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SIGEMPTYSET(3) Library Functions Manual SIGEMPTYSET(3)

sigemptyset, sigfillset, sigaddset, sigdelset, sigismember
manipulate signal sets

#include <signal.h>
sigemptyset(sigset_t *set);
sigfillset(sigset_t *set);
sigaddset(sigset_t *set, int signo);
sigdelset(sigset_t *set, int signo);
sigismember(const sigset_t *set, int signo);

These functions manipulate signal sets stored in a sigset_t. Either sigemptyset() or sigfillset() must be called for every object of type sigset_t before any other use of the object. sigemptyset() and sigfillset() are provided as macros, but actual functions are available if their names are undefined (with #undef name).
The sigemptyset() function initializes a signal set to be empty.
sigfillset() initializes a signal set to contain all signals.
sigaddset() adds the specified signal signo to the signal set.
sigdelset() deletes the specified signal signo from the signal set.
sigismember() returns whether a specified signal signo is contained in the signal set.

The sigismember() function returns 1 if the signal is a member of the set and 0 otherwise. The other functions return 0 upon success. A -1 return value indicates an error occurred and the global variable errno is set to indicate the reason.

These functions may fail if one of the following occurs:
The specified signal signo is not a valid signal number.

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

These functions are defined by IEEE Std 1003.1-1990 (“POSIX.1”).
November 10, 2015 OpenBSD-6.1