BinaryWriter - Too many zeros

It depends on the range of byte values that you are writing to the file.

If the range is just 0 - 127 you can use the ASCIIEncoding which corresponds to code page 20127.

If you're using the full range of 0 - 255, I'd be inclined to use Latin I which is code page 1252. There's a list of Windows code pages here:

http://www.microsoft.com/globaldev/reference/WinCP.mspx

However, as it's binary data, it shouldn't really matter which characters the byte values represent, as long as it's a single byte character set and the other application is reading the file using that assumption.

I suspect the problem at the moment is that the UTF-8 encoding is being used (which I think is the default) and this uses a 2 byte representation for values in the range 128-255.

I'm pretty sure you are right, the encoding is causing the issues.  This no doubt is a dumb question...but how do I work out the encoding I want to use?  I know I need to use Encoding.GetEncoding(codepage) in the constructor for the BinaryWriter, but what to use for the codepage?

Thanks Alan.  The problem is the exported file is used by a client in a different application so I think I need to find a way to get rid of these extra zeros. 

This could be due to the encoding being used by the BinaryWriter which is causing some of the data to be filled out with extra zeros.

As long as the data is read back using the same encoding, it shouldn't be a problem as the extra zeros will be stripped back out again.