library.lua

function boo()
	print "boo"
end

function add(x, y)
	return x + y
end

main.c

#include <lua.h>
#include <lualib.h>
#include <lauxlib.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#pragma comment(lib, "lua53")

struct {
	char name[20];
	int hp;
	int x;
	int y;
} player;

int player_get_info(lua_State *L) {
	lua_pushinteger(L, player.hp);
	lua_pushinteger(L, player.x);
	lua_pushinteger(L, player.y);
	lua_pushlstring(L, player.name, 20);
	return 4;
}

void scripting_start(lua_State **state) {

	*state = luaL_newstate();

	luaL_openlibs(*state);

	lua_register(*state, "player_get_info", player_get_info);
}

void scripting_stop(lua_State *state) {
	lua_close(state);
}

int scripting_runfile(lua_State *state, const char *filename) {

	int status = luaL_loadfile(state, filename);
	if (status) {
		fprintf(stderr, "Couldn't load file: %s\n", lua_tostring(state, -1));
		return 1;
	}

	int result = lua_pcall(state, 0, LUA_MULTRET, 0);
	if (result) {
		fprintf(stderr, "Failed to run script: %s\n", lua_tostring(state, -1));
		return 1;
	}

	return 0;
}

// load a script from a string
int scripting_runscript(lua_State *state, const char *name, const char *script, size_t len) {
	
	int status = luaL_loadbuffer(state, script, len, name);
	if (status) {
		fprintf(stderr, "Couldn't load script: %s\n", lua_tostring(state, -1));
		return 1;
	}

	int result = lua_pcall(state, 0, LUA_MULTRET, 0);
	if (result) {
		fprintf(stderr, "Failed to run script: %s\n", lua_tostring(state, -1));
		return 1;
	}

	return 0;
}
int add(lua_State *state, int x, int y)
{
	lua_pushinteger(state, x);
	lua_pushinteger(state, y);
	lua_call(state, "add", 2);  /* call Lua function */
	//strcpy(s, lua_getstring(lua_getresult(1)));  /* copy result back to 's' */

}

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

	player.x = 10;
	player.y = 20;
	player.hp = 100;
	strcpy(player.name, "Player");

	lua_State *state;

	scripting_start(&state);

	// load a script from disk
	scripting_runfile(state, "scripts/library.lua");

	// load a script from memory
	const char inline_script[] = "print \"hello from inline script\"";
	scripting_runscript(state, "inline.lua", inline_script, strlen(inline_script));

	scripting_runfile(state, "scripts/test.lua");
	scripting_stop(state);

	return 0;
}

test.lua

print "hello"

x, y, hp, name = player_get_info()

print (name)

boo()