(C++)UrlEncode的标准实现

关于UrlEncode的实现(C++)，网上有很多不同的版本，对需要编码的字符集的选取并不统一。那么到底有没有标准呢？答案是有的，参见wiki

绝对不编码的，只有字母、数字、短横线(-)、下划线(_)、点(.)和波浪号(~)，其他字符要视情况而定，所以一般性的urlencode只需保留上述字符不进行编码。

下面给出实现：

    unsigned char ToHex(unsigned char x)
    {
        return  x > 9 ? x + 55 : x + 48;
    }  

    unsigned char FromHex(unsigned char x)
    {
        unsigned char y;
        if (x >= ‘A‘ && x <= ‘Z‘) y = x - ‘A‘ + 10;
        else if (x >= ‘a‘ && x <= ‘z‘) y = x - ‘a‘ + 10;
        else if (x >= ‘0‘ && x <= ‘9‘) y = x - ‘0‘;
        else assert(0);
        return y;
    }  

    std::string UrlEncode(const std::string& str)
    {
        std::string strTemp = "";
        size_t length = str.length();
        for (size_t i = 0; i < length; i++)
        {
            if (isalnum((unsigned char)str[i]) ||
                (str[i] == ‘-‘) ||
                (str[i] == ‘_‘) ||
                (str[i] == ‘.‘) ||
                (str[i] == ‘~‘))
                strTemp += str[i];
            else if (str[i] == ‘ ‘)
                strTemp += "+";
            else
            {
                strTemp += ‘%‘;
                strTemp += ToHex((unsigned char)str[i] >> 4);
                strTemp += ToHex((unsigned char)str[i] % 16);
            }
        }
        return strTemp;
    }  

    std::string UrlDecode(const std::string& str)
    {
        std::string strTemp = "";
        size_t length = str.length();
        for (size_t i = 0; i < length; i++)
        {
            if (str[i] == ‘+‘) strTemp += ‘ ‘;
            else if (str[i] == ‘%‘)
            {
                assert(i + 2 < length);
                unsigned char high = FromHex((unsigned char)str[++i]);
                unsigned char low = FromHex((unsigned char)str[++i]);
                strTemp += high*16 + low;
            }
            else strTemp += str[i];
        }
        return strTemp;
    }