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NAME

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

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.1-2001  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.

CONFORMING TO

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

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 functions 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.1-2001  says  that  the  result of calling exit(3) more than once
       (i.e., calling exit(3) within a function registered using atexit(3)) 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(3).

       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.

       POSIX.1-2001 says that the result is undefined if longjmp(3) is used to
       terminate execution of one of the functions registered 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.

EXAMPLE

       #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), exit(3), on_exit(3)

COLOPHON

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