C++ URL encode/decode (gb2312)

char Dec2HexChar(short int n)   
    {  
        if ( 0 <= n && n <= 9 ) {  
            return char( short('0') + n );  
        } else if ( 10 <= n && n <= 15 ) {  
            return char( short('A') + n - 10 );  
        } else {  
            return char(0);  
        }  
    }  
      
    short int HexChar2Dec(char c)  
    {  
        if ( '0'<=c && c<='9' ) {  
            return short(c-'0');  
        } else if ( 'a'<=c && c<='f' ) {  
            return ( short(c-'a') + 10 );  
        } else if ( 'A'<=c && c<='F' ) {  
            return ( short(c-'A') + 10 );  
        } else {  
            return -1;  
        }  
    }  
      
    string EncodeURL(const string &URL)  
    {  
        string strResult = "";  
        for ( unsigned int i=0; i<URL.size(); i++ )  
        {  
            char c = URL[i];  
            if (  
                ( '0'<=c && c<='9' ) ||  
                ( 'a'<=c && c<='z' ) ||  
                ( 'A'<=c && c<='Z' ) ||  
                c=='/' || c=='.'  
                ) {  
                    strResult += c;  
            }   
            else   
            {  
                int j = (short int)c;  
                if ( j < 0 )  
                {  
                    j += 256;  
                }  
                int i1, i0;  
                i1 = j / 16;  
                i0 = j - i1*16;  
                strResult += '%';  
                strResult += Dec2HexChar(i1);  
                strResult += Dec2HexChar(i0);  
            }  
        }  
      
        return strResult;  
    }  
      
    std::string DecodeURL(const std::string &URL)  
    {  
        string result = "";  
        for ( unsigned int i=0; i<URL.size(); i++ )   
        {  
            char c = URL[i];  
            if ( c != '%' )   
            {  
                result += c;  
            }   
            else   
            {  
                char c1 = URL[++i];  
                char c0 = URL[++i];  
                int num = 0;  
                num += HexChar2Dec(c1) * 16 + HexChar2Dec(c0);  
                result += char(num);  
            }  
        }  
      
        return result;  
    }