c++ encode decode

 std::string UrlEncode(const std::string& szToEncode)
 {
     std::string src = szToEncode;
     char hex[] = "0123456789ABCDEF";
     string dst;

     for (size_t i = ; i < src.size(); ++i)
     {
         unsigned char cc = src[i];
         if (isascii(cc))
         {
             if (cc == ' ')
             {
                 dst += "%20";
             }
             else
                 dst += cc;
         }
         else
         {
             unsigned char c = static_cast<unsigned char>(src[i]);
             dst += '%';
             dst += hex[c / ];
             dst += hex[c % ];
         }
     }
     return dst;
 }

 std::string UrlDecode(const std::string& szToDecode)
 {
     std::string result;
     int hex = ;
     for (size_t i = ; i < szToDecode.length(); ++i)
     {
         switch (szToDecode[i])
         {
         case '+':
             result += ' ';
             break;
         case '%':
             if (isxdigit(szToDecode[i + ]) && isxdigit(szToDecode[i + ]))
             {
                 std::string hexStr = szToDecode.substr(i + , );
                 hex = strtol(hexStr.c_str(), , );
                 //字母和数字[0-9a-zA-Z]、一些特殊符号[$-_.+!*'(),] 、以及某些保留字[$&+,/:;=?@]
                 //可以不经过编码直接用于URL
                 if (!((hex >=  && hex <= ) || //0-9
                     (hex >= && hex <= ) ||   //a-z
                     (hex >= && hex <= ) ||    //A-Z
                     //一些特殊符号及保留字[$-_.+!*'(),]  [$&+,/:;=?@]
                     hex == 0x21 || hex == 0x24 || hex == 0x26 || hex == 0x27 || hex == 0x28 || hex == 0x29
                     || hex == 0x2a || hex == 0x2b|| hex == 0x2c || hex == 0x2d || hex == 0x2e || hex == 0x2f
                     || hex == 0x3A || hex == 0x3B|| hex == 0x3D || hex == 0x3f || hex == 0x40 || hex == 0x5f
                     ))
                 {
                     result += char(hex);
                     i += ;
                 }
                 else result += '%';
             }else {
                 result += '%';
             }
             break;
         default:
             result += szToDecode[i];
             break;
         }
     }
     return result;
 }

在线测试工具：http://tool.chinaz.com/Tools/URLEncode.aspx