Lua 5.1 Reference ManualLua 5.1 Reference Manualby Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes
Copyright © 2006–2012 Lua.org, PUC-Rio.Freely available under the terms of theLua license.
Lua is an extension programming language designed to supportgeneral procedural programming with data descriptionfacilities.It also offers good support for object-oriented programming,functional programming, and data-driven programming.Lua is intended to be used as a powerful, light-weightscripting language for any program that needs one.Lua is implemented as a library, written inclean C(that is, in the common subset of ANSI C and C++).
Being an extension language, Lua has no notion of a "main" program:it only worksembedded in a host client,called theembedding program or simply thehost.This 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 witha wide range of different domains,thus creating customized programming languages sharing a syntactical framework.The Lua distribution includes a sample host program calledlua,which uses the Lua library to offer a complete, stand-alone Lua interpreter.
Lua is free software,and is provided as usual with no guarantees,as stated in its license.The implementation described in this manual is availableat Lua's official web site,www.lua.org.
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,Programming in Lua (Second Edition).
This section describes the lexis, the syntax, and the semantics of Lua.In other words,this section describeswhich tokens are valid,how they can be combined,and what their combinations mean.
The language constructs will be explained using the usual extended BNF notation,in which{a} means 0 or morea's, and[a] means an optionala.Non-terminals are shown like non-terminal,keywords are shown likekword,and other terminal symbols are shown like `=´.The complete syntax of Lua can be found in§8at the end of this manual.
Names(also calledidentifiers)in Lua can be any string of letters,digits, and underscores,not beginning with a digit.This coincides with the definition of names in most languages.(The definition of letter depends on the current locale:any character considered alphabetic by the current localecan be used in an identifier.)Identifiers are used to name variables and table fields.
The followingkeywords are reservedand cannot be used as names:
and break do else elseif end false for function if in local nil not or repeat return then true until while
Lua is a case-sensitive language:and is a reserved word, butAnd andANDare two different, valid names.As a convention, names starting with an underscore followed byuppercase letters (such as_VERSION)are reserved for internal global variables used by Lua.
The following strings denote other tokens:
+ - * / % ^ # == ~= <= >= < > = ( ) { } [ ] ; : , . .. ...Literal stringscan be delimited by matching single or double quotes,and can contain the following C-like escape sequences:'\a' (bell),'\b' (backspace),'\f' (form feed),'\n' (newline),'\r' (carriage return),'\t' (horizontal tab),'\v' (vertical tab),'\\' (backslash),'\"' (quotation mark [double quote]),and '\'' (apostrophe [single quote]).Moreover, a backslash followed by a real newlineresults in a newline in the string.A character in a string can also be specified by its numerical valueusing the escape sequence\ddd,whereddd is a sequence of up to three decimal digits.(Note that if a numerical escape is to be followed by a digit,it must be expressed using exactly three digits.)Strings in Lua can contain any 8-bit value, including embedded zeros,which can be specified as '\0'.
Literal strings can also be defined using a long formatenclosed bylong brackets.We define anopening long bracket of leveln as an openingsquare bracket followed byn equal signs followed by anotheropening square bracket.So, an opening long bracket of level 0 is written as[[,an opening long bracket of level 1 is written as[=[,and so on.Aclosing long bracket is defined similarly;for instance, a closing long bracket of level 4 is written as]====].A long string starts with an opening long bracket of any level andends at the first closing long 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.They can contain anything except a closing bracket of the proper level.
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 'a' is coded as 97,newline is coded as 10, and '1' is coded as 49),the five literal strings below denote the same string:
a = 'alo\n123"' a = "alo\n123\"" a = '\97lo\10\04923"' a = [[alo 123"]] a = [==[ alo 123"]==]
Anumerical constant can be written with an optional decimal partand an optional decimal exponent.Lua also accepts integer hexadecimal constants,by prefixing them with0x.Examples of valid numerical constants are
3 3.0 3.1416 314.16e-2 0.31416E1 0xff 0x56
Acomment starts with a double hyphen (--)anywhere outside a string.If the text immediately after-- is not an opening long bracket,the comment is ashort comment,which runs until the end of the line.Otherwise, it is along comment,which runs until the corresponding closing long bracket.Long comments are frequently used to disable code temporarily.
Lua is adynamically typed language.This means thatvariables do not have types; only values do.There are no type definitions in the language.All values carry their own type.
All values in Lua arefirst-class values.This means that all values can be stored in variables,passed as arguments to other functions, and returned as results.
There are eight basic types in Lua:nil,boolean,number,string,function,userdata,thread, andtable.Nil is the type of the valuenil,whose main property is to be different from any other value;it usually represents the absence of a useful value.Boolean is the type of the valuesfalse andtrue.Bothnil andfalse make a condition false;any other value makes it true.Number represents real (double-precision floating-point) numbers.(It is easy to build Lua interpreters that use otherinternal representations for numbers,such as single-precision float or long integers;see fileluaconf.h.)String represents arrays of characters.Lua is 8-bit clean:strings can contain any 8-bit character,including embedded zeros ('\0') (see§2.1).
Lua can call (and manipulate) functions written in Lua andfunctions written in C(see§2.5.8).
The typeuserdata is provided to allow arbitrary C data tobe stored in Lua variables.This type corresponds to a block of raw memoryand has no pre-defined operations in Lua,except assignment and identity test.However, by usingmetatables,the programmer can define operations for userdata values(see§2.8).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.
The typethread represents independent threads of executionand it is used to implement coroutines (see§2.11).Do not confuse Lua threads with operating-system threads.Lua supports coroutines on all systems,even those that do not support threads.
The typetable implements associative arrays,that is, arrays that can be indexed not only with numbers,but with any value (exceptnil).Tables can beheterogeneous;that is, they can contain values of all types (exceptnil).Tables are the sole data structuring mechanism in Lua;they can be used to represent ordinary arrays,symbol tables, sets, records, graphs, trees, etc.To represent records, Lua uses the field name as an index.The language supports this representation byprovidinga.name as syntactic sugar fora["name"].There are several convenient ways to create tables in Lua(see§2.5.7).
Like indices,the value of a table field can be of any type (exceptnil).In particular,because functions are first-class values,table fields can contain functions.Thus tables can also carrymethods (see§2.5.9).
Tables, functions, threads, and (full) userdata values areobjects:variables do not actuallycontain these values,onlyreferences to them.Assignment, parameter passing, and function returnsalways manipulate references to such values;these operations do not imply any kind of copy.
The library functiontype returns a string describing the typeof a given value.
Lua provides automatic conversion betweenstring and number values at run time.Any arithmetic operation applied to a string tries to convertthis string to a number, following the usual conversion rules.Conversely, whenever a number is used where a string is expected,the number is converted to a string, in a reasonable format.For complete control over how numbers are converted to strings,use theformat function from the string library(seestring.format).
Variables are places that store values.There are three kinds of variables in Lua:global variables, local variables, and table fields.
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):
var ::= Name
Name denotes identifiers, as defined in§2.1.
Any variable is assumed to be global unless explicitly declaredas a local (see§2.4.7).Local variables arelexically scoped:local variables can be freely accessed by functionsdefined inside their scope (see§2.6).
Before the first assignment to a variable, its value isnil.
Square brackets are used to index a table:
var ::= prefixexp `[´ exp `]´
The meaning of accesses to global variables and table fields can be changed via metatables.An access to an indexed variablet[i] is equivalent toa callgettable_event(t,i).(See§2.8 for a complete description of thegettable_event function.This function is not defined or callable in Lua.We use it here only for explanatory purposes.)
The syntaxvar.Name is just syntactic sugar forvar["Name"]:
var ::= prefixexp `.´ Name
All global variables live as fields in ordinary Lua tables,calledenvironment tables or simplyenvironments (see§2.9).Each function has its own reference to an environment,so that all global variables in this functionwill refer to this environment table.When a function is created,it inherits the environment from the function that created it.To get the environment table of a Lua function,you callgetfenv.To replace it,you callsetfenv.(You can only manipulate the environment of C functionsthrough the debug library; (see§5.9).)
An access to a global variablexis equivalent to_env.x,which in turn is equivalent to
gettable_event(_env, "x")
where_env is the environment of the running function.(See§2.8 for a complete description of thegettable_event function.This function is not defined or callable in Lua.Similarly, the_env variable is not defined in Lua.We use them here only for explanatory purposes.)
Lua supports an almost conventional set of statements,similar to those in Pascal or C.This set includesassignments, control structures, function calls,and variable declarations.
The unit of execution of Lua is called achunk.A chunk is simply a sequence of statements,which are executed sequentially.Each statement can be optionally followed by a semicolon:
chunk ::= {stat [`;´]}There are no empty statements and thus ';;' is not legal.
Lua handles a chunk as the body of an anonymous function with a variable number of arguments(see§2.5.9).As such, chunks can define local variables,receive arguments, and return values.
A chunk can be stored in a file or in a string inside the host program.To execute a chunk,Lua first pre-compiles the chunk into instructions for a virtual machine,and then it executes the compiled codewith an interpreter for the virtual machine.
Chunks can also be pre-compiled into binary form;see programluac for details.Programs in source and compiled forms are interchangeable;Lua automatically detects the file type and acts accordingly.
A block is a list of statements;syntactically, a block is the same as a chunk:
block ::= chunk
A block can be explicitly delimited to produce a single statement:
stat ::=do blockend
Explicit blocks are usefulto control the scope of variable declarations.Explicit blocks are also sometimes used toadd areturn orbreak statement in the middleof another block (see§2.4.4).
Lua allows multiple assignments.Therefore, the syntax for assignmentdefines a list of variables on the left sideand a list of expressions on the right side.The elements in both lists are separated by commas:
stat ::= varlist `=´ explistvarlist ::= var {`,´ var}explist ::= exp {`,´ exp}Expressions are discussed in§2.5.
Before the assignment,the list of values isadjusted to the length ofthe 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 manynil'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§2.5).
The assignment statement first evaluates all its expressionsand only then are the assignments performed.Thus the code
i = 3 i, a[i] = i+1, 20
setsa[3] to 20, without affectinga[4]because thei ina[i] is evaluated (to 3)before it is assigned 4.Similarly, the line
x, y = y, x
exchanges the values ofx andy,and
x, y, z = y, z, x
cyclically permutes the values ofx,y, andz.
The meaning of assignments to global variablesand table fields can be changed via metatables.An assignment to an indexed variablet[i] = val is equivalent tosettable_event(t,i,val).(See§2.8 for a complete description of thesettable_event function.This function is not defined or callable in Lua.We use it here only for explanatory purposes.)
An assignment to a global variablex = valis equivalent to the assignment_env.x = val,which in turn is equivalent to
settable_event(_env, "x", val)
where_env is the environment of the running function.(The_env variable is not defined in Lua.We use it here only for explanatory purposes.)
The control structuresif,while, andrepeat have the usual meaning andfamiliar syntax:
stat ::=while expdo blockendstat ::=repeat blockuntil expstat ::=if expthen block {elseif expthen block} [else block]endLua also has afor statement, in two flavors (see§2.4.5).
The condition expression of acontrol structure can return any value.Bothfalse andnil are considered false.All values different fromnil andfalse are considered true(in particular, the number 0 and the empty string are also true).
In therepeat–until loop,the inner block does not end at theuntil keyword,but only after the condition.So, the condition can refer to local variablesdeclared inside the loop block.
Thereturn statement is used to return valuesfrom a function or a chunk (which is just a function).Functions and chunks can return more than one value,and so the syntax for thereturn statement is
stat ::=return [explist]
Thebreak statement is used to terminate the execution of awhile,repeat, orfor loop,skipping to the next statement after the loop:
stat ::=break
Abreak ends the innermost enclosing loop.
Thereturn andbreakstatements can only be written as thelast statement of a block.If it is really necessary toreturn orbreak in themiddle of a block,then an explicit inner block can be used,as in the idiomsdo return end anddo break end,because nowreturn andbreak are the last statements intheir (inner) blocks.
Thefor statement has two forms:one numeric and one generic.
The numericfor loop repeats a block of code while acontrol variable runs through an arithmetic progression.It has the following syntax:
stat ::=for Name `=´ exp `,´ exp [`,´ exp]do blockend
Theblock is repeated forname starting at the value ofthe firstexp, until it passes the secondexp by steps of thethirdexp.More precisely, afor statement like
for v =e1,e2,e3 doblock end
is equivalent to the code:
do localvar,limit,step = tonumber(e1), tonumber(e2), tonumber(e3) if not (var andlimit andstep) then error() end while (step > 0 andvar <=limit) or (step <= 0 andvar >=limit) do local v =varblockvar =var +step end end
Note the following:
var,limit, andstep are invisible variables.The names shown here are for explanatory purposes only.v is local to the loop;you cannot use its value after thefor ends or is broken.If you need this value,assign it to another variable before breaking or exiting the loop.The genericfor statement works over functions,callediterators.On each iteration, the iterator function is called to produce a new value,stopping when this new value isnil.The genericfor loop has the following syntax:
stat ::=for namelistin explistdo blockendnamelist ::= Name {`,´ Name}Afor statement like
forvar_1, ···,var_n inexplist doblock end
is equivalent to the code:
do localf,s,var =explist while true do localvar_1, ···,var_n =f(s,var)var =var_1 ifvar == nil then break endblock end end
Note the following:
explist is evaluated only once.Its results are aniterator function,astate,and an initial value for the firstiterator variable.f,s, andvar are invisible variables.The names are here for explanatory purposes only.var_i are local to the loop;you cannot use their values after thefor ends.If you need these values,then assign them to other variables before breaking or exiting the loop.To allow possible side-effects,function calls can be executed as statements:
stat ::= functioncall
In this case, all returned values are thrown away.Function calls are explained in§2.5.8.
Local variables can be declared anywhere inside a block.The declaration can include an initial assignment:
stat ::=local namelist [`=´ explist]
If present, an initial assignment has the same semanticsof a multiple assignment (see§2.4.3).Otherwise, all variables are initialized withnil.
A chunk is also a block (see§2.4.1),and so local variables can be declared in a chunk outside any explicit block.The scope of such local variables extends until the end of the chunk.
The visibility rules for local variables are explained in§2.6.
The basic expressions in Lua are the following:
exp ::= prefixexpexp ::=nil |false |trueexp ::= Numberexp ::= Stringexp ::= functionexp ::= tableconstructorexp ::= `...´exp ::= exp binop expexp ::= unop expprefixexp ::= var | functioncall | `(´ exp `)´
Numbers and literal strings are explained in§2.1;variables are explained in§2.3;function definitions are explained in§2.5.9;function calls are explained in§2.5.8;table constructors are explained in§2.5.7.Vararg expressions,denoted by three dots ('...'), can only be used whendirectly inside a vararg function;they are explained in§2.5.9.
Binary operators comprise arithmetic operators (see§2.5.1),relational operators (see§2.5.2), logical operators (see§2.5.3),and the concatenation operator (see§2.5.4).Unary operators comprise the unary minus (see§2.5.1),the unarynot (see§2.5.3),and the unarylength operator (see§2.5.5).
Both function calls and vararg expressions can result in multiple values.If an expression is used as a statement(only possible for function calls (see§2.4.6)),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) elementof a list of expressions,then no adjustment is made(unless the call is enclosed in parentheses).In all other contexts,Lua adjusts the result list to one element,discarding all values except the first one.
Here are some examples:
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 resultAny expression enclosed in parentheses always results in only one value.Thus,(f(x,y,z)) is always a single value,even iff returns several values.(The value of(f(x,y,z)) is the first value returned byfornil iff does not return any values.)
Lua supports the usual arithmetic operators:the binary+ (addition),- (subtraction),* (multiplication),/ (division),% (modulo), and^ (exponentiation);and unary- (negation).If the operands are numbers, or strings that can be converted tonumbers (see§2.2.1),then all operations have the usual meaning.Exponentiation works for any exponent.For instance,x^(-0.5) computes the inverse of the square root ofx.Modulo is defined as
a % b == a - math.floor(a/b)*b
That is, it is the remainder of a division that roundsthe quotient towards minus infinity.
The relational operators in Lua are
== ~= < > <= >=
These operators always result infalse ortrue.
Equality (==) first compares the type of its operands.If the types are different, then the result isfalse.Otherwise, the values of the operands are compared.Numbers and strings are compared in the usual way.Objects (tables, userdata, threads, and functions)are compared byreference:two objects are considered equal only if they are thesame object.Every time you create a new object(a table, userdata, thread, or function),this new object is different from any previously existing object.
