C++ - Lua

README.md

Examples of C++ code interacting with Lua. the first one just executes a Lua script, the second one calls a function from the script the third one calls a function from the scripts which calls a function from the c++ code

Howto

Example 1

make ex1
./helloworld

Example 2

make ex2
./stats

Example 3

make ex3
./generator

call_cpp_function.cpp

#include <stdio.h>

extern "C" {
	#include "lua.h"
	#include "lualib.h"
	#include "lauxlib.h"
}

/* the Lua interpreter */
lua_State* L;

class Map {
	private:
	char cells[16];

	public:
	Map() {
		for (int i = 0; i < 16; ++i) {
			cells[i] = ' ';
		}
	}

	void setCell(int i, char val) {
		if (i >= 16) {
			return;
		}
		cells[i] = val;
	}

	void print() {
		for (int i = 0; i < 16; ++i) {
			if (i % 4 == 0) {
				printf("\n");
			}
			printf("%c", cells[i]);
		}
		printf("\n");
	}
};

void generateMap(Map *map, int size) {
	/* the function name */
	lua_getglobal(L, "generateMap");
	/* the first argument */
	lua_pushlightuserdata(L, (void*)map);
	/* the second argument */
	lua_pushinteger(L, size);
	/* call the function with 1 arguments,
	 * return 0 result */
	lua_call(L, 2, 0);
}

int map_setCell(lua_State *L) {
	int n = lua_gettop(L);
	if (n != 3) {
		return 0;
	}

	Map *map = (Map*) lua_touserdata(L, 1);
	int i = lua_tonumber(L, 2);
	char val = lua_tonumber(L, 3);
	map->setCell(i, val);
	return 0;
}

int main(int argc, char *argv[]) {
	/* initialize Lua */
	L = luaL_newstate();

	/* load Lua base libraries */
	luaL_openlibs(L);

	const char *file = "generator.lua";
	Map map = Map();

	/* register our function */
	lua_register(L, "map_setCell", map_setCell);

	/* run the script */
	int res = luaL_dofile(L, file);
	if (res) {
		printf("Script %s not executed: %d\n", file, res);
		printf("cannot run configuration file: %s\n", lua_tostring(L, -1));
	}

	generateMap(&map, 16);

	map.print();

	/* cleanup Lua */
	lua_close(L);

	/* pause */
	printf("Press enter to exit...\n");
	getchar();

	return 0;
}

call_script_function.cpp

#include <stdio.h>

extern "C" {
	#include "lua.h"
	#include "lualib.h"
	#include "lauxlib.h"
}

/* the Lua interpreter */
lua_State* L;

void getRaceInfo(const char* race, int &health, int &intelligence, int &strength) {
	/* the function name */
	lua_getglobal(L, "getStats");

	/* the first argument */
	lua_pushstring(L, race);

	/* call the function with 1 arguments,
	 * return 3 result */
	lua_call(L, 1, 3);

	/* get the result */
	health = (int) lua_tointeger(L, -1);
	intelligence = (int) lua_tointeger(L, -2);
	strength = (int) lua_tointeger(L, -3);
	lua_pop(L, 3);
}

int main(int argc, char *argv[]) {
	/* initialize Lua */
	L = luaL_newstate();

	/* load Lua base libraries */
	luaL_openlibs(L);

	const char *file = "stats.lua";
	/* run the script */
	int res = luaL_dofile(L, file);
	if (res) {
		printf("Script %s not executed: %d\n", file, res);
		printf("cannot run configuration file: %s\n", lua_tostring(L, -1));
	}

	int health = 0,
	    strength = 0,
	    intelligence = 0;
	getRaceInfo("elf", health, intelligence, strength);
	printf(
		"Elves are: %d health, %d intelligence, %d strength\n",
		health, intelligence, strength
	);
	getRaceInfo("human", health, intelligence, strength);
	printf(
		"Humans are: %d health, %d intelligence, %d strength\n",
		health, intelligence, strength
	);
	getRaceInfo("orc", health, intelligence, strength);
	printf(
		"Orcs are: %d health, %d intelligence, %d strength\n",
		health, intelligence, strength
	);
	/* cleanup Lua */
	lua_close(L);

	/* pause */
	printf("Press enter to exit...\n");
	getchar();

	return 0;
}

execute_script.cpp

#include <stdio.h>

extern "C" {
	#include "lua.h"
	#include "lualib.h"
	#include "lauxlib.h"
}

/* the Lua interpreter */
lua_State* L;

int main(int argc, char *argv[]) {
	/* initialize Lua */
	L = luaL_newstate();

	/* load Lua base libraries */
	luaL_openlibs(L);

	const char *file = "helloworld.lua";
	/* run the script */
	int res = luaL_dofile(L, file);
	if (res) {
		printf("Script %s not executed: %d\n", file, res);
		printf("cannot run configuration file: %s\n", lua_tostring(L, -1));
	}

	/* cleanup Lua */
	lua_close(L);

	/* pause */
	printf("Press enter to exit...\n");
	getchar();

	return 0;
}

generator.lua

-- The generateMap function will be called with a map and with a number of cells
-- to generate.
-- The script has access to the map_setCell function, which expects as
-- arguments:
-- - the map
-- - the cell index
-- - the cell value
--
-- This is an amazing procedural map generator...
function generateMap(map, n) -- n is the size of the map
	math.randomseed(os.time())
	for i=0,n-1 do
		map_setCell(map, i, math.random(97, 122)) -- from a to z
	end
end

helloworld.lua

-- Will just be executed...
print "Hello world"

Makefile

.PHONY: ex1 ex2 ex3

INC=
LIB=

LINK=-llua -ldl

all: ex1 ex2 ex3

ex1:
	g++ execute_script.cpp -o helloworld $(LINK) $(INC) $(LIB)

ex2:
	g++ call_script_function.cpp -o stats $(LINK) $(INC) $(LIB)

ex3:
	g++ call_cpp_function.cpp -o generator $(LINK) $(INC) $(LIB)

stats.lua

-- The getStats function is needed with a string as argument and must return
-- 3 integers

races = {}
-- {health, intelligence, strength}
races["elf"] = {30, 100, 50}
races["orc"] = {60, 40, 50}
races["human"] = {50, 70, 40}

function getStats(race)
	return races[race][3], races[race][2], races[race][1]
end