Mike Frysinger wrote: > On Friday 22 February 2008, Michael Kerrisk wrote: >> On Thu, Feb 21, 2008 at 7:59 AM, Mike Frysinger <vapier@xxxxxxxxxx> wrote: >>> On Thursday 21 February 2008, Lasse Kärkkäinen wrote: >>> > The man page says that realloc(ptr, 0) is equivalent to free, even >>> > though it isn't. The text on the man page says >>> > >>> > --- >>> > realloc() changes the size of the memory block pointed to by ptr to >>> > size bytes. The contents will be unchanged to the minimum of the old >>> > and new sizes; newly allocated memory will be uninitialized. If >>> > ptr is NULL, the call is equivalent to malloc(size); if size is >>> > equal to zero, the call is equivalent to free(ptr). Unless ptr is >>> > NULL, it must have been returned by an earlier call to malloc(), >>> > calloc() or realloc(). If the area pointed to was moved, a free(ptr) >>> > is done. [...] >>> > realloc() returns a pointer to the newly allocated memory, which is >>> > suitably aligned for any kind of variable and may be different from >>> > ptr, or NULL if the request fails. If size was equal to 0, either >>> > NULL or a pointer suitable to be passed to free() is returned. If >>> > realloc() fails the original block is left untouched; it is not freed >>> > or moved. >>> >>> i would just word it to say that when realloc() is given a size of 0, it >>> is implementation defined as to the behavior, but it tends to match the >>> behavior of malloc(0) (which too is implementation defined). POSIX and >>> C99 allow both cases to return either a NULL pointer or a "unique" >>> pointer. glibc will return a unique pointer (which cannot actually be >>> used to store anything), but uClibc may return NULL. >>> -mike >> Lasse, thanks for raising this; Mike, thanks for your input. >> >> For man-pages-2.79, I propose to amend the description of realloc() to be: >> >> realloc() changes the size of the memory block pointed to >> by ptr to size bytes. The contents will be unchanged to >> the minimum of the old and new sizes; newly allocated >> memory will be uninitialized. If ptr is NULL, then the >> call is equivalent to malloc(size); if size is equal to >> zero, and ptr is not NULL, then the call is equivalent to >> free(ptr). Unless ptr is NULL, it must have been >> returned by an earlier call to malloc(), calloc() or >> realloc(). If the area pointed to was moved, a free(ptr) >> is done. > > a quick read and it leaves me wondering "what if i call realloc(NULL, 0) ?". > if i re-read it a few times, i can work out that the documentation, by not > saying anything about size in the first statement, implies that malloc(size) > is for all values of size. but perhaps that should be made explicit ? > > ... If ptr is NULL, then the call is equivalent to malloc(size) for all values > of size; ... Yes, good idea. I've made that change. > otherwise, it looks good to me, thanks Thanks for checking it over. Cheers, Michael -- Michael Kerrisk Maintainer of the Linux man-pages project http://www.kernel.org/doc/man-pages/ Want to report a man-pages bug? Look here: http://www.kernel.org/doc/man-pages/reporting_bugs.html - To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
