| .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) |
| .\" |
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| .\" permission notice identical to this one. |
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| .\" Since the Linux kernel and libraries are constantly changing, this |
| .\" manual page may be incorrect or out-of-date. The author(s) assume no |
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| .\" References consulted: |
| .\" Linux libc source code |
| .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) |
| .\" 386BSD man pages |
| .\" Modified 1993-03-29, David Metcalfe |
| .\" Modified 1993-07-24, Rik Faith (faith@cs.unc.edu) |
| .\" Modified 2003-10-25, Walter Harms |
| .\" |
| .TH ATEXIT 3 2021-03-22 "Linux" "Linux Programmer's Manual" |
| .SH NAME |
| atexit \- register a function to be called at normal process termination |
| .SH SYNOPSIS |
| .nf |
| .B #include <stdlib.h> |
| .PP |
| .BI "int atexit(void (*" function )(void)); |
| .fi |
| .SH DESCRIPTION |
| The |
| .BR atexit () |
| function registers the given |
| .I function |
| to be |
| called at normal process termination, either via |
| .BR exit (3) |
| or via return from the program's |
| .IR main (). |
| Functions so registered are called in |
| the reverse order of their registration; no arguments are passed. |
| .PP |
| The same function may be registered multiple times: |
| it is called once for each registration. |
| .PP |
| POSIX.1 requires that an implementation allow at least |
| .\" POSIX.1-2001, POSIX.1-2008 |
| .B ATEXIT_MAX |
| (32) such functions to be registered. |
| The actual limit supported by an implementation can be obtained using |
| .BR sysconf (3). |
| .PP |
| When a child process is created via |
| .BR fork (2), |
| it inherits copies of its parent's registrations. |
| Upon a successful call to one of the |
| .BR exec (3) |
| functions, |
| all registrations are removed. |
| .SH RETURN VALUE |
| The |
| .BR atexit () |
| function returns the value 0 if successful; otherwise |
| it returns a nonzero value. |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .ad l |
| .nh |
| .TS |
| allbox; |
| lbx lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR atexit () |
| T} Thread safety MT-Safe |
| .TE |
| .hy |
| .ad |
| .sp 1 |
| .SH CONFORMING TO |
| POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD. |
| .SH NOTES |
| Functions registered using |
| .BR atexit () |
| (and |
| .BR on_exit (3)) |
| are not called if a process terminates abnormally because |
| of the delivery of a signal. |
| .PP |
| If one of the registered functions calls |
| .BR _exit (2), |
| then any remaining functions are not invoked, |
| and the other process termination steps performed by |
| .BR exit (3) |
| are not performed. |
| .PP |
| POSIX.1 says that the result of calling |
| .\" POSIX.1-2001, POSIX.1-2008 |
| .BR exit (3) |
| more than once (i.e., calling |
| .BR exit (3) |
| within a function registered using |
| .BR atexit ()) |
| is undefined. |
| On some systems (but not Linux), this can result in an infinite recursion; |
| .\" This can happen on OpenBSD 4.2 for example, and is documented |
| .\" as occurring on FreeBSD as well. |
| .\" Glibc does "the Right Thing" -- invocation of the remaining |
| .\" exit handlers carries on as normal. |
| portable programs should not invoke |
| .BR exit (3) |
| inside a function registered using |
| .BR atexit (). |
| .PP |
| The |
| .BR atexit () |
| and |
| .BR 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. |
| .PP |
| According to POSIX.1, the result is undefined if |
| .BR longjmp (3) |
| is used to terminate execution of one of the functions registered using |
| .BR atexit (). |
| .\" In glibc, things seem to be handled okay |
| .SS Linux notes |
| Since glibc 2.2.3, |
| .BR atexit () |
| (and |
| .BR on_exit (3)) |
| can be used within a shared library to establish functions |
| that are called when the shared library is unloaded. |
| .SH EXAMPLES |
| .EX |
| #include <stdio.h> |
| #include <stdlib.h> |
| #include <unistd.h> |
| |
| void |
| bye(void) |
| { |
| printf("That was all, folks\en"); |
| } |
| |
| int |
| main(void) |
| { |
| long a; |
| int i; |
| |
| a = sysconf(_SC_ATEXIT_MAX); |
| printf("ATEXIT_MAX = %ld\en", a); |
| |
| i = atexit(bye); |
| if (i != 0) { |
| fprintf(stderr, "cannot set exit function\en"); |
| exit(EXIT_FAILURE); |
| } |
| |
| exit(EXIT_SUCCESS); |
| } |
| .EE |
| .SH SEE ALSO |
| .BR _exit (2), |
| .BR dlopen (3), |
| .BR exit (3), |
| .BR on_exit (3) |