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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.type()
  • References/Lua/Lua/Standard Libraries/Mathematical Functions

math.type (x) Returns "integer" if x is an integer, "float" if it is a float, or nil if x is not a number.

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

loadfile ([filename [, mode [, env]]]) Similar to load, but gets the chunk

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string.len()
  • References/Lua/Lua/Standard Libraries/String Manipulation

string.len (s)"""a\000bc\000"

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

math.rad (x) Converts the angle x from degrees to radians.

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

file:setvbuf (mode [, size]) Sets the buffering mode for an output file. There are three available modes: "no": no buffering; the result of

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debug.getlocal()
  • References/Lua/Lua/Standard Libraries/The Debug Library

debug.getlocal ([thread,] f, local) This function returns the name and the value of the local variable with index local of the function at level f of

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

load (chunk [, chunkname [, mode [, env]]]) Loads a chunk. If chunk is a string, the chunk is this string. If chunk is a function, load

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debug.sethook()
  • References/Lua/Lua/Standard Libraries/The Debug Library

debug.sethook ([thread,] hook, mask [, count]) Sets the given function as a hook. The string mask and the number count describe when the hook will be

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string.packsize()
  • References/Lua/Lua/Standard Libraries/String Manipulation

string.packsize (fmt) Returns the size of a string resulting from string

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

error (message [, level])messageerror Usually, error adds some information about the error position at the beginning of the message, if

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