| Re: Locating sequence of bytes within binary file [message #71322 is a reply to message #71320] |
Wed, 16 June 2010 02:40  |
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Steve[5]
Messages: 10
Registered: September 2007
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Junior Member |
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medd wrote:
> 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...
How about doint the "dirty solution" as a first pass, then filtering the
returned results to check if they are "real" solutions?
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