【答客問】信件標題解碼範例

網友提問，希望了解中文編碼解析工具關於信件標題(如=?x-gbk?q?=B5=C4=B7=AD=D2=EB?=)的解碼邏輯，特整理為程式範例並加註說明如下:

using System;

using System.Text;

using System.Text.RegularExpressions;

using System.Web;

namespace ConsoleApplication1

class Program

staticvoid Main(string[] args)

string s = "=?big5?B?UmU6IKZVpuyl66bxLKdAt36o06RGLi4u?=";

            Console.WriteLine(decodeMailSubject(s));

            s = "=?big5?Q?=B6=C2=B7t=B0=F5=A6=E6=BA=FC?=";

            Console.WriteLine(decodeMailSubject(s));

            Console.Read();

staticstring decodeMailSubject(string raw)

//若字串結尾是?=會識別失敗，加上一個空白

              raw += " ";

            StringBuilder sb = new StringBuilder();

//先解出一段一段的=?..... ?=

foreach (Match m in Regex.Matches(raw,

"=[?](?<enc>.+?)[?](?<type>.+?)[?](?<body>.+?)[?]=[^0-9A-Z]"))

string enc = m.Groups["enc"].Value.ToLower();

string type = m.Groups["type"].Value.ToLower();

string body = m.Groups["body"].Value;

                Encoding encoder = null;

//識別出Encoding

if (enc == "gbk" || enc == "x-gbk")

                    encoder = Encoding.GetEncoding(936);

elseif (enc == "big5")

                    encoder = Encoding.GetEncoding(950);

elseif (enc == "utf-8")

                    encoder = Encoding.UTF8;

else

return"不支援編碼格式[" + m.Groups["enc"].Value + "]!";

if (type == "q")

                    body = body.Replace("=", "%");

                    body = HttpUtility.UrlDecode(body, encoder);

                    raw = raw.Replace(m.Value, body);

elseif (type == "b")

byte[] buff = Convert.FromBase64String(body);

                    raw = raw.Replace(m.Value, encoder.GetString(buff));

return raw;