man3/atexit.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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  25 .\" References consulted:
  26 .\"     Linux libc source code
  27 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  28 .\"     386BSD man pages
  29 .\" Modified 1993-03-29, David Metcalfe
  30 .\" Modified 1993-07-24, Rik Faith (faith@cs.unc.edu)
  31 .\" Modified 2003-10-25, Walter Harms
  32 .\"
  33 .TH ATEXIT 3  2015-08-08 "Linux" "Linux Programmer's Manual"
  34 .SH NAME
  35 atexit \- register a function to be called at normal process termination
  36 .SH SYNOPSIS
  37 .nf
  38 .B #include <stdlib.h>
  39 .sp
  40 .BI "int atexit(void (*" function )(void));
  41 .fi
  42 .SH DESCRIPTION
  43 The
  44 .BR atexit ()
  45 function registers the given
  46 .I function
  47 to be
  48 called at normal process termination, either via
  49 .BR exit (3)
  50 or via return from the program's
  51 .IR main ().
  52 Functions so registered are called in
  53 the reverse order of their registration; no arguments are passed.
  54
  55 The same function may be registered multiple times:
  56 it is called once for each registration.
  57 .LP
  58 POSIX.1 requires that an implementation allow at least
  59 .\" POSIX.1-2001, POSIX.1-2008
  60 .B ATEXIT_MAX
  61 (32) such functions to be registered.
  62 The actual limit supported by an implementation can be obtained using
  63 .BR sysconf (3).
  64 .LP
  65 When a child process is created via
  66 .BR fork (2),
  67 it inherits copies of its parent's registrations.
  68 Upon a successful call to one of the
  69 .BR exec (3)
  70 functions,
  71 all registrations are removed.
  72 .SH RETURN VALUE
  73 The
  74 .BR atexit ()
  75 function returns the value 0 if successful; otherwise
  76 it returns a nonzero value.
  77 .SH ATTRIBUTES
  78 For an explanation of the terms used in this section, see
  79 .BR attributes (7).
  80 .TS
  81 allbox;
  82 lb lb lb
  83 l l l.
  84 Interface       Attribute       Value
  85 T{
  86 .BR atexit ()
  87 T}      Thread safety   MT-Safe
  88 .TE
  89
  90 .SH CONFORMING TO
  91 POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
  92 .SH NOTES
  93 Functions registered using
  94 .BR atexit ()
  95 (and
  96 .BR on_exit (3))
  97 are not called if a process terminates abnormally because
  98 of the delivery of a signal.
  99
 100 If one of the functions registered functions calls
 101 .BR _exit (2),
 102 then any remaining functions are not invoked,
 103 and the other process termination steps performed by
 104 .BR exit (3)
 105 are not performed.
 106
 107 POSIX.1 says that the result of calling
 108 .\" POSIX.1-2001, POSIX.1-2008
 109 .BR exit (3)
 110 more than once (i.e., calling
 111 .BR exit (3)
 112 within a function registered using
 113 .BR atexit ())
 114 is undefined.
 115 On some systems (but not Linux), this can result in an infinite recursion;
 116 .\" This can happen on OpenBSD 4.2 for example, and is documented
 117 .\" as occurring on FreeBSD as well.
 118 .\" Glibc does "the Right Thing" -- invocation of the remaining
 119 .\" exit handlers carries on as normal.
 120 portable programs should not invoke
 121 .BR exit (3)
 122 inside a function registered using
 123 .BR atexit ().
 124
 125 The
 126 .BR atexit ()
 127 and
 128 .BR on_exit (3)
 129 functions register functions on the same list:
 130 at normal process termination,
 131 the registered functions are invoked in reverse order
 132 of their registration by these two functions.
 133
 134 According to POSIX.1, the result is undefined if
 135 .BR longjmp (3)
 136 is used to terminate execution of one of the functions registered
 137 .BR atexit ().
 138 .\" In glibc, things seem to be handled okay
 139 .SS Linux notes
 140 Since glibc 2.2.3,
 141 .BR atexit ()
 142 (and
 143 .BR on_exit (3))
 144 can be used within a shared library to establish functions
 145 that are called when the shared library is unloaded.
 146 .SH EXAMPLE
 147 .nf
 148 #include <stdio.h>
 149 #include <stdlib.h>
 150 #include <unistd.h>
 151
 152 void
 153 bye(void)
 154 {
 155     printf("That was all, folks\en");
 156 }
 157
 158 int
 159 main(void)
 160 {
 161     long a;
 162     int i;
 163
 164     a = sysconf(_SC_ATEXIT_MAX);
 165     printf("ATEXIT_MAX = %ld\en", a);
 166
 167     i = atexit(bye);
 168     if (i != 0) {
 169         fprintf(stderr, "cannot set exit function\en");
 170         exit(EXIT_FAILURE);
 171     }
 172
 173     exit(EXIT_SUCCESS);
 174 }
 175 .fi
 176 .SH SEE ALSO
 177 .BR _exit (2),
 178 .BR dlopen (3),
 179 .BR exit (3),
 180 .BR on_exit (3)