'\" 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 .

Any typographical or formatting errors that appear

in this page are most likely

to have been introduced during the conversion of the source files to

man page format. To report such errors, see

https://www.kernel.org/doc/man-pages/reporting_bugs.html .