How does C automatically recognize the encoding of a file

Preface

The code of the identification file in C # is a headache. Recently, when importing the background refund data of WeChat merchants, no matter how to set the code, it was garbled. Later, I found the code of the identification file code on the Internet and felt good. Finally, it was identified as gb2312. It seems that I am still too dregs, so I can only eat dirt, and I forgot this code.

The following words do not say much, on the code.

/// <summary> 
 ///  Used to obtain 1 How to encode a text file (Encoding) .  
 /// </summary> 
 public class TxtFileEncoder
 {
  public TxtFileEncoder()
  {
   // 
   // TODO:  Add constructor logic here  
   // 
  }
  /// <summary> 
  ///  Acquire 1 The encoding method of text files. If a valid preamble cannot be found in the file header, Encoding.Default Will be returned.  
  /// </summary> 
  /// <param name="fileName"> File name. </param> 
  /// <returns></returns> 
  public static Encoding GetEncoding(string fileName)
  {
   return GetEncoding(fileName, Encoding.Default);
  }
  /// <summary> 
  ///  Acquire 1 Encoding method of text file stream.  
  /// </summary> 
  /// <param name="stream"> Text file stream. </param> 
  /// <returns></returns> 
  public static Encoding GetEncoding(FileStream stream)
  {
   return GetEncoding(stream, Encoding.Default);
  }
  /// <summary> 
  ///  Acquire 1 The encoding method of text files.  
  /// </summary> 
  /// <param name="fileName"> File name. </param> 
  /// <param name="defaultEncoding"> Default encoding method. This encoding is returned when the method cannot get a valid preamble from the header of the file. </param> 
  /// <returns></returns> 
  public static Encoding GetEncoding(string fileName, Encoding defaultEncoding)
  {
   FileStream fs = new FileStream(fileName, FileMode.Open);
   Encoding targetEncoding = GetEncoding(fs, defaultEncoding);
   fs.Close();
   return targetEncoding;
  }
  /// <summary> 
  ///  Acquire 1 Encoding method of text file stream.  
  /// </summary> 
  /// <param name="stream"> Text file stream. </param> 
  /// <param name="defaultEncoding"> Default encoding method. This encoding is returned when the method cannot get a valid preamble from the header of the file. </param> 
  /// <returns></returns> 
  public static Encoding GetEncoding(FileStream stream, Encoding defaultEncoding)
  {
   Encoding targetEncoding = defaultEncoding;
   if (stream != null && stream.Length >= 2)
   {
    // Before saving the file stream 4 Bytes  
    byte byte1 = 0;
    byte byte2 = 0;
    byte byte3 = 0;
    byte byte4 = 0;
    // Save the current Seek Position  
    long origPos = stream.Seek(0, SeekOrigin.Begin);
    stream.Seek(0, SeekOrigin.Begin);

    int nByte = stream.ReadByte();
    byte1 = Convert.ToByte(nByte);
    byte2 = Convert.ToByte(stream.ReadByte());
    if (stream.Length >= 3)
    {
     byte3 = Convert.ToByte(stream.ReadByte());
    }
    if (stream.Length >= 4)
    {
     byte4 = Convert.ToByte(stream.ReadByte());
    }
    // According to the preamble of the file stream 4 Byte judgment Encoding 
    //Unicode {0xFF, 0xFE}; 
    //BE-Unicode {0xFE, 0xFF}; 
    //UTF8 = {0xEF, 0xBB, 0xBF}; 
    if (byte1 == 0xFE && byte2 == 0xFF)//UnicodeBe 
    {
     targetEncoding = Encoding.BigEndianUnicode;
    }
    if (byte1 == 0xFF && byte2 == 0xFE && byte3 != 0xFF)//Unicode 
    {
     targetEncoding = Encoding.Unicode;
    }
    if (byte1 == 0xEF && byte2 == 0xBB && byte3 == 0xBF)//UTF8 
    {
     targetEncoding = Encoding.UTF8;
    }
    // Recovery Seek Position    
    stream.Seek(origPos, SeekOrigin.Begin);
   }
   return targetEncoding;
  }



  //  New additions 1 A method to solve the problem without BOM Adj.  UTF8  Coding problem  

  /// <summary> 
  ///  The encoding type of the file is judged by the given file stream  
  /// </summary> 
  /// <param name="fs"> File stream </param> 
  /// <returns> Encoding type of file </returns> 
  public static System.Text.Encoding GetEncoding(Stream fs)
  {
   byte[] Unicode = new byte[] { 0xFF, 0xFE, 0x41 };
   byte[] UnicodeBIG = new byte[] { 0xFE, 0xFF, 0x00 };
   byte[] UTF8 = new byte[] { 0xEF, 0xBB, 0xBF }; // Belt BOM 
   Encoding reVal = Encoding.Default;

   BinaryReader r = new BinaryReader(fs, System.Text.Encoding.Default);
   byte[] ss = r.ReadBytes(4);
   if (ss[0] == 0xFE && ss[1] == 0xFF && ss[2] == 0x00)
   {
    reVal = Encoding.BigEndianUnicode;
   }
   else if (ss[0] == 0xFF && ss[1] == 0xFE && ss[2] == 0x41)
   {
    reVal = Encoding.Unicode;
   }
   else
   {
    if (ss[0] == 0xEF && ss[1] == 0xBB && ss[2] == 0xBF)
    {
     reVal = Encoding.UTF8;
    }
    else
    {
     int i;
     int.TryParse(fs.Length.ToString(), out i);
     ss = r.ReadBytes(i);

     if (IsUTF8Bytes(ss))
      reVal = Encoding.UTF8;
    }
   }
   r.Close();
   return reVal;

  }

  /// <summary> 
  ///  Judge whether it is not  BOM  Adj.  UTF8  Format  
  /// </summary> 
  /// <param name="data"></param> 
  /// <returns></returns> 
  private static bool IsUTF8Bytes(byte[] data)
  {
   int charByteCounter = 1; 　  // Calculates the number of additional bytes of the character currently being parsed  
   byte curByte; // Bytes currently parsed . 
   for (int i = 0; i < data.Length; i++)
   {
    curByte = data[i];
    if (charByteCounter == 1)
    {
     if (curByte >= 0x80)
     {
      // Judge the current  
      while (((curByte <<= 1) & 0x80) != 0)
      {
       charByteCounter++;
      }
      // If the first bit of the tag bit is not 0  Then at least with 2 A 1 Begin   Such as :110XXXXX...........1111110X 　  
      if (charByteCounter == 1 || charByteCounter > 6)
      {
       return false;
      }
     }
    }
    else
    {
     // If UTF-8  At this time 1 Bit must be 1 
     if ((curByte & 0xC0) != 0x80)
     {
      return false;
     }
     charByteCounter--;
    }
   }
   if (charByteCounter > 1)
   {
    throw new Exception(" Unexpected byte Format !");
   }
   return true;
  }
 }

Summarize

The above is C # automatic identification of all the contents of file coding, I hope that the content of this article can bring 1 certain help to your study or work, if you have any questions, you can leave a message for communication.