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ATEXIT(3) Linux Programmer's Manual 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 nor-
     mal process termination, either via exit(3) or via return from the pro-
     gram'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 registered functions calls _exit(2), then any remaining
     functions are not invoked, and the other process termination steps per-
     formed 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  unde-
     fined.  On some systems (but not Linux), this can result in an infinite
     recursion; portable programs should not invoke exit(3) inside  a  func-
     tion 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 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.

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); }