You can change the way that Lua compares tables and userdata by using the "eq" metamethod (see§2.8).
The conversion rules of§2.2.1do not apply to equality comparisons.Thus,"0"==0 evaluates tofalse,andt[0] andt["0"] denote differententries in a table.
The operator~= is exactly the negation of equality (==).
The order operators work as follows.If both arguments are numbers, then they are compared as such.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§2.8).A comparisona > b is translated tob < aanda >= b is translated tob <= a.
The logical operators in Lua areand,or, andnot.Like the control structures (see§2.4.4),all logical operators consider bothfalse andnil as falseand anything else as true.
The negation operatornot always returnsfalse ortrue.The conjunction operatorand returns its first argumentif this value isfalse ornil;otherwise,and returns its second argument.The disjunction operatoror returns its first argumentif this value is different fromnil andfalse;otherwise,or returns its second argument.Bothand andor use short-cut evaluation;that is,the second operand is evaluated only if necessary.Here are some examples:
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
(In this manual,--> indicates the result of the preceding expression.)
The string concatenation operator in Lua isdenoted by two dots ('..').If both operands are strings or numbers, then they are converted tostrings according to the rules mentioned in§2.2.1.Otherwise, the "concat" metamethod is called (see§2.8).
The length operator is denoted by the unary operator#.The length of a string is its number of bytes(that is, the usual meaning of string length when eachcharacter is one byte).
The length of a tablet is defined to be anyinteger indexnsuch thatt[n] is notnil andt[n+1] isnil;moreover, ift[1] isnil,n can be zero.For a regular array, with non-nil values from 1 to a givenn,its length is exactly thatn,the index of its last value.If the array has "holes"(that is,nil values between other non-nil values),then#t can be any of the indices thatdirectly precedes anil value(that is, it may consider any suchnil value as the end ofthe array).
Operator precedence in Lua follows the table below,from lower to higher priority:
or and < > <= >= ~= == .. + - * / % not # - (unary) ^
As usual,you can use parentheses to change the precedences of an expression.The concatenation ('..') and exponentiation ('^')operators are right associative.All other binary operators are left associative.
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 tableor to create a table and initialize some of its fields.The general syntax for constructors is
tableconstructor ::= `{´ [fieldlist] `}´fieldlist ::= field {fieldsep field} [fieldsep]field ::= `[´ exp `]´ `=´ exp | Name `=´ exp | expfieldsep ::= `,´ | `;´Each field of the form[exp1] = exp2 adds to the new table an entrywith keyexp1 and valueexp2.A field of the formname = exp is equivalent to["name"] = exp.Finally, fields of the formexp are equivalent to[i] = exp, wherei are consecutive numerical integers,starting with 1.Fields in the other formats do not affect this counting.For example,
a = { [f(1)] = g; "x", "y"; x = 1, f(x), [30] = 23; 45 }is equivalent to
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 endIf the last field in the list has the formexpand the expression is a function call or a vararg expression,then all values returned by this expression enter the list consecutively(see§2.5.8).To avoid this,enclose the function call or the vararg expressionin parentheses (see§2.5).
The field list can have an optional trailing separator,as a convenience for machine-generated code.
A function call in Lua has the following syntax:
functioncall ::= prefixexp args
In a function call,first prefixexp and args are evaluated.If the value of prefixexp has typefunction,then this function is calledwith 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§2.8).
The form
functioncall ::= prefixexp `:´ Name args
can be used to call "methods".A callv:name(args)is syntactic sugar forv.name(v,args),except thatv is evaluated only once.
Arguments have the following syntax:
args ::= `(´ [explist] `)´args ::= tableconstructorargs ::= String
All argument expressions are evaluated before the call.A call of the formf{fields} issyntactic sugar forf({fields});that is, the argument list is a single new table.A call of the formf'string'(orf"string" orf[[string]])is syntactic sugar forf('string');that is, the argument list is a single literal string.
As an exception to the free-format syntax of Lua,you cannot put a line break before the '(' in a function call.This restriction avoids some ambiguities in the language.If you write
a = f (g).x(a)
Lua would see that as a single statement,a = f(g).x(a).So, if you want two statements, you must add a semi-colon between them.If you actually want to callf,you must remove the line break before(g).
A call of the formreturnfunctioncall is calledatail call.Lua implementsproper tail calls(orproper tail recursion):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 thata program can execute.However, a tail call erases any debug information about thecalling function.Note that a tail call only happens with a particular syntax,where thereturn has one single function call as argument;this syntax makes the calling function return exactlythe returns of the called function.So, none of the following examples are tail calls:
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
The syntax for function definition is
function ::=function funcbodyfuncbody ::= `(´ [parlist] `)´ blockend
The following syntactic sugar simplifies function definitions:
stat ::=function funcname funcbodystat ::=localfunction Name funcbodyfuncname ::= Name {`.´ Name} [`:´ Name]The statement
function f ()body end
translates to
f = function ()body end
The statement
function t.a.b.c.f ()body end
translates to
t.a.b.c.f = function ()body end
The statement
local function f ()body end
translates to
local f; f = function ()body end
not to
local f = function ()body end
(This only makes a difference when the body of the functioncontains references tof.)
A function definition is an executable expression,whose value has typefunction.When Lua pre-compiles a chunk,all its function bodies are pre-compiled too.Then, whenever Lua executes the function definition,the function isinstantiated (orclosed).This function instance (orclosure)is the final value of the expression.Different instances of the same functioncan refer to different external local variablesand can have different environment tables.
Parameters act as local variables that areinitialized with the argument values:
parlist ::= namelist [`,´ `...´] | `...´
When a function is called,the list of arguments is adjusted tothe length of the list of parameters,unless the function is a variadic orvararg function,which isindicated by three dots ('...') at the end of its parameter list.A vararg function does not adjust its argument list;instead, it collects all extra arguments and supplies themto the function through avararg expression,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 expressionor 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).
As an example, consider the following definitions:
function f(a, b) end function g(a, b, ...) end function r() return 1,2,3 end
Then, we have the following mapping from arguments to parameters andto the vararg expression:
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
Results are returned using thereturn statement (see§2.4.4).If control reaches the end of a functionwithout encountering areturn statement,then the function returns with no results.
Thecolon syntaxis used for definingmethods,that is, functions that have an implicit extra parameterself.Thus, the statement
function t.a.b.c:f (params)body end
is syntactic sugar for
t.a.b.c.f = function (self,params)body end
Lua is a lexically scoped language.The scope of variables begins at the first statementaftertheir declaration and lasts until the end of the innermost block thatincludes the declaration.Consider the following example:
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)
Notice that, in a declaration likelocal x = x,the newx being declared is not in scope yet,and so the secondx refers to the outside variable.
Because of the lexical scoping rules,local variables can be freely accessed by functionsdefined inside their scope.A local variable used by an inner function is calledanupvalue, orexternal local variable,inside the inner function.
Notice that each execution of alocal statementdefines new local variables.Consider the following example:
a = {} local x = 20 for i=1,10 do local y = 0 a[i] = function () y=y+1; return x+y end endThe loop creates ten closures(that is, ten instances of the anonymous function).Each of these closures uses a differenty variable,while all of them share the samex.
Because Lua is an embedded extension language,all Lua actions start from C code in the host programcalling a function from the Lua library (seelua_pcall).Whenever an error occurs during Lua compilation or execution,control returns to C,which can take appropriate measures(such as printing an error message).
Lua code can explicitly generate an error by calling theerror function.If you need to catch errors in Lua,you can use thepcall function.
Every value in Lua can have ametatable.Thismetatable is an ordinary Lua tablethat defines the behavior of the original valueunder certain special operations.You can change several aspects of the behaviorof 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"__add" in its metatable.If it finds one,Lua calls this function to perform the addition.
We call the keys in a metatableeventsand the valuesmetamethods.In the previous example, the event is"add" and the metamethod is the function that performs the addition.
You can query the metatable of any valuethrough thegetmetatable function.
You can replace the metatable of tablesthrough thesetmetatablefunction.You cannot change the metatable of other types from Lua(except by using the debug library);you must use the C API for that.
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.
A metatable controls how an object behaves in arithmetic operations,order comparisons, concatenation, length operation, and indexing.A metatable also can define a function to be called when a userdatais garbage collected.For each of these operations Lua associates a specific keycalled anevent.When Lua performs one of these operations over a value,it checks whether this value has a metatable with the corresponding event.If so, the value associated with that key (the metamethod)controls how Lua will perform the operation.
Metatables control the operations listed next.Each operation is identified by its corresponding name.The key for each operation is a string with its name prefixed bytwo underscores, '__';for instance, the key for operation "add" is thestring"__add".The semantics of these operations is better explained by a Lua functiondescribing how the interpreter executes the operation.
The code shown here in Lua is only illustrative;the real behavior is hard coded in the interpreterand it is much more efficient than this simulation.All functions used in these descriptions(rawget,tonumber, etc.)are described in§5.1.In particular, to retrieve the metamethod of a given object,we use the expression
metatable(obj)[event]
This should be read as
rawget(getmetatable(obj) or {}, event)That is, the access to a metamethod does not invoke other metamethods,and the access to objects with no metatables does not fail(it simply results innil).
+ operation.The functiongetbinhandler below defines how Lua chooses a handlerfor a binary operation.First, Lua tries the first operand.If its type does not define a handler for the operation,then Lua tries the second operand.
function getbinhandler (op1, op2, event) return metatable(op1)[event] or metatable(op2)[event] end
By using this function,the behavior of theop1 + op2 is
function add_event (op1, op2) local o1, o2 = tonumber(op1), tonumber(op2) if o1 and o2 then -- both operands are numeric? return o1 + o2 -- '+' here is the primitive 'add' else -- at least one of the operands is not numeric local h = getbinhandler(op1, op2, "__add") if h then -- call the handler with both operands return (h(op1, op2)) else -- no handler available: default behavior error(···) end end end
- operation.Behavior similar to the "add" operation.* operation.Behavior similar to the "add" operation./ operation.Behavior similar to the "add" operation.% operation.Behavior similar to the "add" operation,with the operationo1 - floor(o1/o2)*o2 as the primitive operation.^ (exponentiation) operation.Behavior similar to the "add" operation,with the functionpow (from the C math library)as the primitive operation.- operation.function unm_event (op) local o = tonumber(op) if o then -- operand is numeric? return -o -- '-' here is the primitive 'unm' else -- the operand is not numeric. -- Try to get a handler from the operand local h = metatable(op).__unm if h then -- call the handler with the operand return (h(op)) else -- no handler available: default behavior error(···) end end end
.. (concatenation) operation.function concat_event (op1, op2) if (type(op1) == "string" or type(op1) == "number") and (type(op2) == "string" or type(op2) == "number") then return op1 .. op2 -- primitive string concatenation else local h = getbinhandler(op1, op2, "__concat") if h then return (h(op1, op2)) else error(···) end end end
# operation.function len_event (op) if type(op) == "string" then return strlen(op) -- primitive string length elseif type(op) == "table" then return #op -- primitive table length else local h = metatable(op).__len if h then -- call the handler with the operand return (h(op)) else -- no handler available: default behavior error(···) end end end
See§2.5.5 for a description of the length of a table.
== operation.The functiongetcomphandler defines how Lua chooses a metamethodfor comparison operators.A metamethod only is selected when both objectsbeing compared have the same typeand the same metamethod for the selected operation.function getcomphandler (op1, op2, event) if type(op1) ~= type(op2) then return nil end local mm1 = metatable(op1)[event] local mm2 = metatable(op2)[event] if mm1 == mm2 then return mm1 else return nil end end
The "eq" event is defined as follows:
function eq_event (op1, op2) if type(op1) ~= type(op2) then -- different types? return false -- different objects end if op1 == op2 then -- primitive equal? return true -- objects are equal end -- try metamethod local h = getcomphandler(op1, op2, "__eq") if h then return (h(op1, op2)) else return false end end
a ~= b is equivalent tonot (a == b).
< operation.function lt_event (op1, op2) if type(op1) == "number" and type(op2) == "number" then return op1 < op2 -- numeric comparison elseif type(op1) == "string" and type(op2) == "string" then return op1 < op2 -- lexicographic comparison else local h = getcomphandler(op1, op2, "__lt") if h then return (h(op1, op2)) else error(···) end end end
a > b is equivalent tob < a.
<= operation.function le_event (op1, op2) if type(op1) == "number" and type(op2) == "number" then return op1 <= op2 -- numeric comparison elseif type(op1) == "string" and type(op2) == "string" then return op1 <= op2 -- lexicographic comparison else local h = getcomphandler(op1, op2, "__le") if h then return (h(op1, op2)) else h = getcomphandler(op1, op2, "__lt") if h then return not h(op2, op1) else error(···) end end end end
a >= b is equivalent tob <= a.Note that, in the absence of a "le" metamethod,Lua tries the "lt", assuming thata <= b isequivalent tonot (b < a).
table[key].function gettable_event (table, key) local h if type(table) == "table" then local v = rawget(table, key) if v ~= nil then return v end h = metatable(table).__index if h == nil then return nil end else h = metatable(table).__index if h == nil then error(···) end end if type(h) == "function" then return (h(table, key)) -- call the handler else return h[key] -- or repeat operation on it end end
table[key] = value.function settable_event (table, key, value) local h if type(table) == "table" then local v = rawget(table, key) if v ~= nil then rawset(table, key, value); return end h = metatable(table).__newindex if h == nil then rawset(table, key, value); return end else h = metatable(table).__newindex if h == nil then error(···) end end if type(h) == "function" then h(table, key,value) -- call the handler else h[key] = value -- or repeat operation on it end end
function function_event (func, ...) if type(func) == "function" then return func(...) -- primitive call else local h = metatable(func).__call if h then return h(func, ...) else error(···) end end end
Besides metatables,objects of types thread, function, and userdatahave another table associated with them,called theirenvironment.Like metatables, environments are regular tables andmultiple objects can share the same environment.
Threads are created sharing the environment of the creating thread.Userdata and C functions are created sharing the environmentof the creating C function.Non-nested Lua functions(created byloadfile,loadstring orload)are created sharing the environment of the creating thread.Nested Lua functions are created sharing the environment ofthe creating Lua function.
Environments associated with userdata have no meaning for Lua.It is only a convenience feature for programmers to associate a table toa userdata.
Environments associated with threads are calledglobal environments.They are used as the default environment for threads andnon-nested Lua functions created by the threadand can be directly accessed by C code (see§3.3).
The environment associated with a C function can be directlyaccessed by C code (see§3.3).It is used as the default environment for other C functionsand userdata created by the function.
Environments associated with Lua functions are used to resolveall accesses to global variables within the function (see§2.3).They are used as the default environment for nested Lua functionscreated by the function.
You can change the environment of a Lua function or therunning thread by callingsetfenv.You can get the environment of a Lua function or the running threadby callinggetfenv.To manipulate the environment of other objects(userdata, C functions, other threads) you mustuse the C API.
Lua performs automatic memory management.This means thatyou have to worry neither about allocating memory for new objectsnor about freeing it when the objects are no longer needed.Lua manages memory automatically by runningagarbage collector from time to timeto collect alldead objects(that is, objects that are no longer accessible from Lua).All memory used by Lua is subject to automatic management:tables, userdata, functions, threads, strings, etc.
Lua implements an incremental mark-and-sweep collector.It uses two numbers to control its garbage-collection cycles:thegarbage-collector pause andthegarbage-collector step multiplier.Both use percentage points as units(so that a value of 100 means an internal value of 1).
The garbage-collector pausecontrols 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 tostart a new cycle.A value of 200 means that the collector waits for the total memory in useto double before starting a new cycle.
The step multipliercontrols the relative speed of the collector relative tomemory allocation.Larger values make the collector more aggressive but also increasethe size of each incremental step.Values smaller than 100 make the collector too slow andcan result in the collector never finishing a cycle.The default, 200, means that the collector runs at "twice"the speed of memory allocation.
You can change these numbers by callinglua_gc in Corcollectgarbage in Lua.With these functions you can also control the collector directly (e.g., stop and restart it).
Using the C API,you can set garbage-collector metamethods for userdata (see§2.8).These metamethods are also calledfinalizers.Finalizers allow you to coordinate Lua's garbage collectionwith external resource management(such as closing files, network or database connections,or freeing your own memory).
Garbage userdata with a field__gc in their metatables are notcollected immediately by the garbage collector.Instead, Lua puts them in a list.After the collection,Lua does the equivalent of the following functionfor each userdata in that list:
function gc_event (udata) local h = metatable(udata).__gc if h then h(udata) end end
At the end of each garbage-collection cycle,the finalizers for userdata are called inreverseorder of their creation,among those collected in that cycle.That is, the first finalizer to be called is the one associatedwith the userdata created last in the program.The userdata itself is freed only in the next garbage-collection cycle.
