Mojmir Svoboda wrote: > * Andrew Haley <aph@xxxxxxxxxx> [2008-12-02 13:32:46 +0000]: > >> It's undefined behaviour: if you make a pointer by taking the address of an >> object you can dereference that pointer. If it's a pointer to an array >> you can also increment it up to one past the end of that array. You >> can only dereference that pointer if it points to the object you >> took the address of. > > acknowledged. > >> In this case it'll probably work as long as there is no padding between >> x, y, and z. >> But it's not well-defined code. > > and that is exactly why i want to fix it. as i pointerd out to John: like > this i have to go to forums and ask whether this is safe on gcc and then > go to msvc and ask what about their compiler. > > for example i asked whether the "union_cast" works on the msvc and still > the responses were quite foggy, so i don't know really even now. That's an interesting one. We advertise that as a fully-supported gcc extension and as far as I know it works everywhere, but you never know, it might not. > i find this programming style quite uncomfortable... > >> OK, I see. I guess you'll have to proceed slowly, but IMO there is no >> point replacing one case of undefined behaviour with another. If you're >> going to fix it, you might as well fix it right. > > okay, i am moving to "do you know a good basic linear algebra" mailing > list :) Okay, your call. I'm not as pessimistic as John fine regarding "throw out the whole mess of code and rewrite from scratch" because I have had to repair code like this, but good luck whatever you decide. Andrew.
