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., sort).
All libraries are implemented through the official C API and 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 table or as methods of its objects.
To have access to these libraries,
the C host program must call
luaL_openlibs,
which open 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.