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Re: How to see if variable is defined? [message #3435 is a reply to message #3359]

Tue, 24 January 1995 08:22

rep2857
Messages: 28
Registered: December 1994

Junior Member

In article <RFINCH.95Jan20094331@venice.water.ca.gov>,
Ralph Finch <rfinch@water.ca.gov> wrote:
> Is there a nice way of checking if a variable is defined?
>
> I have a widget_control command which removes a menu, and I need to
> see if the menu is defined before destroying it.

In the general case of checking whether a variable is defined you can
use the size() function. For example:

IDL> print, var
% PRINT: Variable is undefined: VAR.
% Execution halted at $MAIN$ (PRINT).
IDL> print, size(var)
0 0 1

The first parameter will be a zero if var is undefined.

For widgets in particular, the widget_info function has a "valid_id"
keyword which can check to see if the widget is a valid ID. Based on
the return from the call you can destroy the widget with
widget_control, /destroy.

if (Widget_Info(tac_base, /valid_id)) then $
Widget_Control, tac_base, /Destroy

Mike Schienle Hughes Santa Barbara Research Center
rep2857@sbsun0010.sbrc.hac.com 75 Coromar Drive, M/S B28/87
Voice: (805)562-7466 Fax: (805)562-7881 Goleta, CA 93117

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[Message index]

		How to see if variable is defined? By: rfinch on Fri, 20 January 1995 09:43
		Re: How to see if variable is defined? By: zawodny on Thu, 26 January 1995 12:28
		Re: How to see if variable is defined? By: nmw on Thu, 26 January 1995 03:18
		Re: How to see if variable is defined? By: thompson on Fri, 27 January 1995 06:49
		Re: How to see if variable is defined? By: rep2857 on Tue, 24 January 1995 08:22
		Re: How to see if variable is defined? By: ps on Thu, 26 January 1995 09:47
		Re: How to see if variable is defined? By: thompson on Mon, 23 January 1995 07:47

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