| Re: help with relational operators [message #16179] |
Thu, 08 July 1999 00:00 |
davidf
Messages: 2866
Registered: September 1996
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Senior Member |
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Dave (dmarshall@ivory.trentu.ca) writes:
> I'm getting near wits end.
Yikes! Me, too, but for a completely different reason today. :-)
> repeat begin
> ...
> ; get user to input file name
> ...
> dataFName='somefile.xdr'
> ...
> fileCheck=findfile(dataFName)
> if fileCheck eq '' then print, 'error: ', dataFName,' file not found'
>
> endrep until fileCheck ne ''
>
> % Expression must be a scalar in this context: <BYTE Array[1]>.
>
> I just want to verify the file exists before opening it.
> This gives my error message if file does not exist, but craps out if file
> does exist.
>
> help, fileCheck ne ''
>
> tells me it _is_ a scalar expression. ?
Whoops. What you don't know is that FINDFILE *always*
returns an array, even if there is only a single element
in it, as in this case. What you need in the IF statement
is a scalar not an array. You could do this:
if fileCheck[0] eq '' then print, 'error: ', dataFName,' file not found'
But a better way to handle this is to use the COUNT
keyword to FINDFILE, like this:
fileCheck=findfile(dataFName, Count=numFiles)
IF numFiles EQ 0 THEN print, 'error: ', dataFName,' file not found'
Then you don't have to worry about this quirk in IDL. :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438 E-Mail: davidf@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155
[Note: This follow-up was e-mailed to the cited author.]
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