Hi Joseph, On 2026-06-16T21:52:57+0000, Joseph Myers wrote: > On Tue, 16 Jun 2026, Alejandro Colomar via Gcc wrote: > > > If one uses a modern GCC with an old glibc (which doesn't know C23), > > then, using -std=c23 will be problematic: the compiler will enable C23 > > language mode, but the library will entirely and silently ignore > > _ISOC23_SOURCE, because it doesn't know about it, thus falling back to > > C89 mode (I guess), and thus will for example enable things like > > gets(3). > > Since the relevant checks in features.h are based on __STDC_VERSION__ > > something or __STDC_VERSION__ >= something, Ahh, yup, it has || for either _ISOCxx_SOURCE or __STDC_VERSION__. That makes sense. > it will fall back to the most > recent C standard version known by that glibc version, which is probably > what you want. Hmmm, it is. Then it's all fine. Thanks! Cheers, Alex --