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Re: Implied do loops in IDL [message #2245 is a reply to message #2238]

Wed, 15 June 1994 10:15

leic
Messages: 2
Registered: June 1994

Junior Member

It is possible to read FORTRAN binary as normal (ie. without the
/F77_unformatted keyword) provided you know how FORTRAN handles
the unformatted records.
I have to do this with data I use which is output in exactly the
same implied DO loop way as is your data.

On our system (SGI IRIX 5) FORTRAN prepends and appends 4 bytes
to each record. This is a long word byte count of the record
length.

To read this data back in use the following algorithm :

; Open the file as a normal data file:
OPENR, lun, /GET_LUN, file

; Define a long word byte count to read at the start and end of
; each record:
byte_count = 1L

; To read a single record, first read the byte count, then create
; an array of the necessary data type and size:
READU,lun, byte_count
data = LONARR(byte_count/4)

; Finally, read the array and the terminating byte count:
READU,lun, data,byte_count

I am pretty sure that SunOS also uses a 4byte prefix/postfix byte
count. The only real way to be sure is to use od to get a dump
of the first few records of the file and see what is in there.

Hope this helps.

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[Message index]

		Re: Implied do loops in IDL By: thompson on Thu, 16 June 1994 06:56
		Re: Implied do loops in IDL By: leic on Wed, 15 June 1994 10:15
		Re: Implied do loops in IDL By: landers on Tue, 14 June 1994 07:33
		Re: Implied do loops in IDL By: knipp on Tue, 14 June 1994 00:53
		Re: Implied do loops in IDL By: sjt on Tue, 14 June 1994 02:25

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