sigaddset() — Add a signal to the signal mask

Standards

Standards / Extensions	C or C++	Dependencies
POSIX.1 XPG4 XPG4.2 Single UNIX Specification, Version 3	both

Format

#define _POSIX_SOURCE
#include <signal.h>

int sigaddset(sigset_t *set, int signal);

General description

Adds a signal to the set of signals already recorded in set.

sigaddset() is part of a family of functions that manipulate signal sets. Signal sets are data objects that let a process keep track of groups of signals. For example, a process can create one signal set to record which signals it is blocking, and another signal set to record which signals are pending. In general, signal sets are used to manipulate groups of signals used by other functions (such as sigprocmask()) or to examine signal sets returned by other functions (such as sigpending()).

Applications should call either sigemptyset() or sigfillset() at least once for each object of type sigset_t prior to any other use of that object. If such an object is not initialized in this way, but is nonetheless supplied as an argument to any of pthread_sigmask(), sigaction(), sigaddset(), sigdelset(), sigismember(), sigpending(), sigprocmask(), sigsuspend(), sigtimedwait(), sigwait(), or sigwaitinfo(), the results are undefined.

Usage note

The use of the SIGTHSTOP and SIGTHCONT signal is not supported with this function.

Returned value

If the signal is successfully added to the signal set, sigaddset() returns 0.

If signal is not supported, sigaddset() returns -1 and sets errno to EINVAL.

Example

CELEBS15

⁄* CELEBS15

   This example adds a set of signals.

 *⁄
#define _POSIX_SOURCE
#include <stdio.h>
#include <signal.h>
#include <unistd.h>

void catcher(int signum) {
  puts("catcher() has gained control");
}

main() {
  struct   sigaction sact;
  sigset_t sigset;

  sigemptyset(&sact.sa_mask);
  sact.sa_flags = 0;
  sact.sa_handler = catcher;
  sigaction(SIGUSR1, &sact, NULL);

  puts("before first kill()");
  kill(getpid(), SIGUSR1);
  puts("before second kill()");

  sigemptyset(&sigset);
  sigaddset(&sigset, SIGUSR1);
  sigprocmask(SIG_SETMASK, &sigset, NULL);

  kill(getpid(), SIGUSR1);
  puts("after second kill()");
}

Output

before first kill()
catcher() has gained control
before second kill()
after second kill()