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C#-计算相对路径

   /// <summary>
        /// 计算相对路径
        /// 后者相对前者的路径。
        /// </summary>
        /// <param name="mainDir">主目录</param>
        /// <param name="fullFilePath">文件的绝对路径</param>
        /// <returns>fullFilePath相对于mainDir的路径</returns>
        /// <example>
        /// @"..\..\regedit.exe" = GetRelativePath(@"D:\Windows\Web\Wallpaper\", @"D:\Windows\regedit.exe" );
        /// </example>
        public static string GetRelativePath(string mainDir, string fullFilePath)
        {
            if (!mainDir.EndsWith("\\"))
            {
                mainDir += "\\"; 
            }

            int intIndex = -1, intPos = mainDir.IndexOf('\\');
          
            while (intPos >= 0)
            {
                intPos++;
                if (string.Compare(mainDir, 0, fullFilePath, 0, intPos, true) != 0) break;
                intIndex = intPos;
                intPos = mainDir.IndexOf('\\', intPos);
            }

              if (intIndex >= 0)
            {
                fullFilePath = fullFilePath.Substring(intIndex);
                intPos = mainDir.IndexOf("\\", intIndex);
                while (intPos >= 0)
                {
                    fullFilePath = "..\\" + fullFilePath;
                    intPos = mainDir.IndexOf("\\", intPos + 1);
                }
            }
           
            return fullFilePath;
        }