Library With Userdata Example

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Description

This example is similar to UserDataExample and UserDataWithPointerExample, except it is updated for the Lua 5.2 API.

Lua input file

function foo()

    local obj = MyLib.MakeObj()

    obj:method()

end



foo()

        

C code

#include <lua.h>

#include <lualib.h>

#include <lauxlib.h>



const static char *Obj_typename = "ObjTypename";



void check_Obj(lua_State *L, int i){

	luaL_checkudata(L, i, Obj_typename);

}



int MyLib_MakeObj(lua_State *L){

	printf("In MyLib_MakeObj\n");

	lua_newuserdata(L, sizeof(int*));

	luaL_setmetatable(L, Obj_typename);

	return 1;

}

int Obj__gc(lua_State *L){

	printf("In Obj__gc\n");

	return 0;

}

int Obj_method(lua_State *L){

	printf("In Obj_method\n");

	check_Obj(L, 1);

	return 0;

}



int luaopen_MyLib(lua_State *L){

	static const luaL_Reg Obj_lib[] = {

		{ "method", &Obj_method },

		{ NULL, NULL }

	};

	

	static const luaL_Reg MyLib_lib[] = {

		{ "MakeObj", &MyLib_MakeObj },

		{ NULL, NULL }

	};

	

	luaL_newlib(L, MyLib_lib);



	// Stack: MyLib

	luaL_newmetatable(L, Obj_typename); // Stack: MyLib meta

	luaL_newlib(L, Obj_lib);

	lua_setfield(L, -2, "__index"); // Stack: MyLib meta

	

	lua_pushstring(L, "__gc");

	lua_pushcfunction(L, Obj__gc); // Stack: MyLib meta "__gc" fptr

	lua_settable(L, -3); // Stack: MyLib meta

	lua_pop(L, 1); // Stack: MyLib

	

	return 1;

}



int main(int argc, char *argv[]){

	int iarg;

	lua_State *L = luaL_newstate();

	luaL_openlibs(L);

	

	luaL_requiref(L, "MyLib", &luaopen_MyLib, 1);

	lua_pop(L, 1); // requiref leaves the library table on the stack



	printf(" stack top: %d\n", lua_gettop(L));

	for(iarg = 1; iarg < argc; ++iarg){

		int s = luaL_loadfile(L, argv[iarg]);



		if(s != 0){

			fprintf(stderr, "Could not load: %s\n", argv[iarg]);

			continue;

		}

		s = lua_pcall(L, 0, 0, 0);

		if(s != 0){

			fprintf(stderr, "Error: %s\n", lua_tostring(L, -1));

			lua_pop(L, 1);

		}

	}

	lua_close(L);

	return 0;

}

        

Compiling the code

gcc -I/usr/include/lua5.2 ex.c -llua5.2 -o lualibex

        

Expected output

 stack top: 0

In MyLib_MakeObj

In Obj_method

In Obj__gc