c调用lua函数
double f (double x, double y) { 
    double z; 
    /* push functions and arguments */ 
     lua_getglobal(L, "f"); /* function to be called */
     lua_pushnumber(L, x); /* push 1st argument */
     lua_pushnumber(L, y); /* push 2nd argument */
    /* do the call (2 arguments, 1 result) */ 
    if (lua_pcall(L, 2, 1, 0) != 0) 
     error(L, "error running function `f': %s", 
     lua_tostring(L, -1)); 
    /* retrieve result */ 
    if (!lua_isnumber(L, -1)) 
     error(L, "function `f' must return a number"); 
     z = lua_tonumber(L, -1); 
     lua_pop(L, 1); /* pop returned value */
    return z; 
}

lua调用c函数
lua_pushcfunction(l, l_sin) //获取c函数的指针，并在lua中创建一个function类型的值来表示这个函数
lua_setglobal(l, "mysin")    //赋值给全局变量mysin

static const struct luaL_reg mylib [] = { 
 {"dir", l_dir}, 
 {NULL, NULL} /* sentinel */
};

int luaopen_mylib (lua_State *L) { 
 luaL_openlib(L, "mylib", mylib, 0); 
return 1; 
}

向lua中注册类

向lua中注册类对象

向lua中注册全局对象