atexit(3) — Linux manual page

atexit(3)               Library Functions Manual               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   │
       ├─────────────────────────────────────┼───────────────┼─────────┤
       │ atexit()                            │ 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)

COLOPHON

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       man-pages@man7.org

Linux man-pages 6.9.1          2024-06-15                      atexit(3)

Pages that refer to this page: execve(2), _exit(2), abort(3), dlopen(3), exit(3), on_exit(3), pmdaopenlog(3), pmfault(3), pmopenlog(3), pthread_atfork(3), pthread_exit(3)

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