NAME
sigemptyset —
initialize and empty a signal set
SYNOPSIS
int sigemptyset(sigset_t *set);
DESCRIPTION
The sigemptyset () function initializes
the signal set pointed to by
set, such
that all signals defined in IEEE Std 1003.1-2001
(“POSIX.1”) are excluded.
RETURN VALUE
Upon successful completion, sigemptyset ()
shall return 0; otherwise, it shall return -1 and set
errno to
indicate the error.
ERRORS
No errors are defined.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
The implementation of the sigemptyset ()
(or sigfillset(3)) function could quite trivially clear
(or set) all the bits in the signal set. Alternatively, it would be
reasonable to initialize part of the structure, such as a version field, to
permit binary-compatibility between releases where the size of the set
varies. For such reasons, either sigemptyset () or
sigfillset(3) must be called prior to any other use of the
signal set, even if such use is read-only (for example, as an argument to
sigpending(3)). This function is not intended for dynamic
allocation.
The sigfillset(3) and
sigemptyset () functions require that the resulting
signal set include (or exclude) all the signals defined in this volume of
IEEE Std 1003.1-2001 (“POSIX.1”).
Although it is outside the scope of this volume of IEEE Std
1003.1-2001 (“POSIX.1”) to place this requirement on
signals that are implemented as extensions, it is recommended that
implementation-defined signals also be affected by these functions. However,
there may be a good reason for a particular signal not to be affected. For
example, blocking or ignoring an implementation-defined signal may have
undesirable side effects, whereas the default action for that signal is
harmless. In such a case, it would be preferable for such a signal to be
excluded from the signal set returned by
sigfillset(3).
In early proposals there was no distinction between invalid and unsupported signals (the names of optional signals that were not supported by an implementation were not defined by that implementation). The [EINVAL] error was thus specified as a required error for invalid signals. With that distinction, it is not necessary to require implementations of these functions to determine whether an optional signal is actually supported, as that could have a significant performance impact for little value. The error could have been required for invalid signals and optional for unsupported signals, but this seemed unnecessarily complex. Thus, the error is optional in both cases.
FUTURE DIRECTIONS
None.
SEE ALSO
xsh_chap02_04(3), sigaction(3), sigaddset(3), sigdelset(3), sigfillset(3), sigismember(3), sigpending(3), sigprocmask(3), sigsuspend(3), the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), <signal.h>
CHANGE HISTORY
First released in Issue 3. Included for alignment with the POSIX.1-1988 standard.
Issue 6
The SYNOPSIS is marked CX since the presence of this function in the <signal.h> header is an extension over the ISO C standard.
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