atexit(3) - Linux manual page (original) (raw)

atexit(3) Library Functions Manual atexit(3)

NAME top

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

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#include <stdlib.h>**

   **int atexit(typeof(void (void)) ***_function_**);**

DESCRIPTION top

   The **atexit**() function registers the given _function_ to be called at
   normal process termination, either via [exit(3)](../man3/exit.3.html) 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)](../man3/sysconf.3.html).

   When a child process is created via [fork(2)](../man2/fork.2.html), it inherits copies of
   its parent's registrations.  Upon a successful call to one of the
   [exec(3)](../man3/exec.3.html) 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
   [attributes(7)](../man7/attributes.7.html).
   ┌──────────────────────────────────────┬───────────────┬─────────┐
   │ **Interface** │ **Attribute** │ **Value** │
   ├──────────────────────────────────────┼───────────────┼─────────┤
   │ **atexit**()                             │ Thread safety │ MT-Safe │
   └──────────────────────────────────────┴───────────────┴─────────┘

VERSIONS top

   POSIX.1 says that the result of calling [exit(3)](../man3/exit.3.html) more than once
   (i.e., calling [exit(3)](../man3/exit.3.html) 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)](../man3/exit.3.html) inside a function registered using **atexit**().

STANDARDS top

   C11, POSIX.1-2008.

HISTORY top

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

NOTES top

   Functions registered using **atexit**() (and [on_exit(3)](../man3/on%5Fexit.3.html)) are not
   called if a process terminates abnormally because of the delivery
   of a signal.

   If one of the registered functions calls [_exit(2)](../man2/%5Fexit.2.html), then any
   remaining functions are not invoked, and the other process
   termination steps performed by [exit(3)](../man3/exit.3.html) are not performed.

   The **atexit**() and [on_exit(3)](../man3/on%5Fexit.3.html) 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)](../man3/longjmp.3.html) 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 top

   #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 top

   [_exit(2)](../man2/%5Fexit.2.html), [dlopen(3)](../man3/dlopen.3.html), [exit(3)](../man3/exit.3.html), [on_exit(3)](../man3/on%5Fexit.3.html)

COLOPHON top

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   man-pages@man7.org

Linux man-pages 6.10 2024-12-13 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)