How to convert Byte Array to hex string in visual c++?

As you have mentioned c++, here is an answer. Iomanip is used to store ints in hex form into stringstream.

#include <iomanip>
#include <sstream>
#include <string>

std::string hexStr(const uint8_t *data, int len)
{
     std::stringstream ss;
     ss << std::hex;

     for( int i(0) ; i < len; ++i )
         ss << std::setw(2) << std::setfill('0') << (int)data[i];

     return ss.str();
}

This code will convert byte array of fixed size 100 into hex string:

BYTE array[100];
char hexstr[201];
int i;
for (i=0; i<ARRAY_SIZE(array); i++) {
    sprintf(hexstr+i*2, "%02x", array[i]);
}
hexstr[i*2] = 0;

Using stringstream, sprintf and other functions in the loop is simply not C++. It's horrible for performance and these kind of functions usually get called a lot (unless you're just writing some things into the log).

Here's one way of doing it. Writing directly into the std::string's buffer is discouraged because specific std::string implementation might behave differently and this will not work then but we're avoiding one copy of the whole buffer this way:

#include <iostream>
#include <string>
#include <vector>

std::string bytes_to_hex_string(const std::vector<uint8_t> &input)
{
  static const char characters[] = "0123456789ABCDEF";

  // Zeroes out the buffer unnecessarily, can't be avoided for std::string.
  std::string ret(input.size() * 2, 0);
  
  // Hack... Against the rules but avoids copying the whole buffer.
  auto buf = const_cast<char *>(ret.data());
  
  for (const auto &oneInputByte : input)
  {
    *buf++ = characters[oneInputByte >> 4];
    *buf++ = characters[oneInputByte & 0x0F];
  }
  return ret;
}

int main()
{
  std::vector<uint8_t> bytes = { 34, 123, 252, 0, 11, 52 };
  std::cout << "Bytes to hex string: " << bytes_to_hex_string(bytes) << std::endl;
}

Here is a somewhat more flexible version (Use uppercase characters? Insert spaces between bytes?) that can be used with plain arrays and various standard containers:

#include <string>
#include <sstream>
#include <iomanip>

template<typename TInputIter>
std::string make_hex_string(TInputIter first, TInputIter last, bool use_uppercase = true, bool insert_spaces = false)
{
    std::ostringstream ss;
    ss << std::hex << std::setfill('0');
    if (use_uppercase)
        ss << std::uppercase;
    while (first != last)
    {
        ss << std::setw(2) << static_cast<int>(*first++);
        if (insert_spaces && first != last)
            ss << " ";
    }
    return ss.str();
}

Example usage (plain array):

uint8_t byte_array[] = { 0xDE, 0xAD, 0xC0, 0xDE, 0x00, 0xFF };
auto from_array = make_hex_string(std::begin(byte_array), std::end(byte_array), true, true);
assert(from_array == "DE AD C0 DE 00 FF");

Example usage (std::vector):

// fill with values from the array above
std::vector<uint8_t> byte_vector(std::begin(byte_array), std::end(byte_array));
auto from_vector = make_hex_string(byte_vector.begin(), byte_vector.end(), false);
assert(from_vector == "deadc0de00ff");

how about using the boost library like this (snippet taken from http://theboostcpplibraries.com/boost.algorithm ):

#include <boost/algorithm/hex.hpp>
#include <vector>
#include <string>
#include <iterator>
#include <iostream>

using namespace boost::algorithm;

int main()
{
  std::vector<char> v{'C', '+', '+'};
  hex(v, std::ostream_iterator<char>{std::cout, ""});
  std::cout << '\n';

  std::string s = "C++";
  std::cout << hex(s) << '\n';

  std::vector<char> w{'4', '3', '2', 'b', '2', 'b'};
  unhex(w, std::ostream_iterator<char>{std::cout, ""});
  std::cout << '\n';

  std::string t = "432b2b";
  std::cout << unhex(t) << '\n';
}