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Re: readu sees unexpected records [message #43895 is a reply to message #43894]

Wed, 04 May 2005 06:49

Paul Van Delst[1]
Messages: 1157
Registered: April 2002

Senior Member

Hjalti Sig wrote:
> Hello group
> I found out that when reading unformatted data, written with a fortran
> 90 program, the readu command detects a couple of extra records before
> and after each line written with the fortran program. For example, I
> wrote a 10x10 array, containing the numbers from 1-100 in a file.
> Reading the file using readu, the content of the file appears as a
> 14x10 array, with very small numbers in columns 1, 2, 13 and 14,
> (producing floating underflow), and the correct numbers in the columns
> 3-12.
> In the data file I actually had to read there are three extra records
> before and two after each line.
> These extra records do certainly not appear when reading the files
> with a fortran program.

Fortran (currently) only really supports record-based I/O. For *sequential* access output
in Fortran, each variable length output record is preceded and followed with a a record
marker indicating the length of the record (the prefix marker is for checking the length,
the suffix marker for facilitating BACKSPACE-ing). To get IDL to emulate this type of I/O,
do as DFanning suggested and use the /F77_UNFORMATTED keyword in your OPENR statement. If
your output records are all the same length, you can modify your Fortran code to output in
*direct* access and you will no longer have the record marker problem.

FWIW, the Fortran2003 standard has a new type of I/O access called "STREAM" (along with
the venerable SEQUENTIAL and DIRECT) which produces the output that just about every
non-Fortran programming type expects. A few Fortran compilers already support this feature
(some fully standard, others only sorta.)

paulv

--
Paul van Delst
CIMSS @ NOAA/NCEP/EMC

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[Message index]

		Re: readu sees unexpected records By: hjalti on Fri, 06 May 2005 06:12
		Re: readu sees unexpected records By: K. Bowman on Wed, 04 May 2005 06:55
		Re: readu sees unexpected records By: Paul Van Delst[1] on Wed, 04 May 2005 06:49
		Re: readu sees unexpected records By: David Fanning on Wed, 04 May 2005 06:27
		Re: readu sees unexpected records By: Paul Van Delst[1] on Fri, 06 May 2005 08:30
		Re: readu sees unexpected records By: David Fanning on Fri, 06 May 2005 06:21

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