以下是获取文件编码的一个类：

using System;using System.IO;using System.Text; /// <summary>/// FileEncoding 的摘要说明/// </summary>namespace FileEncoding{/// <summary>/// 获取文件的编码格式/// </summary>public class EncodingType{/// <summary>/// 给定文件的路径，读取文件的二进制数据，判断文件的编码类型/// </summary>/// <param name="FILE_NAME">文件路径</param>/// <returns>文件的编码类型</returns>public static System.Text.Encoding GetType(string FILE_NAME){FileStream fs = new FileStream(FILE_NAME, FileMode.Open, FileAccess.Read);Encoding r = GetType(fs);fs.Close();return r;} /// <summary>/// 通过给定的文件流，判断文件的编码类型/// </summary>/// <param name="fs">文件流</param>/// <returns>文件的编码类型</returns>public static System.Text.Encoding GetType(FileStream fs){byte[] Unicode = new byte[] { 0xFF, 0xFE, 0x41 };byte[] UnicodeBIG = new byte[] { 0xFE, 0xFF, 0x00 };byte[] UTF8 = new byte[] { 0xEF, 0xBB, 0xBF }; //带BOMEncoding reVal = Encoding.Default; BinaryReader r = new BinaryReader(fs, System.Text.Encoding.Default);int i;int.TryParse(fs.Length.ToString(), out i);byte[] ss = r.ReadBytes(i);if (IsUTF8Bytes(ss) || (ss[0] == 0xEF && ss[1] == 0xBB && ss[2] == 0xBF)){reVal = Encoding.UTF8;}else 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;}r.Close();return reVal; } /// <summary>/// 判断是否是不带 BOM 的 UTF8 格式/// </summary>/// <param name="data"></param>/// <returns></returns>private static bool IsUTF8Bytes(byte[] data){int charByteCounter = 1; //计算当前正分析的字符应还有的字节数byte curByte; //当前分析的字节.for (int i = 0; i < data.Length; i++){curByte = data[i];if (charByteCounter == 1){if (curByte >= 0x80){//判断当前while (((curByte <<= 1) & 0x80) != 0){charByteCounter++;}//标记位首位若为非0 则至少以2个1开始 如:110XXXXX...........1111110X if (charByteCounter == 1 || charByteCounter > 6){return false;}}}else{//若是UTF-8 此时第一位必须为1if ((curByte & 0xC0) != 0x80){return false;}charByteCounter--;}}if (charByteCounter > 1){throw new Exception("非预期的byte格式");}return true;} } }

以下是使用示例：

#region 打开按钮/// <summary>/// 打开按钮/// </summary>/// <param name="sender"></param>/// <param name="e"></param>private void txtMenuOpen_Click(object sender, EventArgs e){string fName;OpenFileDialog openFileDialog = new OpenFileDialog();openFileDialog.InitialDirectory = "";//注意这里写路径时要用c:而不是c: openFileDialog.Filter = "文本文档|*.txt";openFileDialog.RestoreDirectory = true;openFileDialog.FilterIndex = 1;if (openFileDialog.ShowDialog() == DialogResult.OK){fName = openFileDialog.FileName; txtBox.Text = System.IO.File.ReadAllText(fName,FileEncoding.EncodingType.GetType(fName));} }#endregion