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, it will fall back to the most recent C standard version known by that glibc version, which is probably what you want. -- Joseph S. Myers [email protected]
