SIGEMPTYSET(P) POSIX Programmer's Manual SIGEMPTYSET(P)NAMEsigemptyset - initialize and empty a signal set
SYNOPSIS
#include <signal.h>
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 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.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
The implementation of the sigemptyset() (or sigfillset()) function
could quite trivially clear (or set) all the bits in the signal set.
Alternatively, it would be reasonable to initialize part of the struc‐
ture, 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() must be called prior to any other use of
the signal set, even if such use is read-only (for example, as an argu‐
ment to sigpending()). This function is not intended for dynamic allo‐
cation.
The sigfillset() 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. Although it is outside the scope of this vol‐
ume of IEEE Std 1003.1-2001 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 exam‐
ple, 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().
In early proposals there was no distinction between invalid and unsup‐
ported 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 sig‐
nals. With that distinction, it is not necessary to require implementa‐
tions 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 sig‐
nals and optional for unsupported signals, but this seemed unnecessar‐
ily complex. Thus, the error is optional in both cases.
FUTURE DIRECTIONS
None.
SEE ALSO
Signal Concepts , sigaction() , sigaddset() , sigdelset() , sig‐
fillset() , sigismember() , sigpending() , sigprocmask() , sigsuspend()
, the Base Definitions volume of IEEE Std 1003.1-2001, <signal.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 SIGEMPTYSET(P)
