Add byte order mark to a string via StringBuilder

Question

How can I add a byte order mark to a StringBuilder? (I have to pass a string to another method which will save it as a file, but I can't modify that method).

I tried this:

var sb = new StringBuilder();
sb.Append('\xEF');
sb.Append('\xBB');
sb.Append('\xBF');

But when I view it with hex editor, it adds the following sequence: C3 AF C2 BB C2 BF

The string is huge, so it would be good to do it without back and forth converting to byte array.

Edit: Clarification after questions in comments. I have to pass the string to another method which takes a string and creates a file of it on Azure Blob Storage. I can't modify the other method.

Answer 1

Two options:

1. Don't include the byte order mark in your text at all... instead use an encoding which will automatically include it

2. Include it as a character in your StringBuilder:

   sb.Append('\uFEFF'); // U+FEFF is the byte-order mark character
   

Personally I'd go for the first approach normally, but the "I can't modify that method" suggests it may not be an option in your case.