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       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);

   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.


       EINVAL sig is not a valid signal.




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

       int sigisemptyset(sigset_t *set);
              returns 1 if set contains no signals, and 0 otherwise.

       int sigorset(sigset_t *dest, sigset_t *left, sigset_t *right);
              places the union of the sets left and right in dest.

       int sigandset(sigset_t *dest, sigset_t *left, sigset_t *right);
              places the intersection of the sets left and right in dest.

       sigorset() and sigandset() return 0 on success, and -1 on failure.

       These functions are non-standard (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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