On Thu, 21 Jan 2010, Jamie Lokier wrote: > Markus Armbruster wrote: > > malc <av1...@comtv.ru> writes: > > > > > On Tue, 29 Dec 2009, Jamie Lokier wrote: > > > > > >> malc wrote: > > >> > On Mon, 28 Dec 2009, Jamie Lokier wrote: > > >> > > > >> > > Aurelien Jarno wrote: > > >> > > > This fixes the loading of a stripped kernel with zero malloc > > >> > > > disabled. > > >> > > > > >> > > *Raises an eyebrow* > > >> > > > > >> > > Even though there's different perspectives over whether > > >> > > qemu_malloc(0) > > >> > > should be allowed, inherited from ambiguity over malloc(0), > > >> > > realloc(p,0) has always had a standard, well-defined meaning. > > >> > > > >> > No. > > >> > http://groups.google.com/group/comp.std.c/browse_thread/thread/4e9af8847613d71f/6f75ad22e0768a0b?q=realloc++group:comp.std.c#6f75ad22e0768a0b > > >> > > >> Wow, thanks for that. It's a real surprise. Looks like C99's own > > >> rationale is not consistent with itself on the subject, and differs > > >> from C90 where the "standard, well-defined meaning" I referred to was > > >> defined. > > > > > > Yep. > > > > No, this is a misinterpretation of the C99 standard, made possible by > > its poor wording. The C99 Rationale is perfectly clear, though: > > > > 7.20.3.4 The realloc function > > > > A null first argument is permissible. If the first argument is not > > null, and the second argument is 0, then the call frees the memory > > pointed to by the first argument, and a null argument may be > > returned; [...] > > The rationale above does not match C89 behaviour. It says the call > frees the memory, but it does not forbid the call from then proceeding > to do the same as malloc(0) and return a non-NULL pointer. It's quite > explicit: a null argument *may* be returned. Which means the > rationale does not require realloc(p,0) to do the same as C89, which > always frees the memory and doesn't allocate anything. > > > This is hardly surprising, because anything else would break working C89 > > programs, and that would squarely contradict the standard's mission, > > Understood. But it doesn't really matter what's intended or what's > misinterpreted. If there are any significant implementations out > there based on the "misinterpretation", or even based on the > rationale, that's enough of a reason to not depend on realloc(p,0). >
My sentiment exactly. An example: Dinkum Unabridged Library was certified by Perennial (http://peren.com/pages/aboutus_set.htm) to conform to ISO/IEC 9899:1999. Documentation for realloc: http://www.dinkumware.com/manuals/?manual=compleat&Search=realloc&page=stdlib.html#realloc Hallvard B Furuseth analysis fully applies i believe... -- mailto:av1...@comtv.ru
