NAME

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

LIBRARY

       Standard C library (libc, -lc)

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 │
       └───────────────────────────────────────────────────────────────┴───────────────┴─────────┘

VERSIONS

       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().

STANDARDS

       C11, POSIX.1-2008.

HISTORY

       POSIX.1-2001, 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 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.

       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 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

       #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)