On 2012-12-14 14:28:14 +1100, Cameron Simpson wrote: > On 09Sep2012 20:00, Andrew Gaul <and...@gaul.org> wrote: > | - /* suppress GCC aliasing warning */ > | - imap_free_header_data ((void**) (void*) &h.data); > > Pardon my ignorance, but what is (was?) the use of a cast like: > > (void**) (void*) > > A cast of a typed pointer to (void *) when handing it to something > generic like free() I understand, but the above confuses me. I don't > expect C to confuse me.
I suppose that the (void**) was necessary to have the correct type (this is needed when compiling with a C++ compiler such as g++), and (void*) to avoid the GCC aliasing warning (but this was really dangerous, because if there is an aliasing problem, wrong code can be generated). In general, casting a pointer type to another pointer type (except with things like char * and void *) is dangerous, because it may be the source of aliasing problem. See the ISO C standard for more details. -- Vincent Lefèvre <vinc...@vinc17.net> - Web: <http://www.vinc17.net/> 100% accessible validated (X)HTML - Blog: <http://www.vinc17.net/blog/> Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)
