|SIGEMPTYSET(3P)||POSIX Programmer's Manual||SIGEMPTYSET(3P)|
int sigemptyset(sigset_t *set);
The following sections are informative.
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.
The Base Definitions volume of POSIX.1‐2017, <signal.h>
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|2017||IEEE/The Open Group|