>/</code>' for all other systems.</li> + +<li>The second line is the character that separates templates in a path. +Default is '<code>;</code>'.</li> + +<li>The third line is the string that marks the +substitution points in a template. +Default is '<code>?</code>'.</li> + +<li>The fourth line is a string that, in a path in Windows, +is replaced by the executable's directory. +Default is '<code>!</code>'.</li> + +<li>The fifth line is a mark to ignore all text after it +when building the <code>luaopen_</code> function name. +Default is '<code>-</code>'.</li> + +</ul> + + + +<p> +<hr><h3><a name="pdf-package.cpath"><code>package.cpath</code></a></h3> + + +<p> +The path used by <a href="#pdf-require"><code>require</code></a> to search for a C loader. + + +<p> +Lua initializes the C path <a href="#pdf-package.cpath"><code>package.cpath</code></a> in the same way +it initializes the Lua path <a href="#pdf-package.path"><code>package.path</code></a>, +using the environment variable <a name="pdf-LUA_CPATH_5_3"><code>LUA_CPATH_5_3</code></a> +or the environment variable <a name="pdf-LUA_CPATH"><code>LUA_CPATH</code></a> +or a default path defined in <code>luaconf.h</code>. + + + + +<p> +<hr><h3><a name="pdf-package.loaded"><code>package.loaded</code></a></h3> + + +<p> +A table used by <a href="#pdf-require"><code>require</code></a> to control which +modules are already loaded. +When you require a module <code>modname</code> and +<code>package.loaded[modname]</code> is not false, +<a href="#pdf-require"><code>require</code></a> simply returns the value stored there. + + +<p> +This variable is only a reference to the real table; +assignments to this variable do not change the +table used by <a href="#pdf-require"><code>require</code></a>. + + + + +<p> +<hr><h3><a name="pdf-package.loadlib"><code>package.loadlib (libname, funcname)</code></a></h3> + + +<p> +Dynamically links the host program with the C library <code>libname</code>. + + +<p> +If <code>funcname</code> is "<code>*</code>", +then it only links with the library, +making the symbols exported by the library +available to other dynamically linked libraries. +Otherwise, +it looks for a function <code>funcname</code> inside the library +and returns this function as a C function. +So, <code>funcname</code> must follow the <a href="#lua_CFunction"><code>lua_CFunction</code></a> prototype +(see <a href="#lua_CFunction"><code>lua_CFunction</code></a>). + + +<p> +This is a low-level function. +It completely bypasses the package and module system. +Unlike <a href="#pdf-require"><code>require</code></a>, +it does not perform any path searching and +does not automatically adds extensions. +<code>libname</code> must be the complete file name of the C library, +including if necessary a path and an extension. +<code>funcname</code> must be the exact name exported by the C library +(which may depend on the C compiler and linker used). + + +<p> +This function is not supported by Standard C. +As such, it is only available on some platforms +(Windows, Linux, Mac OS X, Solaris, BSD, +plus other Unix systems that support the <code>dlfcn</code> standard). + + + + +<p> +<hr><h3><a name="pdf-package.path"><code>package.path</code></a></h3> + + +<p> +The path used by <a href="#pdf-require"><code>require</code></a> to search for a Lua loader. + + +<p> +At start-up, Lua initializes this variable with +the value of the environment variable <a name="pdf-LUA_PATH_5_3"><code>LUA_PATH_5_3</code></a> or +the environment variable <a name="pdf-LUA_PATH"><code>LUA_PATH</code></a> or +with a default path defined in <code>luaconf.h</code>, +if those environment variables are not defined. +Any "<code>;;</code>" in the value of the environment variable +is replaced by the default path. + + + + +<p> +<hr><h3><a name="pdf-package.preload"><code>package.preload</code></a></h3> + + +<p> +A table to store loaders for specific modules +(see <a href="#pdf-require"><code>require</code></a>). + + +<p> +This variable is only a reference to the real table; +assignments to this variable do not change the +table used by <a href="#pdf-require"><code>require</code></a>. + + + + +<p> +<hr><h3><a name="pdf-package.searchers"><code>package.searchers</code></a></h3> + + +<p> +A table used by <a href="#pdf-require"><code>require</code></a> to control how to load modules. + + +<p> +Each entry in this table is a <em>searcher function</em>. +When looking for a module, +<a href="#pdf-require"><code>require</code></a> calls each of these searchers in ascending order, +with the module name (the argument given to <a href="#pdf-require"><code>require</code></a>) as its +sole parameter. +The function can return another function (the module <em>loader</em>) +plus an extra value that will be passed to that loader, +or a string explaining why it did not find that module +(or <b>nil</b> if it has nothing to say). + + +<p> +Lua initializes this table with four searcher functions. + + +<p> +The first searcher simply looks for a loader in the +<a href="#pdf-package.preload"><code>package.preload</code></a> table. + + +<p> +The second searcher looks for a loader as a Lua library, +using the path stored at <a href="#pdf-package.path"><code>package.path</code></a>. +The search is done as described in function <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>. + + +<p> +The third searcher looks for a loader as a C library, +using the path given by the variable <a href="#pdf-package.cpath"><code>package.cpath</code></a>. +Again, +the search is done as described in function <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>. +For instance, +if the C path is the string + +<pre> + "./?.so;./?.dll;/usr/local/?/init.so" +</pre><p> +the searcher for module <code>foo</code> +will try to open the files <code>./foo.so</code>, <code>./foo.dll</code>, +and <code>/usr/local/foo/init.so</code>, in that order. +Once it finds a C library, +this searcher first uses a dynamic link facility to link the +application with the library. +Then it tries to find a C function inside the library to +be used as the loader. +The name of this C function is the string "<code>luaopen_</code>" +concatenated with a copy of the module name where each dot +is replaced by an underscore. +Moreover, if the module name has a hyphen, +its suffix after (and including) the first hyphen is removed. +For instance, if the module name is <code>a.b.c-v2.1</code>, +the function name will be <code>luaopen_a_b_c</code>. + + +<p> +The fourth searcher tries an <em>all-in-one loader</em>. +It searches the C path for a library for +the root name of the given module. +For instance, when requiring <code>a.b.c</code>, +it will search for a C library for <code>a</code>. +If found, it looks into it for an open function for +the submodule; +in our example, that would be <code>luaopen_a_b_c</code>. +With this facility, a package can pack several C submodules +into one single library, +with each submodule keeping its original open function. + + +<p> +All searchers except the first one (preload) return as the extra value +the file name where the module was found, +as returned by <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>. +The first searcher returns no extra value. + + + + +<p> +<hr><h3><a name="pdf-package.searchpath"><code>package.searchpath (name, path [, sep [, rep]])</code></a></h3> + + +<p> +Searches for the given <code>name</code> in the given <code>path</code>. + + +<p> +A path is a string containing a sequence of +<em>templates</em> separated by semicolons. +For each template, +the function replaces each interrogation mark (if any) +in the template with a copy of <code>name</code> +wherein all occurrences of <code>sep</code> +(a dot, by default) +were replaced by <code>rep</code> +(the system's directory separator, by default), +and then tries to open the resulting file name. + + +<p> +For instance, if the path is the string + +<pre> + "./?.lua;./?.lc;/usr/local/?/init.lua" +</pre><p> +the search for the name <code>foo.a</code> +will try to open the files +<code>./foo/a.lua</code>, <code>./foo/a.lc</code>, and +<code>/usr/local/foo/a/init.lua</code>, in that order. + + +<p> +Returns the resulting name of the first file that it can +open in read mode (after closing the file), +or <b>nil</b> plus an error message if none succeeds. +(This error message lists all file names it tried to open.) + + + + + + + +<h2>6.4 – <a name="6.4">String Manipulation</a></h2> + +<p> +This library provides generic functions for string manipulation, +such as finding and extracting substrings, and pattern matching. +When indexing a string in Lua, the first character is at position 1 +(not at 0, as in C). +Indices are allowed to be negative and are interpreted as indexing backwards, +from the end of the string. +Thus, the last character is at position -1, and so on. + + +<p> +The string library provides all its functions inside the table +<a name="pdf-string"><code>string</code></a>. +It also sets a metatable for strings +where the <code>__index</code> field points to the <code>string</code> table. +Therefore, you can use the string functions in object-oriented style. +For instance, <code>string.byte(s,i)</code> +can be written as <code>s:byte(i)</code>. + + +<p> +The string library assumes one-byte character encodings. + + +<p> +<hr><h3><a name="pdf-string.byte"><code>string.byte (s [, i [, j]])</code></a></h3> +Returns the internal numerical codes of the characters <code>s[i]</code>, +<code>s[i+1]</code>, ..., <code>s[j]</code>. +The default value for <code>i</code> is 1; +the default value for <code>j</code> is <code>i</code>. +These indices are corrected +following the same rules of function <a href="#pdf-string.sub"><code>string.sub</code></a>. + + +<p> +Numerical codes are not necessarily portable across platforms. + + + + +<p> +<hr><h3><a name="pdf-string.char"><code>string.char (···)</code></a></h3> +Receives zero or more integers. +Returns a string with length equal to the number of arguments, +in which each character has the internal numerical code equal +to its corresponding argument. + + +<p> +Numerical codes are not necessarily portable across platforms. + + + + +<p> +<hr><h3><a name="pdf-string.dump"><code>string.dump (function [, strip])</code></a></h3> + + +<p> +Returns a string containing a binary representation +(a <em>binary chunk</em>) +of the given function, +so that a later <a href="#pdf-load"><code>load</code></a> on this string returns +a copy of the function (but with new upvalues). +If <code>strip</code> is a true value, +the binary representation is created without debug information +about the function +(local variable names, lines, etc.). + + +<p> +Functions with upvalues have only their number of upvalues saved. +When (re)loaded, +those upvalues receive fresh instances containing <b>nil</b>. +(You can use the debug library to serialize +and reload the upvalues of a function +in a way adequate to your needs.) + + + + +<p> +<hr><h3><a name="pdf-string.find"><code>string.find (s, pattern [, init [, plain]])</code></a></h3> + + +<p> +Looks for the first match of +<code>pattern</code> (see <a href="#6.4.1">§6.4.1</a>) in the string <code>s</code>. +If it finds a match, then <code>find</code> returns the indices of <code>s</code> +where this occurrence starts and ends; +otherwise, it returns <b>nil</b>. +A third, optional numerical argument <code>init</code> specifies +where to start the search; +its default value is 1 and can be negative. +A value of <b>true</b> as a fourth, optional argument <code>plain</code> +turns off the pattern matching facilities, +so the function does a plain "find substring" operation, +with no characters in <code>pattern</code> being considered magic. +Note that if <code>plain</code> is given, then <code>init</code> must be given as well. + + +<p> +If the pattern has captures, +then in a successful match +the captured values are also returned, +after the two indices. + + + + +<p> +<hr><h3><a name="pdf-string.format"><code>string.format (formatstring, ···)</code></a></h3> + + +<p> +Returns a formatted version of its variable number of arguments +following the description given in its first argument (which must be a string). +The format string follows the same rules as the ISO C function <code>sprintf</code>. +The only differences are that the options/modifiers +<code>*</code>, <code>h</code>, <code>L</code>, <code>l</code>, <code>n</code>, +and <code>p</code> are not supported +and that there is an extra option, <code>q</code>. +The <code>q</code> option formats a string between double quotes, +using escape sequences when necessary to ensure that +it can safely be read back by the Lua interpreter. +For instance, the call + +<pre> + string.format('%q', 'a string with "quotes" and \n new line') +</pre><p> +may produce the string: + +<pre> + "a string with \"quotes\" and \ + new line" +</pre> + +<p> +Options +<code>A</code> and <code>a</code> (when available), +<code>E</code>, <code>e</code>, <code>f</code>, +<code>G</code>, and <code>g</code> all expect a number as argument. +Options <code>c</code>, <code>d</code>, +<code>i</code>, <code>o</code>, <code>u</code>, <code>X</code>, and <code>x</code> +expect an integer. +Option <code>q</code> expects a string; +option <code>s</code> expects a string without embedded zeros. +If the argument to option <code>s</code> is not a string, +it is converted to one following the same rules of <a href="#pdf-tostring"><code>tostring</code></a>. + + + + +<p> +<hr><h3><a name="pdf-string.gmatch"><code>string.gmatch (s, pattern)</code></a></h3> +Returns an iterator function that, +each time it is called, +returns the next captures from <code>pattern</code> (see <a href="#6.4.1">§6.4.1</a>) +over the string <code>s</code>. +If <code>pattern</code> specifies no captures, +then the whole match is produced in each call. + + +<p> +As an example, the following loop +will iterate over all the words from string <code>s</code>, +printing one per line: + +<pre> + s = "hello world from Lua" + for w in string.gmatch(s, "%a+") do + print(w) + end +</pre><p> +The next example collects all pairs <code>key=value</code> from the +given string into a table: + +<pre> + t = {} + s = "from=world, to=Lua" + for k, v in string.gmatch(s, "(%w+)=(%w+)") do + t[k] = v + end +</pre> + +<p> +For this function, a caret '<code>^</code>' at the start of a pattern does not +work as an anchor, as this would prevent the iteration. + + + + +<p> +<hr><h3><a name="pdf-string.gsub"><code>string.gsub (s, pattern, repl [, n])</code></a></h3> +Returns a copy of <code>s</code> +in which all (or the first <code>n</code>, if given) +occurrences of the <code>pattern</code> (see <a href="#6.4.1">§6.4.1</a>) have been +replaced by a replacement string specified by <code>repl</code>, +which can be a string, a table, or a function. +<code>gsub</code> also returns, as its second value, +the total number of matches that occurred. +The name <code>gsub</code> comes from <em>Global SUBstitution</em>. + + +<p> +If <code>repl</code> is a string, then its value is used for replacement. +The character <code>%</code> works as an escape character: +any sequence in <code>repl</code> of the form <code>%<em>d</em></code>, +with <em>d</em> between 1 and 9, +stands for the value of the <em>d</em>-th captured substring. +The sequence <code>%0</code> stands for the whole match. +The sequence <code>%%</code> stands for a single <code>%</code>. + + +<p> +If <code>repl</code> is a table, then the table is queried for every match, +using the first capture as the key. + + +<p> +If <code>repl</code> is a function, then this function is called every time a +match occurs, with all captured substrings passed as arguments, +in order. + + +<p> +In any case, +if the pattern specifies no captures, +then it behaves as if the whole pattern was inside a capture. + + +<p> +If the value returned by the table query or by the function call +is a string or a number, +then it is used as the replacement string; +otherwise, if it is <b>false</b> or <b>nil</b>, +then there is no replacement +(that is, the original match is kept in the string). + + +<p> +Here are some examples: + +<pre> + x = string.gsub("hello world", "(%w+)", "%1 %1") + --> x="hello hello world world" + + x = string.gsub("hello world", "%w+", "%0 %0", 1) + --> x="hello hello world" + + x = string.gsub("hello world from Lua", "(%w+)%s*(%w+)", "%2 %1") + --> x="world hello Lua from" + + x = string.gsub("home = $HOME, user = $USER", "%$(%w+)", os.getenv) + --> x="home = /home/roberto, user = roberto" + + x = string.gsub("4+5 = $return 4+5$", "%$(.-)%$", function (s) + return load(s)() + end) + --> x="4+5 = 9" + + local t = {name="lua", version="5.3"} + x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t) + --> x="lua-5.3.tar.gz" +</pre> + + + +<p> +<hr><h3><a name="pdf-string.len"><code>string.len (s)</code></a></h3> +Receives a string and returns its length. +The empty string <code>""</code> has length 0. +Embedded zeros are counted, +so <code>"a\000bc\000"</code> has length 5. + + + + +<p> +<hr><h3><a name="pdf-string.lower"><code>string.lower (s)</code></a></h3> +Receives a string and returns a copy of this string with all +uppercase letters changed to lowercase. +All other characters are left unchanged. +The definition of what an uppercase letter is depends on the current locale. + + + + +<p> +<hr><h3><a name="pdf-string.match"><code>string.match (s, pattern [, init])</code></a></h3> +Looks for the first <em>match</em> of +<code>pattern</code> (see <a href="#6.4.1">§6.4.1</a>) in the string <code>s</code>. +If it finds one, then <code>match</code> returns +the captures from the pattern; +otherwise it returns <b>nil</b>. +If <code>pattern</code> specifies no captures, +then the whole match is returned. +A third, optional numerical argument <code>init</code> specifies +where to start the search; +its default value is 1 and can be negative. + + + + +<p> +<hr><h3><a name="pdf-string.pack"><code>string.pack (fmt, v1, v2, ···)</code></a></h3> + + +<p> +Returns a binary string containing the values <code>v1</code>, <code>v2</code>, etc. +packed (that is, serialized in binary form) +according to the format string <code>fmt</code> (see <a href="#6.4.2">§6.4.2</a>). + + + + +<p> +<hr><h3><a name="pdf-string.packsize"><code>string.packsize (fmt)</code></a></h3> + + +<p> +Returns the size of a string resulting from <a href="#pdf-string.pack"><code>string.pack</code></a> +with the given format. +The format string cannot have the variable-length options +'<code>s</code>' or '<code>z</code>' (see <a href="#6.4.2">§6.4.2</a>). + + + + +<p> +<hr><h3><a name="pdf-string.rep"><code>string.rep (s, n [, sep])</code></a></h3> +Returns a string that is the concatenation of <code>n</code> copies of +the string <code>s</code> separated by the string <code>sep</code>. +The default value for <code>sep</code> is the empty string +(that is, no separator). +Returns the empty string if <code>n</code> is not positive. + + + + +<p> +<hr><h3><a name="pdf-string.reverse"><code>string.reverse (s)</code></a></h3> +Returns a string that is the string <code>s</code> reversed. + + + + +<p> +<hr><h3><a name="pdf-string.sub"><code>string.sub (s, i [, j])</code></a></h3> +Returns the substring of <code>s</code> that +starts at <code>i</code> and continues until <code>j</code>; +<code>i</code> and <code>j</code> can be negative. +If <code>j</code> is absent, then it is assumed to be equal to -1 +(which is the same as the string length). +In particular, +the call <code>string.sub(s,1,j)</code> returns a prefix of <code>s</code> +with length <code>j</code>, +and <code>string.sub(s, -i)</code> returns a suffix of <code>s</code> +with length <code>i</code>. + + +<p> +If, after the translation of negative indices, +<code>i</code> is less than 1, +it is corrected to 1. +If <code>j</code> is greater than the string length, +it is corrected to that length. +If, after these corrections, +<code>i</code> is greater than <code>j</code>, +the function returns the empty string. + + + + +<p> +<hr><h3><a name="pdf-string.unpack"><code>string.unpack (fmt, s [, pos])</code></a></h3> + + +<p> +Returns the values packed in string <code>s</code> (see <a href="#pdf-string.pack"><code>string.pack</code></a>) +according to the format string <code>fmt</code> (see <a href="#6.4.2">§6.4.2</a>). +An optional <code>pos</code> marks where +to start reading in <code>s</code> (default is 1). +After the read values, +this function also returns the index of the first unread byte in <code>s</code>. + + + + +<p> +<hr><h3><a name="pdf-string.upper"><code>string.upper (s)</code></a></h3> +Receives a string and returns a copy of this string with all +lowercase letters changed to uppercase. +All other characters are left unchanged. +The definition of what a lowercase letter is depends on the current locale. + + + + + +<h3>6.4.1 – <a name="6.4.1">Patterns</a></h3> + +<p> +Patterns in Lua are described by regular strings, +which are interpreted as patterns by the pattern-matching functions +<a href="#pdf-string.find"><code>string.find</code></a>, +<a href="#pdf-string.gmatch"><code>string.gmatch</code></a>, +<a href="#pdf-string.gsub"><code>string.gsub</code></a>, +and <a href="#pdf-string.match"><code>string.match</code></a>. +This section describes the syntax and the meaning +(that is, what they match) of these strings. + + + +<h4>Character Class:</h4><p> +A <em>character class</em> is used to represent a set of characters. +The following combinations are allowed in describing a character class: + +<ul> + +<li><b><em>x</em>: </b> +(where <em>x</em> is not one of the <em>magic characters</em> +<code>^$()%.[]*+-?</code>) +represents the character <em>x</em> itself. +</li> + +<li><b><code>.</code>: </b> (a dot) represents all characters.