There's a little more reasoning in the associated C2x proposal N2464 [0]: > [DR 400] was resolved by loosening the requirements in the standard to allow for th

There's a little more reasoning in the associated C2x proposal N2464 [0]: > [DR 400] was resolved by loosening the requirements in the standard to allow for the existing range of implementations and included in C17. > N2438 Clarification Request requested further clarification [...] > Discussion at the Ithaca meeting and on the mailing list suggested that a call to realloc with a size of 0 be classified as undefined behavior. > [snip] > Classifying a call to realloc with a size of 0 as undefined behavior would allow POSIX to define the otherwise undefined behavior however they please. [0]: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2464.pdf https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2464.pdf