Per Inge Mathisen schreef: > On Mon, Mar 10, 2008 at 9:18 PM, Giel van Schijndel <[EMAIL PROTECTED]> wrote: >> > You will find that passing along a field belonging to >> > an object (psDroid->baseObject) and passing along an enlarged version >> > of an object ((BASE_OBJECT *)psDroid) are two very different things, >> > and to code to handle it has to be written differently. Eg BASE_OBJECT >> > *psTile->psObject cannot be cast back to DROID*, you need a pointer >> > back to the parent to do that, either by a void pointer or a union - >> > either way it gets ugly, IMHO. >> >> Actually in this example case you can just downcast baseObj to a DROID* >> without any problem (provided you checked the type properly), as both >> baseObj and droidObj start at the same address. > > Just to nitpick a little bit. You cannot downcast, since the memory > address points to the child object. Take this example:
Erm to use this example:
typedef struct
{
some_type X;
} a_new_type;
a_new_type Y;
Now my point is that the starting address of Y is _exactly_ the same to
that of Y.X because Y.X is the first struct member of Y.
--
Giel
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