How to visualize bytes with C/C++

Question

I'm working my way through some C++ training. So far so good, but I need some help reinforcing some of the concepts I am learning. My question is how do I go about visualizing the byte patterns for objects I create. For example, how would I print out the byte pattern for structs, longs, ints etc?

I understand it in my head and can understand the diagrams in my study materials, I'd just like to be able to programaticially display byte patterns from within some of my study programs.

I realize this is pretty trivial but any answers would greatly help me hammer in these concepts.

Thanks.

Edit: I use mostly XCode for my other development projects, but have VMs for Windows7 and fedora core. At work I use XP with visual studio 2005. ( I can't comment as I am still a n00b here :D)

I used unwind's solution which is about what I am looking for. I am also thinking that maybe I could just use the dos DEBUG command as I'd also like to look at chunks for memory too. Again, this is just to help me reinforce what I am learning. Thanks again people!

Answer 1

If you are using gcc and X, you can use the DDD debugger to draw pretty pictures of your data structures for you.

Answer 2

Just for completeness, a C++ example:

#include <iostream>

template <typename T>
void print_bytes(const T& input, std::ostream& os = std::cout)
{
  const unsigned char* p = reinterpret_cast<const unsigned char*>(&input);
  os << std::hex << std::showbase;
  os << "[";
  for (unsigned int i=0; i<sizeof(T); ++i)
    os << static_cast<int>(*(p++)) << " ";
  os << "]" << std::endl;;
}

int main()
{
  int i = 12345678;
  print_bytes(i);
  float x = 3.14f;
  print_bytes(x);
}

Answer 3

Most (visual) debuggers have a "View Memory' option. IIRC the one in Xcode is pretty basic, just showing bytes in HEX and ASCII, with a variable line length. Visual Studio (Debug->Windows->Memory in Vs2008) can format the hex portion as different integer lengths, or floating point, change the endianess, and display ANSI or UNICODE text. You can also set just about any number for the width of the window (I think xcode only lets you go to 64 bytes wide) The other IDE I have here at work has a lot of options, though not quite as many as VS.

Answer 4

A little bit by bit console program i whipped up, hope it helps somebody

#include <iostream>
#include <inttypes.h>
#include <vector>
using namespace std;
typedef  vector<uint8_t> ByteVector;
///////////////////////////////////////////////////////////////
uint8_t Flags[8] = { 0x01,0x02,0x04,0x08,0x10,0x20,0x40,0x80};
void print_bytes(ByteVector Bv){
    for (unsigned i = 0; i < Bv.size(); i++){
        printf("Byte %d [ ",i);
        for (int j  = 0;j < 8;++j){
            Bv[i] & Flags[j] ? printf("1") : printf("0");
        }
        printf("]\n");
    }
}
int main(){
    ByteVector Bv;
    for (int i = 0; i < 4; ++i) { Bv.push_back(i); }
    print_bytes(Bv);
}

Answer 5

try this:

MyClass* myObj = new MyClass();
int size=sizeof(*myObj);
int i;
char* ptr = obj; // closest approximation to byte
for( i=0; i<size; i++ )
    std::cout << *ptr << endl;

Cheers,

jrh.

Answer 6

You can use a function such as this, to print the bytes:

void print_bytes(const void *object, size_t size)
{
  // This is for C++; in C just drop the static_cast<>() and assign.
  const unsigned char * const bytes = static_cast<const unsigned char *>(object);
  size_t i;

  printf("[ ");
  for(i = 0; i < size; i++)
  {
    printf("%02x ", bytes[i]);
  }
  printf("]\n");
}

Usage would look like this, for instance:

int x = 37;
float y = 3.14;

print_bytes(&x, sizeof x);
print_bytes(&y, sizeof y);

This shows the bytes just as raw numerical values, in hexadecimal which is commonly used for "memory dumps" like these.

On a random (might even be virtual, for all I know) Linux machine running a "Intel(R) Xeon(R)" CPU, this prints:

[ 25 00 00 00 ]
[ c3 f5 48 40 ]

This handily also demonstrates that the Intel family of CPU:s really are little endian.