| How to see if variable is defined? [message #3359] |
Fri, 20 January 1995 09:43  |
rfinch
Messages: 51
Registered: March 1991
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Member |
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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.
--
Ralph Finch 916-653-8268:voice 916-653-6077:fax
rfinch@dop.water.ca.gov / finger for PGP public key
"Nada burra la chamaca." A.G.
Any opinions expressed are my own; they do not represent my employer
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| Re: How to see if variable is defined? [message #3411 is a reply to message #3359] |
Thu, 26 January 1995 03:18  |
nmw
Messages: 18
Registered: January 1995
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Junior Member |
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In article 95Jan20094331@venice.water.ca.gov, rfinch@water.ca.gov (Ralph Finch) writes:
> 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.
> --
> Ralph Finch 916-653-8268:voice 916-653-6077:fax
> rfinch@dop.water.ca.gov / finger for PGP public key
> "Nada burra la chamaca." A.G.
> Any opinions expressed are my own; they do not represent my employer
There are two possible ways of doing this.
The first is to use the keyword_set function. This returns 1 if a variable
is defined, 0 otherwise. Use of this function to test for a variable being
defined is not recommended and is bad practice - it is meant to test for
the existence of a keyword in a function call, it happens to work.
The proper way is to use the size function. This returns a vector describing
the attributes of a variable. Unfortunately it is a variable length vector
which can make programming using it quite tedious. However, just to check
if a variable is defined is quite simple. The second element of the vector
is the data type of the variable, which is zero if the variable is undefined.
Thus, the code
IF (SIZE(variable))(1) EQ 0 THEN BEGIN
PRINT,'Undefined'
ENDIF ELSE BEGIN
PRINT.'defined'
ENDELSE
should tell you what you want to know.
---
------------------------------------------------------------ ------
Nigel Wade | E-mail : nmw@ion.le.ac.uk
System Administrator |
Ionospheric Physics Group | phone : +44 (0)116 2523568
University of Leicester |
Leicester, LE1 7RH, UK | fax. : +44 (0)116 2523555
------------------------------------------------------------ -------
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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
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Junior Member |
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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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| Re: How to see if variable is defined? [message #3497 is a reply to message #3411] |
Fri, 27 January 1995 06:49 |
thompson
Messages: 584
Registered: August 1991
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Senior Member |
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nmw@ion.le.ac.uk (Nigel Wade) writes:
> In article 95Jan20094331@venice.water.ca.gov, rfinch@water.ca.gov (Ralph Finch) writes:
>> 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.
>> --
>> Ralph Finch 916-653-8268:voice 916-653-6077:fax
>> rfinch@dop.water.ca.gov / finger for PGP public key
>> "Nada burra la chamaca." A.G.
>> Any opinions expressed are my own; they do not represent my employer
> There are two possible ways of doing this.
> The first is to use the keyword_set function. This returns 1 if a variable
> is defined, 0 otherwise. ...
Not quite true. KEYWORD_SET returns 1 if a variable is defined AND IS NOT
ZERO!
Bill Thompson
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| Re: How to see if variable is defined? [message #3499 is a reply to message #3435] |
Thu, 26 January 1995 09:47 |
ps
Messages: 14
Registered: September 1994
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Junior Member |
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Mike Schienle (rep2857@sbsun0010.sbrc.hac.com) wrote:
: 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.
!!NO
that's wrong:
IDL> i=1
IDL> print,size(i)
0 2 1
IDL>
The *second* parameter has to be zero (exactly s(s(0)+1, which defines
the type of the variable)
Peter
------------------ Peter 'PIT' Suetterlin -----------------
| Kiepenheuer Institut | Sternfreunde Breisgau e.V |
| fuer Sonnenphysik | |
| 0761/3198-210 | 0761/71571 |
-<ps@kis.uni-freiburg.de>-<suettpet@sun1.ruf.uni-freiburg.de>--
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