Embedding Lua Scripts into C programs

Readme.md

Embedding Lua into C Programs

• This code was run on macOS with lua version 5.3.5 install via brew brew install lua
• The shows an example calling lua from C and calling C from lua

Expected output:

This line in directly from C

lua init
lua update: 0.0
lua draw
lua update: 0.33333333333333
lua draw
lua update: 0.66666666666667
lua draw
lua update: 1.0
lua draw
lua update: 1.3333333333333
lua draw
lua update: 1.6666666666667
lua draw
lua update: 2.0
lua draw
lua update: 2.3333333333333
lua draw
lua update: 2.6666666666667
lua draw
lua update: 3.0
lua draw
lua update: 3.3333333333333
lua draw
lua update: 3.6666666666667
lua draw
lua update: 4.0
lua draw
lua update: 4.3333333333333
lua draw
lua update: 4.6666666666667
lua draw
lua update: 5.0
lua draw
lua update: 5.3333333333333
lua draw
lua update: 5.6666666666667
lua draw
lua update: 6.0
lua draw

Back to C again

Embed_lua.c

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

int count = 0;

void error (lua_State *L, const char *fmt, ...) {
    va_list argp;
    va_start(argp, fmt);
    vfprintf(stderr, fmt, argp);
    va_end(argp);
    lua_close(L);
    exit(EXIT_FAILURE);
}

void l_call(lua_State *L, const char *f) {
    lua_getglobal(L, f);
    
    if (lua_pcall(L, 0, 1, 0) != LUA_OK) {
        error(L, "error running function 'init': %s", lua_tostring(L, -1));
    }
}

static int l_get_count(lua_State *L) {
    lua_pushnumber(L, count);
    count++;
    return 1;
}

int main (void) {
    char buff[256];
    int error;
    lua_State *L =luaL_newstate();
    luaL_openlibs(L);
    lua_pushcfunction(L, l_get_count);
    lua_setglobal(L, "count");
    printf("This line in directly from C\n\n");
    error = luaL_loadfile(L, "script.lua") || lua_pcall(L, 0, 0, 0);
    if (error) {
        fprintf(stderr, "%s", lua_tostring(L, -1));
        lua_pop(L, 1);  /* pop error message from the stack */
    }

    l_call(L, "init");

    int i;
    while (i < 20) {
        l_call(L, "update");
        l_call(L, "draw");
        i++;
    }

    printf("\nBack to C again\n\n");
    lua_close(L);
    return 0;
}

Makefile

build:
	cc -o embed Embed_lua.c -I/usr/local/include/lua -llua

script.lua

function init()
    print("lua init")
end

function update()
    local c = count()
    c = c/3
    print("lua update: "..c)
end

function draw()
    print("lua draw")
end