---
name: "sigsetops"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/sigsetops"
---

# sigsetops(3)

POSIX signal set operations

## NAME

sigemptyset, sigfillset, sigaddset, sigdelset, sigismember - POSIX signal set operations

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <signal.h>
```

**int sigemptyset(sigset\_t \****set***);** **int sigfillset(sigset\_t \****set***);**

**int sigaddset(sigset\_t \****set***, int** *signum***);** **int sigdelset(sigset\_t \****set***, int** *signum***);**

**int sigismember(const sigset\_t \****set***, int** *signum***);**

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

**sigemptyset**(), **sigfillset**(), **sigaddset**(), **sigdelset**(), **sigismember**():

```
    _POSIX_C_SOURCE
```

## DESCRIPTION

These functions allow the manipulation of POSIX signal sets.

**sigemptyset**() initializes the signal set given by *set* to empty, with all signals excluded from the set.

**sigfillset**() initializes *set* to full, including all signals.

**sigaddset**() and **sigdelset**() add and delete respectively signal *signum* from *set*.

**sigismember**() tests whether *signum* is a member of *set*.

Objects of type *sigset\_t* must be initialized by a call to either **sigemptyset**() or **sigfillset**() before being passed to the functions **sigaddset**(), **sigdelset**(), and **sigismember**() or the additional glibc functions described below (**sigisemptyset**(), **sigandset**(), and **sigorset**()). The results are undefined if this is not done.

## RETURN VALUE

**sigemptyset**(), **sigfillset**(), **sigaddset**(), and **sigdelset**() return 0 on success and -1 on error.

**sigismember**() returns 1 if *signum* is a member of *set*, 0 if *signum* is not a member, and -1 on error.

On error, these functions set *errno* to indicate the error.

## ERRORS

- **EINVAL**

  *signum* is not a valid signal.

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **sigemptyset**(), **sigfillset**(), **sigaddset**(), **sigdelset**(), **sigismember**(), **sigisemptyset**(), **sigorset**(), **sigandset**() | Thread safety | MT-Safe |

## VERSIONS

### GNU

If the **\_GNU\_SOURCE** feature test macro is defined, then *\<signal.h\>* exposes three other functions for manipulating signal sets:

```
int sigisemptyset(const sigset_t *set);
int sigorset(sigset_t *dest, const sigset_t *left,
              const sigset_t *right);
int sigandset(sigset_t *dest, const sigset_t *left,
              const sigset_t *right);
```

**sigisemptyset**() returns 1 if *set* contains no signals, and 0 otherwise.

**sigorset**() places the union of the sets *left* and *right* in *dest*. **sigandset**() places the intersection of the sets *left* and *right* in *dest*. Both functions return 0 on success, and -1 on failure.

These functions are nonstandard (a few other systems provide similar functions) and their use should be avoided in portable applications.

## STANDARDS

POSIX.1-2008.

## HISTORY

POSIX.1-2001.

## NOTES

When creating a filled signal set, the glibc **sigfillset**() function does not include the two real-time signals used internally by the NPTL threading implementation. See [**nptl**(7)](/nptl/7.md) for details.

## SEE ALSO

[**sigaction**(2)](/sigaction/2.md), [**sigpending**(2)](/sigpending/2.md), [**sigprocmask**(2)](/sigprocmask/2.md), [**sigsuspend**(2)](/sigsuspend/2.md)