Comment by jlokier

Not really. The two languages are similar on this. The 'volatile' before 'sig_atomic_t' is still required in C++ for the same reasons as C. You can access non-volatile sig_atomic_t variables in C too, but in both languages that's not enough for the signalling that type exists for, so you have to use 'volatile sig_atomic_t', in C and C++.

An example of scenario 1) is the loop below. The 'volatile' is required in C++ the same as in C. If you interrupt the loop below in C++ with a signal handler that updates 'flag', the loop is not guaranteed to exit unless 'flag' is declared volatile.

You can test this easily. Just now I compiled the C++ code below with Clang/LLVM with -O on a Mac, and GCC with -O on Linux. On both systems and compilers, Control-C fails to stop the process if 'volatile' is not used. If compiled without -O, Control-C always interrupts the process, but you can't rely on behaviour of disabled optimisations.

  #include <signal.h>

  #if 0
  volatile
  #endif
  sig_atomic_t flag = 0;

  void handler(int sig) {
      flag = 1;
  }

  int main(void) {
      signal(SIGINT, handler);
      while (!flag) { /* Spin waiting for flag */ }
      return 0;
  }