Terminate execution of the program from which they are called.
These functions are nonreentrant.
Format
#include <stdlib.h>
void exit (int status);
#include <unistd.h>
void _exit (int status);
1 – Argument
status
For non-POSIX behavior, a status value of EXIT_SUCCESS (1), EXIT_
FAILURE (2), or a number from 3 to 255, as follows:
o A status value of 0, 1 or EXIT_SUCCESS is translated to the
OpenVMS SS$_NORMAL status code to return the OpenVMS success
value.
o A status value of 2 or EXIT_FAILURE is translated to an error-
level exit status. The status value is passed to the parent
process.
o Any other status value is left the same.
For POSIX behavior:
o A status value of 0 is translated to the OpenVMS SS$_NORMAL
status code to return the OpenVMS success value.
o Any other status is returned to the parent process as an
OpenVMS message symbol with facility set to C, severity
set to success, and with the status in the message number
field. For more information on the format of message symbols,
see "message code" in the VSI OpenVMS Command Definition,
Librarian, and Message Utilities Manual.
To get POSIX behavior, include <unistd.h> and compile with the
_POSIX_EXIT feature-test macro set (either with /DEFINE=_POSIX_
EXIT, or with #define _POSIX_EXIT at the top of your file, before
any file inclusions). This behavior is available only on OpenVMS
Version 7.0 and higher systems.
2 – Description
If the process was invoked by DCL, the status is interpreted by
DCL, and a message is displayed.
If the process was a child process created using vfork or an exec
function, then the child process exits and control returns to the
parent. The two functions are identical; the _exit function is
retained for reasons of compatibility with VAX C.
The exit and _exit functions make use of the $EXIT system
service. If your process is being invoked by the RUN command
using any of the hibernation and scheduled wakeup qualifiers, the
process might not correctly return to hibernation state when an
exit or _exit call is made.
The C compiler command-line qualifier /[NO]MAIN=POSIX_EXIT can be
used to direct the compiler to call __posix_exit instead of exit
when returning from main. The default is /NOMAIN.
Beginning with OpenVMS Version 8.3, C RTL contains a fix for
the problem in which a call to _exit after a failed execl really
exits but must not.
In the OpenVMS implementation of vfork, a child process is not
actually started as it is started on most UNIX systems. However,
the C RTL creates some internal data structures intended to mimic
child-process functionality (called the "child context").
A bug occurred whereby after a vfork while in the child context,
a call to an exec function justifiably fails, then calls _exit.
On UNIX systems, after the failed exec call, the child process
continues to execute. A subsequent call to _exit terminates
the child. In the OpenVMS implementation, after the failed exec
call, the child context terminates. A subsequent call to _exit
terminates the parent. The C RTL fix is enabled by a feature
logical switch, DECC$EXIT_AFTER_ FAILED_EXEC. Enabling this
feature logical allows the child context to continue execution.
With DECC$EXIT_AFTER_FAILED_EXEC disabled or not defined, the
current behavior remains the default.
NOTE
EXIT_SUCCESS and EXIT_FAILURE are portable across any
ANSI C compiler to indicate success or failure. On OpenVMS
systems, they are mapped to OpenVMS condition codes with
the severity set to success or failure, respectively. Values
in the range of 3 to 255 can be used by a child process to
communicate a small amount of data to the parent. The parent
retrieves this data using the wait, wait3, wait4, or waitpid
functions.