Aweak table is a table whose elements areweak references.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 this object.
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 ofboth 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__mode field of its metatable.If the__mode field is a string containing the character 'k',the keys in the table are weak.If__mode contains 'v',the values in the table are weak.
After you use a table as a metatable,you should not change the value of its__mode field.Otherwise, the weak behavior of the tables controlled by thismetatable is undefined.
Lua supports coroutines,also calledcollaborative multithreading.A coroutine in Lua represents an independent thread of execution.Unlike threads in multithread systems, however,a coroutine only suspends its execution by explicitly callinga yield function.
You create a coroutine with a call tocoroutine.create.Its sole argument is a functionthat is the main function of the coroutine.Thecreate function only creates a new coroutine andreturns a handle to it (an object of typethread);it does not start the coroutine execution.
When you first callcoroutine.resume,passing as its first argumenta thread returned bycoroutine.create,the coroutine starts its execution,at the first line of its main function.Extra arguments passed tocoroutine.resume are passed onto the coroutine main function.After the coroutine starts running,it runs until it terminates oryields.
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 the first case,coroutine.resume returnstrue,plus any values returned by the coroutine main function.In case of errors,coroutine.resume returnsfalseplus an error message.
A coroutine yields by callingcoroutine.yield.When a coroutine yields,the correspondingcoroutine.resume 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,coroutine.resume also returnstrue,plus any values passed tocoroutine.yield.The next time you resume the same coroutine,it continues its execution from the point where it yielded,with the call tocoroutine.yield returning any extraarguments passed tocoroutine.resume.
Likecoroutine.create,thecoroutine.wrap 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 functiongo as extra arguments tocoroutine.resume.coroutine.wrap returns all the values returned bycoroutine.resume,except the first one (the boolean error code).Unlikecoroutine.resume,coroutine.wrap does not catch errors;any error is propagated to the caller.
As an example,consider the following code:
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"))When you run it, it produces the following output:
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
This section describes the C API for Lua, that is,the set of C functions available to the host program to communicatewith Lua.All API functions and related types and constantsare declared in the header filelua.h.
Even when we use the term "function",any facility in the API may be provided as a macro instead.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.
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 Luawith a proper definition for the macroluai_apicheck,in fileluaconf.h.
Lua uses avirtual stack to pass values to and from C.Each element in this stack represents a Lua value(nil, number, string, etc.).
Whenever Lua calls C, the called function gets a new stack,which is independent of previous stacks and of stacks ofC functions that are still active.This stack initially contains any arguments to the C functionand it is where the C function pushes its resultsto be returned to the caller (seelua_CFunction).
For convenience,most query operations in the API do not follow a strict stack discipline.Instead, they can refer to any element in the stackby using anindex:A positive index represents anabsolute stack position(starting at 1);a negative index represents anoffset relative to the top of the stack.More specifically, if the stack hasn elements,then index 1 represents the first element(that is, the element that was pushed onto the stack first)andindex n represents the last element;index -1 also represents the last element(that is, the element at the top)and index-n represents the first element.We say that an index isvalidif it lies between 1 and the stack top(that is, if1 ≤ abs(index) ≤ top).
When you interact with Lua API,you are responsible for ensuring consistency.In particular,you are responsible for controlling stack overflow.You can use the functionlua_checkstackto grow the stack size.
Whenever Lua calls C,it ensures that at leastLUA_MINSTACK stack positions are available.LUA_MINSTACK is defined as 20,so that usually you do not have to worry about stack spaceunless your code has loops pushing elements onto the stack.
Most query functions accept as indices any value inside theavailable stack space, that is, indices up to the maximum stack sizeyou have set throughlua_checkstack.Such indices are calledacceptable indices.More formally, we define anacceptable indexas follows:
(index < 0 && abs(index) <= top) || (index > 0 && index <= stackspace)
Note that 0 is never an acceptable index.
Unless otherwise noted,any function that accepts valid indices can also be called withpseudo-indices,which represent some Lua values that are accessible to C codebut which are not in the stack.Pseudo-indices are used to access the thread environment,the function environment,the registry,and the upvalues of a C function (see§3.4).
The thread environment (where global variables live) isalways at pseudo-indexLUA_GLOBALSINDEX.The environment of the running C function is alwaysat pseudo-indexLUA_ENVIRONINDEX.
To access and change the value of global variables,you can use regular table operations over an environment table.For instance, to access the value of a global variable, do
lua_getfield(L, LUA_GLOBALSINDEX, varname);
When a C function is created,it is possible to associate some values with it,thus creating aC closure;these values are calledupvalues and areaccessible to the function whenever it is called(seelua_pushcclosure).
Whenever a C function is called,its upvalues are located at specific pseudo-indices.These pseudo-indices are produced by the macrolua_upvalueindex.The first value associated with a function is at positionlua_upvalueindex(1), and so on.Any access tolua_upvalueindex(n),wheren is greater than the number of upvalues of thecurrent function (but not greater than 256),produces an acceptable (but invalid) index.
Lua provides aregistry,a pre-defined table that can be used by any C code tostore whatever Lua value it needs to store.This table is always located at pseudo-indexLUA_REGISTRYINDEX.Any C library can store data into this table,but it should take care to choose keys different from those usedby other libraries, to avoid collisions.Typically, you should use as key a string containing your library nameor a light userdata with the address of a C object in your code.
The integer keys in the registry are used by the reference mechanism,implemented by the auxiliary library,and therefore should not be used for other purposes.
Internally, Lua uses the Clongjmp facility to handle errors.(You can also choose to use exceptions if you use C++;see fileluaconf.h.)When Lua faces any error(such as memory allocation errors, type errors, syntax errors,and runtime errors)itraises an error;that is, it does a long jump.Aprotected environment usessetjmpto set a recover point;any error jumps to the most recent active recover point.
Most functions in the API can throw an error,for instance due to a memory allocation error.The documentation for each function indicates whetherit can throw errors.
Inside a C function you can throw an error by callinglua_error.
Here we list all functions and types from the C API inalphabetical order.Each function has an indicator like this:[-o, +p,x]
The first field,o,is how many elements the function pops from the stack.The second field,p,is how many elements the function pushes onto the stack.(Any function always pushes its results after popping its arguments.)A field in the formx|y means the function can push (or pop)x ory elements,depending on the situation;an interrogation mark '?' means thatwe cannot know how many elements the function pops/pushesby looking only at its arguments(e.g., they may depend on what is on the stack).The third field,x,tells whether the function may throw errors:'-' means the function never throws any error;'m' means the function may throw an erroronly due to not enough memory;'e' means the function may throw other kinds of errors;'v' means the function may throw an error on purpose.
lua_Alloctypedef void * (*lua_Alloc) (void *ud, void *ptr, size_t osize, size_t nsize);
The type of the memory-allocation function used by Lua states.The allocator function must provide afunctionality similar torealloc,but not exactly the same.Its arguments areud, an opaque pointer passed tolua_newstate;ptr, a pointer to the block being allocated/reallocated/freed;osize, the original size of the block;nsize, the new size of the block.ptr isNULL if and only ifosize is zero.Whennsize is zero, the allocator must returnNULL;ifosize is not zero,it should free the block pointed to byptr.Whennsize is not zero, the allocator returnsNULLif and only if it cannot fill the request.Whennsize is not zero andosize is zero,the allocator should behave likemalloc.Whennsize andosize are not zero,the allocator behaves likerealloc.Lua assumes that the allocator never fails whenosize >= nsize.
Here is a simple implementation for the allocator function.It is used in the auxiliary library byluaL_newstate.
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); }This code assumesthatfree(NULL) has no effect and thatrealloc(NULL, size) is equivalent tomalloc(size).ANSI C ensures both behaviors.
lua_atpanic[-0, +0,-]
lua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf);
Sets a new panic function and returns the old one.
If an error happens outside any protected environment,Lua calls apanic functionand then callsexit(EXIT_FAILURE),thus exiting the host application.Your panic function can avoid this exit bynever returning (e.g., doing a long jump).
The panic function can access the error message at the top of the stack.
lua_call[-(nargs + 1), +nresults,e]
void lua_call (lua_State *L, int nargs, int nresults);
Calls a function.
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 pushedin direct order;that is, the first argument is pushed first.Finally you calllua_call;nargs is the number of arguments that you pushed onto the stack.All arguments and the function value are popped from the stackwhen the function is called.The function results are pushed onto the stack when the function returns.The number of results is adjusted tonresults,unlessnresults isLUA_MULTRET.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.
Any error inside the called function is propagated upwards(with alongjmp).
The following example shows how the host program can do theequivalent to this Lua code:
a = f("how", t.x, 14)Here it is in C:
lua_getfield(L, LUA_GLOBALSINDEX, "f"); /* function to be called */ lua_pushstring(L, "how"); /* 1st argument */ lua_getfield(L, LUA_GLOBALSINDEX, "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_setfield(L, LUA_GLOBALSINDEX, "a"); /* set global 'a' */
Note that the code above is "balanced":at its end, the stack is back to its original configuration.This is considered good programming practice.
lua_CFunctiontypedef int (*lua_CFunction) (lua_State *L);
Type for C functions.
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 stackin direct order (the first argument is pushed first).So, when the function starts,lua_gettop(L) returns the number of arguments received by the function.The first argument (if any) is at index 1and its last argument is at indexlua_gettop(L).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 properlydiscarded by Lua.Like a Lua function, a C function called by Lua can also returnmany results.
As an example, the following function receives a variable numberof numerical arguments and returns their average and sum:
static int foo (lua_State *L) { int n = lua_gettop(L); /* number of arguments */ lua_Number sum = 0; int i; for (i = 1; i <= n; i++) { if (!lua_isnumber(L, i)) { lua_pushstring(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 */ }lua_checkstack[-0, +0,m]
int lua_checkstack (lua_State *L, int extra);
Ensures that there are at leastextra free stack slots in the stack.It returns false if it cannot grow the stack to that size.This function never shrinks the stack;if the stack is already larger than the new size,it is left unchanged.
lua_close[-0, +0,-]
void lua_close (lua_State *L);
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,such as a daemon or a web server,might need to release states as soon as they are not needed,to avoid growing too large.
lua_concat[-n, +1,e]
void lua_concat (lua_State *L, int n);
Concatenates then values at the top of the stack,pops them, and leaves the result at the top.Ifn is 1, the result is the single value on the stack(that is, the function does nothing);ifn is 0, the result is the empty string.Concatenation is performed following the usual semantics of Lua(see§2.5.4).
lua_cpcall[-0, +(0|1),-]
int lua_cpcall (lua_State *L, lua_CFunction func, void *ud);
Calls the C functionfunc in protected mode.func starts with only one element in its stack,a light userdata containingud.In case of errors,lua_cpcall returns the same error codes aslua_pcall,plus the error object on the top of the stack;otherwise, it returns zero, and does not change the stack.All values returned byfunc are discarded.
lua_createtable[-0, +1,m]
void lua_createtable (lua_State *L, int narr, int nrec);
Creates a new empty table and pushes it onto the stack.The new table has space pre-allocatedfornarr array elements andnrec non-array elements.This pre-allocation is useful when you know exactly how many elementsthe table will have.Otherwise you can use the functionlua_newtable.
lua_dump[-0, +0,m]
int lua_dump (lua_State *L, lua_Writer writer, void *data);
Dumps a function as a binary chunk.Receives a Lua function on the top of the stackand produces a binary chunk that,if loaded again,results in a function equivalent to the one dumped.As it produces parts of the chunk,lua_dump calls functionwriter (seelua_Writer)with the givendatato write them.
The value returned is the error code returned by the lastcall to the writer;0 means no errors.
This function does not pop the Lua function from the stack.
lua_equal[-0, +0,e]
int lua_equal (lua_State *L, int index1, int index2);
Returns 1 if the two values in acceptable indicesindex1 andindex2 are equal,following the semantics of the Lua== operator(that is, may call metamethods).Otherwise returns 0.Also returns 0 if any of the indices is non valid.
lua_error[-1, +0,v]
int lua_error (lua_State *L);
Generates a Lua error.The error message (which can actually be a Lua value of any type)must be on the stack top.This function does a long jump,and therefore never returns.(seeluaL_error).
lua_gc[-0, +0,e]
int lua_gc (lua_State *L, int what, int data);
Controls the garbage collector.
This function performs several tasks,according to the value of the parameterwhat:
LUA_GCSTOP:stops the garbage collector.LUA_GCRESTART:restarts the garbage collector.LUA_GCCOLLECT:performs a full garbage-collection cycle.LUA_GCCOUNT:returns the current amount of memory (in Kbytes) in use by Lua.LUA_GCCOUNTB:returns the remainder of dividing the current amount of bytes ofmemory in use by Lua by 1024.LUA_GCSTEP:performs an incremental step of garbage collection.The step "size" is controlled bydata(larger values mean more steps) in a non-specified way.If you want to control the step sizeyou must experimentally tune the value ofdata.The function returns 1 if the step finished agarbage-collection cycle.LUA_GCSETPAUSE:setsdata as the new valuefor thepause of the collector (see§2.10).The function returns the previous value of the pause.LUA_GCSETSTEPMUL:setsdata as the new value for thestep multiplier ofthe collector (see§2.10).The function returns the previous value of the step multiplier.lua_getallocf[-0, +0,-]
lua_Alloc lua_getallocf (lua_State *L, void **ud);
Returns the memory-allocation function of a given state.Ifud is notNULL, Lua stores in*ud theopaque pointer passed tolua_newstate.
lua_getfenv[-0, +1,-]
void lua_getfenv (lua_State *L, int index);
Pushes onto the stack the environment table ofthe value at the given index.
lua_getfield[-0, +1,e]
void lua_getfield (lua_State *L, int index, const char *k);
Pushes onto the stack the valuet[k],wheret is the value at the given valid index.As in Lua, this function may trigger a metamethodfor the "index" event (see§2.8).
lua_getglobal[-0, +1,e]
void lua_getglobal (lua_State *L, const char *name);
Pushes onto the stack the value of the globalname.It is defined as a macro:
#define lua_getglobal(L,s) lua_getfield(L, LUA_GLOBALSINDEX, s)
lua_getmetatable[-0, +(0|1),-]
int lua_getmetatable (lua_State *L, int index);
Pushes onto the stack the metatable of the value at the givenacceptable index.If the index is not valid,or if the value does not have a metatable,the function returns 0 and pushes nothing on the stack.
lua_gettable[-1, +1,e]
void lua_gettable (lua_State *L, int index);
Pushes onto the stack the valuet[k],wheret is the value at the given valid indexandk is the value at the top of the stack.
This function pops the key from the stack(putting the resulting value in its place).As in Lua, this function may trigger a metamethodfor the "index" event (see§2.8).
lua_gettop[-0, +0,-]
int lua_gettop (lua_State *L);
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(and so 0 means an empty stack).
lua_insert[-1, +1,-]
void lua_insert (lua_State *L, int index);
Moves the top element into the given valid index,shifting up the elements above this index to open space.Cannot be called with a pseudo-index,because a pseudo-index is not an actual stack position.
lua_Integertypedef ptrdiff_t lua_Integer;
The type used by the Lua API to represent integral values.
