How can I detect if a .NET StreamReader found a UTF8 BOM on the underlying stream?

c# utf-8 filestream streamreader byte-order-mark
bookclub picture bookclub · Feb 16, 2011 · Viewed 10.5k times · Source

I get a FileStream(filename,FileMode.Open,FileAccess.Read,FileShare.ReadWrite) and then a StreamReader(stream,true).

Is there a way I can check if the stream started with a UTF8 BOM? I am noticing that files without the BOM are read as UTF8 by the StreamReader.

How can I tell them apart?

Answer

Carlo V. Dango picture Carlo V. Dango · Feb 27, 2012

Rather than hardcoding the bytes, it is prettier to use the API

public string ConvertFromUtf8(byte[] bytes)
{
  var enc = new UTF8Encoding(true);
  var preamble = enc.GetPreamble();
  if (preamble.Where((p, i) => p != bytes[i]).Any()) 
    throw new ArgumentException("Not utf8-BOM");
  return enc.GetString(bytes.Skip(preamble.Length).ToArray());
}

Related questions

How can I transform string to UTF-8 in C#?

I have a string that I receive from a third party app and I would like to display it correctly in any language using C# on my Windows Surface. Due to incorrect encoding, a piece of my string looks like …

Read More
C# Convert string from UTF-8 to ISO-8859-1 (Latin1) H

I have googled on this topic and I have looked at every answer, but I still don't get it. Basically I need to convert UTF-8 string to ISO-8859-1 and I do it using following code: Encoding iso = Encoding.GetEncoding("…

Read More
Using StringWriter for XML Serialization

I'm currently searching for an easy way to serialize objects (in C# 3). I googled some examples and came up with something like: MemoryStream memoryStream = new MemoryStream ( ); XmlSerializer xs = new XmlSerializer ( typeof ( MyObject) ); XmlTextWriter xmlTextWriter = new XmlTextWriter ( memoryStream, Encoding.UTF8 ); xs.…

Read More