Re: replacing text data in a binary file

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From: Jay B. Harlow [MVP - Outlook] (Jay_Harlow_MVP_at_msn.com)
Date: 06/09/04 

Date: Wed, 9 Jun 2004 09:24:40 -0500

Adam,
&hFF (-1) is a valid Byte value, returning an integer allows -1 for EOF &
&HFF for the byte.

Hope this helps
Jay

"Adam J. Schaff" <aschaff@cascocdev.com> wrote in message
news:OU0vfXiTEHA.3944@tk2msftngp13.phx.gbl...
> p.s. I just notice that value is an integer. That explains the cbyte in
your
> code, but now I'm confused why ReadByte returns an integer?? Is it
something
> to do with testing for EOF? (-1 isn't a typical byte value it occurs to me
> ;)
>
> "Jay B. Harlow [MVP - Outlook]" <Jay_Harlow_MVP@msn.com> wrote in message
> news:uAuSP4hTEHA.1984@TK2MSFTNGP12.phx.gbl...
> > Adam,
> > If you are editing a binary file I would recommend opening the file with
a
> > BinaryReader or even just FileStream directly.
> >
> > > Dim sr As New StreamReader(fs, System.Text.Encoding.UTF8)
> >
> > If you use a StreamReader, you are actually converting the file into
Text
> > (8bit bytes to 16 bit chars) then converting the file back into Binary.
> >
> > My two concerns with using a StreamReader are:
> > 1. depending on what the binary file actually contains (an exe for
> example)
> > removing or adding characters may actually corrupt the file, as the file
> > contains length & offset fields...
> > 2. Loosing certain bytes, ones that are not translated nicely from
> arbitrary
> > bytes back & forth to Unicode. For example using Encoding.ASCII will
trash
> > your file as ASCII is 7 bit, you will loose all the high order bits. I
> > suspect with UTF8 you will be OK, however it just does not feel right...
> >
> > Here is a simple program that will copy a file one byte at a time, the
> trick
> > is going to be modify it so it looks for "g:\" one byte at a time and
> skips
> > those bytes, only if all three are found... Especially if you want to
> ensure
> > they are prefaced with "file//".
> >
> > Dim input As New FileStream("Only Fools.fpl", FileMode.Open)
> > Dim output As New FileStream("Only Fools2.fpl", FileMode.Create)
> > Dim value As Integer
> > value = input.ReadByte()
> > Do Until value = -1
> > output.WriteByte(CByte(value))
> > value = input.ReadByte()
> > Loop
> > input.Close()
> > output.Close()
> >
> > Hope this helps
> > Jay
> >
> > "Adam J. Schaff" <abjunk@adelphia.net> wrote in message
> > news:OkxC3hdTEHA.1508@TK2MSFTNGP11.phx.gbl...
> > > I am writing a quick program to edit a binary file that contains file
> > paths
> > > (amongst other things). If I look at the files in notepad, they look
> like:
> > >
> > >
> <gibberish>file//g:\pathtofile1<gibberish>file//g:\pathtofile2<gibberish>
> > > etc.
> > >
> > > I want to remove the "g:\" from the file paths. I wrote a console app
> that
> > > successfully reads the file and writes a duplicate of it, but fails
for
> > some
> > > reason to do the "replacing" of the "g:\". The code follows with a
note
> > > showing the line that is not working. When I look at the "s" variable
in
> > > break mode, I see that VB does not show the entire file contents, even
> > > though when I write "s" to the second file stream, the entire original
> > file
> > > is duplicated. I suppose this is because the file content isn't
intended
> > to
> > > be interpreted as a string (its binary after all). It is probably
> hitting
> > > some unfriendly bytes that it can't interpret for string operations
like
> > > Replace. If that's the case, maybe I need to interact with it a
> character
> > at
> > > a time, although I'm not sure how I would do a replace that way. Any
> ideas
> > > or code would be greatly appreciated. As you can tell, I don't do much
> > > binary file I/O.
> > >
> > > Sub Main()
> > > 'read the binary file into a string var
> > > Dim fs As New FileStream("C:\Source\Sample and
> > > Demo\Foobar\EditFpl\Only Fools.fpl", FileMode.Open, FileAccess.Read)
> > > Dim sr As New StreamReader(fs, System.Text.Encoding.UTF8)
> > > Dim s As String = sr.ReadToEnd
> > > sr.Close()
> > > fs.Close()
> > >
> > > 'remove the hard-coded drive letter specification
> > > s.Replace("file://G:\", "file://") 'THIS LINE DOES NOT WORK
> > >
> > > 'write a new binary file with my changes
> > > Dim fs2 As New FileStream("C:\Source\Sample and
> > > Demo\Foobar\EditFpl\Only Fools2.fpl", FileMode.CreateNew,
> > FileAccess.Write)
> > > Dim sw As New StreamWriter(fs2, System.Text.Encoding.UTF8)
> > > sw.Write(s)
> > >
> > > sw.Close()
> > > fs2.Close()
> > > End Sub
> > >
> > >
> >
> >
>
>

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