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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 non-zero 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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