sigemptyset, sigfillset, sigaddset, sigdelset, sigismember — POSIX signal set operations


#include <signal.h>
int sigemptyset( sigset_t *set);
int sigfillset( sigset_t *set);
int sigaddset( sigset_t *set,
  int signum);
int sigdelset( sigset_t *set,
  int signum);
int sigismember( const sigset_t *set,
  int signum);
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
sigemptyset(), sigfillset(), sigaddset(), sigdelset(), sigismember():


These functions allow the manipulation of POSIX signal sets.

sigemptyset() initializes the signal set given by set to empty, with all signals excluded from the set.

sigfillset() initializes set to full, including all signals.

sigaddset() and sigdelset() add and delete respectively signal signum from set.

sigismember() tests whether signum is a member of set.

Objects of type sigset_t must be initialized by a call to either sigemptyset() or sigfillset() before being passed to the functions sigaddset(), sigdelset(), and sigismember() or the additional glibc functions described below (sigisemptyset(), sigandset(), and sigorset()). The results are undefined if this is not done.


sigemptyset(), sigfillset(), sigaddset(), and sigdelset() return 0 on success and −1 on error.

sigismember() returns 1 if signum is a member of set, 0 if signum is not a member, and −1 on error.

On error, these functions set errno to indicate the error.



signum is not a valid signal.


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
sigemptyset(), sigfillset(), sigaddset(), sigdelset(), sigismember(), sigisemptyset(), sigorset(), sigandset() Thread safety MT-Safe


POSIX.1-2001, POSIX.1-2008.


When creating a filled signal set, the glibc sigfillset() function does not include the two real-time signals used internally by the NPTL threading implementation. See nptl(7) for details.

Glibc extensions

If the _GNU_SOURCE feature test macro is defined, then <signal.h> exposes three other functions for manipulating signal sets:

  int sigisemptyset(const sigset_t *set);
  int sigorset(sigset_t *dest, const sigset_t *left, const sigset_t *right);
  int sigandset(sigset_t *dest, const sigset_t *left, const sigset_t *right);

sigisemptyset() returns 1 if set contains no signals, and 0 otherwise.

sigorset() places the union of the sets left and right in dest. sigandset() places the intersection of the sets left and right in dest. Both functions return 0 on success, and −1 on failure.

These functions are nonstandard (a few other systems provide similar functions) and their use should be avoided in portable applications.


sigaction(2), sigpending(2), sigprocmask(2), sigsuspend(2)


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  Copyright (c) 1994 Mike Battersby

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Modified by aeb, 960721
2005-11-21, mtk, added descriptions of sigisemptyset(), sigandset(),
                 and sigorset()
2007-10-26 mdw   added wording that a sigset_t must be initialized
                 prior to use