overwrite binary data

[Christine Nguyen]

I've written a program in VB.net. I need to open a file in binary mode and
edit it. I cannot find a way to partially overwrite existing data. There
are certain hex values I need to replace in the file. I am looking at the
System.IO.Binar yWriter class. There only seems to be a way to append or
completely truncate the contents of a file. Does anybody have an idea how I
might accomplish this??

Thanks,
Christine

[Christine Nguyen]

Re: overwrite binary data

I should state that I actually want to delete parts of the binary data also
(but not all of it).

-Christine



"Christine Nguyen" <hch_nguyen@hot mail.com> wrote in message
news:e7denP0XDH A.1736@TK2MSFTN GP10.phx.gbl...[color=blue]
> I've written a program in VB.net. I need to open a file in binary mode[/color]
and[color=blue]
> edit it. I cannot find a way to partially overwrite existing data. There
> are certain hex values I need to replace in the file. I am looking at the
> System.IO.Binar yWriter class. There only seems to be a way to append or
> completely truncate the contents of a file. Does anybody have an idea how[/color]
I[color=blue]
> might accomplish this??
>
> Thanks,
> Christine
>
>[/color]

[Chris Devol]

Re: overwrite binary data


"Christine Nguyen" <hch_nguyen@hot mail.com> wrote in message
news:%23eaopZ0X DHA.1744@TK2MSF TNGP12.phx.gbl. ..[color=blue]
> I should state that I actually want to delete parts of the binary data also
> (but not all of it).
>
> -Christine
>
> "Christine Nguyen" <hch_nguyen@hot mail.com> wrote in message
> news:e7denP0XDH A.1736@TK2MSFTN GP10.phx.gbl...[color=green]
> > I've written a program in VB.net. I need to open a file in binary mode[/color]
> and[color=green]
> > edit it. I cannot find a way to partially overwrite existing data. There
> > are certain hex values I need to replace in the file. I am looking at the
> > System.IO.Binar yWriter class. There only seems to be a way to append or
> > completely truncate the contents of a file. Does anybody have an idea how[/color]
> I[color=green]
> > might accomplish this??
> >
> > Thanks,
> > Christine[/color][/color]

I don't think you can edit a file directly on the disk.

You have to load the file into an array or other structure using a streamreader,
then operate on it, and then overwrite the file using a streamwriter.

[Chris Devol]

Re: overwrite binary data

"Jon Skeet" <skeet@pobox.co m> wrote in message
news:MPG.19a06f 76251136498a2c7 @news.microsoft .com...[color=blue]
> Chris Devol <xyz@defghijk.l mn> wrote:[color=green]
> > I don't think you can edit a file directly on the disk.[/color]
>
> Yes you can - there's no problem doing that. You can't insert or delete
> bits from the start of middle of the file, of course, but that's a
> different matter.[/color]

It seems to me that inserting and deleting is what "editing" is. So if you can't
insert/delete then you can't edit. Or am I missing something?
[color=blue][color=green]
> > You have to load the file into an array or other structure using a
> > streamreader, then operate on it, and then overwrite the file using
> > a streamwriter.[/color]
>
> Note that StreamReader and StreamWriter are meant for text operations,
> not the binary operations Christine is interested in.[/color]

That's true. I should have said "BinaryReader". .........

[Jon Skeet]

Re: overwrite binary data

Chris Devol <xyz@defghijk.l mn> wrote:[color=blue][color=green]
> > Chris Devol <xyz@defghijk.l mn> wrote:[color=darkred]
> > > I don't think you can edit a file directly on the disk.[/color]
> >
> > Yes you can - there's no problem doing that. You can't insert or delete
> > bits from the start of middle of the file, of course, but that's a
> > different matter.[/color]
>
> It seems to me that inserting and deleting is what "editing" is. So
> if you can't insert/delete then you can't edit. Or am I missing something?[/color]

Yes. You can overwrite. Consider a file which has fixed length records
- it's perfectly possible to overwrite those records with new ones.
Alternatively, you might have something which goes through an assembly
marking all public methods as internal, or vice versa - something which
just requires changing a single byte for each method. No need to read
the whole file in and write it all out again.

--
Jon Skeet - <skeet@pobox.co m>

http://www.pobox.com/~skeet/

If replying to the group, please do not mail me too

[Christine Nguyen]

Re: overwrite binary data

Hi,

I accomplished using the FileStream Class. It will do binary operations and
insert without copying to a temp file and will delete at the tail end of the
file using Filestream.SetL ength.

Thanks,
Christine


"Chris Dunaway" <dunawayc@_lunc hmeat_sbcglobal .net> wrote in message
news:Xns93D579C 8AF076CAD@207.4 6.248.16...[color=blue]
> "Christine Nguyen" <hch_nguyen@hot mail.com> wrote in
> news:e7denP0XDH A.1736@TK2MSFTN GP10.phx.gbl:
>[color=green]
> > I've written a program in VB.net. I need to open a file in binary
> > mode and edit it. I cannot find a way to partially overwrite existing
> > data. There are certain hex values I need to replace in the file. I
> > am looking at the System.IO.Binar yWriter class. There only seems to
> > be a way to append or completely truncate the contents of a file. Does
> > anybody have an idea how I might accomplish this??
> >
> >[/color]
>
> The BinaryWriter class has a seek method which you can use to position the
> file pointer at any point and overwrite the data at that position.
>
> As far as inserting, you will have to use a temp file and read all the[/color]
data[color=blue]
> up to the insertion point, write that data to the temp file, then write[/color]
the[color=blue]
> data you want to insert to the temp file, and finally read the remaining
> data and write it to the temp file. Assuming all has gone well, delete[/color]
the[color=blue]
> original file and rename the temp file.
>
> A similar procedure must be used to delete information from a file.
>
> Chris
>
>
> --
> If you don't like lunchmeat, please remove it from my e-mail address to
> send me an e-mail[/color]