NAME
atexit — register
a function to be called from .I exit () or after return from .I main
()
SYNOPSIS
#include
<stdlib.h>
int atexit(void (*func)(void));
DESCRIPTION
[CX] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2024 defers to the ISO C standard.
The atexit () function shall
register the function pointed to by
func, to be called
without arguments from exit(3), or after return from the
initial call to
main (),
or on the last thread termination. If the exit(3) function
is called, it is unspecified whether a call to the
atexit () function that does not happen before
exit(3) is called will succeed.
At least 32 functions can be registered with
atexit ().
RETURN VALUE
Upon successful completion, atexit ()
shall return 0; otherwise, it shall return a non-zero value.
ERRORS
No errors are defined.
EXAMPLES
None.
APPLICATION USAGE
The atexit () function registrations are
distinct from the at_quick_exit(3) registrations, so
applications might need to call both registration functions with the same
argument.
The functions registered by a call to
atexit () must return to ensure that all registered
functions are called.
The application should call sysconf(3) to obtain
the value of {ATEXIT_MAX}, the number of functions that can be registered.
There is no way for an application to tell how many functions have already
been registered with atexit ().
Since the behavior is undefined if the exit(3)
function is called more than once, portable applications calling
atexit () must ensure that the
exit(3) function is not called when the functions
registered by the atexit () function are called.
If a function registered by the atexit ()
function is called and a portable application needs to stop further
exit(3) processing, it must call the
_exit(3) function or the _Exit(3)
function or one of the functions which cause abnormal process
termination.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
at_quick_exit(3), exec(3), exit(3), sysconf(3)
XBD <stdlib.h>
CHANGE HISTORY
First released in Issue 4. Derived from the ANSI C standard.
Issue 6
Extensions beyond the ISO C standard are marked.
The DESCRIPTION is updated for alignment with the ISO/IEC 9899:1999 (“ISO C99”) standard.
IEEE Std 1003.1-2001 (“POSIX.1”)/Cor 2-2004, item XSH/TC2/D6/19 is applied, adding further clarification to the APPLICATION USAGE section.
Issue 8
Austin Group Defect 1302 is applied, aligning this function with the ISO/IEC 9899:2018 standard.
Austin Group Defect 1646 is applied, removing redundant text relating to the exec family of functions.