man3/atexit.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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  23 .\" References consulted:
  24 .\"     Linux libc source code
  25 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  26 .\"     386BSD man pages
  27 .\" Modified 1993-03-29, David Metcalfe
  28 .\" Modified 1993-07-24, Rik Faith (faith@cs.unc.edu)
  29 .\" Modified 2003-10-25, Walter Harms
  30 .\"
  31 .TH ATEXIT 3  2003-11-01 "" "Linux Programmer's Manual"
  32 .SH NAME
  33 atexit \- register a function to be called at normal process termination
  34 .SH SYNOPSIS
  35 .nf
  36 .B #include <stdlib.h>
  37 .sp
  38 .BI "int atexit(void (*" function )(void));
  39 .fi
  40 .SH DESCRIPTION
  41 The \fBatexit\fP() function registers the given \fIfunction\fP to be
  42 called at normal process termination, either via
  43 .BR exit (3)
  44 or via return from the program's \fImain\fP().
  45 Functions so registered are called in
  46 the reverse order of their registration; no arguments are passed.
  47 .LP
  48 POSIX.1-2001 requires that an implementation allow at least ATEXIT_MAX (32)
  49 such functions to be registered.
  50 The actual limit supported by an implementation can be obtained using
  51 .BR sysconf (3).
  52 .LP
  53 When a child process is created via
  54 .BR fork (),
  55 it inherits copies of the its parents registrations.
  56 Upon a successful call to one of the
  57 .BR exec ()
  58 functions,
  59 all registrations are removed.
  60 .SH "RETURN VALUE"
  61 The \fBatexit\fP() function returns the value 0 if successful; otherwise
  62 it returns a non-zero value.
  63 .SH EXAMPLE
  64 .nf
  65 #include <stdio.h>
  66 #include <stdlib.h>
  67 #include <unistd.h>
  68
  69 void bye(void) {
  70         printf("That was all, folks\en");
  71 }
  72
  73 int main(){
  74         long a;
  75         int i;
  76
  77         a = sysconf(_SC_ATEXIT_MAX);
  78         printf("ATEXIT_MAX = %ld\en", a);
  79
  80         i = atexit(bye);
  81         if (i != 0) {
  82                 fprintf(stderr, "cannot set exit function\en");
  83                 return EXIT_FAILURE;
  84         }
  85         return EXIT_SUCCESS;
  86 }
  87 .fi
  88 .SH NOTES
  89 Since glibc 2.2.3, \fBatexit\fP() (and \fBon_exit\fP())
  90 can be used to within a shared library to establish functions
  91 that are called when the shared library is unloaded.
  92 .PP
  93 Functions registered using \fBatexit\fP() (and \fBon_exit\fP())
  94 are not called if a process terminates abnormally because
  95 of the delivery of a signal.
  96 .SH "CONFORMING TO"
  97 SVr4, 4.3BSD, C89, C99, POSIX.1-2001.
  98 .SH "SEE ALSO"
  99 .BR _exit (3),
 100 .BR exit (3),
 101 .BR on_exit (3)