</li> + +<li><b><code>%a</code>: </b> represents all letters.</li> + +<li><b><code>%c</code>: </b> represents all control characters.</li> + +<li><b><code>%d</code>: </b> represents all digits.</li> + +<li><b><code>%g</code>: </b> represents all printable characters except space.</li> + +<li><b><code>%l</code>: </b> represents all lowercase letters.</li> + +<li><b><code>%p</code>: </b> represents all punctuation characters.</li> + +<li><b><code>%s</code>: </b> represents all space characters.</li> + +<li><b><code>%u</code>: </b> represents all uppercase letters.</li> + +<li><b><code>%w</code>: </b> represents all alphanumeric characters.</li> + +<li><b><code>%x</code>: </b> represents all hexadecimal digits.</li> + +<li><b><code>%<em>x</em></code>: </b> (where <em>x</em> is any non-alphanumeric character) +represents the character <em>x</em>. +This is the standard way to escape the magic characters. +Any non-alphanumeric character +(including all punctuations, even the non-magical) +can be preceded by a '<code>%</code>' +when used to represent itself in a pattern. +</li> + +<li><b><code>[<em>set</em>]</code>: </b> +represents the class which is the union of all +characters in <em>set</em>. +A range of characters can be specified by +separating the end characters of the range, +in ascending order, with a '<code>-</code>'. +All classes <code>%</code><em>x</em> described above can also be used as +components in <em>set</em>. +All other characters in <em>set</em> represent themselves. +For example, <code>[%w_]</code> (or <code>[_%w]</code>) +represents all alphanumeric characters plus the underscore, +<code>[0-7]</code> represents the octal digits, +and <code>[0-7%l%-]</code> represents the octal digits plus +the lowercase letters plus the '<code>-</code>' character. + + +<p> +The interaction between ranges and classes is not defined. +Therefore, patterns like <code>[%a-z]</code> or <code>[a-%%]</code> +have no meaning. +</li> + +<li><b><code>[^<em>set</em>]</code>: </b> +represents the complement of <em>set</em>, +where <em>set</em> is interpreted as above. +</li> + +</ul><p> +For all classes represented by single letters (<code>%a</code>, <code>%c</code>, etc.), +the corresponding uppercase letter represents the complement of the class. +For instance, <code>%S</code> represents all non-space characters. + + +<p> +The definitions of letter, space, and other character groups +depend on the current locale. +In particular, the class <code>[a-z]</code> may not be equivalent to <code>%l</code>. + + + + + +<h4>Pattern Item:</h4><p> +A <em>pattern item</em> can be + +<ul> + +<li> +a single character class, +which matches any single character in the class; +</li> + +<li> +a single character class followed by '<code>*</code>', +which matches zero or more repetitions of characters in the class. +These repetition items will always match the longest possible sequence; +</li> + +<li> +a single character class followed by '<code>+</code>', +which matches one or more repetitions of characters in the class. +These repetition items will always match the longest possible sequence; +</li> + +<li> +a single character class followed by '<code>-</code>', +which also matches zero or more repetitions of characters in the class. +Unlike '<code>*</code>', +these repetition items will always match the shortest possible sequence; +</li> + +<li> +a single character class followed by '<code>?</code>', +which matches zero or one occurrence of a character in the class. +It always matches one occurrence if possible; +</li> + +<li> +<code>%<em>n</em></code>, for <em>n</em> between 1 and 9; +such item matches a substring equal to the <em>n</em>-th captured string +(see below); +</li> + +<li> +<code>%b<em>xy</em></code>, where <em>x</em> and <em>y</em> are two distinct characters; +such item matches strings that start with <em>x</em>, end with <em>y</em>, +and where the <em>x</em> and <em>y</em> are <em>balanced</em>. +This means that, if one reads the string from left to right, +counting <em>+1</em> for an <em>x</em> and <em>-1</em> for a <em>y</em>, +the ending <em>y</em> is the first <em>y</em> where the count reaches 0. +For instance, the item <code>%b()</code> matches expressions with +balanced parentheses. +</li> + +<li> +<code>%f[<em>set</em>]</code>, a <em>frontier pattern</em>; +such item matches an empty string at any position such that +the next character belongs to <em>set</em> +and the previous character does not belong to <em>set</em>. +The set <em>set</em> is interpreted as previously described. +The beginning and the end of the subject are handled as if +they were the character '<code>\0</code>'. +</li> + +</ul> + + + + +<h4>Pattern:</h4><p> +A <em>pattern</em> is a sequence of pattern items. +A caret '<code>^</code>' at the beginning of a pattern anchors the match at the +beginning of the subject string. +A '<code>$</code>' at the end of a pattern anchors the match at the +end of the subject string. +At other positions, +'<code>^</code>' and '<code>$</code>' have no special meaning and represent themselves. + + + + + +<h4>Captures:</h4><p> +A pattern can contain sub-patterns enclosed in parentheses; +they describe <em>captures</em>. +When a match succeeds, the substrings of the subject string +that match captures are stored (<em>captured</em>) for future use. +Captures are numbered according to their left parentheses. +For instance, in the pattern <code>"(a*(.)%w(%s*))"</code>, +the part of the string matching <code>"a*(.)%w(%s*)"</code> is +stored as the first capture (and therefore has number 1); +the character matching "<code>.</code>" is captured with number 2, +and the part matching "<code>%s*</code>" has number 3. + + +<p> +As a special case, the empty capture <code>()</code> captures +the current string position (a number). +For instance, if we apply the pattern <code>"()aa()"</code> on the +string <code>"flaaap"</code>, there will be two captures: 3 and 5. + + + + + + + +<h3>6.4.2 – <a name="6.4.2">Format Strings for Pack and Unpack</a></h3> + +<p> +The first argument to <a href="#pdf-string.pack"><code>string.pack</code></a>, +<a href="#pdf-string.packsize"><code>string.packsize</code></a>, and <a href="#pdf-string.unpack"><code>string.unpack</code></a> +is a format string, +which describes the layout of the structure being created or read. + + +<p> +A format string is a sequence of conversion options. +The conversion options are as follows: + +<ul> +<li><b><code><</code>: </b>sets little endian</li> +<li><b><code>></code>: </b>sets big endian</li> +<li><b><code>=</code>: </b>sets native endian</li> +<li><b><code>![<em>n</em>]</code>: </b>sets maximum alignment to <code>n</code> +(default is native alignment)</li> +<li><b><code>b</code>: </b>a signed byte (<code>char</code>)</li> +<li><b><code>B</code>: </b>an unsigned byte (<code>char</code>)</li> +<li><b><code>h</code>: </b>a signed <code>short</code> (native size)</li> +<li><b><code>H</code>: </b>an unsigned <code>short</code> (native size)</li> +<li><b><code>l</code>: </b>a signed <code>long</code> (native size)</li> +<li><b><code>L</code>: </b>an unsigned <code>long</code> (native size)</li> +<li><b><code>j</code>: </b>a <code>lua_Integer</code></li> +<li><b><code>J</code>: </b>a <code>lua_Unsigned</code></li> +<li><b><code>T</code>: </b>a <code>size_t</code> (native size)</li> +<li><b><code>i[<em>n</em>]</code>: </b>a signed <code>int</code> with <code>n</code> bytes +(default is native size)</li> +<li><b><code>I[<em>n</em>]</code>: </b>an unsigned <code>int</code> with <code>n</code> bytes +(default is native size)</li> +<li><b><code>f</code>: </b>a <code>float</code> (native size)</li> +<li><b><code>d</code>: </b>a <code>double</code> (native size)</li> +<li><b><code>n</code>: </b>a <code>lua_Number</code></li> +<li><b><code>c<em>n</em></code>: </b>a fixed-sized string with <code>n</code> bytes</li> +<li><b><code>z</code>: </b>a zero-terminated string</li> +<li><b><code>s[<em>n</em>]</code>: </b>a string preceded by its length +coded as an unsigned integer with <code>n</code> bytes +(default is a <code>size_t</code>)</li> +<li><b><code>x</code>: </b>one byte of padding</li> +<li><b><code>X<em>op</em></code>: </b>an empty item that aligns +according to option <code>op</code> +(which is otherwise ignored)</li> +<li><b>'<code> </code>': </b>(empty space) ignored</li> +</ul><p> +(A "<code>[<em>n</em>]</code>" means an optional integral numeral.) +Except for padding, spaces, and configurations +(options "<code>xX <=>!</code>"), +each option corresponds to an argument (in <a href="#pdf-string.pack"><code>string.pack</code></a>) +or a result (in <a href="#pdf-string.unpack"><code>string.unpack</code></a>). + + +<p> +For options "<code>!<em>n</em></code>", "<code>s<em>n</em></code>", "<code>i<em>n</em></code>", and "<code>I<em>n</em></code>", +<code>n</code> can be any integer between 1 and 16. +All integral options check overflows; +<a href="#pdf-string.pack"><code>string.pack</code></a> checks whether the given value fits in the given size; +<a href="#pdf-string.unpack"><code>string.unpack</code></a> checks whether the read value fits in a Lua integer. + + +<p> +Any format string starts as if prefixed by "<code>!1=</code>", +that is, +with maximum alignment of 1 (no alignment) +and native endianness. + + +<p> +Alignment works as follows: +For each option, +the format gets extra padding until the data starts +at an offset that is a multiple of the minimum between the +option size and the maximum alignment; +this minimum must be a power of 2. +Options "<code>c</code>" and "<code>z</code>" are not aligned; +option "<code>s</code>" follows the alignment of its starting integer. + + +<p> +All padding is filled with zeros by <a href="#pdf-string.pack"><code>string.pack</code></a> +(and ignored by <a href="#pdf-string.unpack"><code>string.unpack</code></a>). + + + + + + + +<h2>6.5 – <a name="6.5">UTF-8 Support</a></h2> + +<p> +This library provides basic support for UTF-8 encoding. +It provides all its functions inside the table <a name="pdf-utf8"><code>utf8</code></a>. +This library does not provide any support for Unicode other +than the handling of the encoding. +Any operation that needs the meaning of a character, +such as character classification, is outside its scope. + + +<p> +Unless stated otherwise, +all functions that expect a byte position as a parameter +assume that the given position is either the start of a byte sequence +or one plus the length of the subject string. +As in the string library, +negative indices count from the end of the string. + + +<p> +<hr><h3><a name="pdf-utf8.char"><code>utf8.char (···)</code></a></h3> +Receives zero or more integers, +converts each one to its corresponding UTF-8 byte sequence +and returns a string with the concatenation of all these sequences. + + + + +<p> +<hr><h3><a name="pdf-utf8.charpattern"><code>utf8.charpattern</code></a></h3> +The