On 2025-06-19 22:55:32 -0700, Paul Eggert wrote: > Thanks for the detailed summary. Here are a few more details. In this > summary "realloc(p,0)" assumes p is nonnull. > > As I understand it: > > (a) These guarantees are for compatibility with glibc 2.2+. In older glibc > versions realloc(p,0) behaved like (free(p),malloc(0)). > > (b) Ulrich Drepper changed glibc 2.2 realloc(p,0) after Andreas Jaeger told > him[1] that draft C99 and UNIX98 required realloc(p,0) to free(p). > Conformance to these standards was the only motivation given for the glibc > change.
BTW, at that time, the lack of consistency between realloc(...,0) and malloc(0) was known and not regarded as an issue: https://sourceware.org/pipermail/libc-alpha/1999-April/002398.html > (c) Ulrich's change[2] to glibc was to make realloc(p,0) equivalent to > (free(p),0). Draft C99 and UNIX98 did not require this, and Ulrich could > have made realloc(p,0) continue to be equivalent to (free(p),malloc(0)). [...] Indeed, at least the N843 C9x draft (August 1998) did not require this. It had new text, saying: If the realloc function returns a null pointer when size is zero and ptr is not a null pointer, the object it pointed to has been freed. There are also some changes for realloc proposed in https://www.open-std.org/jtc1/sc22/wg14/www/docs/n868.htm (Final CD Ballot for FCD 9899), but nothing for the case of size = 0. -- Vincent Lefèvre <vinc...@vinc17.net> - Web: <https://www.vinc17.net/> 100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/> Work: CR INRIA - computer arithmetic / Pascaline project (LIP, ENS-Lyon)
