This is the goto example: https://markshroyer.com/2012/06/c-both-true-and-false/
On Wed, Sep 16, 2026 at 12:39 PM Bryan Green <[email protected]> wrote: > If we are pulling in stdbool.h and this is C11...that is undefined > behavior and because it wasn't validly initialized it is an > indeterminate-value read...which means for optimization that the compiler > is within its right to assume it is a 0 or 1 and could test it in different > ways depending on the surrounding code (nonzero test, compare to 1, etc). > > On Wed, Sep 16, 2026 at 12:34 PM Jacob Champion < > [email protected]> wrote: > >> On Wed, Sep 16, 2026 at 10:14 AM Tom Lane <[email protected]> wrote: >> > However, what I'm seeing as I trace through the crash on >> > longfin is that nulls[19] has a value that's not either 0 or 1 (not >> > too surprising), and somehow heap_compute_data_size is interpreting >> > that as "true" while fill_val is reading it as "false". According >> > to my understanding of the C standard, fill_val is in the wrong here. >> >> Is the _Bool representation allowed to contain anything but zero/false >> or one/true? I thought that was undefined behavior. (IIRC, mixing C++ >> bool with our C89-era bool definition suffered from similar UB >> excitement.) >> >> --Jacob >> >> >>
