How to read/write continuous hex dump using STL

Hello all,

The program below has a bug... The program is supposed to convert a
string to a continuous hex dump and back to a string. The output
should be as follows:

abcd
61626364
abcd

But the output I see is as follows:

abcd
61626364
dddd

Can someone please show me what I'm doing wrong and what is the proper
way of reading a continuous hex dump using the STL?

// BEGIN SAMPLE PROGRAM
#include <iostream> // For std::cout
#include <string> // For std::string
#include <sstream> // For std::ostringstream
#include <iomanip> // For std::setfill

int
main()
{
  // Set "input"
  //
  std::string input = "abcd";
  std::cout << input << std::endl;

  // Set "hexDump"
  //
  std::ostringstream oss;
  oss << std::hex << std::setfill('0');
  for(int i = 0; i < input.length(); i++)
  {
    int temp = input[i];
    oss << std::setw(2) << temp;
  }
  std::string hexDump = oss.str();
  assert(hexDump.length() == 2 * input.length());
  std::cout << hexDump << std::endl;

  // Set "output"
  //
  std::string output;
  int numChars = hexDump.length() / 2;
  output.resize(numChars);
  std::istringstream iss(hexDump);
  iss >> std::hex;
  for(int i = 0; i < numChars; i++)
  {
    int temp;
    iss >> std::setw(2) >> temp; // BUG: Using setw DOES NOT WORK!!!
    output[i] = temp;
  }
  std::cout << output << std::endl;
}
// END SAMPLE PROGRAM