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 (v) and getmetatable (object)); 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., 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;
- package library;
- string manipulation;
- table manipulation;
- mathematical functions (sin, log, etc.);
- input and output;
- operating system facilities;
- debug facilities.
Except for the basic and 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, it can open them individually by calling luaopen_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 and the Operating System libraries), and luaopen_debug (for the debug library). These functions are declared in lualib.h and should not be called directly: you must call them like any other Lua C function, e.g., by using lua_call.