By default it is aptrdiff_t,which is usually the largest signed integral type the machine handles"comfortably".
lua_isboolean[-0, +0,-]
int lua_isboolean (lua_State *L, int index);
Returns 1 if the value at the given acceptable index has type boolean,and 0 otherwise.
lua_iscfunction[-0, +0,-]
int lua_iscfunction (lua_State *L, int index);
Returns 1 if the value at the given acceptable index is a C function,and 0 otherwise.
lua_isfunction[-0, +0,-]
int lua_isfunction (lua_State *L, int index);
Returns 1 if the value at the given acceptable index is a function(either C or Lua), and 0 otherwise.
lua_islightuserdata[-0, +0,-]
int lua_islightuserdata (lua_State *L, int index);
Returns 1 if the value at the given acceptable index is a light userdata,and 0 otherwise.
lua_isnil[-0, +0,-]
int lua_isnil (lua_State *L, int index);
Returns 1 if the value at the given acceptable index isnil,and 0 otherwise.
lua_isnone[-0, +0,-]
int lua_isnone (lua_State *L, int index);
Returns 1 if the given acceptable index is not valid(that is, it refers to an element outside the current stack),and 0 otherwise.
lua_isnoneornil[-0, +0,-]
int lua_isnoneornil (lua_State *L, int index);
Returns 1 if the given acceptable index is not valid(that is, it refers to an element outside the current stack)or if the value at this index isnil,and 0 otherwise.
lua_isnumber[-0, +0,-]
int lua_isnumber (lua_State *L, int index);
Returns 1 if the value at the given acceptable index is a numberor a string convertible to a number,and 0 otherwise.
lua_isstring[-0, +0,-]
int lua_isstring (lua_State *L, int index);
Returns 1 if the value at the given acceptable index is a stringor a number (which is always convertible to a string),and 0 otherwise.
lua_istable[-0, +0,-]
int lua_istable (lua_State *L, int index);
Returns 1 if the value at the given acceptable index is a table,and 0 otherwise.
lua_isthread[-0, +0,-]
int lua_isthread (lua_State *L, int index);
Returns 1 if the value at the given acceptable index is a thread,and 0 otherwise.
lua_isuserdata[-0, +0,-]
int lua_isuserdata (lua_State *L, int index);
Returns 1 if the value at the given acceptable index is a userdata(either full or light), and 0 otherwise.
lua_lessthan[-0, +0,e]
int lua_lessthan (lua_State *L, int index1, int index2);
Returns 1 if the value at acceptable indexindex1 is smallerthan the value at acceptable indexindex2,following the semantics of the Lua< operator(that is, may call metamethods).Otherwise returns 0.Also returns 0 if any of the indices is non valid.
lua_load[-0, +1,-]
int lua_load (lua_State *L, lua_Reader reader, void *data, const char *chunkname);
Loads a Lua chunk.If there are no errors,lua_load pushes the compiled chunk as a Luafunction on top of the stack.Otherwise, it pushes an error message.The return values oflua_load are:
LUA_ERRSYNTAX:syntax error during pre-compilation;LUA_ERRMEM:memory allocation error.This function only loads a chunk;it does not run it.
lua_load automatically detects whether the chunk is text or binary,and loads it accordingly (see programluac).
Thelua_load function uses a user-suppliedreader functionto read the chunk (seelua_Reader).Thedata argument is an opaque value passed to the reader function.
Thechunkname argument gives a name to the chunk,which is used for error messages and in debug information (see§3.8).
lua_newstate[-0, +0,-]
lua_State *lua_newstate (lua_Alloc f, void *ud);
Creates a new, independent state.ReturnsNULL if cannot create the state(due to lack of memory).The argumentf is the allocator function;Lua does all memory allocation for this state through this function.The second argument,ud, is an opaque pointer that Luasimply passes to the allocator in every call.
lua_newtable[-0, +1,m]
void lua_newtable (lua_State *L);
Creates a new empty table and pushes it onto the stack.It is equivalent tolua_createtable(L, 0, 0).
lua_newthread[-0, +1,m]
lua_State *lua_newthread (lua_State *L);
Creates a new thread, pushes it on the stack,and returns a pointer to alua_State that represents this new thread.The new state returned by this function shares with the original stateall global objects (such as tables),but has an independent execution stack.
There is no explicit function to close or to destroy a thread.Threads are subject to garbage collection,like any Lua object.
lua_newuserdata[-0, +1,m]
void *lua_newuserdata (lua_State *L, size_t size);
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.
Userdata represent C values in Lua.Afull userdata represents a block of memory.It is an object (like a table):you must create it, it can have its own metatable,and you can detect when it is being collected.A full userdata is only equal to itself (under raw equality).
When Lua collects a full userdata with agc metamethod,Lua calls the metamethod and marks the userdata as finalized.When this userdata is collected again thenLua frees its corresponding memory.
lua_next[-1, +(2|0),e]
int lua_next (lua_State *L, int index);
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,thenlua_next returns 0 (and pushes nothing).
A typical traversal looks like this:
/* 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); }While traversing a table,do not calllua_tolstring directly on a key,unless you know that the key is actually a string.Recall thatlua_tolstringchangesthe value at the given index;this confuses the next call tolua_next.
lua_Numbertypedef double lua_Number;
The type of numbers in Lua.By default, it is double, but that can be changed inluaconf.h.
Through the configuration file you can changeLua to operate with another type for numbers (e.g., float or long).
lua_objlen[-0, +0,-]
size_t lua_objlen (lua_State *L, int index);
Returns the "length" of the value at the given acceptable index:for strings, this is the string length;for tables, this is the result of the length operator ('#');for userdata, this is the size of the block of memory allocatedfor the userdata;for other values, it is 0.
lua_pcall[-(nargs + 1), +(nresults|1),-]
int lua_pcall (lua_State *L, int nargs, int nresults, int errfunc);
Calls a function in protected mode.
Bothnargs andnresults have the same meaning asinlua_call.If there are no errors during the call,lua_pcall behaves exactly likelua_call.However, if there is any error,lua_pcall catches it,pushes a single value on the stack (the error message),and returns an error code.Likelua_call,lua_pcall always removes the functionand its arguments from the stack.
Iferrfunc is 0,then the error message returned on the stackis exactly the original error message.Otherwise,errfunc is the stack index of anerror handler function.(In the current implementation, this index cannot be a pseudo-index.)In case of runtime errors,this function will be called with the error messageand its return value will be the message returned on the stack bylua_pcall.
Typically, the error handler function is used to add more debuginformation to the error message, such as a stack traceback.Such information cannot be gathered after the return oflua_pcall,since by then the stack has unwound.
Thelua_pcall function returns 0 in case of successor one of the following error codes(defined inlua.h):
LUA_ERRRUN:a runtime error.LUA_ERRMEM:memory allocation error.For such errors, Lua does not call the error handler function.LUA_ERRERR:error while running the error handler function.lua_pop[-n, +0,-]
void lua_pop (lua_State *L, int n);
Popsn elements from the stack.
lua_pushboolean[-0, +1,-]
void lua_pushboolean (lua_State *L, int b);
Pushes a boolean value with valueb onto the stack.
lua_pushcclosure[-n, +1,m]
void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);
Pushes a new C closure onto the stack.
When a C function is created,it is possible to associate some values with it,thus creating a C closure (see§3.4);these values are then accessible to the function whenever it is called.To associate values with a C function,first these values should be pushed onto the stack(when there are multiple values, the first value is pushed first).Thenlua_pushcclosureis called to create and push the C function onto the stack,with the argumentn telling how many values should beassociated with the function.lua_pushcclosure also pops these values from the stack.
The maximum value forn is 255.
lua_pushcfunction[-0, +1,m]
void lua_pushcfunction (lua_State *L, lua_CFunction f);
Pushes a C function onto the stack.This function receives a pointer to a C functionand pushes onto the stack a Lua value of typefunction that,when called, invokes the corresponding C function.
Any function to be registered in Lua mustfollow the correct protocol to receive its parametersand return its results (seelua_CFunction).
lua_pushcfunction is defined as a macro:
#define lua_pushcfunction(L,f) lua_pushcclosure(L,f,0)
lua_pushfstring[-0, +1,m]
const char *lua_pushfstring (lua_State *L, const char *fmt, ...);
Pushes onto the stack a formatted stringand returns a pointer to this string.It is similar to the C functionsprintf,but has some important differences:
%%' (inserts a '%' in the string),'%s' (inserts a zero-terminated string, with no size restrictions),'%f' (inserts alua_Number),'%p' (inserts a pointer as a hexadecimal numeral),'%d' (inserts anint), and'%c' (inserts anint as a character).lua_pushinteger[-0, +1,-]
void lua_pushinteger (lua_State *L, lua_Integer n);
Pushes a number with valuen onto the stack.
lua_pushlightuserdata[-0, +1,-]
void lua_pushlightuserdata (lua_State *L, void *p);
Pushes a light userdata onto the stack.
Userdata represent C values in Lua.Alight userdata represents a pointer.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.
lua_pushliteral[-0, +1,m]
void lua_pushliteral (lua_State *L, const char *s);
This macro is equivalent tolua_pushlstring,but can be used only whens is a literal string.In these cases, it automatically provides the string length.
lua_pushlstring[-0, +1,m]
void lua_pushlstring (lua_State *L, const char *s, size_t len);
Pushes the string pointed to bys with sizelenonto the stack.Lua makes (or reuses) an internal copy of the given string,so the memory ats can be freed or reused immediately afterthe function returns.The string can contain embedded zeros.
lua_pushnil[-0, +1,-]
void lua_pushnil (lua_State *L);
Pushes a nil value onto the stack.
lua_pushnumber[-0, +1,-]
void lua_pushnumber (lua_State *L, lua_Number n);
Pushes a number with valuen onto the stack.
lua_pushstring[-0, +1,m]
void lua_pushstring (lua_State *L, const char *s);
Pushes the zero-terminated string pointed to bysonto the stack.Lua makes (or reuses) an internal copy of the given string,so the memory ats can be freed or reused immediately afterthe function returns.The string cannot contain embedded zeros;it is assumed to end at the first zero.
lua_pushthread[-0, +1,-]
int lua_pushthread (lua_State *L);
Pushes the thread represented byL onto the stack.Returns 1 if this thread is the main thread of its state.
lua_pushvalue[-0, +1,-]
void lua_pushvalue (lua_State *L, int index);
Pushes a copy of the element at the given valid indexonto the stack.
lua_pushvfstring[-0, +1,m]
const char *lua_pushvfstring (lua_State *L, const char *fmt, va_list argp);
Equivalent tolua_pushfstring, except that it receives ava_listinstead of a variable number of arguments.
lua_rawequal[-0, +0,-]
int lua_rawequal (lua_State *L, int index1, int index2);
Returns 1 if the two values in acceptable indicesindex1 andindex2 are primitively equal(that is, without calling metamethods).Otherwise returns 0.Also returns 0 if any of the indices are non valid.
lua_rawget[-1, +1,-]
void lua_rawget (lua_State *L, int index);
Similar tolua_gettable, but does a raw access(i.e., without metamethods).
lua_rawgeti[-0, +1,-]
void lua_rawgeti (lua_State *L, int index, int n);
Pushes onto the stack the valuet[n],wheret is the value at the given valid index.The access is raw;that is, it does not invoke metamethods.
lua_rawset[-2, +0,m]
void lua_rawset (lua_State *L, int index);
Similar tolua_settable, but does a raw assignment(i.e., without metamethods).
lua_rawseti[-1, +0,m]
void lua_rawseti (lua_State *L, int index, int n);
Does the equivalent oft[n] = v,wheret is the value at the given valid indexandv is the value at the top of the stack.
This function pops the value from the stack.The assignment is raw;that is, it does not invoke metamethods.
lua_Readertypedef const char * (*lua_Reader) (lua_State *L, void *data, size_t *size);
The reader function used bylua_load.Every time it needs another piece of the chunk,lua_load calls the reader,passing along itsdata parameter.The reader must return a pointer to a block of memorywith a new piece of the chunkand setsize 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 returnNULL or setsize to zero.The reader function may return pieces of any size greater than zero.
lua_register[-0, +0,e]
void lua_register (lua_State *L, const char *name, lua_CFunction f);
Sets the C functionf as the new value of globalname.It is defined as a macro:
#define lua_register(L,n,f) \ (lua_pushcfunction(L, f), lua_setglobal(L, n))
lua_remove[-1, +0,-]
void lua_remove (lua_State *L, int index);
Removes the element at the given valid index,shifting down the elements above this index to fill the gap.Cannot be called with a pseudo-index,because a pseudo-index is not an actual stack position.
lua_replace[-1, +0,-]
void lua_replace (lua_State *L, int index);
Moves the top element into the given position (and pops it),without shifting any element(therefore replacing the value at the given position).
lua_resume[-?, +?,-]
int lua_resume (lua_State *L, int narg);
Starts and resumes a coroutine in a given thread.
To start a coroutine, you first create a new thread(seelua_newthread);then you push onto its stack the main function plus any arguments;then you calllua_resume,withnarg 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 tolua_yield,or all values returned by the body function.lua_resume returnsLUA_YIELD if the coroutine yields,0 if the coroutine finishes its executionwithout errors,or an error code in case of errors (seelua_pcall).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.To restart a coroutine, you put on its stack only the values tobe passed as results fromyield,and then calllua_resume.
lua_setallocf[-0, +0,-]
void lua_setallocf (lua_State *L, lua_Alloc f, void *ud);
Changes the allocator function of a given state tofwith user dataud.
lua_setfenv[-1, +0,-]
int lua_setfenv (lua_State *L, int index);
Pops a table from the stack and sets it asthe new environment for the value at the given index.If the value at the given index isneither a function nor a thread nor a userdata,lua_setfenv returns 0.Otherwise it returns 1.
lua_setfield[-1, +0,e]
void lua_setfield (lua_State *L, int index, const char *k);
Does the equivalent tot[k] = v,wheret is the value at the given valid indexandv is the value at the top of the stack.
This function pops the value from the stack.As in Lua, this function may trigger a metamethodfor the "newindex" event (see§2.8).
lua_setglobal[-1, +0,e]
void lua_setglobal (lua_State *L, const char *name);
Pops a value from the stack andsets it as the new value of globalname.It is defined as a macro:
#define lua_setglobal(L,s) lua_setfield(L, LUA_GLOBALSINDEX, s)
lua_setmetatable[-1, +0,-]
int lua_setmetatable (lua_State *L, int index);
Pops a table from the stack andsets it as the new metatable for the value at the givenacceptable index.
lua_settable[-2, +0,e]
void lua_settable (lua_State *L, int index);
Does the equivalent tot[k] = v,wheret is the value at the given valid index,v is the value at the top of the stack,andk is the value just below the top.
This function pops both the key and the value from the stack.As in Lua, this function may trigger a metamethodfor the "newindex" event (see§2.8).
lua_settop[-?, +?,-]
void lua_settop (lua_State *L, int index);
Accepts any acceptable 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 withnil.Ifindex is 0, then all stack elements are removed.
lua_Statetypedef struct lua_State lua_State;
Opaque structure that keeps the whole state of a Lua interpreter.The Lua library is fully reentrant:it has no global variables.All information about a state is kept in this structure.
A pointer to this state must be passed as the first argument toevery function in the library, except tolua_newstate,which creates a Lua state from scratch.
lua_status[-0, +0,-]
int lua_status (lua_State *L);
Returns the status of the threadL.
The status can be 0 for a normal thread,an error code if the thread finished its execution with an error,orLUA_YIELD if the thread is suspended.
lua_toboolean[-0, +0,-]
int lua_toboolean (lua_State *L, int index);
Converts the Lua value at the given acceptable index to a C booleanvalue (0 or 1).Like all tests in Lua,lua_toboolean returns 1 for any Lua valuedifferent fromfalse andnil;otherwise it returns 0.It also returns 0 when called with a non-valid index.(If you want to accept only actual boolean values,uselua_isboolean to test the value's type.)
lua_tocfunction[-0, +0,-]
lua_CFunction lua_tocfunction (lua_State *L, int index);
Converts a value at the given acceptable index to a C function.That value must be a C function;otherwise, returnsNULL.
lua_tointeger[-0, +0,-]
lua_Integer lua_tointeger (lua_State *L, int index);
Converts the Lua value at the given acceptable indexto the signed integral typelua_Integer.The Lua value must be a number or a string convertible to a number(see§2.2.1);otherwise,lua_tointeger returns 0.
If the number is not an integer,it is truncated in some non-specified way.
lua_tolstring[-0, +0,m]
const char *lua_tolstring (lua_State *L, int index, size_t *len);
Converts the Lua value at the given acceptable index to a C string.Iflen is notNULL,it also sets*len with the string length.The Lua value must be a string or a number;otherwise, the function returnsNULL.If the value is a number,thenlua_tolstring alsochanges the actual value in the stack to a string.(This change confuseslua_nextwhenlua_tolstring is applied to keys during a table traversal.)
lua_tolstring returns a fully aligned pointerto a string inside the Lua state.This string always has a zero ('\0')after its last character (as in C),but can contain other zeros in its body.Because Lua has garbage collection,there is no guarantee that the pointer returned bylua_tolstringwill be valid after the corresponding value is removed from the stack.
lua_tonumber[-0, +0,-]
lua_Number lua_tonumber (lua_State *L, int index);
Converts the Lua value at the given acceptable indexto the C typelua_Number (seelua_Number).The Lua value must be a number or a string convertible to a number(see§2.2.1);otherwise,lua_tonumber returns 0.
lua_topointer[-0, +0,-]
const void *lua_topointer (lua_State *L, int index);
Converts the value at the given acceptable index to a genericC pointer (void*).The value can be a userdata, a table, a thread, or a function;otherwise,lua_topointer returnsNULL.Different objects will give different pointers.There is no way to convert the pointer back to its original value.
