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sigemptyset - Man Page

initialize and empty a signal set


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.


#include <signal.h>

int sigemptyset(sigset_t *set);


The sigemptyset() function initializes the signal set pointed to by set, such that all signals defined in POSIX.1-2008 are excluded.

Return Value

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.



Application Usage



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 POSIX.1-2017. Although it is outside the scope of this volume of POSIX.1-2017 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


See Also

Section 2.4, Signal Concepts, pthread_sigmask(), sigaction(), sigaddset(), sigdelset(), sigfillset(), sigismember(), sigpending(), sigsuspend()

The Base Definitions volume of POSIX.1-2017, <signal.h>

Referenced By

pthread_sigmask(3p), sigaction(3p), sigaddset(3p), sigdelset(3p), sigfillset(3p), sigismember(3p), signal.h(0p), sigpending(3p), sigsuspend(3p).

2017 IEEE/The Open Group POSIX Programmer's Manual