This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 115c. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
2024-09-25
[Accepted as a DR at the February, 2023 meeting.]
Prior to the adoption of paper N3624 (resolving issue 1512), comparison of void* pointers was explicitly unspecified. The current wording of 7.6.9 [expr.rel], however, describes only comparison of “pointers to objects” (paragraphs 4 and 5), but a pointer to void is not a pointer to an object, only an object pointer type (as opposed to a function pointer type). Formally, that means that comparing void* pointers is undefined behavior, which seems undesirable.
As a related note, there is implementation divergence over whether relational comparisons of void* pointers are accepted in constant expressions (when the void* values are converted from pointers that would otherwise be comparable in constant expressions).
CWG 2022-11-11
Paper N3624 erroneously removed support for void* and function pointer relational comparisons. That ought to be restored.
Proposed resolution (approved by CWG 2023-02-09):
Change in 7.6.9 [expr.rel] paragraph 5 as follows:
... Otherwise, the result of each of the operators is unspecified. [ Note: A relational operator applied to unequal function pointers or to unequal pointers to void yields an unspecified result. -- end note ]