How does one write the hex values of a char in ASCII to a text file?

Question

Here is what I currently have so far:

void WriteHexToFile( std::ofstream &stream, void *ptr, int buflen, char *prefix )
{
    unsigned char *buf = (unsigned char*)ptr;

    for( int i = 0; i < buflen; ++i ) {
        if( i % 16 == 0 ) {
            stream << prefix;
        }

        stream << buf[i] << ' ';
    }
}

I've tried doing stream.hex, stream.setf( std::ios::hex ), as well as searching Google for a bit. I've also tried:

stream << stream.hex << (int)buf[i] << ' ';

But that doesn't seem to work either.

Here is an example of some output that it currently produces:

Í Í Í Í Í Í Í Í Í Í Í Í Í Í Í Í 
Í Í Í Í Í Í Í Í Í Í Í Í Í Í Í Í 
Í Í Í Í Í Í Í Í Í Í Í Í Í Í Í Í 
Í Í Í Í Í Í Í Í Í Í Í Í Í Í Í Í 
Í Í Í Í Í Í Í Í Í Í Í Í Í Í Í Í 
Í Í Í Í Í Í Í Í Í Í Í Í Í Í Í Í 

I would like the output to look like the following:

FF EE DD CC BB AA 99 88 77 66 55 44 33 22 11 00
FF EE DD CC BB AA 99 88 77 66 55 44 33 22 11 00
FF EE DD CC BB AA 99 88 77 66 55 44 33 22 11 00
FF EE DD CC BB AA 99 88 77 66 55 44 33 22 11 00
FF EE DD CC BB AA 99 88 77 66 55 44 33 22 11 00
FF EE DD CC BB AA 99 88 77 66 55 44 33 22 11 00

Solution 1

#include <iostream>
using namespace std;
int main() {
    char c = 123;
    cout << hex << int(c) << endl;
}

Edit: with zero padding:

#include <iostream>
#include <iomanip>
using namespace std;
int main() {
    char c = 13;
    cout << hex << setw(2) << setfill('0') << int(c) << endl;
}

Solution 2

char upperToHex(int byteVal)
{
    int i = (byteVal & 0xF0) >> 4;
    return nibbleToHex(i);
}

char lowerToHex(int byteVal)
{
    int i = (byteVal & 0x0F);
    return nibbleToHex(i);
}

char nibbleToHex(int nibble)
{
    const int ascii_zero = 48;
    const int ascii_a = 65;

    if((nibble >= 0) && (nibble <= 9))
    {
        return (char) (nibble + ascii_zero);
    }
    if((nibble >= 10) && (nibble <= 15))
    {
        return (char) (nibble - 10 + ascii_a);
    }
    return '?';
}

More code here.

Solution 3

Try:

#include <iomanip>
....
stream << std::hex << static_cast<int>(buf[i]);

Solution 4

You can also do it using something a bit more old-fashioned:

char buffer[4];//room for 2 hex digits, one extra ' ' and \0
sprintf(buffer,"%02X ",onebyte);

View more solutions

Comments

[mmmmmmmm]

BTW: You should use const void *ptr and const char *prefix to make clear that you won't modify these buffers.

[John Doe]

this is why I like stack overflow so much. these fun little problems come up from time to time and someone drops in a snippet of code and its solved...

[xian]

Won't that just output it to the console?

[Rob Kennedy]

Could you explain why that should work any differently from using stream.hex, like the asker already tried?

[Arnold Spence]

I find the 'hex' stream modifier a bit of a pain. If you are outputting other types you have to keep switching the stream back (using 'dec' for example) and as far as I know, it doesn't do leading zeros.

[Admin]

@kitchen - replace cout with your own stream.

[Rob Kennedy]

OK, I'll explain it myself. Using stream.hex prints the value of the member-function pointer ostream::hex. (For me the value is 8.) Then it prints the integer value of the character in decimal.

[Admin]

@rob the hex manipul;ator is not a member of the stream class. The hex you are printing is acually an enumeration value

[Mr.Ree]

You might want to use unsigned(c) instead of int(c) if c<0.

[RBerteig]

And this is why I love C++ streams: cout << hex << setw(2) << setfill('0') << int(c) << endl is just so much clearer than printf("%02x", c) ;-) I know its typesafe(er) but couldn't they have dreamed up something less grotesque?

[Edouard A.]

Clarity is a question of point of view... I don't think printf("%02x", c) can be considered as "clear"

[Lightness Races in Orbit]

-1 This is wrong. How has it avoided downvotes for over two years?!

[Mooing Duck]

@RBerteig: nitpick: those aren't quite equivalent, the C++ shouldn't have the endl there.

[Neo]

With c value being 197, it prints ffffffc5. Can anybody explain why it's not printing C5 and how to avoid extra 'f' padding?