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6 – Standard Libraries

The standard Lua libraries provide useful functions that are implemented directly through the C API. Some of these functions provide essential services to the language (e.g., type and getmetatable); others provide access to "outside" services (e.g., I/O); and others could be implemented in Lua itself, but are quite useful or have critical performance requirements that deserve an implementation in C (e.g., table.sort).

All libraries are implemented through the official C API and are provided as separate C modules. Currently, Lua has the following standard libraries:

  • basic library (§6.1);
  • coroutine library (§6.2);
  • package library (§6.3);
  • string manipulation (§6.4);
  • basic UTF-8 support (§6.5);
  • table manipulation (§6.6);
  • mathematical functions (§6.7) (sin, log, etc.);
  • input and output (§6.8);
  • operating system facilities (§6.9);
  • debug facilities (§6.10).

Except for the basic and the package libraries, each library provides all its functions as fields of a global table or as methods of its objects.

To have access to these libraries, the C host program should call the luaL_openlibs function, which opens all standard libraries. Alternatively, the host program can open them individually by using luaL_requiref to call luaopen_base (for the basic library), luaopen_package (for the package library), luaopen_coroutine (for the coroutine library), luaopen_string (for the string library), luaopen_utf8 (for the UTF8 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), and luaopen_debug (for the debug library). These functions are declared in lualib.h.

math.max()
  • References/Lua/Lua/Standard Libraries/Mathematical Functions

math.max (x, ···) Returns the argument with the maximum value, according to the Lua operator <. (integer/float)

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rawlen()
  • References/Lua/Lua/Standard Libraries/Basic Functions

rawlen (v)v__len

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math.fmod()
  • References/Lua/Lua/Standard Libraries/Mathematical Functions

math.fmod (x, y) Returns the remainder of the division of x by y that rounds the quotient towards zero. (integer/float)

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_G
  • References/Lua/Lua/Standard Libraries/Basic Functions

_G§2.2

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utf8.offset()
  • References/Lua/Lua/Standard Libraries/UTF-8 Support

utf8.offset (s, n [, i])nsiniin#s + 1utf8.offset(s, -n)nnil

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math.ult()
  • References/Lua/Lua/Standard Libraries/Mathematical Functions

math.ult (m, n) Returns a boolean, true if and only if integer m is below integer n when they are compared as unsigned integers.

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file:lines()
  • References/Lua/Lua/Standard Libraries/Input and Output Facilities

file:lines (···) Returns an iterator function that, each time it is called, reads the file according to the given formats. When no format is given, uses "l" as a

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io.write()
  • References/Lua/Lua/Standard Libraries/Input and Output Facilities

io.write (···) Equivalent to io.output():write(···).

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package.loaded
  • References/Lua/Lua/Standard Libraries/Modules

package.loaded A table used by require to control which modules are already loaded

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require()
  • References/Lua/Lua/Standard Libraries/Modules

require (modname) Loads the given module. The function starts by looking into the package

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