c++ encode decode

std::string UrlEncode(const std::string& szToEncode)
{
    std::string src = szToEncode;
    char hex[] = "0123456789ABCDEF";
    string dst;
 
    for (size_t i = 0; 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 / 16];
            dst += hex[c % 16];
        }
    }
    return dst;
}
 
 
std::string UrlDecode(const std::string& szToDecode)
{
    std::string result;
    int hex = 0;
    for (size_t i = 0; i < szToDecode.length(); ++i)
    {
        switch (szToDecode[i])
        {
        case '+':
            result += ' ';
            break;
        case '%':
            if (isxdigit(szToDecode[i + 1]) && isxdigit(szToDecode[i + 2]))
            {
                std::string hexStr = szToDecode.substr(i + 1, 2);
                hex = strtol(hexStr.c_str(), 0, 16);
                //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 >= 48 && hex <= 57) || //0-9
                    (hex >=97 && hex <= 122) ||   //a-z
                    (hex >=65 && hex <= 90) ||    //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 += 2;
                }
                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