Getting a Buffer into a Stringstream in Hex Representation:

Getting a buffer into a stringstream in hex representation:

#include <sstream>
#include <iomanip>

std::stringstream ss;
ss << std::hex << std::setfill('0');
for (int i = 0; i < 32; ++i)
{
    ss << std::setw(2) << static_cast<unsigned>(buffer[i]);
}

Inputting data to stringstream with hexadecimal representation

First, the std::hex format modifier applies to integers, not to characters. Since you are trying to print unsigned char, the format modifier is not applied. You can fix this by casting to int instead. In your first example, it works because the literal 100 is interpreted as an integer. If you replace 100 with e.g. static_cast<unsigned char>(100), you would no longer get the hexadecimal representation.

Second, std::hex is not enough, since you likely want to pad each character to a 2-digit hex value (i.e. F should be printed as 0F). You can fix this by also applying the format modifiers std::setfill('0') and std::setw(2) (reference, reference).

Applying these modifications, your code would then look like this:

#include <iomanip>

...

    buffer << std::hex << std::setfill('0') << std::setw(2);
    for (size_t i = 0; i < SHA256::DIGESTSIZE; i++) {
        buffer << static_cast<int>(*(digest+i));
    }

How to save hex representation of binary file into a std::string?

You don't have a std::string; you have an std::stringstream. And you can't "print" a stringstream, but you can obtain the std::string representation of its buffer, using the str() member function.

You probably meant, then:

std::cout << buffer.str();

There are cleaner ways to do this, but the above will get you started.

As an aside, your loop is wrong. You're checking for EOF too soon.

Wrong values in raw data to hex string convertion?

OK Guys, sorry for the delay, I ran into the weekend and had some FIFA World Cup games to watch.

I was getting the same result no matter the change I made, so I decided to make some changes in the code before and I switched the input param from

std::string ByteUtil::rawByteStringToHexString(std::string str)

to

std::string ByteUtil::rawByteStringToHexString(vector<unsigned char> v)

and also kept the changes suggested by @sharth. Now I am getting the correct result.

Thank you all for the help!!

Integer to hex string in C++

Use <iomanip>'s std::hex. If you print, just send it to std::cout, if not, then use std::stringstream

std::stringstream stream;
stream << std::hex << your_int;
std::string result( stream.str() );

You can prepend the first << with << "0x" or whatever you like if you wish.

Other manips of interest are std::oct (octal) and std::dec (back to decimal).

One problem you may encounter is the fact that this produces the exact amount of digits needed to represent it. You may use setfill and setw this to circumvent the problem:

stream << std::setfill ('0') << std::setw(sizeof(your_type)*2) 
       << std::hex << your_int;

So finally, I'd suggest such a function:

template< typename T >
std::string int_to_hex( T i )
{
  std::stringstream stream;
  stream << "0x" 
         << std::setfill ('0') << std::setw(sizeof(T)*2) 
         << std::hex << i;
  return stream.str();
}

c++ stringstream read doesn't seem to read the whole buffer

stringstream is not eligible for parsing the character representation into a value in byte.

You may use something lik strtol to actually parse the string into value.

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

int main() {
  std::string line = "fa0834dd";

  for(int i = 0; i < line.length(); i += 2) {
    std::string ss = line.substr(i,2);
    
    std::cout << ss << " ";

    std::uint8_t byte = static_cast<std::uint8_t>(strtol(ss.c_str(), NULL, 16));
    std::cout << std::hex << static_cast(byte) << std::endl;
  }
}

Ref post

Converting unsigned char * to hexstring

The output of an unsigned char is like the output of a char which obviously does not what the OP expects.

I tested the following on coliru:

#include <iomanip>
#include <iostream>

int main()
{
  std::cout << "Output of (unsigned char)0xc0: "
    << std::hex << std::setw(2) << std::setfill('0') << (unsigned char)0xc0 << '\n';
  return 0;
}

and got:

Output of (unsigned char)0xc0: 0�

This is caused by the std::ostream::operator<<() which is chosen out of the available operators. I looked on cppreference

• operator<<(std::basic_ostream) and
• std::basic_ostream::operator<<

and found

template< class Traits >
basic_ostream<char,Traits>& operator<<( basic_ostream<char,Traits>& os,
                                        unsigned char ch );

in the former (with a little bit help from M.M).

The OP suggested a fix: bit-wise And with 0xff which seemed to work. Checking this in coliru.com:

#include <iomanip>
#include <iostream>

int main()
{
  std::cout << "Output of (unsigned char)0xc0: "
    << std::hex << std::setw(2) << std::setfill('0') << (0xff & (unsigned char)0xc0) << '\n';
  return 0;
}

Output:

Output of (unsigned char)0xc0: c0

Really, this seems to work. Why?

0xff is an int constant (stricly speaking: an integer literal) and has type int. Hence, the bit-wise And promotes (unsigned char)0xc0 to int as well, yields the result of type int, and hence, the std::ostream::operator<< for int is applied.

This is an option to solve this. I can provide another one – just converting the unsigned char to unsigned.

Where the promotion of unsigned char to int introduces a possible sign-bit extension (which is undesired in this case), this doesn't happen when unsigned char is converted to unsigned. The output stream operator for unsigned provides the intended output as well:

#include <iomanip>
#include <iostream>

int main()
{
  std::cout << "Output of (unsigned char)0xc0: "
    << std::hex << std::setw(2) << std::setfill('0') << (unsigned)(unsigned char)0xc0 << '\n';
  const unsigned char c = 0xc0;
  std::cout << "Output of unsigned char c = 0xc0: "
    << std::hex << std::setw(2) << std::setfill('0') << (unsigned)c << '\n';
  return 0;
}

Output:

Output of (unsigned char)0xc0: c0
Output of unsigned char c = 0xc0: c0

Live Demo on coliru

---

Related Topics