What is lua_pcall doing here?

Question

I am trying to learn lua and I seem to be stuck here.

For some reason the following code doesn't actually run the lua file.

int main()
{
    lua_State* L = luaL_newstate();
    luaL_openlibs(L);

    int width = 0;
    int height = 0;

    if(!luaL_loadfile(L, "./src/luaconf.lua") || !lua_pcall(L, 0, 0, 0)) 
    {
            lua_getglobal(L, "width");
            lua_getglobal(L, "height");

            if(!lua_isnumber(L, -2)) 
            {
                    luaL_error(L, "width isn't a number");
            }
            else
            {
                    width = lua_tointeger(L, -2);
            }

            if(!lua_isnumber(L, -1)) 
            {
                    luaL_error(L, "height isn't a number");
            }
            else
            {
                    height = lua_tointeger(L, -1);
            }
    }

    printf("%i x %i", width, height);

    return 0;

 }

I know that if I change if(!luaL_loadfile(L, "./src/luaconf.lua") || !lua_pcall(L, 0, 0, 0) to if(luaL_dofile(L, "./src/luaconf.lua")) it would work but I want to know why the above code doesn't work.

Shouldn't lua_pcall run the lua code? If not why not?

luaconf.lua

width = 500
height = 40

Answer 1

Note that in the code:

if(!luaL_loadfile(L, "./src/luaconf.lua") || !lua_pcall(L, 0, 0, 0)) 

if luaL_loadfile succeeds, it returns LUA_OK which has the value of 0 , so the left operand of || evaluates as 1 , according to short circuit, lua_pcall won't be executed.

So what you want is probably:

if ((luaL_loadfile(L, "./src/luaconf.lua") || lua_pcall(L, 0, 0, 0))
{
    //error handle
}
else
{
    //normal handle
}