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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  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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