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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

Junior Member

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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[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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