atexit(3) — Linux manual page


ATEXIT(3)                 Linux Programmer's Manual                ATEXIT(3)

NAME         top

       atexit  - register a function to be called at normal process termina‐

SYNOPSIS         top

       #include <stdlib.h>

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

DESCRIPTION         top

       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         top

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

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface Attribute     Value   │
       │atexit()  │ Thread safety │ MT-Safe │

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.

NOTES         top

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

       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.

       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().

       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

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

   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         top

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

           printf("That was all, folks\n");

           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");


SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.09 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                            2020-06-09                        ATEXIT(3)

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