How to get the maximal signal number on a posix-compatible way?

Question

Update: the whole problem was on a bad line, it was a syntax error in my c++ code.

On Linux I've found

#define _NSIG            64

in asm-generic/signal.h, but I think including that wouldn't be a really standard-compliant solution.

signal.h in the glibc uses this _NSIG definition, but it hides behind a complex structure of include-define-undef-ifdef and similar preprocessor commands, and it isn't a visible symbol after a simple #include <signal.h>.

I am simply looking for a way to find the maximal signum I can give to sigaction and similar signal handling api calls, including the realtime signals. Is it somehow possible?

Answer 1

The POSIX.1-2001 standard requires the definition of SIGRTMIN and SIGRTMAX. On linux they are defined using _NSIG.

To be POSIX compliant, use the above definitions instead of directly using _NSIG

#include <stdio.h>
#include <signal.h>

int main() {
  printf("%lu\n", SIGRTMAX);
  return 0;
}

This prints 64 on my system when compiled using gcc main.cpp