StreamWriter erroneous characters

Question

Having an problem where streamwriter is producing erroneous characters in a csv that I\'m producing. The characters,  , only appear at the start of the file:

Answer 1

You have specified that you want to use UTF-8 encoding for the stream and those initial bytes is a valid UTF-8 Byte Order Mark (BOM). The problem is apparently that your viewer/editor doesn't decode the UTF-8 stream correctly. If it only is the BOM that is the problem and you want to create a stream without a BOM you can create your own instance of the UTF8Encoding class:

var encoding = new UTF8Encoding(encoderShouldEmitUTF8Identifier: false);
using (StreamWriter sw = new StreamWriter(Response.OutputStream, encoding)) ...

In case you really want to work with ASCII data you should use that encoding instead:

using (StreamWriter sw = new StreamWriter(Response.OutputStream, Encoding.ASCII)) ...

Answer 2

Those are probably characters designating that the file is unicode, and not ansi.

Are you opening the file as an ANSI file, in a text editor? If so, that's why you're seeing the characters. Either try opening it as unicode, or set your encoding to not be unicode.