On Jul 08 2023, Paul Smith wrote: > Unfortunately because I am using limits.h from the clang intrinsics / > resource directory (else many other things break), _POSIX_SEM_VALUE_MAX > is not defined.
POSIX requires conforming implementations to define _POSIX_SEM_VALUE_MAX. > I can't quite figure out why, and my attempts to generate preprocessor > output to track it down through the #include / #define maze have > failed. But the error I get (from clangd) suggests I want to be using > _SC_SEM_VALUE_MAX and indeed if I make that change it works. _SC_SEM_VALUE_MAX is related, but has a different role. It is the argument to sysconf to retrieve the runtime value of SEM_VALUE_MAX. > Or at least expanding the above to use it as a last resort, as in: > > #if defined(SEM_VALUE_MAX) > static constexpr ptrdiff_t _S_max = SEM_VALUE_MAX; > #elif defined(_POSIX_SEM_VALUE_MAX) > static constexpr ptrdiff_t _S_max = _POSIX_SEM_VALUE_MAX; > #else > static constexpr ptrdiff_t _S_max = _SC_SEM_VALUE_MAX; That needs to be sysconf (_SC_SEM_VALUE_MAX), and thus is not suitable for a constexpr. -- Andreas Schwab, sch...@linux-m68k.org GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510 2552 DF73 E780 A9DA AEC1 "And now for something completely different."
