| Re: Null terminated strings [message #28673] |
Mon, 07 January 2002 18:26  |
Craig Markwardt
Messages: 1869
Registered: November 1996
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Senior Member |
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James Kuyper <kuyper@gscmail.gsfc.nasa.gov> writes:
> I'm reading a string-valued file attribute from an HDF file that was
> created using C code. As seems quite reasonable for C programs, the
> attribute was written with a length that includes a terminating null
> character. When I read it in using IDL, that null character got included
> as well. This causes a number of bizarre effects, most notably:
>
> IDL> print,date
> 2001-10-07
> IDL> print,date+'T12:00:00'
> 2001-10-07'T12:00:0
>
> I can handle this particular case by using strmid(date,0,10), but in
> general a file attribute might contain multiple null-delimited strings,
> of unknown length. Is there an efficient way of converting such a string
> into an IDL string array?
What happens when you swizzle it through a STRING-BYTE-STRING
transformation?
I.e.,
date = string(byte(date))
I believe that STRING will ignore any trailing 0-bytes, hence this may
solve your problem exactly, at the expense of some extra CPU.
Good luck,
Craig
--
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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@cow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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| Re: Null terminated strings [message #28765 is a reply to message #28673] |
Tue, 08 January 2002 07:49  |
James Kuyper
Messages: 425
Registered: March 2000
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Senior Member |
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Craig Markwardt wrote:
> James Kuyper <kuyper@gscmail.gsfc.nasa.gov> writes:
>
>
>> I'm reading a string-valued file attribute from an HDF file that was
>> created using C code. As seems quite reasonable for C programs, the
>> attribute was written with a length that includes a terminating null
>> character. When I read it in using IDL, that null character got included
>> as well. This causes a number of bizarre effects, most notably:
>>
>> IDL> print,date
>> 2001-10-07
>> IDL> print,date+'T12:00:00'
>> 2001-10-07'T12:00:0
>>
>> I can handle this particular case by using strmid(date,0,10), but in
>> general a file attribute might contain multiple null-delimited strings,
>> of unknown length. Is there an efficient way of converting such a string
>> into an IDL string array?
>
>
> What happens when you swizzle it through a STRING-BYTE-STRING
> transformation?
>
> I.e.,
>
> date = string(byte(date))
>
> I believe that STRING will ignore any trailing 0-bytes, hence this may
> solve your problem exactly, at the expense of some extra CPU.
Thanks - that worked. It only solves the single-string case, but that's
the case I am currently facing. It saves me the trouble of figuring out
how long the string is, and it does the right thing, whether or not the
string is null-terminated.
I'm still wonder how to best convert a null-delimited list of strings
into an IDL string array (it's just curiousity, I don't have any
immediate need for that ability). My best solution so far is to convert
it to a byte array, find the null delimiting characters with where(),
and then write a loop to convert each subarray into a seperate IDL
string. This should work, but I'm always suspicious of the efficiency of
any solution for an IDL problem that involves an explicit loop.
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