C#获取文件编码

/// <summary>
 /// 检测字符编码的类
 /// <seealso cref="System.IO.Stream"/>
 /// <seealso cref="System.Uri"/>
 /// <seealso cref="System.IO.FileInfo"/>
 /// </summary>
 /// <remarks>
 /// <![CDATA[
 /// FileEncoder 用来检测 <see cref="Uri"/>,<see cref="System.IO.FileInfo"/>,<see cref="sbyte"/> 字节数组的编码．
 /// Create By lion 
 /// 2005-02-21 22:00 
 /// Support .Net Framework v1.1.4322 
 /// WebSite：www.lionsky.net(lion-a AT sohu.com) 
 /// ]]>
 /// </remarks>
 public class FileEncoder
 {
 #region Fields.....

        // Frequency tables to hold the GB, Big5, and EUC-TW character
        // frequencies
        internal static int[][] GBFreq = new int[94][];
        internal static int[][] GBKFreq = new int[126][];
        internal static int[][] Big5Freq = new int[94][];
        internal static int[][] EUC_TWFreq = new int[94][];

        internal static string[] nicename = new string[]
   {
    "GB2312", "GBK", "HZ", "Big5", "CNS 11643"
    , "ISO 2022CN", "UTF-8", "Unicode", "ASCII", "OTHER"
   };

#endregion

#region Methods.....

/// <summary>
 /// 初始化 <see cref="IdentifyEncoding"/> 的实例
 /// </summary>
 public FileEncoder()
 {
 Initialize_Frequencies();
 }

#region GetEncodingName.....

/// <summary>
 /// 从指定的 <see cref="Uri"/> 中判断编码类型
 /// </summary>
 /// <param name="testurl">要判断的 <see cref="Uri"/> </param>
 /// <returns>返回编码类型("GB2312", "GBK", "HZ", "Big5", "CNS 11643", "ISO 2022CN", "UTF-8", "Unicode", "ASCII", "OTHER")</returns>
 /// <example>
 /// 以下示例演示了如何调用 <see cref="GetEncodingName"/> 方法：
 /// <code>
 /// IdentifyEncoding ide = new IdentifyEncoding();
 /// Response.Write(ide.GetEncodingName(new Uri("http://china5.nikkeibp.co.jp/china/news/com/200307/pr_com200307170131.html")));
 /// </code>
 /// </example>
 public virtual string GetEncodingName(System.Uri testurl)
 {
 sbyte[] rawtext = new sbyte[1024];
 int bytesread = 0, byteoffset = 0;
 System.IO.Stream chinesestream;
 try
 {
 chinesestream = System.Net.WebRequest.Create(testurl.AbsoluteUri).GetResponse().GetResponseStream();
 while ((bytesread = ReadInput(chinesestream, ref rawtext, byteoffset, rawtext.Length - byteoffset)) > 0)
 {
 byteoffset += bytesread;
 }
 chinesestream.Close();
 }
 catch (System.Exception e)
 {
 System.Console.Error.WriteLine("Error loading or using URL " + e.ToString());
 }
 return GetEncodingName(rawtext);
 }

/// <summary>
 /// 从指定的 <see cref="System.IO.FileInfo"/> 中判断编码类型
 /// </summary>
 /// <param name="testfile">要判断的 <see cref="System.IO.FileInfo"/> </param>
 /// <returns>返回编码类型("GB2312", "GBK", "HZ", "Big5", "CNS 11643", "ISO 2022CN", "UTF-8", "Unicode", "ASCII", "OTHER")</returns>
 /// <example>
 /// 以下示例演示了如何调用 <see cref="GetEncodingName"/> 方法：
 /// <code>
 /// IdentifyEncoding ide = new IdentifyEncoding();
 /// Response.Write(ide.GetEncodingName(new System.IO.FileInfo(@"C: est.txt")));
 &n

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