pattern (a string, not a function) "<code>[\0-\x7F\xC2-\xF4][\x80-\xBF]*</code>" +(see <a href="#6.4.1">§6.4.1</a>), +which matches exactly one UTF-8 byte sequence, +assuming that the subject is a valid UTF-8 string. + + + + +<p> +<hr><h3><a name="pdf-utf8.codes"><code>utf8.codes (s)</code></a></h3> + + +<p> +Returns values so that the construction + +<pre> + for p, c in utf8.codes(s) do <em>body</em> end +</pre><p> +will iterate over all characters in string <code>s</code>, +with <code>p</code> being the position (in bytes) and <code>c</code> the code point +of each character. +It raises an error if it meets any invalid byte sequence. + + + + +<p> +<hr><h3><a name="pdf-utf8.codepoint"><code>utf8.codepoint (s [, i [, j]])</code></a></h3> +Returns the codepoints (as integers) from all characters in <code>s</code> +that start between byte position <code>i</code> and <code>j</code> (both included). +The default for <code>i</code> is 1 and for <code>j</code> is <code>i</code>. +It raises an error if it meets any invalid byte sequence. + + + + +<p> +<hr><h3><a name="pdf-utf8.len"><code>utf8.len (s [, i [, j]])</code></a></h3> +Returns the number of UTF-8 characters in string <code>s</code> +that start between positions <code>i</code> and <code>j</code> (both inclusive). +The default for <code>i</code> is 1 and for <code>j</code> is -1. +If it finds any invalid byte sequence, +returns a false value plus the position of the first invalid byte. + + + + +<p> +<hr><h3><a name="pdf-utf8.offset"><code>utf8.offset (s, n [, i])</code></a></h3> +Returns the position (in bytes) where the encoding of the +<code>n</code>-th character of <code>s</code> +(counting from position <code>i</code>) starts. +A negative <code>n</code> gets characters before position <code>i</code>. +The default for <code>i</code> is 1 when <code>n</code> is non-negative +and <code>#s + 1</code> otherwise, +so that <code>utf8.offset(s, -n)</code> gets the offset of the +<code>n</code>-th character from the end of the string. +If the specified character is neither in the subject +nor right after its end, +the function returns <b>nil</b>. + + +<p> +As a special case, +when <code>n</code> is 0 the function returns the start of the encoding +of the character that contains the <code>i</code>-th byte of <code>s</code>. + + +<p> +This function assumes that <code>s</code> is a valid UTF-8 string. + + + + + + + +<h2>6.6 – <a name="6.6">Table Manipulation</a></h2> + +<p> +This library provides generic functions for table manipulation. +It provides all its functions inside the table <a name="pdf-table"><code>table</code></a>. + + +<p> +Remember that, whenever an operation needs the length of a table, +the table must be a proper sequence +or have a <code>__len</code> metamethod (see <a href="#3.4.7">§3.4.7</a>). +All functions ignore non-numeric keys +in the tables given as arguments. + + +<p> +<hr><h3><a name="pdf-table.concat"><code>table.concat (list [, sep [, i [, j]]])</code></a></h3> + + +<p> +Given a list where all elements are strings or numbers, +returns the string <code>list[i]..sep..list[i+1] ··· sep..list[j]</code>. +The default value for <code>sep</code> is the empty string, +the default for <code>i</code> is 1, +and the default for <code>j</code> is <code>#list</code>. +If <code>i</code> is greater than <code>j</code>, returns the empty string. + + + + +<p> +<hr><h3><a name="pdf-table.insert"><code>table.insert (list, [pos,] value)</code></a></h3> + + +<p> +Inserts element <code>value</code> at position <code>pos</code> in <code>list</code>, +shifting up the elements +<code>list[pos], list[pos+1], ···, list[#list]</code>. +The default value for <code>pos</code> is <code>#list+1</code>, +so that a call <code>table.insert(t,x)</code> inserts <code>x</code> at the end +of list <code>t</code>. + + + + +<p> +<hr><h3><a name="pdf-table.move"><code>table.move (a1, f, e, t [,a2])</code></a></h3> + + +<p> +Moves elements from table <code>a1</code> to table <code>a2</code>. +This function performs the equivalent to the following +multiple assignment: +<code>a2[t],··· = a1[f],···,a1[e]</code>. +The default for <code>a2</code> is <code>a1</code>. +The destination range can overlap with the source range. +Index <code>f</code> must be positive. + + + + +<p> +<hr><h3><a name="pdf-table.pack"><code>table.pack (···)</code></a></h3> + + +<p> +Returns a new table with all parameters stored into keys 1, 2, etc. +and with a field "<code>n</code>" with the total number of parameters. +Note that the resulting table may not be a sequence. + + + + +<p> +<hr><h3><a name="pdf-table.remove"><code>table.remove (list [, pos])</code></a></h3> + + +<p> +Removes from <code>list</code> the element at position <code>pos</code>, +returning the value of the removed element. +When <code>pos</code> is an integer between 1 and <code>#list</code>, +it shifts down the elements +<code>list[pos+1], list[pos+2], ···, list[#list]</code> +and erases element <code>list[#list]</code>; +The index <code>pos</code> can also be 0 when <code>#list</code> is 0, +or <code>#list + 1</code>; +in those cases, the function erases the element <code>list[pos]</code>. + + +<p> +The default value for <code>pos</code> is <code>#list</code>, +so that a call <code>table.remove(l)</code> removes the last element +of list <code>l</code>. + + + + +<p> +<hr><h3><a name="pdf-table.sort"><code>table.sort (list [, comp])</code></a></h3> + + +<p> +Sorts list elements in a given order, <em>in-place</em>, +from <code>list[1]</code> to <code>list[#list]</code>. +If <code>comp</code> is given, +then it must be a function that receives two list elements +and returns true when the first element must come +before the second in the final order +(so that <code>not comp(list[i+1],list[i])</code> will be true after the sort). +If <code>comp</code> is not given, +then the standard Lua operator <code><</code> is used instead. + + +<p> +The sort algorithm is not stable; +that is, elements considered equal by the given order +may have their relative positions changed by the sort. + + + + +<p> +<hr><h3><a name="pdf-table.unpack"><code>table.unpack (list [, i [, j]])</code></a></h3> + + +<p> +Returns the elements from the given list. +This function is equivalent to + +<pre> + return list[i], list[i+1], ···, list[j] +</pre><p> +By default, <code>i</code> is 1 and <code>j</code> is <code>#list</code>. + + + + + + + +<h2>6.7 – <a name="6.7">Mathematical Functions</a></h2> + +<p> +This library provides basic mathematical functions. +It provides all its functions and constants inside the table <a name="pdf-math"><code>math</code></a>. +Functions with the annotation "<code>integer/float</code>" give +integer results for integer arguments +and float results for float (or mixed) arguments. +Rounding functions +(<a href="#pdf-math.ceil"><code>math.ceil</code></a>, <a href="#pdf-math.floor"><code>math.floor</code></a>, and <a href="#pdf-math.modf"><code>math.modf</code></a>) +return an integer when the result fits in the range of an integer, +or a float otherwise. + + +<p> +<hr><h3><a name="pdf-math.abs"><code>math.abs (x)</code></a></h3> + + +<p> +Returns the absolute value of <code>x</code>. (integer/float) + + + + +<p> +<hr><h3><a name="pdf-math.acos"><code>math.acos (x)</code></a></h3> + + +<p> +Returns the arc cosine of <code>x</code> (in radians). + + + + +<p> +<hr><h3><a name="pdf-math.asin"><code>math.asin (x)</code></a></h3> + + +<p> +Returns the arc sine of <code>x</code> (in radians). + + + + +<p> +<hr><h3><a name="pdf-math.atan"><code>math.atan (y [, x])</code></a></h3> + + +<p> + +Returns the arc tangent of <code>y/x</code> (in radians), +but uses the signs of both parameters to find the +quadrant of the result. +(It also handles correctly the case of <code>x</code> being zero.) + + +<p> +The default value for <code>x</code> is 1, +so that the call <code>math.atan(y)</code> +returns the arc tangent of <code>y</code>. + + + + +<p> +<hr><h3><a name="pdf-math.ceil"><code>math.ceil (x)</code></a></h3> + + +<p> +Returns the smallest integral value larger than or equal to <code>x</code>. + + + + +<p> +<hr><h3><a name="pdf-math.cos"><code>math.cos (x)</code></a></h3> + + +<p> +Returns the cosine of <code>x</code> (assumed to be in radians). + + + + +<p> +<hr><h3><a name="pdf-math.deg"><code>math.deg (x)</code></a></h3> + + +<p> +Converts the angle <code>x</code> from radians to degrees. + + + + +<p> +<hr><h3><a name="pdf-math.exp"><code>math.exp (x)</code></a></h3> + + +<p> +Returns the value <em>e<sup>x</sup></em> +(where <code>e</code> is the base of natural logarithms). + + + + +<p> +<hr><h3><a name="pdf-math.floor"><code>math.floor (x)</code></a></h3> + + +<p> +Returns the largest integral value smaller than or equal to <code>x</code>. + + + + +<p> +<hr><h3><a name="pdf-math.fmod"><code>math.fmod (x, y)</code></a></h3> + + +<p> +Returns the remainder of the division of <code>x</code> by <code>y</code> +that rounds the quotient towards zero. (integer/float) + + + + +<p> +<hr><h3><a name="pdf-math.huge"><code>math.huge</code></a></h3> + + +<p> +The float value <code>HUGE_VAL</code>, +a value larger than any other numerical value. + + + + +<p> +<hr><h3><a name="pdf-math.log"><code>math.log (x [, base])</code></a></h3> + + +<p> +Returns the logarithm of <code>x</code> in the given base. +The default for <code>base</code> is <em>e</em> +(so that the function returns the natural logarithm of <code>x</code>). + + + + +<p> +<hr><h3><a name="pdf-math.max"><code>math.max (x, ···)</code></a></h3> + + +<p> +Returns the argument with the maximum value, +according to the Lua operator <code><</code>. (integer/float) + + + + +<p> +<hr><h3><a name="pdf-math.maxinteger"><code>math.maxinteger</code></a></h3> +An integer with the maximum value for an integer. + + + + +<p> +<hr><h3><a name="pdf-math.min"><code>math.min (x, ···)</code></a></h3> + + +<p> +Returns the argument with the minimum value, +according to the Lua operator <code><</code>. (integer/float) + + + + +<p> +<hr><h3><a name="pdf-math.mininteger"><code>math.mininteger</code></a></h3> +An integer with the minimum value for an integer. + + + + +<p> +<hr><h3><a name="pdf-math.modf"><code>math.modf (x)</code></a></h3> + + +<p> +Returns the integral part of <code>x</code> and the fractional part of <code>x</code>. +Its second result is always a float. + + + + +<p> +<hr><h3><a name="pdf-math.pi"><code>math.pi</code></a></h3> + + +<p> +The value of <em>π</em>. + + + + +<p> +<hr><h3><a name="pdf-math.rad"><code>math.rad (x)</code></a></h3> + + +<p> +Converts the angle <code>x</code> from degrees to radians. + + + + +<p> +<hr><h3><a name="pdf-math.random"><code>math.random ([m [, n]])</code></a></h3> + + +<p> +When called without arguments, +returns a pseudo-random float with uniform distribution +in the range <em>[0,1)</em>. +When called with two integers <code>m</code> and <code>n</code>, +<code>math.random</code> returns