Typically this function is used only for debug information.
lua_tostring[-0, +0,m]
const char *lua_tostring (lua_State *L, int index);
Equivalent tolua_tolstring withlen equal toNULL.
lua_tothread[-0, +0,-]
lua_State *lua_tothread (lua_State *L, int index);
Converts the value at the given acceptable index to a Lua thread(represented aslua_State*).This value must be a thread;otherwise, the function returnsNULL.
lua_touserdata[-0, +0,-]
void *lua_touserdata (lua_State *L, int index);
If the value at the given acceptable index is a full userdata,returns its block address.If the value is a light userdata,returns its pointer.Otherwise, returnsNULL.
lua_type[-0, +0,-]
int lua_type (lua_State *L, int index);
Returns the type of the value in the given acceptable index,orLUA_TNONE for a non-valid index(that is, an index to an "empty" stack position).The types returned bylua_type are coded by the following constantsdefined inlua.h:LUA_TNIL,LUA_TNUMBER,LUA_TBOOLEAN,LUA_TSTRING,LUA_TTABLE,LUA_TFUNCTION,LUA_TUSERDATA,LUA_TTHREAD,andLUA_TLIGHTUSERDATA.
lua_typename[-0, +0,-]
const char *lua_typename (lua_State *L, int tp);
Returns the name of the type encoded by the valuetp,which must be one the values returned bylua_type.
lua_Writertypedef int (*lua_Writer) (lua_State *L, const void* p, size_t sz, void* ud);
The type of the writer function used bylua_dump.Every time it produces another piece of chunk,lua_dump calls the writer,passing along the buffer to be written (p),its size (sz),and thedata parameter supplied tolua_dump.
The writer returns an error code:0 means no errors;any other value means an error and stopslua_dump fromcalling the writer again.
lua_xmove[-?, +?,-]
void lua_xmove (lua_State *from, lua_State *to, int n);
Exchange values between different threads of thesame global state.
This function popsn values from the stackfrom,and pushes them onto the stackto.
lua_yield[-?, +?,-]
int lua_yield (lua_State *L, int nresults);
Yields a coroutine.
This function should only be called as thereturn expression of a C function, as follows:
return lua_yield (L, nresults);
When a C function callslua_yield in that way,the running coroutine suspends its execution,and the call tolua_resume that started this coroutine returns.The parameternresults is the number of values from the stackthat are passed as results tolua_resume.
Lua has no built-in debugging facilities.Instead, it offers a special interfaceby means of functions andhooks.This interface allows the construction of differentkinds of debuggers, profilers, and other toolsthat need "inside information" from the interpreter.
lua_Debugtypedef 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 nups; /* (u) number of upvalues */ int linedefined; /* (S) */ int lastlinedefined; /* (S) */ char short_src[LUA_IDSIZE]; /* (S) */ /* private part */other fields} lua_Debug;A structure used to carry different pieces ofinformation about an active function.lua_getstack fills only the private partof this structure, for later use.To fill the other fields oflua_Debug with useful information,calllua_getinfo.
The fields oflua_Debug have the following meaning:
source:If the function was defined in a string,thensource is that string.If the function was defined in a file,thensource starts with a '@' followed by the file name.short_src:a "printable" version ofsource, to be used in error messages.linedefined:the line number where the definition of the function starts.lastlinedefined:the line number where the definition of the function ends.what:the string"Lua" if the function is a Lua function,"C" if it is a C function,"main" if it is the main part of a chunk,and"tail" if it was a function that did a tail call.In the latter case,Lua has no other information about the function.currentline:the current line where the given function is executing.When no line information is available,currentline is set to -1.name: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.Thelua_getinfo function checks how the function wascalled to find a suitable name.If it cannot find a name,thenname is set toNULL.namewhat:explains thename field.The value ofnamewhat can be"global","local","method","field","upvalue", or"" (the empty string),according to how the function was called.(Lua uses the empty string when no other option seems to apply.)nups:the number of upvalues of the function.lua_gethook[-0, +0,-]
lua_Hook lua_gethook (lua_State *L);
Returns the current hook function.
lua_gethookcount[-0, +0,-]
int lua_gethookcount (lua_State *L);
Returns the current hook count.
lua_gethookmask[-0, +0,-]
int lua_gethookmask (lua_State *L);
Returns the current hook mask.
lua_getinfo[-(0|1), +(0|1|2),m]
int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar);
Returns information about a specific function or function invocation.
To get information about a function invocation,the parameterar must be a valid activation record that wasfilled by a previous call tolua_getstack orgiven as argument to a hook (seelua_Hook).
To get information about a function you push it onto the stackand start thewhat string with the character '>'.(In that case,lua_getinfo pops the function in the top of the stack.)For instance, to know in which line a functionf was defined,you can write the following code:
lua_Debug ar; lua_getfield(L, LUA_GLOBALSINDEX, "f"); /* get global 'f' */ lua_getinfo(L, ">S", &ar); printf("%d\n", ar.linedefined);Each character in the stringwhatselects some fields of the structurear to be filled ora value to be pushed on the stack:
n': fills in the fieldname andnamewhat;S':fills in the fieldssource,short_src,linedefined,lastlinedefined, andwhat;l': fills in the fieldcurrentline;u': fills in the fieldnups;f':pushes onto the stack the function that isrunning at the given level;L':pushes onto the stack a table whose indices are thenumbers of the lines that are valid on the function.(Avalid line 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.)This function returns 0 on error(for instance, an invalid option inwhat).
lua_getlocal[-0, +(0|1),-]
const char *lua_getlocal (lua_State *L, lua_Debug *ar, int n);
Gets information about a local variable of a given activation record.The parameterar must be a valid activation record that wasfilled by a previous call tolua_getstack orgiven as argument to a hook (seelua_Hook).The indexn selects which local variable to inspect(1 is the first parameter or active local variable, and so on,until the last active local variable).lua_getlocal pushes the variable's value onto the stackand returns its name.
Variable names starting with '(' (open parentheses)represent internal variables(loop control variables, temporaries, and C function locals).
ReturnsNULL (and pushes nothing)when the index is greater thanthe number of active local variables.
lua_getstack[-0, +0,-]
int lua_getstack (lua_State *L, int level, lua_Debug *ar);
Get information about the interpreter runtime stack.
This function fills parts of alua_Debug structure withan identification of theactivation recordof the function executing at a given level.Level 0 is the current running function,whereas leveln+1 is the function that has called leveln.When there are no errors,lua_getstack returns 1;when called with a level greater than the stack depth,it returns 0.
lua_getupvalue[-0, +(0|1),-]
const char *lua_getupvalue (lua_State *L, int funcindex, int n);
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.)lua_getupvalue gets the indexn of an upvalue,pushes the upvalue's value onto the stack,and returns its name.funcindex 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.)
ReturnsNULL (and pushes nothing)when the index is greater than the number of upvalues.For C functions, this function uses the empty string""as a name for all upvalues.
lua_Hooktypedef void (*lua_Hook) (lua_State *L, lua_Debug *ar);
Type for debugging hook functions.
Whenever a hook is called, itsar argument has its fieldevent set to the specific event that triggered the hook.Lua identifies these events with the following constants:LUA_HOOKCALL,LUA_HOOKRET,LUA_HOOKTAILRET,LUA_HOOKLINE,andLUA_HOOKCOUNT.Moreover, for line events, the fieldcurrentline is also set.To get the value of any other field inar,the hook must calllua_getinfo.For return events,event can beLUA_HOOKRET,the normal value, orLUA_HOOKTAILRET.In the latter case, Lua is simulating a return froma function that did a tail call;in this case, it is useless to calllua_getinfo.
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.
lua_sethook[-0, +0,-]
int lua_sethook (lua_State *L, lua_Hook f, int mask, int count);
Sets the debugging hook function.
Argumentf is the hook function.mask specifies on which events the hook will be called:it is formed by a bitwise or of the constantsLUA_MASKCALL,LUA_MASKRET,LUA_MASKLINE,andLUA_MASKCOUNT.Thecount argument is only meaningful when the maskincludesLUA_MASKCOUNT.For each event, the hook is called as explained below:
count instructions.(This event only happens while Lua is executing a Lua function.)A hook is disabled by settingmask to zero.
lua_setlocal[-(0|1), +0,-]
const char *lua_setlocal (lua_State *L, lua_Debug *ar, int n);
Sets the value of a local variable of a given activation record.Parametersar andn are as inlua_getlocal(seelua_getlocal).lua_setlocal assigns the value at the top of the stackto the variable and returns its name.It also pops the value from the stack.
ReturnsNULL (and pops nothing)when the index is greater thanthe number of active local variables.
lua_setupvalue[-(0|1), +0,-]
const char *lua_setupvalue (lua_State *L, int funcindex, int n);
Sets the value of a closure's upvalue.It assigns the value at the top of the stackto the upvalue and returns its name.It also pops the value from the stack.Parametersfuncindex andn are as in thelua_getupvalue(seelua_getupvalue).
ReturnsNULL (and pops nothing)when the index is greater than the number of upvalues.
Theauxiliary library provides several convenient functionsto 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 somecommon tasks.
All functions from the auxiliary libraryare defined in header filelauxlib.h andhave a prefixluaL_.
All functions in the auxiliary library are built ontop of the basic API,and so they provide nothing that cannot be done with this API.
Several functions in the auxiliary library are used tocheck C function arguments.Their names are alwaysluaL_check* orluaL_opt*.All of these functions throw an error if the check is not satisfied.Because the error message is formatted for arguments(e.g., "bad argument #1"),you should not use these functions for other stack values.
Here we list all functions and types from the auxiliary libraryin alphabetical order.
luaL_addchar[-0, +0,m]
void luaL_addchar (luaL_Buffer *B, char c);
Adds the characterc to the bufferB(seeluaL_Buffer).
luaL_addlstring[-0, +0,m]
void luaL_addlstring (luaL_Buffer *B, const char *s, size_t l);
Adds the string pointed to bys with lengthl tothe bufferB(seeluaL_Buffer).The string may contain embedded zeros.
luaL_addsize[-0, +0,m]
void luaL_addsize (luaL_Buffer *B, size_t n);
Adds to the bufferB (seeluaL_Buffer)a string of lengthn previously copied to thebuffer area (seeluaL_prepbuffer).
luaL_addstring[-0, +0,m]
void luaL_addstring (luaL_Buffer *B, const char *s);
Adds the zero-terminated string pointed to bysto the bufferB(seeluaL_Buffer).The string may not contain embedded zeros.
luaL_addvalue[-1, +0,m]
void luaL_addvalue (luaL_Buffer *B);
Adds the value at the top of the stackto the bufferB(seeluaL_Buffer).Pops the value.
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.
luaL_argcheck[-0, +0,v]
void luaL_argcheck (lua_State *L, int cond, int narg, const char *extramsg);
Checks whethercond is true.If not, raises an error with the following message,wherefunc is retrieved from the call stack:
bad argument #<narg> to <func> (<extramsg>)
luaL_argerror[-0, +0,v]
int luaL_argerror (lua_State *L, int narg, const char *extramsg);
Raises an error with the following message,wherefunc is retrieved from the call stack:
bad argument #<narg> to <func> (<extramsg>)
This function never returns,but it is an idiom to use it in C functionsasreturn luaL_argerror(args).
luaL_Buffertypedef struct luaL_Buffer luaL_Buffer;
Type for astring buffer.
A string buffer allows C code to build Lua strings piecemeal.Its pattern of use is as follows:
b of typeluaL_Buffer.luaL_buffinit(L, &b).luaL_add* functions.luaL_pushresult(&b).This call leaves the final string on the top of the stack.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 wherethe top of the stack is.You can use the stack between successive calls to buffer operationsas long as that use is balanced;that is,when you call a buffer operation,the stack is at the same levelit was immediately after the previous buffer operation.(The only exception to this rule isluaL_addvalue.)After callingluaL_pushresult the stack is back to itslevel when the buffer was initialized,plus the final string on its top.
luaL_buffinit[-0, +0,-]
void luaL_buffinit (lua_State *L, luaL_Buffer *B);
Initializes a bufferB.This function does not allocate any space;the buffer must be declared as a variable(seeluaL_Buffer).
luaL_callmeta[-0, +(0|1),e]
int luaL_callmeta (lua_State *L, int obj, const char *e);
Calls a metamethod.
If the object at indexobj has a metatable and thismetatable has a fielde,this function calls this field and passes the object as its only argument.In this case this function returns 1 and pushes onto thestack the value returned by the call.If there is no metatable or no metamethod,this function returns 0 (without pushing any value on the stack).
luaL_checkany[-0, +0,v]
void luaL_checkany (lua_State *L, int narg);
Checks whether the function has an argumentof any type (includingnil) at positionnarg.
luaL_checkint[-0, +0,v]
int luaL_checkint (lua_State *L, int narg);
Checks whether the function argumentnarg is a numberand returns this number cast to anint.
luaL_checkinteger[-0, +0,v]
lua_Integer luaL_checkinteger (lua_State *L, int narg);
Checks whether the function argumentnarg is a numberand returns this number cast to alua_Integer.
luaL_checklong[-0, +0,v]
long luaL_checklong (lua_State *L, int narg);
Checks whether the function argumentnarg is a numberand returns this number cast to along.
luaL_checklstring[-0, +0,v]
const char *luaL_checklstring (lua_State *L, int narg, size_t *l);
Checks whether the function argumentnarg is a stringand returns this string;ifl is notNULL fills*lwith the string's length.
This function useslua_tolstring to get its result,so all conversions and caveats of that function apply here.
luaL_checknumber[-0, +0,v]
lua_Number luaL_checknumber (lua_State *L, int narg);
Checks whether the function argumentnarg is a numberand returns this number.
luaL_checkoption[-0, +0,v]
int luaL_checkoption (lua_State *L, int narg, const char *def, const char *const lst[]);
Checks whether the function argumentnarg is a string andsearches for this string in the arraylst(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 orif the string cannot be found.
Ifdef is notNULL,the function usesdef as a default value whenthere is no argumentnarg or if this argument isnil.
This is a useful function for mapping strings to C enums.(The usual convention in Lua libraries isto use strings instead of numbers to select options.)
luaL_checkstack[-0, +0,v]
void luaL_checkstack (lua_State *L, int sz, const char *msg);
Grows the stack size totop + sz elements,raising an error if the stack cannot grow to that size.msg is an additional text to go into the error message.
luaL_checkstring[-0, +0,v]
const char *luaL_checkstring (lua_State *L, int narg);
Checks whether the function argumentnarg is a stringand returns this string.
This function useslua_tolstring to get its result,so all conversions and caveats of that function apply here.
luaL_checktype[-0, +0,v]
void luaL_checktype (lua_State *L, int narg, int t);
Checks whether the function argumentnarg has typet.Seelua_type for the encoding of types fort.
luaL_checkudata[-0, +0,v]
void *luaL_checkudata (lua_State *L, int narg, const char *tname);
Checks whether the function argumentnarg is a userdataof the typetname (seeluaL_newmetatable).
luaL_dofile[-0, +?,m]
int luaL_dofile (lua_State *L, const char *filename);
Loads and runs the given file.It is defined as the following macro:
(luaL_loadfile(L, filename) || lua_pcall(L, 0, LUA_MULTRET, 0))
It returns 0 if there are no errorsor 1 in case of errors.
luaL_dostring[-0, +?,m]
int luaL_dostring (lua_State *L, const char *str);
Loads and runs the given string.It is defined as the following macro:
(luaL_loadstring(L, str) || lua_pcall(L, 0, LUA_MULTRET, 0))
It returns 0 if there are no errorsor 1 in case of errors.
luaL_error[-0, +0,v]
int luaL_error (lua_State *L, const char *fmt, ...);
Raises an error.The error message format is given byfmtplus any extra arguments,following the same rules oflua_pushfstring.It also adds at the beginning of the message the file name andthe line number where the error occurred,if this information is available.
