Question

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:

• 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 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.