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 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 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);
       }

SEE ALSO

       _exit(2), dlopen(3), exit(3), on_exit(3)

COLOPHON

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