This function never returns,but it is an idiom to use it in C functionsasreturn luaL_error(args).
luaL_getmetafield[-0, +(0|1),m]
int luaL_getmetafield (lua_State *L, int obj, const char *e);
Pushes onto the stack the fielde from the metatableof the object at indexobj.If the object does not have a metatable,or if the metatable does not have this field,returns 0 and pushes nothing.
luaL_getmetatable[-0, +1,-]
void luaL_getmetatable (lua_State *L, const char *tname);
Pushes onto the stack the metatable associated with nametnamein the registry (seeluaL_newmetatable).
luaL_gsub[-0, +1,m]
const char *luaL_gsub (lua_State *L, const char *s, const char *p, const char *r);
Creates a copy of strings by replacingany occurrence of the stringpwith the stringr.Pushes the resulting string on the stack and returns it.
luaL_loadbuffer[-0, +1,m]
int luaL_loadbuffer (lua_State *L, const char *buff, size_t sz, const char *name);
Loads a buffer as a Lua chunk.This function useslua_load to load the chunk in thebuffer pointed to bybuff with sizesz.
This function returns the same results aslua_load.name is the chunk name,used for debug information and error messages.
luaL_loadfile[-0, +1,m]
int luaL_loadfile (lua_State *L, const char *filename);
Loads a file as a Lua chunk.This function useslua_load to load the chunk in the filenamedfilename.Iffilename isNULL,then it loads from the standard input.The first line in the file is ignored if it starts with a#.
This function returns the same results aslua_load,but it has an extra error codeLUA_ERRFILEif it cannot open/read the file.
Aslua_load, this function only loads the chunk;it does not run it.
luaL_loadstring[-0, +1,m]
int luaL_loadstring (lua_State *L, const char *s);
Loads a string as a Lua chunk.This function useslua_load to load the chunk inthe zero-terminated strings.
This function returns the same results aslua_load.
Also aslua_load, this function only loads the chunk;it does not run it.
luaL_newmetatable[-0, +1,m]
int luaL_newmetatable (lua_State *L, const char *tname);
If the registry already has the keytname,returns 0.Otherwise,creates a new table to be used as a metatable for userdata,adds it to the registry with keytname,and returns 1.
In both cases pushes onto the stack the final value associatedwithtname in the registry.
luaL_newstate[-0, +0,-]
lua_State *luaL_newstate (void);
Creates a new Lua state.It callslua_newstate with anallocator based on the standard Crealloc functionand then sets a panic function (seelua_atpanic) that printsan error message to the standard error output in case of fatalerrors.
Returns the new state,orNULL if there is a memory allocation error.
luaL_openlibs[-0, +0,m]
void luaL_openlibs (lua_State *L);
Opens all standard Lua libraries into the given state.
luaL_optint[-0, +0,v]
int luaL_optint (lua_State *L, int narg, int d);
If the function argumentnarg is a number,returns this number cast to anint.If this argument is absent or isnil,returnsd.Otherwise, raises an error.
luaL_optinteger[-0, +0,v]
lua_Integer luaL_optinteger (lua_State *L, int narg, lua_Integer d);
If the function argumentnarg is a number,returns this number cast to alua_Integer.If this argument is absent or isnil,returnsd.Otherwise, raises an error.
luaL_optlong[-0, +0,v]
long luaL_optlong (lua_State *L, int narg, long d);
If the function argumentnarg is a number,returns this number cast to along.If this argument is absent or isnil,returnsd.Otherwise, raises an error.
luaL_optlstring[-0, +0,v]
const char *luaL_optlstring (lua_State *L, int narg, const char *d, size_t *l);
If the function argumentnarg is a string,returns this string.If this argument is absent or isnil,returnsd.Otherwise, raises an error.
Ifl is notNULL,fills the position*l with the results's length.
luaL_optnumber[-0, +0,v]
lua_Number luaL_optnumber (lua_State *L, int narg, lua_Number d);
If the function argumentnarg is a number,returns this number.If this argument is absent or isnil,returnsd.Otherwise, raises an error.
luaL_optstring[-0, +0,v]
const char *luaL_optstring (lua_State *L, int narg, const char *d);
If the function argumentnarg is a string,returns this string.If this argument is absent or isnil,returnsd.Otherwise, raises an error.
luaL_prepbuffer[-0, +0,-]
char *luaL_prepbuffer (luaL_Buffer *B);
Returns an address to a space of sizeLUAL_BUFFERSIZEwhere you can copy a string to be added to bufferB(seeluaL_Buffer).After copying the string into this space you must callluaL_addsize with the size of the string to actually add it to the buffer.
luaL_pushresult[-?, +1,m]
void luaL_pushresult (luaL_Buffer *B);
Finishes the use of bufferB leaving the final string onthe top of the stack.
luaL_ref[-1, +0,m]
int luaL_ref (lua_State *L, int t);
Creates and returns areference,in the table at indext,for the object at the top of the stack (and pops the object).
A reference is a unique integer key.As long as you do not manually add integer keys into tablet,luaL_ref ensures the uniqueness of the key it returns.You can retrieve an object referred by referencerby callinglua_rawgeti(L, t, r).FunctionluaL_unref frees a reference and its associated object.
If the object at the top of the stack isnil,luaL_ref returns the constantLUA_REFNIL.The constantLUA_NOREF is guaranteed to be differentfrom any reference returned byluaL_ref.
luaL_Regtypedef struct luaL_Reg { const char *name; lua_CFunction func;} luaL_Reg;Type for arrays of functions to be registered byluaL_register.name is the function name andfunc is a pointer tothe function.Any array ofluaL_Reg must end with an sentinel entryin which bothname andfunc areNULL.
luaL_register[-(0|1), +1,m]
void luaL_register (lua_State *L, const char *libname, const luaL_Reg *l);
Opens a library.
When called withlibname equal toNULL,it simply registers all functions in the listl(seeluaL_Reg) into the table on the top of the stack.
When called with a non-nulllibname,luaL_register creates a new tablet,sets it as the value of the global variablelibname,sets it as the value ofpackage.loaded[libname],and registers on it all functions in the listl.If there is a table inpackage.loaded[libname] or invariablelibname,reuses this table instead of creating a new one.
In any case the function leaves the tableon the top of the stack.
luaL_typename[-0, +0,-]
const char *luaL_typename (lua_State *L, int index);
Returns the name of the type of the value at the given index.
luaL_typerror[-0, +0,v]
int luaL_typerror (lua_State *L, int narg, const char *tname);
Generates an error with a message like the following:
location: bad argumentnarg to 'func' (tname expected, gotrt)
wherelocation is produced byluaL_where,func is the name of the current function,andrt is the type name of the actual argument.
luaL_unref[-0, +0,-]
void luaL_unref (lua_State *L, int t, int ref);
Releases referenceref from the table at indext(seeluaL_ref).The entry is removed from the table,so that the referred object can be collected.The referenceref is also freed to be used again.
Ifref isLUA_NOREF orLUA_REFNIL,luaL_unref does nothing.
luaL_where[-0, +1,m]
void luaL_where (lua_State *L, int lvl);
Pushes onto the stack a string identifying the current positionof the control at levellvl in the call stack.Typically this string has the following format:
chunkname:currentline:
Level 0 is the running function,level 1 is the function that called the running function,etc.
This function is used to build a prefix for error messages.
The standard Lua libraries provide useful functionsthat are implemented directly through the C API.Some of these functions provide essential services to the language(e.g.,type andgetmetatable);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 thatdeserve an implementation in C (e.g.,table.sort).
All libraries are implemented through the official C APIand are provided as separate C modules.Currently, Lua has the following standard libraries:
Except for the basic and package libraries,each library provides all its functions as fields of a global tableor as methods of its objects.
To have access to these libraries,the C host program should call theluaL_openlibs function,which opens all standard libraries.Alternatively,it can open them individually by callingluaopen_base (for the basic library),luaopen_package (for the package library),luaopen_string (for the string library),luaopen_table (for the table library),luaopen_math (for the mathematical library),luaopen_io (for the I/O library),luaopen_os (for the Operating System library),andluaopen_debug (for the debug library).These functions are declared inlualib.hand should not be called directly:you must call them like any other Lua C function,e.g., by usinglua_call.
The basic library provides some 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.
assert (v [, message])v is false (i.e.,nil orfalse);otherwise, returns all its arguments.message is an error message;when absent, it defaults to "assertion failed!"collectgarbage ([opt [, arg]])This function is a generic interface to the garbage collector.It performs different functions according to its first argument,opt:
arg(larger values mean more steps) in a non-specified way.If you want to control the step sizeyou must experimentally tune the value ofarg.Returnstrue if the step finished a collection cycle.arg as the new value for thepause ofthe collector (see§2.10).Returns the previous value forpause.arg as the new value for thestep multiplier ofthe collector (see§2.10).Returns the previous value forstep.dofile ([filename])dofile executes the contents of the standard input (stdin).Returns all values returned by the chunk.In case of errors,dofile propagates the errorto its caller (that is,dofile does not run in protected mode).error (message [, level])message as the error message.Functionerror never returns.Usually,error adds some information about the error positionat the beginning of the message.Thelevel argument specifies how to get the error position.With level 1 (the default), the error position is where theerror function was called.Level 2 points the error to where the functionthat callederror was called; and so on.Passing a level 0 avoids the addition of error position informationto the message.
_G_G._G = _G).Lua itself does not use this variable;changing its value does not affect any environment,nor vice-versa.(Usesetfenv to change environments.)getfenv ([f])f can be a Lua function or a numberthat specifies the function at that stack level:Level 1 is the function callinggetfenv.If the given function is not a Lua function,or iff is 0,getfenv returns the global environment.The default forf is 1.getmetatable (object)Ifobject does not have a metatable, returnsnil.Otherwise,if the object's metatable has a"__metatable" field,returns the associated value.Otherwise, returns the metatable of the given object.
ipairs (t)Returns three values: an iterator function, the tablet, and 0,so that the construction
for i,v in ipairs(t) dobody end
will iterate over the pairs (1,t[1]), (2,t[2]), ···,up to the first integer key absent from the table.
load (func [, chunkname])Loads a chunk using functionfunc to get its pieces.Each call tofunc must return a string that concatenateswith previous results.A return of an empty string,nil, or no value signals the end of the chunk.
If there are no errors, returns the compiled chunk as a function;otherwise, returnsnil plus the error message.The environment of the returned function is the global environment.
chunkname is used as the chunk name for error messagesand debug information.When absent,it defaults to "=(load)".
loadfile ([filename])Similar toload,but gets the chunk from filefilenameor from the standard input,if no file name is given.
loadstring (string [, chunkname])Similar toload,but gets the chunk from the given string.
To load and run a given string, use the idiom
assert(loadstring(s))()
When absent,chunkname defaults to the given string.
next (table [, index])Allows a program to traverse all fields of a table.Its first argument is a table and its second argumentis an index in this table.next returns the next index of the tableand its associated value.When called withnil as its second argument,next returns an initial indexand its associated value.When called with the last index,or withnil in an empty table,next returnsnil.If the second argument is absent, then it is interpreted asnil.In particular,you can usenext(t) to check whether a table is empty.
The order in which the indices are enumerated is not specified,even for numeric indices.(To traverse a table in numeric order,use a numericalfor or theipairs function.)
The behavior ofnext isundefined 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.
pairs (t)Returns three values: thenext function, the tablet, andnil,so that the construction
for k,v in pairs(t) dobody end
will iterate over all key–value pairs of tablet.
See functionnext for the caveats of modifyingthe table during its traversal.
pcall (f, arg1, ···)Calls functionf withthe given arguments inprotected mode.This means that any error inside f is not propagated;instead,pcall catches the errorand 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,pcall also returns all results from the call,after this first result.In case of any error,pcall returnsfalse plus the error message.
print (···)stdout,using thetostring function to convert them to strings.print is not intended for formatted output,but only as a quick way to show a value,typically for debugging.For formatted output, usestring.format.rawequal (v1, v2)v1 is equal tov2,without invoking any metamethod.Returns a boolean.rawget (table, index)table[index],without invoking any metamethod.table must be a table;index may be any value.rawset (table, index, value)table[index] tovalue,without invoking any metamethod.table must be a table,index any value different fromnil,andvalue any Lua value.This function returnstable.
select (index, ···)Ifindex is a number,returns all arguments after argument numberindex.Otherwise,index must be the string"#",andselect returns the total number of extra arguments it received.
setfenv (f, table)Sets the environment to be used by the given function.f can be a Lua function or a numberthat specifies the function at that stack level:Level 1 is the function callingsetfenv.setfenv returns the given function.
As a special case, whenf is 0setfenv changesthe environment of the running thread.In this case,setfenv returns no values.
setmetatable (table, metatable)Sets the metatable for the given table.(You cannot change the metatable of other types from Lua, only from C.)Ifmetatable isnil,removes the metatable of the given table.If the original metatable has a"__metatable" field,raises an error.
This function returnstable.
tonumber (e [, base])tonumber returns this number;otherwise, it returnsnil.An optional argument specifies the base to interpret the numeral.The base may be any integer between 2 and 36, inclusive.In bases above 10, the letter 'A' (in either upper or lower case)represents 10, 'B' represents 11, and so forth,with 'Z' representing 35.In base 10 (the default), the number can have a decimal part,as well as an optional exponent part (see§2.1).In other bases, only unsigned integers are accepted.
tostring (e)string.format.If the metatable ofe has a"__tostring" field,thentostring calls the corresponding valuewithe as argument,and uses the result of the call as its result.
type (v)nil" (a string, not the valuenil),"number","string","boolean","table","function","thread",and "userdata".unpack (list [, i [, j]])return list[i], list[i+1], ···, list[j]
except that the above code can be written only for a fixed numberof elements.By default,i is 1 andj is the length of the list,as defined by the length operator (see§2.5.5).
_VERSIONLua 5.1".xpcall (f, err)This function is similar topcall,except that you can set a new error handler.
xpcall calls functionf in protected mode,usingerr as the error handler.Any error insidef is not propagated;instead,xpcall catches the error,calls theerr function with the original error object,and returns a status code.Its first result is the status code (a boolean),which is true if the call succeeds without errors.In this case,xpcall also returns all results from the call,after this first result.In case of any error,xpcall returnsfalse plus the result fromerr.
The operations related to coroutines comprise a sub-library ofthe basic library and come inside the tablecoroutine.See§2.11 for a general description of coroutines.
coroutine.create (f)Creates a new coroutine, with bodyf.f must be a Lua function.Returns this new coroutine,an object with type"thread".
coroutine.resume (co [, val1, ···])Starts or continues the execution of coroutineco.The first time you resume a coroutine,it starts running its body.The valuesval1, ··· are passedas the arguments to the body function.If the coroutine has yielded,resume restarts it;the valuesval1, ··· are passedas the results from the yield.
If the coroutine runs without any errors,resume returnstrue plus any values passed toyield(if the coroutine yields) or any values returned by the body function(if the coroutine terminates).If there is any error,resume returnsfalse plus the error message.
coroutine.running ()Returns the running coroutine,ornil when called by the main thread.
coroutine.status (co)Returns the status of coroutineco, as a string:"running",if the coroutine is running (that is, it calledstatus);"suspended", if the coroutine is suspended in a call toyield,or if it has not started running yet;"normal" if the coroutine is active but not running(that is, it has resumed another coroutine);and"dead" if the coroutine has finished its body function,or if it has stopped with an error.
coroutine.wrap (f)Creates a new coroutine, with bodyf.f 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 theextra arguments toresume.Returns the same values returned byresume,except the first boolean.In case of error, propagates the error.
coroutine.yield (···)Suspends the execution of the calling coroutine.The coroutine cannot be running a C function,a metamethod, or an iterator.Any arguments toyield are passed as extra results toresume.
The package library provides basicfacilities for loading and building modules in Lua.It exports two of its functions directly in the global environment:require andmodule.Everything else is exported in a tablepackage.
module (name [, ···])Creates a module.If there is a table inpackage.loaded[name],this table is the module.Otherwise, if there is a global tablet with the given name,this table is the module.Otherwise creates a new tablet andsets it as the value of the globalname andthe value ofpackage.loaded[name].This function also initializest._NAME with the given name,t._M with the module (t itself),andt._PACKAGE with the package name(the full module name minus last component; see below).Finally,module setst as the new environmentof the current function and the new value ofpackage.loaded[name],so thatrequire returnst.
Ifname is a compound name(that is, one with components separated by dots),module creates (or reuses, if they already exist)tables for each component.For instance, ifname isa.b.c,thenmodule stores the module table in fieldc offieldb of globala.
This function can receive optionaloptions afterthe module name,where each option is a function to be applied over the module.
require (modname)Loads the given module.The function starts by looking into thepackage.loaded tableto determine whethermodname is already loaded.If it is, thenrequire returns the value storedatpackage.loaded[modname].Otherwise, it tries to find aloader for the module.
