Reading in binary data and displaying as hex.

[Lemony Lime]

Trying to figure out how to read in data from a binary file one byte at a time, then display it in hex. From my googling, I've figured out this much, but when I cast it to an int, it displays the hex values as 4 bytes instead of 1 (so ff is ffffffff). I want it to only display as one byte, and I'd also like it to be in all caps. Anyone know how?

What I've got so far:

#include <iostream>
#include <fstream>

using namespace std;

int main()
{
  ifstream fin( "test.dat", ios::in | ios::binary );
  char data[10];
  if ( fin.is_open() )
    fin.read( data, 10 );
    else
      return -1;

  for ( int i = 0; i < 10; i++ )
    cout << hex << static_cast<int>(data[i]) << " ";

  return 0;
}

[maeriden]

To show them in uppercase you can try the format flag "uppercase"
http://www.cplusplus.com/reference/ios/ios_base/fmtflags/

it displays the hex values as 4 bytes instead of 1 (so ff is ffffffff).

That's because of the cast to int.
For signed char 0xFF == -1.
After the cast you end up with an int whose value is -1
For signed int -1 == 0xFFFFFFFF.

Try using unsigned char (to read from ifsteam you might need to cast them to signed).

[LB]

ff is not ffffffff. Make sure you convert from unsigned char to unsigned int, or you will get sign involved.

[Lemony Lime]

It says "invalid conversion from 'unsigned char*' to 'std::basic_istream<char>::char_type* {aka char*}'" when using an unsigned char.

When I cast it to signed char it says "invalid static_cast from type 'unsigned char [10]' to type 'char'|" and if I use a c-style cast it says "cast from 'unsigned char*' to 'char' loses precision"

[LB]

I never said to change the types of your existing variables - just nest casts.

[maeriden]

The error seems to say you're trying to cast an unsigned char[] to signed char. Is that the case?

[Lemony Lime]

The error seems to say you're trying to cast an unsigned char[] to signed char. Is that the case?

You said to use unsigned chars, and that I'd have to cast them to signed while reading in from the file. That's what I was trying to do.


cout << hex << static_cast<unsigned int>(static_cast<unsigned char>(data[i])) << " ";
This seems to work, although it seems... unusual. Is it okay to do that?

Edit: Oh wait, that's what L B meant by nest casts?

[maeriden]

Yes that's probably it. What I was saying was

ifstream fin( "test.dat", ios::in | ios::binary );
  unsigned char data[10];
  if ( fin.is_open() )
    fin.read(static_cast<char*>(data), 10 );
    else
      return -1;

  for ( int i = 0; i < 10; i++ )
    cout << hex << static_cast<int>(data[i]) << " ";

I didn't test this, so if LB's sugestion works just go with that.