a pseudo-random integer +with uniform distribution in the range <em>[m, n]</em>. +(The value <em>m-n</em> cannot be negative and must fit in a Lua integer.) +The call <code>math.random(n)</code> is equivalent to <code>math.random(1,n)</code>. + + +<p> +This function is an interface to the underling +pseudo-random generator function provided by C. +No guarantees can be given for its statistical properties. + + + + +<p> +<hr><h3><a name="pdf-math.randomseed"><code>math.randomseed (x)</code></a></h3> + + +<p> +Sets <code>x</code> as the "seed" +for the pseudo-random generator: +equal seeds produce equal sequences of numbers. + + + + +<p> +<hr><h3><a name="pdf-math.sin"><code>math.sin (x)</code></a></h3> + + +<p> +Returns the sine of <code>x</code> (assumed to be in radians). + + + + +<p> +<hr><h3><a name="pdf-math.sqrt"><code>math.sqrt (x)</code></a></h3> + + +<p> +Returns the square root of <code>x</code>. +(You can also use the expression <code>x^0.5</code> to compute this value.) + + + + +<p> +<hr><h3><a name="pdf-math.tan"><code>math.tan (x)</code></a></h3> + + +<p> +Returns the tangent of <code>x</code> (assumed to be in radians). + + + + +<p> +<hr><h3><a name="pdf-math.tointeger"><code>math.tointeger (x)</code></a></h3> + + +<p> +If the value <code>x</code> is convertible to an integer, +returns that integer. +Otherwise, returns <b>nil</b>. + + + + +<p> +<hr><h3><a name="pdf-math.type"><code>math.type (x)</code></a></h3> + + +<p> +Returns "<code>integer</code>" if <code>x</code> is an integer, +"<code>float</code>" if it is a float, +or <b>nil</b> if <code>x</code> is not a number. + + + + +<p> +<hr><h3><a name="pdf-math.ult"><code>math.ult (m, n)</code></a></h3> + + +<p> +Returns a boolean, +true if integer <code>m</code> is below integer <code>n</code> when +they are compared as unsigned integers. + + + + + + + +<h2>6.8 – <a name="6.8">Input and Output Facilities</a></h2> + +<p> +The I/O library provides two different styles for file manipulation. +The first one uses implicit file handles; +that is, there are operations to set a default input file and a +default output file, +and all input/output operations are over these default files. +The second style uses explicit file handles. + + +<p> +When using implicit file handles, +all operations are supplied by table <a name="pdf-io"><code>io</code></a>. +When using explicit file handles, +the operation <a href="#pdf-io.open"><code>io.open</code></a> returns a file handle +and then all operations are supplied as methods of the file handle. + + +<p> +The table <code>io</code> also provides +three predefined file handles with their usual meanings from C: +<a name="pdf-io.stdin"><code>io.stdin</code></a>, <a name="pdf-io.stdout"><code>io.stdout</code></a>, and <a name="pdf-io.stderr"><code>io.stderr</code></a>. +The I/O library never closes these files. + + +<p> +Unless otherwise stated, +all I/O functions return <b>nil</b> on failure +(plus an error message as a second result and +a system-dependent error code as a third result) +and some value different from <b>nil</b> on success. +On non-POSIX systems, +the computation of the error message and error code +in case of errors +may be not thread safe, +because they rely on the global C variable <code>errno</code>. + + +<p> +<hr><h3><a name="pdf-io.close"><code>io.close ([file])</code></a></h3> + + +<p> +Equivalent to <code>file:close()</code>. +Without a <code>file</code>, closes the default output file. + + + + +<p> +<hr><h3><a name="pdf-io.flush"><code>io.flush ()</code></a></h3> + + +<p> +Equivalent to <code>io.output():flush()</code>. + + + + +<p> +<hr><h3><a name="pdf-io.input"><code>io.input ([file])</code></a></h3> + + +<p> +When called with a file name, it opens the named file (in text mode), +and sets its handle as the default input file. +When called with a file handle, +it simply sets this file handle as the default input file. +When called without parameters, +it returns the current default input file. + + +<p> +In case of errors this function raises the error, +instead of returning an error code. + + + + +<p> +<hr><h3><a name="pdf-io.lines"><code>io.lines ([filename ···])</code></a></h3> + + +<p> +Opens the given file name in read mode +and returns an iterator function that +works like <code>file:lines(···)</code> over the opened file. +When the iterator function detects the end of file, +it returns no values (to finish the loop) and automatically closes the file. + + +<p> +The call <code>io.lines()</code> (with no file name) is equivalent +to <code>io.input():lines("*l")</code>; +that is, it iterates over the lines of the default input file. +In this case it does not close the file when the loop ends. + + +<p> +In case of errors this function raises the error, +instead of returning an error code. + + + + +<p> +<hr><h3><a name="pdf-io.open"><code>io.open (filename [, mode])</code></a></h3> + + +<p> +This function opens a file, +in the mode specified in the string <code>mode</code>. +It returns a new file handle, +or, in case of errors, <b>nil</b> plus an error message. + + +<p> +The <code>mode</code> string can be any of the following: + +<ul> +<li><b>"<code>r</code>": </b> read mode (the default);</li> +<li><b>"<code>w</code>": </b> write mode;</li> +<li><b>"<code>a</code>": </b> append mode;</li> +<li><b>"<code>r+</code>": </b> update mode, all previous data is preserved;</li> +<li><b>"<code>w+</code>": </b> update mode, all previous data is erased;</li> +<li><b>"<code>a+</code>": </b> append update mode, previous data is preserved, + writing is only allowed at the end of file.</li> +</ul><p> +The <code>mode</code> string can also have a '<code>b</code>' at the end, +which is needed in some systems to open the file in binary mode. + + + + +<p> +<hr><h3><a name="pdf-io.output"><code>io.output ([file])</code></a></h3> + + +<p> +Similar to <a href="#pdf-io.input"><code>io.input</code></a>, but operates over the default output file. + + + + +<p> +<hr><h3><a name="pdf-io.popen"><code>io.popen (prog [, mode])</code></a></h3> + + +<p> +This function is system dependent and is not available +on all platforms. + + +<p> +Starts program <code>prog</code> in a separated process and returns +a file handle that you can use to read data from this program +(if <code>mode</code> is <code>"r"</code>, the default) +or to write data to this program +(if <code>mode</code> is <code>"w"</code>). + + + + +<p> +<hr><h3><a name="pdf-io.read"><code>io.read (···)</code></a></h3> + + +<p> +Equivalent to <code>io.input():read(···)</code>. + + + + +<p> +<hr><h3><a name="pdf-io.tmpfile"><code>io.tmpfile ()</code></a></h3> + + +<p> +Returns a handle for a temporary file. +This file is opened in update mode +and it is automatically removed when the program ends. + + + + +<p> +<hr><h3><a name="pdf-io.type"><code>io.type (obj)</code></a></h3> + + +<p> +Checks whether <code>obj</code> is a valid file handle. +Returns the string <code>"file"</code> if <code>obj</code> is an open file handle, +<code>"closed file"</code> if <code>obj</code> is a closed file handle, +or <b>nil</b> if <code>obj</code> is not a file handle. + + + + +<p> +<hr><h3><a name="pdf-io.write"><code>io.write (···)</code></a></h3> + + +<p> +Equivalent to <code>io.output():write(···)</code>. + + + + +<p> +<hr><h3><a name="pdf-file:close"><code>file:close ()</code></a></h3> + + +<p> +Closes <code>file</code>. +Note that files are automatically closed when +their handles are garbage collected, +but that takes an unpredictable amount of time to happen. + + +<p> +When closing a file handle created with <a href="#pdf-io.popen"><code>io.popen</code></a>, +<a href="#pdf-file:close"><code>file:close</code></a> returns the same values +returned by <a href="#pdf-os.execute"><code>os.execute</code></a>. + + + + +<p> +<hr><h3><a name="pdf-file:flush"><code>file:flush ()</code></a></h3> + + +<p> +Saves any written data to <code>file</code>. + + + + +<p> +<hr><h3><a name="pdf-file:lines"><code>file:lines (···)</code></a></h3> + + +<p> +Returns an iterator function that, +each time it is called, +reads the file according to the given formats. +When no format is given, +uses "<code>l</code>" as a default. +As an example, the construction + +<pre> + for c in file:lines(1) do <em>body</em> end +</pre><p> +will iterate over all characters of the file, +starting at the current position. +Unlike <a href="#pdf-io.lines"><code>io.lines</code></a>, this function does not close the file +when the loop ends. + + +<p> +In case of errors this function raises the error, +instead of returning an error code. + + + + +<p> +<hr><h3><a name="pdf-file:read"><code>file:read (···)</code></a></h3> + + +<p> +Reads the file <code>file</code>, +according to the given formats, which specify what to read. +For each format, +the function returns a string or a number with the characters read, +or <b>nil</b> if it cannot read data with the specified format. +(In this latter case, +the function does not read subsequent formats.) +When called without formats, +it uses a default format that reads the next line +(see below). + + +<p> +The available formats are + +<ul> + +<li><b>"<code>n</code>": </b> +reads a numeral and returns it as a float or an integer, +following the lexical conventions of Lua. +(The numeral may have leading spaces and a sign.) +This format always reads the longest input sequence that +is a valid prefix for a number; +if that prefix does not form a valid number +(e.g., an empty string, "<code>0x</code>", or "<code>3.4e-</code>"), +it is discarded and the function returns <b>nil</b>. +</li> + +<li><b>"<code>i</code>": </b> +reads an integral number and returns it as an integer. +</li> + +<li><b>"<code>a</code>": </b> +reads the whole file, starting at the current position. +On end of file, it returns the empty string. +</li> + +<li><b>"<code>l</code>": </b> +reads the next line skipping the end of line, +returning <b>nil</b> on end of file. +This is the default format. +</li> + +<li><b>"<code>L</code>": </b> +reads the next line keeping the end-of-line character (if present), +returning <b>nil</b> on end of file. +</li> + +<li><b><em>number</em>: </b> +reads a string with up to this number of bytes, +returning <b>nil</b> on end of file. +If <code>number</code> is zero, +it reads nothing and returns an empty string, +or <b>nil</b> on end of file. +</li> + +</ul><p> +The formats "<code>l</code>" and "<code>L</code>" should be used only for text files. + + + + +<p> +<hr><h3><a name="pdf-file:seek"><code>file:seek ([whence [, offset]])</code></a></h3> + + +<p> +Sets and gets the file position, +measured from the beginning of the file, +to the position given by <code>offset</code> plus a base +specified by the string <code>whence</code>, as follows: + +<ul> +<li><b>"<code>set</code>": </b> base is position 0 (beginning of the file);</li> +<li><b>"<code>cur</code>": </b> base is current