The output char buffer is too small to contain the decoded characters, encoding 'Unicode (UTF-8)' fallback 'System.Text.DecoderReplacementFallback'.

Exception when executing

if (br.PeekChar() != -)

br is a binary reader.

The data to peak is D000 (D0=208)

The cause is, for PeekChar, after peak, the value will be transformed to char.

But Unicode and normal char has different length.

If I use br.ReadByte(), there will be no problem.

But if it hit the end of one file, br.ReadByte() would threw an error.

I googled and found many similar errors.

The best article that solved my problem is

https://social.msdn.microsoft.com/Forums/vstudio/en-US/7bd62472-b4ff-47c7-9bbd-7af9512d0301/binaryreaderpeekchar-fails-when-checking-for-end-of-file?forum=clr

Use the following to identify a file end and don't use PeekChar().

if(reader.BaseStream.Position == reader.BaseStream.Length)

or exclaim the Encoding format. Then PeekChar will be OK to use.

BinaryReader binaryReader = new BinaryReader(memoryStream, Encoding.ASCII);

I used the second one. problem solved.