1ATEXIT(3P) POSIX Programmer's Manual ATEXIT(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 atexit — register a function to run at process termination
13
15 #include <stdlib.h>
16 int atexit(void (*func)(void));
18
20 The functionality described on this reference page is aligned with the
21 ISO C standard. Any conflict between the requirements described here
22 and the ISO C standard is unintentional. This volume of POSIX.1‐2017
23 defers to the ISO C standard.
24 The atexit() function shall register the function pointed to by func,
26 to be called without arguments at normal program termination. At normal
27 program termination, all functions registered by the atexit() function
28 shall be called, in the reverse order of their registration, except
29 that a function is called after any previously registered functions
30 that had already been called at the time it was registered. Normal
31 termination occurs either by a call to exit() or a return from main().
32 At least 32 functions can be registered with atexit().
34 After a successful call to any of the exec functions, any functions
36 previously registered by atexit() shall no longer be registered.
37
39 Upon successful completion, atexit() shall return 0; otherwise, it
40 shall return a non-zero value.
41
43 No errors are defined.
44 The following sections are informative.
46
48 None.
49
51 The functions registered by a call to atexit() must return to ensure
52 that all registered functions are called.
53 The application should call sysconf() to obtain the value of
55 {ATEXIT_MAX}, the number of functions that can be registered. There is
56 no way for an application to tell how many functions have already been
57 registered with atexit().
58 Since the behavior is undefined if the exit() function is called more
60 than once, portable applications calling atexit() must ensure that the
61 exit() function is not called at normal process termination when all
62 functions registered by the atexit() function are called.
63 All functions registered by the atexit() function are called at normal
65 process termination, which occurs by a call to the exit() function or a
66 return from main() or on the last thread termination, when the behavior
67 is as if the implementation called exit() with a zero argument at
68 thread termination time.
69 If, at normal process termination, a function registered by the
71 atexit() function is called and a portable application needs to stop
72 further exit() processing, it must call the _exit() function or the
73 _Exit() function or one of the functions which cause abnormal process
74 termination.
75
77 None.
78
80 None.
81
83 exec, exit(), sysconf()
84 The Base Definitions volume of POSIX.1‐2017, <stdlib.h>
86
88 Portions of this text are reprinted and reproduced in electronic form
89 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
90 table Operating System Interface (POSIX), The Open Group Base Specifi‐
91 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
92 Electrical and Electronics Engineers, Inc and The Open Group. In the
93 event of any discrepancy between this version and the original IEEE and
94 The Open Group Standard, the original IEEE and The Open Group Standard
95 is the referee document. The original Standard can be obtained online
96 at http://www.opengroup.org/unix/online.html .
97 Any typographical or formatting errors that appear in this page are
99 most likely to have been introduced during the conversion of the source
100 files to man page format. To report such errors, see https://www.ker‐
101 nel.org/doc/man-pages/reporting_bugs.html .
102IEEE/The Open Group 2017 ATEXIT(3P)