.NET – Keep text file encoding (ASCII, UTF-8, UTF-16)

using (StreamReader reader = new StreamReader(absFileName, true)) // auto detect encoding
 using (StreamWriter writer = new StreamWriter(tmpFileName, false, reader.CurrentEncoding)) // open writer with the same encoding as reader
 { 
 string line;
 while ((line = reader.ReadLine()) != null)
 {
 // do something with line
 writer.WriteLine(line );
 }
 }

I have a simple text file processing tool written in C#, The skeleton looks like this:

using (StreamReader reader = new StreamReader(absFileName, true)) // auto detect encoding
 using (StreamWriter writer = new StreamWriter(tmpFileName, false, reader.CurrentEncoding)) // open writer with the same encoding as reader
 {
 string line;
 while ((line = reader.ReadLine()) != null)
 {
 // do something with line
 writer.WriteLine(line);
 }
 }

It runs most The files are all ASCII files, and occasionally there will be UTF-16. I want to keep the file encoding, the newly created file should have the same encoding as the file being read-this is why I opened the StreamWriter with the reader’s CurrentEncoding.

My problem is that some UTF-16 files are missing the preamble, and after StreamReader is opened, it sets CurrentEncoding to UTF-8, which causes the writer to open in UTF-8 mode. While debugging, I can see Until the reader changes its CurrentEncoding property to UTF-16 after calling ReadLine for the first time, but by then the writer has been opened.

I can think of some solutions (open the writer later or twice Look at the source file-the first one is just to detect the encoding), but I think I will ask an expert for advice first. Please note that I don’t care about the code page of the ASCII file, I only care about the ASCII/UTF-8/UTF-16 encoding.

Before trying to open the writer, I will try to be a reader. Pek() should be enough in your case Yes, I think.