Re: Lua stack clean

[Sean Conner <sean@...>]

It was thus said that the Great Ranier Vilela once stated:
> Hi Hackers,
> How should the stack look after the calls below?
> 
>     lua_pushinteger(L, p1);
>     lua_pushinteger(L, p2);
>     lua_pushinteger(L, p3);
>     lua_pushnumber(L, p4);
>     lua_call(L, 4, 1);
>     if (lua_isuserdata(L, -1)) {
>         value = lua_tonumber(L, -1);
>         lua_pop(L, 1);
>     }
>     lua_pop(L, lua_gettop(L));
> 
> What is the correct way to clean the stack?

  The lua_call() function is defined as:

	void lua_call(lua_State *L,int nargs,int nresults);

The manual states that lua_call() will remove nargs+1 items from the stack,
and push nresults on the stack.  So for your example:

	lua_pushcfunction(L,myfunc);
	lua_pushinteger(L,p1);
	lua_pushinteger(L,p2);
	lua_pushinteger(L,p3);
	lua_pushinteger(L,p4); /* [1] */
	lua_call(L,4,1);       /* [2] */

At point [1], the stack looks like:

	+index	-index	value
	----------------------
	n-1	-6	previous entries...
	n	-5	myfunc
	n+1	-4	p1
	n+2	-3	p2
	n+3	-2	p3
	n+4	-1	p4

At point [2], the stack will look like:

	+index	-index	value
	----------------------
	n-1	-2	previous entries...
	n	-1	result

In your example, the code should be:

	if (lua_is<type>(L,-1))
	{
	  value = lua_to<type>(L,-1);
	  /* use the value */
	}
	lua_pop(L,1);	/* remove result from stack */

  -spc