C extension and stack cleanup on error

[David Welch <david.welch@...>]

Hi,

I am trying to write a C extension to lua and I am wondering what the 
rules are when it comes to stack cleanup. 

Specifically I have a function which checks for a field in a table and 
checks its metamethod:

static MyStruct ToStructIndirect(lua_State * L, int index, const char * 
name)
{
   void * p = NULL;
   lua_getfield(L, index, name);
   if (lua_isnil(L, index)) luaL_error(L, "Field `%s' does not exist", 
name);
   p = luaL_checkudata(L, -1, MYSTRUCT_METATABLE);
   lua_pop(L, 1);
   return *(MyStruct*)p;
}

So this function is effectively type checking a tables field and 
returning its value.  If the field doesn't exist then an error
is raised and a nil value is left on the stack.  If the field is there 
but checkudata fails, once again a value is left on the stack.

What actually happens to the value left on the stack?  Can I basically 
just forget about it?