1ATEXIT(3) Linux Programmer's Manual ATEXIT(3)
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6 atexit - register a function to be called at normal process termination
7
9 #include <stdlib.h>
10 int atexit(void (*function)(void));
12
14 The atexit() function registers the given function to be called at nor‐
15 mal process termination, either via exit(3) or via return from the pro‐
16 gram's main(). Functions so registered are called in the reverse order
17 of their registration; no arguments are passed.
18 The same function may be registered multiple times: it is called once
20 for each registration.
21 POSIX.1 requires that an implementation allow at least ATEXIT_MAX (32)
23 such functions to be registered. The actual limit supported by an im‐
24 plementation can be obtained using sysconf(3).
25 When a child process is created via fork(2), it inherits copies of its
27 parent's registrations. Upon a successful call to one of the exec(3)
28 functions, all registrations are removed.
29
31 The atexit() function returns the value 0 if successful; otherwise it
32 returns a nonzero value.
33
35 For an explanation of the terms used in this section, see at‐
36 tributes(7).
37 ┌────────────────────────────────────────────┬───────────────┬─────────┐
39 │Interface │ Attribute │ Value │
40 ├────────────────────────────────────────────┼───────────────┼─────────┤
41 │atexit() │ Thread safety │ MT-Safe │
42 └────────────────────────────────────────────┴───────────────┴─────────┘
43
45 POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
46
48 Functions registered using atexit() (and on_exit(3)) are not called if
49 a process terminates abnormally because of the delivery of a signal.
50 If one of the registered functions calls _exit(2), then any remaining
52 functions are not invoked, and the other process termination steps per‐
53 formed by exit(3) are not performed.
54 POSIX.1 says that the result of calling exit(3) more than once (i.e.,
56 calling exit(3) within a function registered using atexit()) is unde‐
57 fined. On some systems (but not Linux), this can result in an infinite
58 recursion; portable programs should not invoke exit(3) inside a func‐
59 tion registered using atexit().
60 The atexit() and on_exit(3) functions register functions on the same
62 list: at normal process termination, the registered functions are in‐
63 voked in reverse order of their registration by these two functions.
64 According to POSIX.1, the result is undefined if longjmp(3) is used to
66 terminate execution of one of the functions registered using atexit().
67 Linux notes
69 Since glibc 2.2.3, atexit() (and on_exit(3)) can be used within a
70 shared library to establish functions that are called when the shared
71 library is unloaded.
72
74 #include <stdio.h>
75 #include <stdlib.h>
76 #include <unistd.h>
77 void
79 bye(void)
80 {
81 printf("That was all, folks\n");
82 }
83 int
85 main(void)
86 {
87 long a;
88 int i;
89 a = sysconf(_SC_ATEXIT_MAX);
91 printf("ATEXIT_MAX = %ld\n", a);
92 i = atexit(bye);
94 if (i != 0) {
95 fprintf(stderr, "cannot set exit function\n");
96 exit(EXIT_FAILURE);
97 }
98 exit(EXIT_SUCCESS);
100 }
101
103 _exit(2), dlopen(3), exit(3), on_exit(3)
104
106 This page is part of release 5.12 of the Linux man-pages project. A
107 description of the project, information about reporting bugs, and the
108 latest version of this page, can be found at
109 https://www.kernel.org/doc/man-pages/.
110Linux 2021-03-22 ATEXIT(3)