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cunixsignals

Set a custom function as handler to all signals

I have this assignment to do:

Write a function void myfunct(void(*f)(int sig)) which sets f as handler to all the possible signals.

I have two problems:

  1. How can a get all the possible signals? Is there a function for this? Can I iterate through them in some way?
  2. Will it really work to set the function f as handler given that it takes a parameter? Shouldn't it not have any parameters?

Thank you.

Solution
    1. How can a get all the possible signals? Is there a function for this? Can I iterate through them in some way?

    Most implementation provide a constant such as NSIG (Glibc provides NSIG) or _NSIG (Linux provides _NSIG). So, you can loop through that constant and set the same signal handling function for all of them.

    There's no POSIX defined value for "highest signal number". There's been a proposal in POSIX to add a macro NSIG_MAX.

    {NSIG_MAX}

    Maximum possible return value of sysconf(_SC_NSIG). See [cross-ref to XSH sysconf()]. The value of {NSIG_MAX} shall be no greater than the number of signals that the sigset_t type (see [cross-ref to ]) is capable of representing, ignoring any restrictions imposed by sigfillset() or sigaddset().

    But it hasn't made it to POSIX yet (most probably it'll a part of the POSIX version - issue 8).

    1. Will it really work to set the function f as handler given that it takes a parameter? Shouldn't it not have any parameters?

    The parameter that the signal handling function takes doesn't matter when you are setting a signal disposition. It takes the signal number but that doesn't prevent you from using it as a handler for multiple signals.

    But there are special cases you need to handle. Certain signals that can't caught or ignored (SIGKILL and SIGSTOP). There are other signals (SIGFPE, SIGILL and SIGSEGV) for which, while allowed to caught, the signal handler can't return to its caller (i.e. you need exit from the signal handler).