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 ```

Accepted Answer

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
}
```

What is lua_pcall doing here?

Solution

Problem