ATEXIT(3) Linux Programmer s Manual ATEXIT(3)

NAME atexit - register a function to be called at normal process termination

SYNOPSIS #include <stdlib.h>

int atexit(void (*function)(void));

DESCRIPTION The atexit() function registers the given function to be called at nor- mal process termination, either via exit(3) or via return from the pro- gram s main(). Functions so registered are called in the reverse order of their registration; no arguments are passed.

The same function may be registered multiple times: it is called once for each registration.

POSIX.1-2001 requires that an implementation allow at least ATEXIT_MAX (32) such functions to be registered. The actual limit supported by an implementation can be obtained using sysconf(3).

When a child process is created via fork(2), it inherits copies of its parents registrations. Upon a successful call to one of the exec(3) functions, all registrations are removed.

RETURN VALUE The atexit() function returns the value 0 if successful; otherwise it returns a non-zero value.

CONFORMING TO SVr4, 4.3BSD, C89, C99, POSIX.1-2001.

NOTES Functions registered using atexit() (and on_exit(3)) are not called if a process terminates abnormally because of the delivery of a signal.

If one of the functions registered functions calls _exit(2), then any remaining functions are not invoked, and the other process termination steps performed by exit(3) are not performed.

POSIX.1-2001 says that the result of calling exit(3) more than once (i.e., calling exit(3) within a function registered using atexit(3)) is undefined. On some systems (but not Linux), this can result in an infinite recursion; portable programs should not invoke exit(3) inside a function registered using atexit(3).

The atexit() and 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.

POSIX.1-2001 says that the result is undefined if longjmp(3) is used to terminate execution of one of the functions registered atexit().

Linux Notes Since glibc 2.2.3, atexit() (and on_exit(3)) can be used within a shared library to establish functions that are called when the shared library is unloaded.

EXAMPLE #include <stdio.h> #include <stdlib.h> #include <unistd.h>

void bye(void) { printf("That was all, folks0); }

int main(void) { long a; int i;

a = sysconf(_SC_ATEXIT_MAX); printf("ATEXIT_MAX = %ld0, a);

i = atexit(bye); if (i != 0) { fprintf(stderr, "cannot set exit function0); exit(EXIT_FAILURE); }


SEE ALSO _exit(2), exit(3), on_exit(3)

COLOPHON This page is part of release 3.22 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at

Linux 2008-12-05 ATEXIT(3)