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Locating sequence of bytes within binary file [message #71334]

Tue, 15 June 2010 04:30

medd
Messages: 8
Registered: June 2010

Junior Member

Hi,

I need to locate a given sequence of bytes within a binary file. I do
not manage to do it efficiently, and I wanted to ask if somebody here
has a clue.

I saw that there are no functions in IDL to look for a given sequence
within a byte array, but there are very powerful functions to look for
a sequence within a string using regular expressions. This is what I
tried:

fcontent = BYTARR((FILE_INFO(fn)).size, /NOZERO) ;Variable where to
read in the file
OPENU, unit, fn, /GET_LUN;, /SWAP_ENDIAN
READU, unit, fcontent
IF(STREGEX(STRING(fcontent), STRING(sequence_searched)) LT 0) THEN
print, 'sequence not found'

This works!! ... But only as long as the file does not contain a byte
with the value 0 (which, too bad!, it does...)

After looking a while, I found in this forum (message "Null terminated
strings") and in the IDL help that a string is truncated as soon as
this value is found. This explains why this method fails. But it does
not propose solutions... :(

Do you know some smart workaround? Or do you know other efficient ways
in IDL to locate a sequence of bytes within a binary file?

Thanks!

PS. I thought about replacing all 0's by 1's, but it is a really dirty
solution, which might find the sequence at the wrong place in case
there is a similar sequence which really contains a 1 instead...

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[Message index]

		Locating sequence of bytes within binary file By: medd on Tue, 15 June 2010 04:30
		Re: Locating sequence of bytes within binary file By: JDS on Thu, 17 June 2010 10:48
		Re: Locating sequence of bytes within binary file By: Axel Martínez on Fri, 18 June 2010 09:47
		Re: Locating sequence of bytes within binary file By: medd on Thu, 17 June 2010 01:03
		Re: Locating sequence of bytes within binary file By: penteado on Wed, 16 June 2010 10:46
		Re: Locating sequence of bytes within binary file By: David Fanning on Fri, 18 June 2010 15:21
		Re: Locating sequence of bytes within binary file By: kamal on Thu, 24 June 2010 01:42
		Re: Locating sequence of bytes within binary file By: JDS on Fri, 18 June 2010 15:12

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