atexit(3)

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  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 
   

CONFORMING TO

   POSIX.1-2001, POSIX.1-2008, 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 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 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 functions.

   According to POSIX.1, 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), dlopen(3), exit(3), on_exit(3)

COLOPHON

   This  page  is  part of release 4.09 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
   https://www.kernel.org/doc/man-pages/.

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