To find a loader,require is guided by thepackage.loaders array.By changing this array,we can change howrequire looks for a module.The following explanation is based on the default configurationforpackage.loaders.
Firstrequire queriespackage.preload[modname].If it has a value,this value (which should be a function) is the loader.Otherwiserequire searches for a Lua loader using thepath stored inpackage.path.If that also fails, it searches for a C loader using thepath stored inpackage.cpath.If that also fails,it tries anall-in-one loader (seepackage.loaders).
Once a loader is found,require calls the loader with a single argument,modname.If the loader returns any value,require assigns the returned value topackage.loaded[modname].If the loader returns no value andhas not assigned any value topackage.loaded[modname],thenrequire assignstrue to this entry.In any case,require returns thefinal value ofpackage.loaded[modname].
If there is any error loading or running the module,or if it cannot find any loader for the module,thenrequire signals an error.
package.cpathThe path used byrequire to search for a C loader.
Lua initializes the C pathpackage.cpath in the same wayit initializes the Lua pathpackage.path,using the environment variableLUA_CPATHor a default path defined inluaconf.h.
package.loadedA table used byrequire to control whichmodules are already loaded.When you require a modulemodname andpackage.loaded[modname] is not false,require simply returns the value stored there.
package.loadersA table used byrequire to control how to load modules.
Each entry in this table is asearcher function.When looking for a module,require calls each of these searchers in ascending order,with the module name (the argument given torequire) as itssole parameter.The function can return another function (the moduleloader)or a string explaining why it did not find that module(ornil if it has nothing to say).Lua initializes this table with four functions.
The first searcher simply looks for a loader in thepackage.preload table.
The second searcher looks for a loader as a Lua library,using the path stored atpackage.path.A path is a sequence oftemplates separated by semicolons.For each template,the searcher will change each interrogationmark in the template byfilename,which is the module name with each dot replaced by a"directory separator" (such as "/" in Unix);then it will try to open the resulting file name.So, for instance, if the Lua path is the string
"./?.lua;./?.lc;/usr/local/?/init.lua"
the search for a Lua file for modulefoowill try to open the files./foo.lua,./foo.lc, and/usr/local/foo/init.lua, in that order.
The third searcher looks for a loader as a C library,using the path given by the variablepackage.cpath.For instance,if the C path is the string
"./?.so;./?.dll;/usr/local/?/init.so"
the searcher for modulefoowill try to open the files./foo.so,./foo.dll,and/usr/local/foo/init.so, in that order.Once it finds a C library,this searcher first uses a dynamic link facility to link theapplication with the library.Then it tries to find a C function inside the library tobe used as the loader.The name of this C function is the string "luaopen_"concatenated with a copy of the module name where each dotis replaced by an underscore.Moreover, if the module name has a hyphen,its prefix up to (and including) the first hyphen is removed.For instance, if the module name isa.v1-b.c,the function name will beluaopen_b_c.
The fourth searcher tries anall-in-one loader.It searches the C path for a library forthe root name of the given module.For instance, when requiringa.b.c,it will search for a C library fora.If found, it looks into it for an open function forthe submodule;in our example, that would beluaopen_a_b_c.With this facility, a package can pack several C submodulesinto one single library,with each submodule keeping its original open function.
package.loadlib (libname, funcname)Dynamically links the host program with the C librarylibname.Inside this library, looks for a functionfuncnameand returns this function as a C function.(So,funcname must follow the protocol (seelua_CFunction)).
This is a low-level function.It completely bypasses the package and module system.Unlikerequire,it does not perform any path searching anddoes not automatically adds extensions.libname must be the complete file name of the C library,including if necessary a path and extension.funcname must be the exact name exported by the C library(which may depend on the C compiler and linker used).
This function is not supported by ANSI C.As such, it is only available on some platforms(Windows, Linux, Mac OS X, Solaris, BSD,plus other Unix systems that support thedlfcn standard).
package.pathThe path used byrequire to search for a Lua loader.
At start-up, Lua initializes this variable withthe value of the environment variableLUA_PATH orwith a default path defined inluaconf.h,if the environment variable is not defined.Any ";;" in the value of the environment variableis replaced by the default path.
package.preloadA table to store loaders for specific modules(seerequire).
package.seeall (module)Sets a metatable formodule withits__index field referring to the global environment,so that this module inherits valuesfrom the global environment.To be used as an option to functionmodule.
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.
The string library provides all its functions inside the tablestring.It also sets a metatable for stringswhere the__index field points to thestring table.Therefore, you can use the string functions in object-oriented style.For instance,string.byte(s, i)can be written ass:byte(i).
The string library assumes one-byte character encodings.
string.byte (s [, i [, j]])s[i],s[i+1], ···,s[j].The default value fori is 1;the default value forj is i.Note that numerical codes are not necessarily portable across platforms.
string.char (···)Note that numerical codes are not necessarily portable across platforms.
string.dump (function)Returns a string containing a binary representation of the given function,so that a laterloadstring on this string returnsa copy of the function.function must be a Lua function without upvalues.
string.find (s, pattern [, init [, plain]])pattern in the strings.If it finds a match, thenfind returns the indices of swhere this occurrence starts and ends;otherwise, it returnsnil.A third, optional numerical argumentinit specifieswhere to start the search;its default value is 1 and can be negative.A value oftrue as a fourth, optional argumentplainturns off the pattern matching facilities,so the function does a plain "find substring" operation,with no characters inpattern being considered "magic".Note that ifplain is given, theninit must be given as well.If the pattern has captures,then in a successful matchthe captured values are also returned,after the two indices.
string.format (formatstring, ···)printf family ofstandard C functions.The only differences are that the options/modifiers*,l,L,n,p,andh are not supportedand that there is an extra option,q.Theq option formats a string in a form suitable to be safely readback by the Lua interpreter:the string is written between double quotes,and all double quotes, newlines, embedded zeros,and backslashes in the stringare correctly escaped when written.For instance, the call string.format('%q', 'a string with "quotes" and \n new line')will produce the string:
"a string with \"quotes\" and \ new line"
The optionsc,d,E,e,f,g,G,i,o,u,X, andx allexpect a number as argument,whereasq ands expect a string.
This function does not accept string valuescontaining embedded zeros,except as arguments to theq option.
string.gmatch (s, pattern)pattern over strings.Ifpattern specifies no captures,then the whole match is produced in each call.As an example, the following loop
s = "hello world from Lua" for w in string.gmatch(s, "%a+") do print(w) end
will iterate over all the words from strings,printing one per line.The next example collects all pairskey=value from thegiven string into a table:
t = {} s = "from=world, to=Lua" for k, v in string.gmatch(s, "(%w+)=(%w+)") do t[k] = v endFor this function, a '^' at the start of a pattern does notwork as an anchor, as this would prevent the iteration.
string.gsub (s, pattern, repl [, n])sin which all (or the firstn, if given)occurrences of thepattern have beenreplaced by a replacement string specified byrepl,which can be a string, a table, or a function.gsub also returns, as its second value,the total number of matches that occurred.Ifrepl is a string, then its value is used for replacement.The character % works as an escape character:any sequence inrepl of the form%n,withn between 1 and 9,stands for the value of then-th captured substring (see below).The sequence%0 stands for the whole match.The sequence%% stands for a single %.
Ifrepl is a table, then the table is queried for every match,using the first capture as the key;if the pattern specifies no captures,then the whole match is used as the key.
Ifrepl is a function, then this function is called every time amatch occurs, with all captured substrings passed as arguments,in order;if the pattern specifies no captures,then the whole match is passed as a sole argument.
If the value returned by the table query or by the function callis a string or a number,then it is used as the replacement string;otherwise, if it isfalse ornil,then there is no replacement(that is, the original match is kept in the string).
Here are some examples:
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 loadstring(s)() end) --> x="4+5 = 9" local t = {name="lua", version="5.1"} x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t) --> x="lua-5.1.tar.gz"string.len (s)"" has length 0.Embedded zeros are counted,so"a\000bc\000" has length 5.string.lower (s)string.match (s, pattern [, init])pattern in the strings.If it finds one, thenmatch returnsthe captures from the pattern;otherwise it returnsnil.Ifpattern specifies no captures,then the whole match is returned.A third, optional numerical argumentinit specifieswhere to start the search;its default value is 1 and can be negative.string.rep (s, n)n copies ofthe strings.string.reverse (s)s reversed.string.sub (s, i [, j])s thatstarts ati and continues untilj;i andj can be negative.Ifj is absent, then it is assumed to be equal to -1(which is the same as the string length).In particular,the callstring.sub(s,1,j) returns a prefix ofswith lengthj,andstring.sub(s, -i) returns a suffix ofswith lengthi.string.upper (s)Acharacter class is used to represent a set of characters.The following combinations are allowed in describing a character class:
^$()%.[]*+-?)represents the characterx itself..: (a dot) represents all characters.%a: represents all letters.%c: represents all control characters.%d: represents all digits.%l: represents all lowercase letters.%p: represents all punctuation characters.%s: represents all space characters.%u: represents all uppercase letters.%w: represents all alphanumeric characters.%x: represents all hexadecimal digits.%z: represents the character with representation 0.%x: (wherex is any non-alphanumeric character)represents the characterx.This is the standard way to escape the magic characters.Any punctuation character (even the non magic)can be preceded by a '%'when used to represent itself in a pattern.[set]:represents the class which is the union of allcharacters inset.A range of characters can be specified byseparating the end characters of the range with a '-'.All classes%x described above can also be used ascomponents inset.All other characters inset represent themselves.For example,[%w_] (or[_%w])represents all alphanumeric characters plus the underscore,[0-7] represents the octal digits,and[0-7%l%-] represents the octal digits plusthe lowercase letters plus the '-' character.The interaction between ranges and classes is not defined.Therefore, patterns like[%a-z] or[a-%%]have no meaning.
[^set]:represents the complement ofset,whereset is interpreted as above.For all classes represented by single letters (%a,%c, etc.),the corresponding uppercase letter represents the complement of the class.For instance,%S represents all non-space characters.
The definitions of letter, space, and other character groupsdepend on the current locale.In particular, the class[a-z] may not be equivalent to%l.
Apattern item can be
*',which matches 0 or more repetitions of characters in the class.These repetition items will always match the longest possible sequence;+',which matches 1 or more repetitions of characters in the class.These repetition items will always match the longest possible sequence;-',which also matches 0 or more repetitions of characters in the class.Unlike '*',these repetition items will always match theshortest possible sequence;?',which matches 0 or 1 occurrence of a character in the class;%n, forn between 1 and 9;such item matches a substring equal to then-th captured string(see below);%bxy, wherex andy are two distinct characters;such item matches strings that start with x, end with y,and where thex andy arebalanced.This means that, if one reads the string from left to right,counting+1 for anx and-1 for ay,the endingy is the firsty where the count reaches 0.For instance, the item%b() matches expressions withbalanced parentheses.Apattern is a sequence of pattern items.A '^' at the beginning of a pattern anchors the match at thebeginning of the subject string.A '$' at the end of a pattern anchors the match at theend of the subject string.At other positions,'^' and '$' have no special meaning and represent themselves.
A pattern can contain sub-patterns enclosed in parentheses;they describecaptures.When a match succeeds, the substrings of the subject stringthat match captures are stored (captured) for future use.Captures are numbered according to their left parentheses.For instance, in the pattern"(a*(.)%w(%s*))",the part of the string matching"a*(.)%w(%s*)" isstored as the first capture (and therefore has number 1);the character matching "." is captured with number 2,and the part matching "%s*" has number 3.
As a special case, the empty capture() capturesthe current string position (a number).For instance, if we apply the pattern"()aa()" on thestring"flaaap", there will be two captures: 3 and 5.
A pattern cannot contain embedded zeros. Use%z instead.
This library provides generic functions for table manipulation.It provides all its functions inside the tabletable.
Most functions in the table library assume that the tablerepresents an array or a list.For these functions, when we talk about the "length" of a tablewe mean the result of the length operator.
table.concat (table [, sep [, i [, j]]])table[i]..sep..table[i+1] ··· sep..table[j].The default value forsep is the empty string,the default fori is 1,and the default forj is the length of the table.Ifi is greater thanj, returns the empty string.table.insert (table, [pos,] value)Inserts elementvalue at positionpos intable,shifting up other elements to open space, if necessary.The default value forpos isn+1,wheren is the length of the table (see§2.5.5),so that a calltable.insert(t,x) insertsx at the endof tablet.
table.maxn (table)Returns the largest positive numerical index of the given table,or zero if the table has no positive numerical indices.(To do its job this function does a linear traversal ofthe whole table.)
table.remove (table [, pos])Removes fromtable the element at positionpos,shifting down other elements to close the space, if necessary.Returns the value of the removed element.The default value forpos isn,wheren is the length of the table,so that a calltable.remove(t) removes the last elementof tablet.
table.sort (table [, comp])table[1] totable[n],wheren is the length of the table.Ifcomp is given,then it must be a function that receives two table elements,and returns truewhen the first is less than the second(so thatnot comp(a[i+1],a[i]) will be true after the sort).Ifcomp is not given,then the standard Lua operator< is used instead.The sort algorithm is not stable;that is, elements considered equal by the given ordermay have their relative positions changed by the sort.
This library is an interface to the standard C math library.It provides all its functions inside the tablemath.
math.abs (x)Returns the absolute value ofx.
math.acos (x)Returns the arc cosine ofx (in radians).
math.asin (x)Returns the arc sine ofx (in radians).
math.atan (x)Returns the arc tangent ofx (in radians).
math.atan2 (y, x)Returns the arc tangent ofy/x (in radians),but uses the signs of both parameters to find thequadrant of the result.(It also handles correctly the case ofx being zero.)
math.ceil (x)Returns the smallest integer larger than or equal tox.
math.cos (x)Returns the cosine ofx (assumed to be in radians).
math.cosh (x)Returns the hyperbolic cosine ofx.
math.deg (x)Returns the anglex (given in radians) in degrees.
math.exp (x)Returns the valueex.
math.floor (x)Returns the largest integer smaller than or equal tox.
math.fmod (x, y)Returns the remainder of the division ofx byythat rounds the quotient towards zero.
math.frexp (x)Returnsm ande such thatx = m2e,e is an integer and the absolute value ofm isin the range[0.5, 1)(or zero whenx is zero).
math.hugeThe valueHUGE_VAL,a value larger than or equal to any other numerical value.
math.ldexp (m, e)Returnsm2e (e should be an integer).
math.log (x)Returns the natural logarithm ofx.
math.log10 (x)Returns the base-10 logarithm ofx.
math.max (x, ···)Returns the maximum value among its arguments.
math.min (x, ···)Returns the minimum value among its arguments.
math.modf (x)Returns two numbers,the integral part ofx and the fractional part ofx.
math.piThe value ofpi.
math.pow (x, y)Returnsxy.(You can also use the expressionx^y to compute this value.)
math.rad (x)Returns the anglex (given in degrees) in radians.
math.random ([m [, n]])This function is an interface to the simplepseudo-random generator functionrand provided by ANSI C.(No guarantees can be given for its statistical properties.)
When called without arguments,returns a uniform pseudo-random real numberin the range[0,1). When called with an integer numberm,math.random returnsa uniform pseudo-random integer in the range[1, m].When called with two integer numbersm andn,math.random returns a uniform pseudo-randominteger in the range[m, n].
math.randomseed (x)Setsx as the "seed"for the pseudo-random generator:equal seeds produce equal sequences of numbers.
math.sin (x)Returns the sine ofx (assumed to be in radians).
math.sinh (x)Returns the hyperbolic sine ofx.
math.sqrt (x)Returns the square root ofx.(You can also use the expressionx^0.5 to compute this value.)
math.tan (x)Returns the tangent ofx (assumed to be in radians).
math.tanh (x)Returns the hyperbolic tangent ofx.
The I/O library provides two different styles for file manipulation.The first one uses implicit file descriptors;that is, there are operations to set a default input file and adefault output file,and all input/output operations are over these default files.The second style uses explicit file descriptors.
When using implicit file descriptors,all operations are supplied by tableio.When using explicit file descriptors,the operationio.open returns a file descriptorand then all operations are supplied as methods of the file descriptor.
The tableio also providesthree predefined file descriptors with their usual meanings from C:io.stdin,io.stdout, andio.stderr.The I/O library never closes these files.
Unless otherwise stated,all I/O functions returnnil on failure(plus an error message as a second result anda system-dependent error code as a third result)and some value different fromnil on success.
io.close ([file])Equivalent tofile:close().Without afile, closes the default output file.
io.flush ()Equivalent tofile:flush over the default output file.
io.input ([file])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.
