Re: New Lua C API Tutorial

[Tom N Harris <telliamed@...>]

On 10/31/2011 06:48 AM, Patrick Rapin wrote:
> In the "Functions" chapter, you give the following example :
>
> int move_player (lua_Stack * ls)
> {
> 	const int xoffset = lua_tointeger(ls, 1);
> 	const int yoffset = lua_tointeger(ls, 2);
> 	lua_settop(ls, 0);       //<-- I am talking about this line
> 	
... snip ...
> You say it is good practice to maintain a nice clean stack and
> recommend to use lua_settop(0). Well certainly not in such a
> situation.

Not to mention that the function is assuming the stack has 2 valid 
values on it. I think the properly defensive function would begin:

    lua_settop(ls, 2);       // expect two arguments
    const int xoffset = lua_tointeger(ls, 1);
    const int yoffset = lua_tointeger(ls, 2);

As you say, Lua will clean up the stack afterwards, so the function need 
not pop the consumed values. And of course, if the arguments are 
mandatory then you should also be checking for nil.

--
- tom
telliamed@whoopdedo.org