position;</li> +<li><b>"<code>end</code>": </b> base is end of file;</li> +</ul><p> +In case of success, <code>seek</code> returns the final file position, +measured in bytes from the beginning of the file. +If <code>seek</code> fails, it returns <b>nil</b>, +plus a string describing the error. + + +<p> +The default value for <code>whence</code> is <code>"cur"</code>, +and for <code>offset</code> is 0. +Therefore, the call <code>file:seek()</code> returns the current +file position, without changing it; +the call <code>file:seek("set")</code> sets the position to the +beginning of the file (and returns 0); +and the call <code>file:seek("end")</code> sets the position to the +end of the file, and returns its size. + + + + +<p> +<hr><h3><a name="pdf-file:setvbuf"><code>file:setvbuf (mode [, size])</code></a></h3> + + +<p> +Sets the buffering mode for an output file. +There are three available modes: + +<ul> + +<li><b>"<code>no</code>": </b> +no buffering; the result of any output operation appears immediately. +</li> + +<li><b>"<code>full</code>": </b> +full buffering; output operation is performed only +when the buffer is full or when +you explicitly <code>flush</code> the file (see <a href="#pdf-io.flush"><code>io.flush</code></a>). +</li> + +<li><b>"<code>line</code>": </b> +line buffering; output is buffered until a newline is output +or there is any input from some special files +(such as a terminal device). +</li> + +</ul><p> +For the last two cases, <code>size</code> +specifies the size of the buffer, in bytes. +The default is an appropriate size. + + + + +<p> +<hr><h3><a name="pdf-file:write"><code>file:write (···)</code></a></h3> + + +<p> +Writes the value of each of its arguments to <code>file</code>. +The arguments must be strings or numbers. + + +<p> +In case of success, this function returns <code>file</code>. +Otherwise it returns <b>nil</b> plus a string describing the error. + + + + + + + +<h2>6.9 – <a name="6.9">Operating System Facilities</a></h2> + +<p> +This library is implemented through table <a name="pdf-os"><code>os</code></a>. + + +<p> +<hr><h3><a name="pdf-os.clock"><code>os.clock ()</code></a></h3> + + +<p> +Returns an approximation of the amount in seconds of CPU time +used by the program. + + + + +<p> +<hr><h3><a name="pdf-os.date"><code>os.date ([format [, time]])</code></a></h3> + + +<p> +Returns a string or a table containing date and time, +formatted according to the given string <code>format</code>. + + +<p> +If the <code>time</code> argument is present, +this is the time to be formatted +(see the <a href="#pdf-os.time"><code>os.time</code></a> function for a description of this value). +Otherwise, <code>date</code> formats the current time. + + +<p> +If <code>format</code> starts with '<code>!</code>', +then the date is formatted in Coordinated Universal Time. +After this optional character, +if <code>format</code> is the string "<code>*t</code>", +then <code>date</code> returns a table with the following fields: +<code>year</code> (four digits), <code>month</code> (1–12), <code>day</code> (1–31), +<code>hour</code> (0–23), <code>min</code> (0–59), <code>sec</code> (0–61), +<code>wday</code> (weekday, Sunday is 1), +<code>yday</code> (day of the year), +and <code>isdst</code> (daylight saving flag, a boolean). +This last field may be absent +if the information is not available. + + +<p> +If <code>format</code> is not "<code>*t</code>", +then <code>date</code> returns the date as a string, +formatted according to the same rules as the ISO C function <code>strftime</code>. + + +<p> +When called without arguments, +<code>date</code> returns a reasonable date and time representation that depends on +the host system and on the current locale +(that is, <code>os.date()</code> is equivalent to <code>os.date("%c")</code>). + + +<p> +On non-POSIX systems, +this function may be not thread safe +because of its reliance on C function <code>gmtime</code> and C function <code>localtime</code>. + + + + +<p> +<hr><h3><a name="pdf-os.difftime"><code>os.difftime (t2, t1)</code></a></h3> + + +<p> +Returns the difference, in seconds, +from time <code>t1</code> to time <code>t2</code> +(where the times are values returned by <a href="#pdf-os.time"><code>os.time</code></a>). +In POSIX, Windows, and some other systems, +this value is exactly <code>t2</code><em>-</em><code>t1</code>. + + + + +<p> +<hr><h3><a name="pdf-os.execute"><code>os.execute ([command])</code></a></h3> + + +<p> +This function is equivalent to the ISO C function <code>system</code>. +It passes <code>command</code> to be executed by an operating system shell. +Its first result is <b>true</b> +if the command terminated successfully, +or <b>nil</b> otherwise. +After this first result +the function returns a string plus a number, +as follows: + +<ul> + +<li><b>"<code>exit</code>": </b> +the command terminated normally; +the following number is the exit status of the command. +</li> + +<li><b>"<code>signal</code>": </b> +the command was terminated by a signal; +the following number is the signal that terminated the command. +</li> + +</ul> + +<p> +When called without a <code>command</code>, +<code>os.execute</code> returns a boolean that is true if a shell is available. + + + + +<p> +<hr><h3><a name="pdf-os.exit"><code>os.exit ([code [, close]])</code></a></h3> + + +<p> +Calls the ISO C function <code>exit</code> to terminate the host program. +If <code>code</code> is <b>true</b>, +the returned status is <code>EXIT_SUCCESS</code>; +if <code>code</code> is <b>false</b>, +the returned status is <code>EXIT_FAILURE</code>; +if <code>code</code> is a number, +the returned status is this number. +The default value for <code>code</code> is <b>true</b>. + + +<p> +If the optional second argument <code>close</code> is true, +closes the Lua state before exiting. + + + + +<p> +<hr><h3><a name="pdf-os.getenv"><code>os.getenv (varname)</code></a></h3> + + +<p> +Returns the value of the process environment variable <code>varname</code>, +or <b>nil</b> if the variable is not defined. + + + + +<p> +<hr><h3><a name="pdf-os.remove"><code>os.remove (filename)</code></a></h3> + + +<p> +Deletes the file (or empty directory, on POSIX systems) +with the given name. +If this function fails, it returns <b>nil</b>, +plus a string describing the error and the error code. + + + + +<p> +<hr><h3><a name="pdf-os.rename"><code>os.rename (oldname, newname)</code></a></h3> + + +<p> +Renames file or directory named <code>oldname</code> to <code>newname</code>. +If this function fails, it returns <b>nil</b>, +plus a string describing the error and the error code. + + + + +<p> +<hr><h3><a name="pdf-os.setlocale"><code>os.setlocale (locale [, category])</code></a></h3> + + +<p> +Sets the current locale of the program. +<code>locale</code> is a system-dependent string specifying a locale; +<code>category</code> is an optional string describing which category to change: +<code>"all"</code>, <code>"collate"</code>, <code>"ctype"</code>, +<code>"monetary"</code>, <code>"numeric"</code>, or <code>"time"</code>; +the default category is <code>"all"</code>. +The function returns the name of the new locale, +or <b>nil</b> if the request cannot be honored. + + +<p> +If <code>locale</code> is the empty string, +the current locale is set to an implementation-defined native locale. +If <code>locale</code> is the string "<code>C</code>", +the current locale is set to the standard C locale. + + +<p> +When called with <b>nil</b> as the first argument, +this function only returns the name of the current locale +for the given category. + + +<p> +This function may be not thread safe +because of its reliance on C function <code>setlocale</code>. + + + + +<p> +<hr><h3><a name="pdf-os.time"><code>os.time ([table])</code></a></h3> + + +<p> +Returns the current time when called without arguments, +or a time representing the date and time specified by the given table. +This table must have fields <code>year</code>, <code>month</code>, and <code>day</code>, +and may have fields +<code>hour</code> (default is 12), +<code>min</code> (default is 0), +<code>sec</code> (default is 0), +and <code>isdst</code> (default is <b>nil</b>). +For a description of these fields, see the <a href="#pdf-os.date"><code>os.date</code></a> function. + + +<p> +The returned value is a number, whose meaning depends on your system. +In POSIX, Windows, and some other systems, +this number counts the number +of seconds since some given start time (the "epoch"). +In other systems, the meaning is not specified, +and the number returned by <code>time</code> can be used only as an argument to +<a href="#pdf-os.date"><code>os.date</code></a> and <a href="#pdf-os.difftime"><code>os.difftime</code></a>. + + + + +<p> +<hr><h3><a name="pdf-os.tmpname"><code>os.tmpname ()</code></a></h3> + + +<p> +Returns a string with a file name that can +be used for a temporary file. +The file must be explicitly opened before its use +and explicitly removed when no longer needed. + + +<p> +On POSIX systems, +this function also creates a file with that name, +to avoid security risks. +(Someone else might create the file with wrong permissions +in the time between getting the name and creating the file.) +You still have to open the file to use it +and to remove it (even if you do not use it). + + +<p> +When possible, +you may prefer to use <a href="#pdf-io.tmpfile"><code>io.tmpfile</code></a>, +which automatically removes the file when the program ends. + + + + + + + +<h2>6.10 – <a name="6.10">The Debug Library</a></h2> + +<p> +This library provides +the functionality of the debug interface (<a href="#4.9">§4.9</a>) to Lua programs. +You should exert care when using this library. +Several of its functions +violate basic assumptions about Lua code +(e.g., that variables local to a function +cannot be accessed from outside; +that userdata metatables cannot be changed by Lua code; +that Lua programs do not crash) +and therefore can compromise otherwise secure code. +Moreover, some functions in this library may be slow. + + +<p> +All functions in this library are provided +inside the <a name="pdf-debug"><code>debug</code></a> table. +All functions that operate over a thread +have an optional first argument which is the +thread to operate over. +The default is always the current thread. + + +<p> +<hr><h3><a name="pdf-debug.debug"><code>debug.debug ()</code></a></h3> + + +<p> +Enters an interactive mode with the user, +running each string that the user enters. +Using simple commands and other debug facilities, +the user can inspect global and local variables, +change their values, evaluate expressions, and so on. +A line containing only the word <code>cont</code> finishes this function, +so that the caller continues its execution. + + +<p> +Note that commands for <code>debug.debug</code> are not lexically nested +within any function and so have no direct access to local