In case of errors this function raises the error,instead of returning an error code.
io.lines ([filename])Opens the given file name in read modeand returns an iterator function that,each time it is called,returns a new line from the file.Therefore, the construction
for line in io.lines(filename) dobody end
will iterate over all lines of the file.When the iterator function detects the end of file,it returnsnil (to finish the loop) and automatically closes the file.
The callio.lines() (with no file name) is equivalenttoio.input():lines();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.
io.open (filename [, mode])This function opens a file,in the mode specified in the stringmode.It returns a new file handle,or, in case of errors,nil plus an error message.
Themode string can be any of the following:
Themode string can also have a 'b' at the end,which is needed in some systems to open the file in binary mode.This string is exactly what is used in thestandard C functionfopen.
io.output ([file])Similar toio.input, but operates over the default output file.
io.popen (prog [, mode])Starts programprog in a separated process and returnsa file handle that you can use to read data from this program(ifmode is"r", the default)or to write data to this program(ifmode is"w").
This function is system dependent and is not availableon all platforms.
io.read (···)Equivalent toio.input():read.
io.tmpfile ()Returns a handle for a temporary file.This file is opened in update modeand it is automatically removed when the program ends.
io.type (obj)Checks whetherobj is a valid file handle.Returns the string"file" ifobj is an open file handle,"closed file" ifobj is a closed file handle,ornil ifobj is not a file handle.
io.write (···)Equivalent toio.output():write.
file:close ()Closesfile.Note that files are automatically closed whentheir handles are garbage collected,but that takes an unpredictable amount of time to happen.
file:flush ()Saves any written data tofile.
file:lines ()Returns an iterator function that,each time it is called,returns a new line from the file.Therefore, the construction
for line in file:lines() dobody end
will iterate over all lines of the file.(Unlikeio.lines, this function does not close the filewhen the loop ends.)
file:read (···)Reads the filefile,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,ornil if it cannot read data with the specified format.When called without formats,it uses a default format that reads the entire next line(see below).
The available formats are
file:seek ([whence] [, offset])Sets and gets the file position,measured from the beginning of the file,to the position given byoffset plus a basespecified by the stringwhence, as follows:
In case of success, functionseek returns the final file position,measured in bytes from the beginning of the file.If this function fails, it returnsnil,plus a string describing the error.
The default value forwhence is"cur",and foroffset is 0.Therefore, the callfile:seek() returns the currentfile position, without changing it;the callfile:seek("set") sets the position to thebeginning of the file (and returns 0);and the callfile:seek("end") sets the position to theend of the file, and returns its size.
file:setvbuf (mode [, size])Sets the buffering mode for an output file.There are three available modes:
flush the file(seeio.flush)).For the last two cases,sizespecifies the size of the buffer, in bytes.The default is an appropriate size.
file:write (···)Writes the value of each of its arguments tothefile.The arguments must be strings or numbers.To write other values,usetostring orstring.format beforewrite.
This library is implemented through tableos.
os.clock ()Returns an approximation of the amount in seconds of CPU timeused by the program.
os.date ([format [, time]])Returns a string or a table containing date and time,formatted according to the given stringformat.
If thetime argument is present,this is the time to be formatted(see theos.time function for a description of this value).Otherwise,date formats the current time.
Ifformat starts with '!',then the date is formatted in Coordinated Universal Time.After this optional character,ifformat is the string "*t",thendate returns a table with the following fields:year (four digits),month (1--12),day (1--31),hour (0--23),min (0--59),sec (0--61),wday (weekday, Sunday is 1),yday (day of the year),andisdst (daylight saving flag, a boolean).
Ifformat is not "*t",thendate returns the date as a string,formatted according to the same rules as the C functionstrftime.
When called without arguments,date returns a reasonable date and time representation that depends onthe host system and on the current locale(that is,os.date() is equivalent toos.date("%c")).
os.difftime (t2, t1)Returns the number of seconds from timet1 to timet2.In POSIX, Windows, and some other systems,this value is exactlyt2-t1.
os.execute ([command])This function is equivalent to the C functionsystem.It passescommand to be executed by an operating system shell.It returns a status code, which is system-dependent.Ifcommand is absent, then it returns nonzero if a shell is availableand zero otherwise.
os.exit ([code])Calls the C functionexit,with an optionalcode,to terminate the host program.The default value forcode is the success code.
os.getenv (varname)Returns the value of the process environment variablevarname,ornil if the variable is not defined.
os.remove (filename)Deletes the file or directory with the given name.Directories must be empty to be removed.If this function fails, it returnsnil,plus a string describing the error.
os.rename (oldname, newname)Renames file or directory namedoldname tonewname.If this function fails, it returnsnil,plus a string describing the error.
os.setlocale (locale [, category])Sets the current locale of the program.locale is a string specifying a locale;category is an optional string describing which category to change:"all","collate","ctype","monetary","numeric", or"time";the default category is"all".The function returns the name of the new locale,ornil if the request cannot be honored.
Iflocale is the empty string,the current locale is set to an implementation-defined native locale.Iflocale is the string "C",the current locale is set to the standard C locale.
When called withnil as the first argument,this function only returns the name of the current localefor the given category.
os.time ([table])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 fieldsyear,month, andday,and may have fieldshour,min,sec, andisdst(for a description of these fields, see theos.date function).
The returned value is a number, whose meaning depends on your system.In POSIX, Windows, and some other systems, this number counts the numberof seconds since some given start time (the "epoch").In other systems, the meaning is not specified,and the number returned bytime can be used only as an argument todate anddifftime.
os.tmpname ()Returns a string with a file name that canbe used for a temporary file.The file must be explicitly opened before its useand explicitly removed when no longer needed.
On some systems (POSIX),this function also creates a file with that name,to avoid security risks.(Someone else might create the file with wrong permissionsin the time between getting the name and creating the file.)You still have to open the file to use itand to remove it (even if you do not use it).
When possible,you may prefer to useio.tmpfile,which automatically removes the file when the program ends.
This library providesthe functionality of the debug interface to Lua programs.You should exert care when using this library.The functions provided here should be used exclusively for debuggingand similar tasks, such as profiling.Please resist the temptation to use them as ausual programming tool:they can be very slow.Moreover, several of these functionsviolate some assumptions about Lua code(e.g., that variables local to a functioncannot be accessed from outside orthat userdata metatables cannot be changed by Lua code)and therefore can compromise otherwise secure code.
All functions in this library are providedinside thedebug table.All functions that operate over a threadhave an optional first argument which is thethread to operate over.The default is always the current thread.
debug.debug ()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 wordcont finishes this function,so that the caller continues its execution.
Note that commands fordebug.debug are not lexically nestedwithin any function, and so have no direct access to local variables.
debug.getfenv (o)o.debug.gethook ([thread])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 thedebug.sethook function).
debug.getinfo ([thread,] function [, what])Returns a table with information about a function.You can give the function directly,or you can give a number as the value offunction,which means the function running at levelfunction of the call stackof the given thread:level 0 is the current function (getinfo itself);level 1 is the function that calledgetinfo;and so on.Iffunction is a number larger than the number of active functions,thengetinfo returnsnil.
The returned table can contain all the fields returned bylua_getinfo,with the stringwhat describing which fields to fill in.The default forwhat is to get all information available,except the table of valid lines.If present,the option 'f'adds a field namedfunc with the function itself.If present,the option 'L'adds a field namedactivelines with the table ofvalid lines.
For instance, the expressiondebug.getinfo(1,"n").name returnsa table with a name for the current function,if a reasonable name can be found,and the expressiondebug.getinfo(print)returns a table with all available informationabout theprint function.
debug.getlocal ([thread,] level, local)This function returns the name and the value of the local variablewith indexlocal of the function at levellevel of the stack.(The first parameter or local variable has index 1, and so on,until the last active local variable.)The function returnsnil if there is no localvariable with the given index,and raises an error when called with alevel out of range.(You can calldebug.getinfo to check whether the level is valid.)
Variable names starting with '(' (open parentheses)represent internal variables(loop control variables, temporaries, and C function locals).
debug.getmetatable (object)Returns the metatable of the givenobjectornil if it does not have a metatable.
debug.getregistry ()Returns the registry table (see§3.5).
debug.getupvalue (func, up)This function returns the name and the value of the upvaluewith indexup of the functionfunc.The function returnsnil if there is no upvalue with the given index.
debug.setfenv (object, table)Sets the environment of the givenobject to the giventable.Returnsobject.
debug.sethook ([thread,] hook, mask [, count])Sets the given function as a hook.The stringmask and the numbercount describewhen the hook will be called.The string mask may have the following characters,with the given meaning:
"c": the hook is called every time Lua calls a function;"r": the hook is called every time Lua returns from a function;"l": the hook is called every time Lua enters a new line of code.With acount different from zero,the hook is called after everycount instructions.
When called without arguments,debug.sethook turns off the hook.
When the hook is called, its first parameter is a stringdescribing the event that has triggered its call:"call","return" (or"tail return",when simulating a return from a tail call),"line", and"count".For line events,the hook also gets the new line number as its second parameter.Inside a hook,you can callgetinfo with level 2 to get more information aboutthe running function(level 0 is thegetinfo function,and level 1 is the hook function),unless the event is"tail return".In this case, Lua is only simulating the return,and a call togetinfo will return invalid data.
debug.setlocal ([thread,] level, local, value)This function assigns the valuevalue to the local variablewith indexlocal of the function at levellevel of the stack.The function returnsnil if there is no localvariable with the given index,and raises an error when called with alevel out of range.(You can callgetinfo to check whether the level is valid.)Otherwise, it returns the name of the local variable.
debug.setmetatable (object, table)Sets the metatable for the givenobject to the giventable(which can benil).
debug.setupvalue (func, up, value)This function assigns the valuevalue to the upvaluewith indexup of the functionfunc.The function returnsnil if there is no upvaluewith the given index.Otherwise, it returns the name of the upvalue.
debug.traceback ([thread,] [message [, level]])Returns a string with a traceback of the call stack.An optionalmessage string is appendedat the beginning of the traceback.An optionallevel number tells at which levelto start the traceback(default is 1, the function callingtraceback).
Although Lua has been designed as an extension language,to be embedded in a host C program,it is also frequently used as a stand-alone language.An interpreter for Lua as a stand-alone language,called simplylua,is provided with the standard distribution.The stand-alone interpreter includesall standard libraries, including the debug library.Its usage is:
lua [options] [script [args]]
The options are:
-estat: executes stringstat;-lmod: "requires"mod;-i: enters interactive mode after runningscript;-v: prints version information;--: stops handling options;-: executesstdin as a file and stops handling options.After handling its options,lua runs the givenscript,passing to it the givenargs as string arguments.When called without arguments,lua behaves aslua -v -iwhen the standard input (stdin) is a terminal,and aslua - otherwise.
Before running any argument,the interpreter checks for an environment variableLUA_INIT.If its format is@filename,thenlua executes the file.Otherwise,lua executes the string itself.
All options are handled in order, except-i.For instance, an invocation like
$ lua -e'a=1' -e 'print(a)' script.lua
will first seta to 1, then print the value ofa (which is '1'),and finally run the filescript.lua with no arguments.(Here$ is the shell prompt. Your prompt may be different.)
Before starting to run the script,lua collects all arguments in the command linein a global table calledarg.The script name is stored at 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 the options)go to negative indices.For instance, in the call
$ lua -la b.lua t1 t2
the interpreter first runs the filea.lua,then creates a table
arg = { [-2] = "lua", [-1] = "-la", [0] = "b.lua", [1] = "t1", [2] = "t2" }and finally runs the fileb.lua.The script is called witharg[1],arg[2], ···as arguments;it can also access these arguments with the vararg expression '...'.
In interactive mode,if you write an incomplete statement,the interpreter waits for its completionby issuing a different prompt.
If the global variable_PROMPT contains a string,then its value is used as the prompt.Similarly, if the global variable_PROMPT2 contains a string,its value is used as the secondary prompt(issued during incomplete statements).Therefore, both prompts can be changed directly on the command lineor in any Lua programs by assigning to_PROMPT.See the next example:
$ lua -e"_PROMPT='myprompt> '" -i
(The outer pair of quotes is for the shell,the inner pair is for Lua.)Note the use of-i to enter interactive mode;otherwise,the program would just end silentlyright after the assignment to_PROMPT.
To allow the use of Lua as ascript interpreter in Unix systems,the stand-alone interpreter skipsthe first line of a chunk if it starts with#.Therefore, Lua scripts can be made into executable programsby usingchmod +x and the #! form,as in
#!/usr/local/bin/lua
(Of course,the location of the Lua interpreter may be different in your machine.Iflua is in yourPATH,then
#!/usr/bin/env lua
is a more portable solution.)
Here we list the incompatibilities that you may find when moving a programfrom Lua 5.0 to Lua 5.1.You can avoid most of the incompatibilities compiling Lua withappropriate options (see fileluaconf.h).However,all these compatibility options will be removed in the next version of Lua.
arg with atable with the extra arguments to the vararg expression.(See compile-time optionLUA_COMPAT_VARARG inluaconf.h.)[[string]])does not allow nesting.You can use the new syntax ([=[string]=]) in these cases.(See compile-time optionLUA_COMPAT_LSTR inluaconf.h.)string.gfind was renamedstring.gmatch.(See compile-time optionLUA_COMPAT_GFIND inluaconf.h.)string.gsub is called with a function as itsthird argument,whenever this function returnsnil orfalse thereplacement string is the whole match,instead of the empty string.table.setn was deprecated.Functiontable.getn correspondsto the new length operator (#);use the operator instead of the function.(See compile-time optionLUA_COMPAT_GETN inluaconf.h.)loadlib was renamedpackage.loadlib.(See compile-time optionLUA_COMPAT_LOADLIB inluaconf.h.)math.mod was renamedmath.fmod.(See compile-time optionLUA_COMPAT_MOD inluaconf.h.)table.foreach andtable.foreachi are deprecated.You can use a for loop withpairs oripairs instead.require due tothe new module system.However, the new behavior is mostly compatible with the old,butrequire gets the path frompackage.path insteadof fromLUA_PATH.collectgarbage has different arguments.Functiongcinfo is deprecated;usecollectgarbage("count") instead.luaopen_* functions (to open libraries)cannot be called directly,like a regular C function.They must be called through Lua,like a Lua function.lua_open was replaced bylua_newstate toallow the user to set a memory-allocation function.You can useluaL_newstate from the standard library tocreate a state with a standard allocation function(based onrealloc).luaL_getn andluaL_setn(from the auxiliary library) are deprecated.Uselua_objlen instead ofluaL_getnand nothing instead ofluaL_setn.luaL_openlib was replaced byluaL_register.luaL_checkudata now throws an error when the given valueis not a userdata of the expected type.(In Lua 5.0 it returnedNULL.)Here is the complete syntax of Lua in extended BNF.(It does not describe operator precedences.)
chunk ::= {stat [`;´]} [laststat [`;´]]block ::= chunkstat ::= varlist `=´ explist | functioncall |do blockend |while expdo blockend |repeat blockuntil exp |if expthen block {elseif expthen block} [else block]end |for Name `=´ exp `,´ exp [`,´ exp]do blockend |for namelistin explistdo blockend |function funcname funcbody |localfunction Name funcbody |local namelist [`=´ explist] laststat ::=return [explist] |breakfuncname ::= Name {`.´ Name} [`:´ Name]varlist ::= var {`,´ var}var ::= Name | prefixexp `[´ exp `]´ | prefixexp `.´ Name namelist ::= Name {`,´ Name}explist ::= {exp `,´} expexp ::=nil |false |true | Number | String | `...´ | function | prefixexp | tableconstructor | exp binop exp | unop exp prefixexp ::= var | functioncall | `(´ exp `)´functioncall ::= prefixexp args | prefixexp `:´ Name args args ::= `(´ [explist] `)´ | tableconstructor | String function ::=function funcbodyfuncbody ::= `(´ [parlist] `)´ blockendparlist ::= namelist [`,´ `...´] | `...´tableconstructor ::= `{´ [fieldlist] `}´fieldlist ::= field {fieldsep field} [fieldsep]field ::= `[´ exp `]´ `=´ exp | Name `=´ exp | expfieldsep ::= `,´ | `;´binop ::= `+´ | `-´ | `*´ | `/´ | `^´ | `%´ | `..´ | `<´ | `<=´ | `>´ | `>=´ | `==´ | `~=´ |and |orunop ::= `-´ |not | `#´Last update:Thu Aug 29 20:43:58 UTC 2019