c# base64转字符串实例

string a = "base64字符串与普通字符串互转"; 
 byte[] b = System.Text.Encoding.Default.GetBytes(a); 
 //转成 Base64 形式的 System.String 
 a = Convert.ToBase64String(b); 
 Response.Write(a); 

 byte[] c = Convert.FromBase64String(a); 
 a = System.Text.Encoding.Default.GetString(c); 
 Response.Write(a);

#region base64转图片
    /// <summary>
    /// 图片上传 Base64解码
    /// </summary>
    /// <param name="dataURL">Base64数据</param>
    /// <param name="imgName">图片名字</param>
    /// <returns>返回一个相对路径</returns>
    public string decodeBase64ToImage(string dataURL,string imgName)
    {
 
      string filename = "";//声明一个string类型的相对路径
 
      String base64 = dataURL.Substring(dataURL.IndexOf(",") + 1);   //将‘，'以前的多余字符串删除
      System.Drawing.Bitmap bitmap = null;//定义一个Bitmap对象，接收转换完成的图片
 
      try//会有异常抛出，try，catch一下
      {
 
        byte[] arr = Convert.FromBase64String(base64);//将纯净资源Base64转换成等效的8位无符号整形数组
 
        System.IO.MemoryStream ms = new System.IO.MemoryStream(arr);//转换成无法调整大小的MemoryStream对象
        bitmap = new System.Drawing.Bitmap(ms);//将MemoryStream对象转换成Bitmap对象
 
        filename ="Knowledge_" + imgName + ".jpg";//所要保存的相对路径及名字
        string url =HttpRuntime.AppDomainAppPath.ToString();
        string tmpRootDir = System.Web.HttpContext.Current.Server.MapPath(System.Web.HttpContext.Current.Request.ApplicationPath.ToString()); //获取程序根目录 
        string imagesurl2 = tmpRootDir + filename; //转换成绝对路径 
        bitmap.Save(imagesurl2, System.Drawing.Imaging.ImageFormat.Jpeg);//保存到服务器路径
        //bitmap.Save(filePath + ".bmp", System.Drawing.Imaging.ImageFormat.Bmp);
        //bitmap.Save(filePath + ".gif", System.Drawing.Imaging.ImageFormat.Gif);
        //bitmap.Save(filePath + ".png", System.Drawing.Imaging.ImageFormat.Png);
        ms.Close();//关闭当前流，并释放所有与之关联的资源
        bitmap.Dispose();
      }
      catch (Exception e)
      {
        string massage= e.Message;
      }
      return filename;//返回相对路径
    }
    #endregion
 
    #region 图片转base64
    /// <summary>
    /// 图片转base64
    /// </summary>
    /// <param name="path">图片路径</param><br>    /// <returns>返回一个base64字符串</returns>
    public string decodeImageToBase64(string path) {
      path = "E:/vs 2015/newaqtcprj/WEB/UpFile/2018/12/20181229174708_7471722c425a2ec08fa513ddf4f8c76306d55fbb0fbd9d8.jpg";
      string base64str = "";
 
      //站点文件目录
      string fileDir = HttpContext.Current.Server.MapPath("/");
      string[] arrfileDir = fileDir.Split('\\');
      fileDir = arrfileDir[0] + "\\" + arrfileDir[1] + "\\" + arrfileDir[2];
      try
      {
        //读图片转为Base64String
        System.Drawing.Bitmap bmp = new System.Drawing.Bitmap(Path.Combine(fileDir, "WEB\\UpFile\\2018\\12\\20181229174708_7471722c425a2ec08fa513ddf4f8c76306d55fbb0fbd9d8.jpg"));
        //System.Drawing.Bitmap bmp = new System.Drawing.Bitmap(path);
        MemoryStream ms = new MemoryStream();
        bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
        byte[] arr = new byte[ms.Length];
        ms.Position = 0;
        ms.Read(arr, 0, (int)ms.Length);
        ms.Close();
        bmp.Dispose();
        base64str = Convert.ToBase64String(arr);
      }
      catch (Exception e)
      {
        string mss = e.Message;
      }
      return "data:image/jpg;base64," + base64str;
    }
    #endregion