variables. + + + + +<p> +<hr><h3><a name="pdf-debug.gethook"><code>debug.gethook ([thread])</code></a></h3> + + +<p> +Returns the current hook settings of the thread, as three values: +the current hook function, the current hook mask, +and the current hook count +(as set by the <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> function). + + + + +<p> +<hr><h3><a name="pdf-debug.getinfo"><code>debug.getinfo ([thread,] f [, what])</code></a></h3> + + +<p> +Returns a table with information about a function. +You can give the function directly +or you can give a number as the value of <code>f</code>, +which means the function running at level <code>f</code> of the call stack +of the given thread: +level 0 is the current function (<code>getinfo</code> itself); +level 1 is the function that called <code>getinfo</code> +(except for tail calls, which do not count on the stack); +and so on. +If <code>f</code> is a number larger than the number of active functions, +then <code>getinfo</code> returns <b>nil</b>. + + +<p> +The returned table can contain all the fields returned by <a href="#lua_getinfo"><code>lua_getinfo</code></a>, +with the string <code>what</code> describing which fields to fill in. +The default for <code>what</code> is to get all information available, +except the table of valid lines. +If present, +the option '<code>f</code>' +adds a field named <code>func</code> with the function itself. +If present, +the option '<code>L</code>' +adds a field named <code>activelines</code> with the table of +valid lines. + + +<p> +For instance, the expression <code>debug.getinfo(1,"n").name</code> returns +a table with a name for the current function, +if a reasonable name can be found, +and the expression <code>debug.getinfo(print)</code> +returns a table with all available information +about the <a href="#pdf-print"><code>print</code></a> function. + + + + +<p> +<hr><h3><a name="pdf-debug.getlocal"><code>debug.getlocal ([thread,] f, local)</code></a></h3> + + +<p> +This function returns the name and the value of the local variable +with index <code>local</code> of the function at level <code>f</code> of the stack. +This function accesses not only explicit local variables, +but also parameters, temporaries, etc. + + +<p> +The first parameter or local variable has index 1, and so on, +following the order that they are declared in the code, +counting only the variables that are active +in the current scope of the function. +Negative indices refer to vararg parameters; +-1 is the first vararg parameter. +The function returns <b>nil</b> if there is no variable with the given index, +and raises an error when called with a level out of range. +(You can call <a href="#pdf-debug.getinfo"><code>debug.getinfo</code></a> to check whether the level is valid.) + + +<p> +Variable names starting with '<code>(</code>' (open parenthesis) +represent variables with no known names +(internal variables such as loop control variables, +and variables from chunks saved without debug information). + + +<p> +The parameter <code>f</code> may also be a function. +In that case, <code>getlocal</code> returns only the name of function parameters. + + + + +<p> +<hr><h3><a name="pdf-debug.getmetatable"><code>debug.getmetatable (value)</code></a></h3> + + +<p> +Returns the metatable of the given <code>value</code> +or <b>nil</b> if it does not have a metatable. + + + + +<p> +<hr><h3><a name="pdf-debug.getregistry"><code>debug.getregistry ()</code></a></h3> + + +<p> +Returns the registry table (see <a href="#4.5">§4.5</a>). + + + + +<p> +<hr><h3><a name="pdf-debug.getupvalue"><code>debug.getupvalue (f, up)</code></a></h3> + + +<p> +This function returns the name and the value of the upvalue +with index <code>up</code> of the function <code>f</code>. +The function returns <b>nil</b> if there is no upvalue with the given index. + + +<p> +Variable names starting with '<code>(</code>' (open parenthesis) +represent variables with no known names +(variables from chunks saved without debug information). + + + + +<p> +<hr><h3><a name="pdf-debug.getuservalue"><code>debug.getuservalue (u)</code></a></h3> + + +<p> +Returns the Lua value associated to <code>u</code>. +If <code>u</code> is not a userdata, +returns <b>nil</b>. + + + + +<p> +<hr><h3><a name="pdf-debug.sethook"><code>debug.sethook ([thread,] hook, mask [, count])</code></a></h3> + + +<p> +Sets the given function as a hook. +The string <code>mask</code> and the number <code>count</code> describe +when the hook will be called. +The string mask may have any combination of the following characters, +with the given meaning: + +<ul> +<li><b>'<code>c</code>': </b> the hook is called every time Lua calls a function;</li> +<li><b>'<code>r</code>': </b> the hook is called every time Lua returns from a function;</li> +<li><b>'<code>l</code>': </b> the hook is called every time Lua enters a new line of code.</li> +</ul><p> +Moreover, +with a <code>count</code> different from zero, +the hook is called also after every <code>count</code> instructions. + + +<p> +When called without arguments, +<a href="#pdf-debug.sethook"><code>debug.sethook</code></a> turns off the hook. + + +<p> +When the hook is called, its first parameter is a string +describing the event that has triggered its call: +<code>"call"</code> (or <code>"tail call"</code>), +<code>"return"</code>, +<code>"line"</code>, and <code>"count"</code>. +For line events, +the hook also gets the new line number as its second parameter. +Inside a hook, +you can call <code>getinfo</code> with level 2 to get more information about +the running function +(level 0 is the <code>getinfo</code> function, +and level 1 is the hook function). + + + + +<p> +<hr><h3><a name="pdf-debug.setlocal"><code>debug.setlocal ([thread,] level, local, value)</code></a></h3> + + +<p> +This function assigns the value <code>value</code> to the local variable +with index <code>local</code> of the function at level <code>level</code> of the stack. +The function returns <b>nil</b> if there is no local +variable with the given index, +and raises an error when called with a <code>level</code> out of range. +(You can call <code>getinfo</code> to check whether the level is valid.) +Otherwise, it returns the name of the local variable. + + +<p> +See <a href="#pdf-debug.getlocal"><code>debug.getlocal</code></a> for more information about +variable indices and names. + + + + +<p> +<hr><h3><a name="pdf-debug.setmetatable"><code>debug.setmetatable (value, table)</code></a></h3> + + +<p> +Sets the metatable for the given <code>value</code> to the given <code>table</code> +(which can be <b>nil</b>). +Returns <code>value</code>. + + + + +<p> +<hr><h3><a name="pdf-debug.setupvalue"><code>debug.setupvalue (f, up, value)</code></a></h3> + + +<p> +This function assigns the value <code>value</code> to the upvalue +with index <code>up</code> of the function <code>f</code>. +The function returns <b>nil</b> if there is no upvalue +with the given index. +Otherwise, it returns the name of the upvalue. + + + + +<p> +<hr><h3><a name="pdf-debug.setuservalue"><code>debug.setuservalue (udata, value)</code></a></h3> + + +<p> +Sets the given <code>value</code> as +the Lua value associated to the given <code>udata</code>. +<code>udata</code> must be a full userdata. + + +<p> +Returns <code>udata</code>. + + + + +<p> +<hr><h3><a name="pdf-debug.traceback"><code>debug.traceback ([thread,] [message [, level]])</code></a></h3> + + +<p> +If <code>message</code> is present but is neither a string nor <b>nil</b>, +this function returns <code>message</code> without further processing. +Otherwise, +it returns a string with a traceback of the call stack. +The optional <code>message</code> string is appended +at the beginning of the traceback. +An optional <code>level</code> number tells at which level +to start the traceback +(default is 1, the function calling <code>traceback</code>). + + + + +<p> +<hr><h3><a name="pdf-debug.upvalueid"><code>debug.upvalueid (f, n)</code></a></h3> + + +<p> +Returns a unique identifier (as a light userdata) +for the upvalue numbered <code>n</code> +from the given function. + + +<p> +These unique identifiers allow a program to check whether different +closures share upvalues. +Lua closures that share an upvalue +(that is, that access a same external local variable) +will return identical ids for those upvalue indices. + + + + +<p> +<hr><h3><a name="pdf-debug.upvaluejoin"><code>debug.upvaluejoin (f1, n1, f2, n2)</code></a></h3> + + +<p> +Make the <code>n1</code>-th upvalue of the Lua closure <code>f1</code> +refer to the <code>n2</code>-th upvalue of the Lua closure <code>f2</code>. + + + + + + + +<h1>7 – <a name="7">Lua Standalone</a></h1> + +<p> +Although Lua has been designed as an extension language, +to be embedded in a host C program, +it is also frequently used as a standalone language. +An interpreter for Lua as a standalone language, +called simply <code>lua</code>, +is provided with the standard distribution. +The standalone interpreter includes +all standard libraries, including the debug library. +Its usage is: + +<pre> + lua [options] [script [args]] +</pre><p> +The options are: + +<ul> +<li><b><code>-e <em>stat</em></code>: </b> executes string <em>stat</em>;</li> +<li><b><code>-l <em>mod</em></code>: </b> "requires" <em>mod</em>;</li> +<li><b><code>-i</code>: </b> enters interactive mode after running <em>script</em>;</li> +<li><b><code>-v</code>: </b> prints version information;</li> +<li><b><code>-E</code>: </b> ignores environment variables;</li> +<li><b><code>--</code>: </b> stops handling options;</li> +<li><b><code>-</code>: </b> executes <code>stdin</code> as a file and stops handling options.