Why isn't the Byte Order Mark emitted from UTF8Encoding.GetBytes?

Question

The snippet says it all :-)

UTF8Encoding enc = new UTF8Encoding(true/*include Byte Order Mark*/);
byte[] data = enc.GetBytes("a");
// data has length 1.
// I expected the BOM to be included. What's up?

Answer 1

You wouldn't want it to be used for every call to GetBytes, otherwise you'd have no way of (say) writing a file a line at a time.

By exposing it with GetPreamble, callers can insert the preamble just at the appropriate point (i.e. at the start of their data). I agree that the documentation could be a lot clearer though.

Answer 2

Thank you both. The following works, and LINQ makes the combination simple :-)

UTF8Encoding enc = new UTF8Encoding(true);
byte[] data = enc.GetBytes("a");
byte[] combo = enc.GetPreamble().Concat(data).ToArray();