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


       #include <stdlib.h>

       int atexit(void (*function)(void));


       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.


       The  atexit()  function returns the value 0 if successful; otherwise it
       returns a nonzero value.


       For  an  explanation  of  the  terms  used   in   this   section,   see

       │InterfaceAttributeValue   │
       │atexit()  │ Thread safety │ MT-Safe │


       POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.


       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.


       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>

           printf("That was all, folks\n");

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


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