SIGEMPTYSET(P) POSIX Programmer's Manual SIGEMPTYSET(P)
sigemptyset - initialize and empty a signal set
int sigemptyset(sigset_t *set);
The sigemptyset() function initializes the signal set pointed to by set, such that all
signals defined in IEEE Std 1003.1-2001 are excluded.
Upon successful completion, sigemptyset() shall return 0; otherwise, it shall return -1
and set errno to indicate the error.
No errors are defined.
The following sections are informative.
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 sig-
nal 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 unnec-
essarily complex. Thus, the error is optional in both cases.
Signal Concepts , sigaction() , sigaddset() , sigdelset() , sigfillset() , sigismember() ,
sigpending() , sigprocmask() , sigsuspend() , the Base Definitions volume of
IEEE Std 1003.1-2001, <signal.h>
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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 SIGEMPTYSET(P)