</li> +</ul><p> +After handling its options, <code>lua</code> runs the given <em>script</em>. +When called without arguments, +<code>lua</code> behaves as <code>lua -v -i</code> +when the standard input (<code>stdin</code>) is a terminal, +and as <code>lua -</code> otherwise. + + +<p> +When called without option <code>-E</code>, +the interpreter checks for an environment variable <a name="pdf-LUA_INIT_5_3"><code>LUA_INIT_5_3</code></a> +(or <a name="pdf-LUA_INIT"><code>LUA_INIT</code></a> if the versioned name is not defined) +before running any argument. +If the variable content has the format <code>@<em>filename</em></code>, +then <code>lua</code> executes the file. +Otherwise, <code>lua</code> executes the string itself. + + +<p> +When called with option <code>-E</code>, +besides ignoring <code>LUA_INIT</code>, +Lua also ignores +the values of <code>LUA_PATH</code> and <code>LUA_CPATH</code>, +setting the values of +<a href="#pdf-package.path"><code>package.path</code></a> and <a href="#pdf-package.cpath"><code>package.cpath</code></a> +with the default paths defined in <code>luaconf.h</code>. + + +<p> +All options are handled in order, except <code>-i</code> and <code>-E</code>. +For instance, an invocation like + +<pre> + $ lua -e'a=1' -e 'print(a)' script.lua +</pre><p> +will first set <code>a</code> to 1, then print the value of <code>a</code>, +and finally run the file <code>script.lua</code> with no arguments. +(Here <code>$</code> is the shell prompt. Your prompt may be different.) + + +<p> +Before running any code, +<code>lua</code> collects all command-line arguments +in a global table called <code>arg</code>. +The script name goes to index 0, +the first argument after the script name goes to index 1, +and so on. +Any arguments before the script name +(that is, the interpreter name plus its options) +go to negative indices. +For instance, in the call + +<pre> + $ lua -la b.lua t1 t2 +</pre><p> +the table is like this: + +<pre> + arg = { [-2] = "lua", [-1] = "-la", + [0] = "b.lua", + [1] = "t1", [2] = "t2" } +</pre><p> +If there is no script in the call, +the interpreter name goes to index 0, +followed by the other arguments. +For instance, the call + +<pre> + $ lua -e "print(arg[1])" +</pre><p> +will print "<code>-e</code>". +If there is a script, +the script is called with parameters +<code>arg[1]</code>, ···, <code>arg[#arg]</code>. +(Like all chunks in Lua, +the script is compiled as a vararg function.) + + +<p> +In interactive mode, +Lua repeatedly prompts and waits for a line. +After reading a line, +Lua first try to interpret the line as an expression. +If it succeeds, it prints its value. +Otherwise, it interprets the line as a statement. +If you write an incomplete statement, +the interpreter waits for its completion +by issuing a different prompt. + + +<p> +In case of unprotected errors in the script, +the interpreter reports the error to the standard error stream. +If the error object is not a string but +has a metamethod <code>__tostring</code>, +the interpreter calls this metamethod to produce the final message. +Otherwise, the interpreter converts the error object to a string +and adds a stack traceback to it. + + +<p> +When finishing normally, +the interpreter closes its main Lua state +(see <a href="#lua_close"><code>lua_close</code></a>). +The script can avoid this step by +calling <a href="#pdf-os.exit"><code>os.exit</code></a> to terminate. + + +<p> +To allow the use of Lua as a +script interpreter in Unix systems, +the standalone interpreter skips +the first line of a chunk if it starts with <code>#</code>. +Therefore, Lua scripts can be made into executable programs +by using <code>chmod +x</code> and the <code>#!</code> form, +as in + +<pre> + #!/usr/local/bin/lua +</pre><p> +(Of course, +the location of the Lua interpreter may be different in your machine. +If <code>lua</code> is in your <code>PATH</code>, +then + +<pre> + #!/usr/bin/env lua +</pre><p> +is a more portable solution.) + + + +<h1>8 – <a name="8">Incompatibilities with the Previous Version</a></h1> + +<p> +Here we list the incompatibilities that you may find when moving a program +from Lua 5.2 to Lua 5.3. +You can avoid some incompatibilities by compiling Lua with +appropriate options (see file <code>luaconf.h</code>). +However, +all these compatibility options will be removed in the future. + + +<p> +Lua versions can always change the C API in ways that +do not imply source-code changes in a program, +such as the numeric values for constants +or the implementation of functions as macros. +Therefore, +you should not assume that binaries are compatible between +different Lua versions. +Always recompile clients of the Lua API when +using a new version. + + +<p> +Similarly, Lua versions can always change the internal representation +of precompiled chunks; +precompiled chunks are not compatible between different Lua versions. + + +<p> +The standard paths in the official distribution may +change between versions. + + + +<h2>8.1 – <a name="8.1">Changes in the Language</a></h2> +<ul> + +<li> +The main difference between Lua 5.2 and Lua 5.3 is the +introduction of an integer subtype for numbers. +Although this change should not affect "normal" computations, +some computations +(mainly those that involve some kind of overflow) +can give different results. + + +<p> +You can fix these differences by forcing a number to be a float +(in Lua 5.2 all numbers were float), +in particular writing constants with an ending <code>.0</code> +or using <code>x = x + 0.0</code> to convert a variable. +(This recommendation is only for a quick fix +for an occasional incompatibility; +it is not a general guideline for good programming. +For good programming, +use floats where you need floats +and integers where you need integers.) +</li> + +<li> +The conversion of a float to a string now adds a <code>.0</code> suffix +to the result if it looks like an integer. +(For instance, the float 2.0 will be printed as <code>2.0</code>, +not as <code>2</code>.) +You should always use an explicit format +when you need a specific format for numbers. + + +<p> +(Formally this is not an incompatibility, +because Lua does not specify how numbers are formatted as strings, +but some programs assumed a specific format.) +</li> + +<li> +The generational mode for the garbage collector was removed. +(It was an experimental feature in Lua 5.2.) +</li> + +</ul> + + + + +<h2>8.2 – <a name="8.2">Changes in the Libraries</a></h2> +<ul> + +<li> +The <code>bit32</code> library has been deprecated. +It is easy to require a compatible external library or, +better yet, to replace its functions with appropriate bitwise operations. +(Keep in mind that <code>bit32</code> operates on 32-bit integers, +while the bitwise operators in standard Lua operate on 64-bit integers.) +</li> + +<li> +The Table library now respects metamethods +for setting and getting elements. +</li> + +<li> +The <a href="#pdf-ipairs"><code>ipairs</code></a> iterator now respects metamethods and +its <code>__ipairs</code> metamethod has been deprecated. +</li> + +<li> +Option names in <a href="#pdf-io.read"><code>io.read</code></a> do not have a starting '<code>*</code>' anymore. +For compatibility, Lua will continue to ignore this character. +</li> + +<li> +The following functions were deprecated in the mathematical library: +<code>atan2</code>, <code>cosh</code>, <code>sinh</code>, <code>tanh</code>, <code>pow</code>, +<code>frexp</code>, and <code>ldexp</code>. +You can replace <code>math.pow(x,y)</code> with <code>x^y</code>; +you can replace <code>math.atan2</code> with <code>math.atan</code>, +which now accepts one or two parameters; +you can replace <code>math.ldexp(x,exp)</code> with <code>x * 2.0^exp</code>. +For the other operations, +you can either use an external library or +implement them in Lua. +</li> + +<li> +The searcher for C loaders used by <a href="#pdf-require"><code>require</code></a> +changed the way it handles versioned names. +Now, the version should come after the module name +(as is usual in most other tools). +For compatibility, that searcher still tries the old format +if it cannot find an open function according to the new style. +(Lua 5.2 already worked that way, +but it did not document the change.) +</li> + +</ul> + + + + +<h2>8.3 – <a name="8.3">Changes in the API</a></h2> + + +<ul> + +<li> +Continuation functions now receive as parameters what they needed +to get through <code>lua_getctx</code>, +so <code>lua_getctx</code> has been removed. +Adapt your code accordingly. +</li> + +<li> +Function <a href="#lua_dump"><code>lua_dump</code></a> has an extra parameter, <code>strip</code>. +Use 0 as the value of this parameter to get the old behavior. +</li> + +<li> +Functions to inject/project unsigned integers +(<code>lua_pushunsigned</code>, <code>lua_tounsigned</code>, <code>lua_tounsignedx</code>, +<code>luaL_checkunsigned</code>, <code>luaL_optunsigned</code>) +were deprecated. +Use their signed equivalents with a type cast. +</li> + +<li> +Macros to project non-default integer types +(<code>luaL_checkint</code>, <code>luaL_optint</code>, <code>luaL_checklong</code>, <code>luaL_optlong</code>) +were deprecated. +Use their equivalent over <a href="#lua_Integer"><code>lua_Integer</code></a> with a type cast +(or, when possible, use <a href="#lua_Integer"><code>lua_Integer</code></a> in your code). +</li> + +</ul> + + + + +<h1>9 – <a name="9">The Complete Syntax of Lua</a></h1> + +<p> +Here is the complete syntax of Lua in extended BNF. +As usual in extended BNF, +{A} means 0 or more As, +and [A] means an optional A. +(For operator precedences, see <a href="#3.4.8">§3.4.8</a>; +for a description of the terminals +Name, Numeral, +and LiteralString, see <a href="#3.1">§3.1</a>.) + + + + +<pre> + + chunk ::= block + + block ::= {stat} [retstat] + + stat ::= ‘<b>;</b>’ | + varlist ‘<b>=</b>’ explist | + functioncall | + label | + <b>break</b> | + <b>goto</b> Name | + <b>do</b> block <b>end</b> | + <b>while</b> exp <b>do</b> block <b>end</b> | + <b>repeat</b> block <b>until</b> exp | + <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b> | + <b>for</b> Name ‘<b>=</b>’ exp ‘<b>,</b>’ exp [‘<b>,</b>’ exp] <b>do</b> block <b>end</b> | + <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b> | + <b>function</b> funcname funcbody | + <b>local</b> <b>function</b> Name funcbody | + <b>local</b> namelist [‘<b>=</b>’ explist] + + retstat ::= <b>return</b> [explist] [‘<b>;</b>’] + + label ::= ‘<b>::</b>’ Name ‘<b>::</b>’ + + funcname ::= Name {‘<b>.</b>’ Name} [‘<b>:</b>’ Name] + + varlist ::= var {‘<b>,</b>’ var} + + var ::= Name | prefixexp ‘<b>[</b>’ exp ‘<b>]</b>’ | prefixexp ‘<b>.</b>’ Name + + namelist ::= Name {‘<b>,</b>’ Name} + + explist ::= exp {‘<b>,</b>’ exp} + + exp ::= <b>nil</b> | <b>false</b> | <b>true</b> | Numeral | LiteralString | ‘<b>...</b>’ | functiondef | + prefixexp | tableconstructor | exp binop exp | unop exp + + prefixexp ::= var | functioncall | ‘<b>(</b>’ exp ‘<b>)</b>’ + + functioncall ::= prefixexp args | prefixexp ‘<b>:</b>’ Name args + + args ::= ‘<b>(</b>’ [explist] ‘<b>)</b>’ | tableconstructor | LiteralString + + functiondef ::= <b>function</b> funcbody + + funcbody ::= ‘<b>(</b>’ [parlist] ‘<b>)</b>’ block <b>end</b> + + parlist ::= namelist [‘<b>,</b>’ ‘<b>...</b>’] | ‘<b>...</b>’ + + tableconstructor ::= ‘<b>{</b>’ [fieldlist] ‘<b>}</b>’ + + fieldlist ::= field {fieldsep field} [fieldsep] + + field ::= ‘<b>[</b>’ exp ‘<b>]</b>’ ‘<b>=</b>’ exp | Name ‘<b>=</b>’ exp | exp + + fieldsep ::= ‘<b>,</b>’ | ‘<b>;</b>’ + + binop ::= ‘<b>+</b>’ | ‘<b>-</b>’ | ‘<b>*</b>’ | ‘<b>/</b>’ | ‘<b>//</b>’ | ‘<b>^</b>’ | ‘<b>%</b>’ | + ‘<b>&</b>’ | ‘<b>~</b>’ | ‘<b>|</b>’ | ‘<b>>></b>’ | ‘<b><<</b>’ | ‘<b>..</b>’ | + ‘<b><</b>’ | ‘<b><=</b>’ | ‘<b>></b>’ | ‘<b>>=</b>’ | ‘<b>==</b>’ | ‘<b>~=</b>’ | + <b>and</b> | <b>or</b> + + unop ::= ‘<b>-</b>’ | <b>not</b> | ‘<b>#</b>’ | ‘<b>~</b>’ + +</pre> + +<p> + + + + + + + + +<HR> +<SMALL CLASS="footer"> +Last update: +Fri Jan 16 00:58:20 BRST 2015 +</SMALL> +<!-- +Last change: minor edit +--> + +</body></html> +