Hi Ulli, Section 5.2.10-3 states that this usage is implementation defined, i.e. not portable. That said, if we refer to Sutter[2005] section 92. After he finishes with how bad it is to lie to the compiler he recommends that if it's absolutely necessary it should be done via a void pointer. Given that MHO would be that if the cast really is unavoidable then gil_reinterpret_cast is the correct way to do it (by the book). As for your other example -> rgb16s_t * rgbdata = (rgb16s_t *)imagedata; That's not even C++ is it :-) Matt

[mailto:boost-bounces@lists.boost.org] On Behalf Of Ullrich Koethe Hi again,

since there was no response to my earlier questions about undefined behavior, I'd like to bring this up again:

GIL makes extensive use of reinterpret_cast and gil_reinterpret_cast. The former is, for example, used in code similar to the following:

short * imagedata = new short[3*image_size]; rgb16s_t * rgbdata = (rgb16s_t *)imagedata;

gil_reinterpret_cast is defined as

template <class OutPtr, class In> OutPtr gil_reinterpret_cast(In * p) { return static_cast<OutPtr>(static_cast<void *>(p)); }

I suspect that undefined behavior results in both cases. IIRC, there is no guarantee that the memory layout of an rgb array is equal to that of a corresponding scalar array with three times as many elements (although this will probably work in practice). Likewise, a static_cast from void * is only allowed back to the original pointer type, not to a different type.

Can someone more familiar with the fine points of C++ confirm these suspicions? If they are true, I think the issue should be resolved before inclusion into boost.

Regards Ulli --

________________________________________________________________ | | | Ullrich Koethe Universitaet Hamburg / University of Hamburg | | FB Informatik / Dept. of Informatics | | AB Kognitive Systeme / Cognitive Systems Group | | | | Phone: +49 (0)40 42883-2573 Vogt-Koelln-Str. 30 | | Fax: +49 (0)40 42883-2572 D - 22527 Hamburg | | Email: u.koethe@computer.org Germany | | koethe@informatik.uni-hamburg.de | | WWW: http://kogs-www.informatik.uni-hamburg.de/~koethe/ | |________________________________________________________________| _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost

Scanned by McAfee GroupShield {X3BTB534}