NAME
atexit — register
a function to run at process termination
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.1-2008 defers to the ISO C standard.
The atexit () function shall
register the function pointed to by
func, to be called
without arguments at normal program termination. At normal program
termination, all functions registered by the atexit
() function shall be called, in the reverse order of their registration,
except that a function is called after any previously registered functions
that had already been called at the time it was registered. Normal
termination occurs either by a call to exit(3) or a return
from main ().
At least 32 functions can be registered with
atexit ().
[CX] After a successful call to any of
the exec functions,
any functions previously registered by atexit ()
shall no longer be registered.
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 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 at normal process
termination when all functions registered by the
atexit () function are called.
All functions registered by the atexit ()
function are called at normal process termination, which occurs by a call to
the exit(3) function or a return from
main () or on the last thread termination, when the
behavior is as if the implementation called exit(3) with a
zero argument at thread termination time.
If, at normal process termination, 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
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.