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Conference vaxaxp::vmsnotes

Title:	VAX and Alpha VMS
Notice:	This is a new VMSnotes, please read note 2.1
Moderator:	VAXAXP::BERNARDO

Created:	Wed Jan 22 1997
Last Modified:	Fri Jun 06 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	703
Total number of notes:	3722

135.0. "ON CONTROL_Y also traps CTRL/C ?" by TKTV20::HASHIMOTO () Mon Feb 03 1997 21:59

One of my customer wants to trap CTRL/Y in a command procedure.
He was trying ON CONTROL_Y command, but he found that the command also
catches CTRL/C although online-help does not mention about CTRL/C.
He is working on V6.1 of OpenVMS Alpha.

My questions are:

1. Is this an officially correct function which ON CONTROL_Y command has ?
2. How can he control CTRL/Y or CTRL/C separately in a command procedure ?

Thanks in advance,

CSC-Tokyo
Junshi

$!
$! This is a sample procedure to reproduce the problem.
$!
$ On CONTROL_Y Then GoTo CTRL$Y
$ Set On
$
$ LOOP:
$   Wait 00:00:02
$   Show Time
$ GoTo LOOP
$
$ CTRL$Y:
$ Write SYS$OUTPUT "CTRL/Y ( or CTRL/C ? ) pressed"
$ Exit

T.R	Title	User	Personal Name	Date	Lines
135.1		POMPY::LESLIE	[email protected] as of Feb 14	`Tue Feb 04 1997 02:53`	6
	1) Dunno about official, but it's been this way for a very long time. I'm not sure dcl differentiates between CTRL_C and CTRL_Y at all. 2) He can't that I know of. You may wish to try the EPS::COMMAND_PROCEDURES and NOTED::HACKERS conferences for workarounds etc.
135.2	See HELP SET CONTROL	GREGOR::OPP		`Tue Feb 04 1997 08:00`	5
	Refer also to HELP SET CONTROL. You may be able to develop a 'hack' that works for your specific application. Greg
135.3	QAR The Docs	XDELTA::HOFFMAN	Steve, OpenVMS Engineering	`Tue Feb 04 1997 09:28`	17
	:1. Is this an officially correct function which ON CONTROL_Y command has ? Yes, this is expected and long-standing behaviour of DCL. Log a QAR against the DCL dictionary and the user's manual, as both do not clearly document this behaviour. (One has to read through the fine print in the terminal driver section -- if no <CTRL/C> AST is enabled, the terminal driver converts a <CTRL/C> to a <CTRL/Y> -- in the I/O user's manual to learn of this behaviour.) :2. How can he control CTRL/Y or CTRL/C separately in a command procedure ? DCL processes both interrupts -- <CTRL/Y> and <CTRL/C> -- the same, it establishes no <CTRL/C> handler. Images can choose to behave differently, and can establish -- via calls to the terminal driver and a call to the run-time libraru LIB$ENABLE_CTRL routine.
135.4		AUSS::GARSON	DECcharity Program Office	`Tue Feb 04 1997 17:11`	21
	re .* Note also that the terminal driver echoes CTRL/C in a context specific way. That is, if no CTRL/C handler is enabled, CTRL/C is echoed as a CTRL/Y (Interrupt) and processed as one. If a CTRL/C handler is enabled, CTRL/C is echoed as Cancel. (Try for example pressing CTRL/C while TYPEing a longish file.) DCL is blameless and it is not surprising that DCL documentation doesn't cover this. I can't see any easy way of achieving separate CTRL/C processing in a DCL command procedure and DCL would not want to have an unconditionally enabled CTRL/C handler itself since that would break lots of applications that have their own handler. You may have to change the "user interface" to take account of this behaviour of the terminal driver e.g. have CTRL/Y handling ask indirectly whether Y or C was required, or e.g. require two CTRL/Y presses in reasonably quick succession to get the CTRL/C behaviour (but that won't work too well if logged in via SET HOST).
135.5		TKTV20::HASHIMOTO		`Wed Feb 05 1997 19:55`	1
	Thank you for your many precious information. They help me a lot.