xxdev

We often need to display the exact bytes stored within a region of memory, or we might be interested in the byte representation of a variable. Typically we want such things during debugging, or trying to understand binary based protocols.

Bytes are best displayed in hexadecimal notation (hex). So we require a function that takes a memory region (described by a pointer and size) and builds a string of the hex values for all bytes within the region.

The C++ function below does this. It is called hexdump because it is similar in spirit to the UNIX utility of the same name.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31

#include <iostream>
#include <iomanip>
 
/**
 * Represent a memory region in hex.
 * Darren Smith, www.xxdev.com
 */
void hexdump(const unsigned char * p, size_t size, std::ostream& os,
             const char* prefix = NULL,
             bool brackets = false)
{
  std::ios_base::fmtflags flags = os.flags(); // save state
 
  if (brackets) os << "[";
 
  // set up our stream for hex output
  os << std::setfill('0');
  os << std::hex;
  os << std::uppercase;
  os << std::right;
 
  for (size_t i = 0; i < size; ++i)
    {
      if (prefix) os << prefix;
      os << std::setw(2) << static_cast<int>(p[i]) ;
    }
 
  os.flags(flags);   // reset stream state
 
  if (brackets) os << "]";
}

Note that it builds the hex string by inserting the hex values onto an output stream. For instant debugging we can use the C++ stream object cout to write the hex to stdout:

1
2
3
4
5
6
7
8
9
10
11

int main(int argc, const char* argv[])
{
  if (argc > 1)
    {
      const char* buf = argv[1];
      size_t bufSize = strlen(argv[1]);
 
      hexdump((const unsigned char*) buf, bufSize, std::cout, " ");
      std::cout << "n";
    }
}

This entry was posted on Friday, March 13th, 2009 at 1:53 am and is filed under C++, C++ utils. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.