'\" et
.TH SIGEMPTYSET "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.

.SH NAME
sigemptyset
\(em initialize and empty a signal set
.SH SYNOPSIS
.LP
.nf
#include <signal.h>
.P
int sigemptyset(sigset_t *\fIset\fP);
.fi
.SH DESCRIPTION
The
\fIsigemptyset\fR()
function initializes the signal set pointed to by
.IR set ,
such that all signals defined in POSIX.1\(hy2008 are excluded.
.SH "RETURN VALUE"
Upon successful completion,
\fIsigemptyset\fR()
shall return 0; otherwise, it shall return \(mi1 and set
.IR errno
to indicate the error.
.SH ERRORS
No errors are defined.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
None.
.SH RATIONALE
The implementation of the
\fIsigemptyset\fR()
(or
\fIsigfillset\fR())
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
\fIsigemptyset\fR()
or
\fIsigfillset\fR()
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
\fIsigpending\fR()).
This function is not intended for dynamic allocation.
.P
The
\fIsigfillset\fR()
and
\fIsigemptyset\fR()
functions require that the resulting signal set include (or exclude)
all the signals defined in this volume of POSIX.1\(hy2008. Although it is outside the scope of
\&this volume of POSIX.1\(hy2008 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
\fIsigfillset\fR().
.P
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
.BR [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.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.ad l
.IR "Section 2.4" ", " "Signal Concepts",
.IR "\fIpthread_sigmask\fR\^(\|)",
.IR "\fIsigaction\fR\^(\|)",
.IR "\fIsigaddset\fR\^(\|)",
.IR "\fIsigdelset\fR\^(\|)",
.IR "\fIsigfillset\fR\^(\|)",
.IR "\fIsigismember\fR\^(\|)",
.IR "\fIsigpending\fR\^(\|)",
.IR "\fIsigsuspend\fR\^(\|)"
.ad b
.P
The Base Definitions volume of POSIX.1\(hy2008,
.IR "\fB<signal.h>\fP"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

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