Char array to hex string C++

Question

I searched char* to hex string before but implementation I found adds some non-existent garbage at the end of hex string. I receive packets from socket, and I need to convert them to hex strings for log (null-terminated buffer). Can somebody advise me a good implementation for C++?

Thanks!

Solution 1

Supposing data is a char*. Working example using std::hex:

for(int i=0; i<data_length; ++i)
    std::cout << std::hex << (int)data[i];

Or if you want to keep it all in a string:

std::stringstream ss;
for(int i=0; i<data_length; ++i)
    ss << std::hex << (int)data[i];
std::string mystr = ss.str();

Solution 2

Here is something:

char const hex_chars[16] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };

for( int i = data; i < data_length; ++i )
{
    char const byte = data[i];

    string += hex_chars[ ( byte & 0xF0 ) >> 4 ];
    string += hex_chars[ ( byte & 0x0F ) >> 0 ];
}

Solution 3

The simplest:

int main()
{
    const char* str = "hello";
    for (const char* p = str; *p; ++p)
    {
        printf("%02x", *p);
    }
    printf("\n");
    return 0;
}

Solution 4

I've found good example here Display-char-as-Hexadecimal-String-in-C++:

  std::vector<char> randomBytes(n);
  file.read(&randomBytes[0], n);

  // Displaying bytes: method 1
  // --------------------------
  for (auto& el : randomBytes)
    std::cout << std::setfill('0') << std::setw(2) << std::hex << (0xff & (unsigned int)el);
  std::cout << '\n';

  // Displaying bytes: method 2
  // --------------------------
  for (auto& el : randomBytes)
    printf("%02hhx", el);
  std::cout << '\n';
  return 0;

Method 1 as shown above is probably the more C++ way:

Cast to an unsigned int
Use std::hex to represent the value as hexadecimal digits
Use std::setw and std::setfill from <iomanip> to format
Note that you need to mask the cast int against 0xff to display the least significant byte:
(0xff & (unsigned int)el).

Otherwise, if the highest bit is set the cast will result in the three most significant bytes being set to ff.

Solution 5

Code snippet above provides incorrect byte order in string, so I fixed it a bit.

char const hex[16] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A',   'B','C','D','E','F'};

std::string byte_2_str(char* bytes, int size) {
  std::string str;
  for (int i = 0; i < size; ++i) {
    const char ch = bytes[i];
    str.append(&hex[(ch  & 0xF0) >> 4], 1);
    str.append(&hex[ch & 0xF], 1);
  }
  return str;
}

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