NAME
sigemptyset - 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
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() 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()). This function is not intended for dynamic
allocation.
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
volume 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 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().
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
Signal Concepts , sigaction() , sigaddset() , sigdelset() ,
sigfillset() , 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 .