atexit(3)

NAME
atexit - register a function to be called at normal process termination

LIBRARY
Standard C library (libc, -lc)

SYNOPSIS
#include <stdlib.h>

int atexit(void (*function)(void));

DESCRIPTION
The atexit() function registers the given function to be called at normal process termination, either via exit(3) or via return from the program's main(). Functions so registered are called in the reverse order of their registration; no arguments are passed.

The same function may be registered multiple times: it is called once for each registration.

POSIX.1 requires that an implementation allow at least ATEXIT_MAX (32) such functions to be registered. The actual limit supported by an implementation can be obtained using sysconf(3).

When a child process is created via fork(2), it inherits copies of its parent's registrations. Upon a successful call to one of the exec(3) functions, all registrations are removed.

RETURN VALUE
The atexit() function returns the value 0 if successful; otherwise it returns a nonzero value.

ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
Interface | Attribute | Value
 | Thread safety | MT-Safe

VERSIONS
POSIX.1 says that the result of calling exit(3) more than once (i.e., calling exit(3) within a function registered using atexit()) is undefined. On some systems (but not Linux), this can result in an infinite recursion; portable programs should not invoke exit(3) inside a function registered using atexit().

STANDARDS
C11, POSIX.1-2008.

HISTORY
POSIX.1-2001, C89, C99, SVr4, 4.3BSD.

NOTES
Functions registered using atexit() (and on_exit(3)) are not called if a process terminates abnormally because of the delivery of a signal.

If one of the registered functions calls _exit(2), then any remaining functions are not invoked, and the other process termination steps performed by exit(3) are not performed.

The atexit() and on_exit(3) functions register functions on the same list: at normal process termination, the registered functions are invoked in reverse order of their registration by these two functions.

According to POSIX.1, the result is undefined if longjmp(3) is used to terminate execution of one of the functions registered using atexit().

  Linux notes
Since glibc 2.2.3, atexit() (and on_exit(3)) can be used within a shared library to establish functions that are called when the shared library is unloaded.

EXAMPLES
    #include <stdio.h>
    #include <stdlib.h>
    #include <unistd.h>

    void
    bye(void)
    {
        printf("That was all, folks\n");
    }

    int
    main(void)
    {
        long a;
        int i;

        a = sysconf(_SC_ATEXIT_MAX);
        printf("ATEXIT_MAX = %ld\n", a);

        i = atexit(bye);
        if (i != 0) {
            fprintf(stderr, "cannot set exit function\n");
            exit(EXIT_FAILURE);
        }

        exit(EXIT_SUCCESS);
    }

SEE ALSO
_exit(2), dlopen(3), exit(3), on_exit(3)