7.3 – Changes in the API

• The luaopen_* functions (to open libraries) cannot be called directly, like a regular C function. They must be called through Lua, like a Lua function.
• Function lua_open was replaced by lua_newstate to allow the user to set a memory-allocation function. You can use luaL_newstate from the standard library to create a state with a standard allocation function (based on realloc).
• Functions luaL_getn and luaL_setn (from the auxiliary library) are deprecated. Use lua_objlen instead of luaL_getn and nothing instead of luaL_setn.
• Function luaL_openlib was replaced by luaL_register.
• Function luaL_checkudata now throws an error when the given value is not a userdata of the expected type. (In Lua 5.0 it returned NULL.)