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]

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

-Christine

"Christine Nguyen" <hc********@hot mail.com> wrote in message
news:e7******** ******@TK2MSFTN GP10.phx.gbl...

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

[Chris Devol]

"Christine Nguyen" <hc********@hot mail.com> wrote in message
news:%2******** ********@TK2MSF TNGP12.phx.gbl. ..

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

-Christine

"Christine Nguyen" <hc********@hot mail.com> wrote in message
news:e7******** ******@TK2MSFTN GP10.phx.gbl...

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

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]

"Jon Skeet" <sk***@pobox.co m> wrote in message
news:MP******** *************** @news.microsoft .com...

Chris Devol <xy*@defghijk.l mn> wrote:

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

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.

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?

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.

Note that StreamReader and StreamWriter are meant for text operations,
not the binary operations Christine is interested in.

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

[Jon Skeet]

Chris Devol <xy*@defghijk.l mn> wrote:

Chris Devol <xy*@defghijk.l mn> wrote:

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

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.

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?

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 - <sk***@pobox.co m>
http://www.pobox.com/~skeet/
If replying to the group, please do not mail me too

[Christine Nguyen]

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:Xn******** *********@207.4 6.248.16...

"Christine Nguyen" <hc********@hot mail.com> wrote in
news:e7******** ******@TK2MSFTN GP10.phx.gbl:

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??
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

data up to the insertion point, write that data to the temp file, then write the 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 the 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