Wrong values in raw data to hex string convertion?

Question

I am using the following code to convert the raw data values to a hexstring so I can find some information. But I am getting FFFFFFFF where I was supposed to get FF.

For example, the result should be "FF 01 00 00 EC 00 00 00 00 00 00 00 00 00 E9", but I am getting "FFFFFFFFF 01 00 00 FFFFFFEC 00 00 00 00 00 00 00 00 00 FFFFFFE9".

Does anyone know what is happening here?

std::vector<unsigned char> buf;
buf.resize( ANSWER_SIZE);

// Read from socket
m_pSocket->Read( &buf[0], buf.size() );
string result( buf.begin(), buf.end() );
result = ByteUtil::rawByteStringToHexString( result );

std::string ByteUtil::int_to_hex( int i )
{
    std::stringstream sstream;
    sstream << std::hex << i;
    return sstream.str();
}

std::string ByteUtil::rawByteStringToHexString(std::string str)
{
    std::string aux = "", temp = "";
    for (unsigned int i=0; i<str.size(); i++) {
        temp += int_to_hex(str[i]);

        if (temp.size() == 1) {
            aux += "0" + temp + " "; // completes with 0
        } else if(i != (str.size() -1)){
            aux += temp + " ";
        }
        temp = "";
    }

    // System.out.println(aux);
    return aux;
}

UPDATE: Debugging, I noticed that the int_to_hex is returning FFFFFFFF instead of FF. How can I fix that?

Answer 1

Note the use of unsigned instead of int in int_to_hex() .

#include <iostream>
#include <sstream>

std::string int_to_hex(unsigned i)
{
    std::stringstream sstream;
    sstream << std::hex << i;
    return sstream.str();
}

int main() {
    std::cout << int_to_hex(0xFF) << "\n";
}

Output

[1:58pm][wlynch@watermelon /tmp] ./foo
ff

Additionally...

We also can see in the question you are looking at , that they do a static_cast to achieve the same result.

ss << std::setw(2) << static_cast<unsigned>(buffer[i]);

Answer 2

OK Guys, sorry for the delay, I ran into the weekend and had some FIFA World Cup games to watch.

I was getting the same result no matter the change I made, so I decided to make some changes in the code before and I switched the input param from

std::string ByteUtil::rawByteStringToHexString(std::string str)

to

std::string ByteUtil::rawByteStringToHexString(vector<unsigned char> v)

and also kept the changes suggested by @sharth. Now I am getting the correct result.

Thank you all for the help!!