C++ Cout Hex Values

c++ std::cout in hexadecimal

You need to cast it to an `int:

char c = 15;
cout << hex << setfill('0') << setw(2) << static_cast<int>(c); // prints "0f"

hex only affects integer I/O, which char isn't considered part of - so your code ends up still outputting the actual chars.

Note that if char is signed and you need this to work on values larger than 0x7f, you will have to cast it first to unsigned char and then to unsigned int:

cout << hex << setfill('0') << setw(2)
     << static_cast<unsigned int>(static_cast<unsigned char>(c));

cout print hex instead of decimal

You probably have set std::cout to print hex in prior in the context of your code but forget to reset. For example:

std::cout<<std::hex<<12;
/*blah blah blah*/
std::cout<<12; //this will print in hex form still

so you have to do like the following

std::cout<<std::dec<<12;

to print in decimal form.

How can I print 0x0a instead of 0xa using cout?

This works for me in GCC:

#include  <iostream>
#include  <iomanip>

using namespace std;

int main()
{
    cout << "0x" << setfill('0') << setw(2) << right << hex << 10 << endl;
}

If you are getting sick and tired of iostream's formatting quirkiness, give Boost.Format a try. It allows good-old-fashioned, printf-style format specifiers, yet it is type-safe.

#include <iostream>
#include <boost/format.hpp>

int main()
{
    std::cout << boost::format("0x%02x\n") % 10;
}

UPDATE (2019)

Check out the {fmt} library that's been accepted into C++20. Benchmarks show it to be faster than Boost.Format.

#if __has_include(<format>)
    #include <format>
    using std::format;
#else
    #include <fmt/format.h>
    using fmt::format;
#endif

std::cout << format("{:#04x}\n", 10);

cout' displays integer as hex

That's because you changed the base of the output in the following line:

out << "ADS read " << std::dec << bytesRead << " bytes:" << std::hex;

The std::hex in the end of the line will apply to every subsequent input stream to out.

Change it back to decimal before printing the last line:

out << " ---> " << std::dec << result << '\n';

Strange output when printing char assigned to hex value using std::cout

Most likely you expect data1 and data3 to be printed as some kind of numbers. However, the data type is character, which is why C++ (or C) would interpret them as characters, mapping 0x11 to the corresponding ASCII character (a control character), similar for 0x22 except some other character (see an ASCII table).
If you want to print those characters as number, you need to convert them to int prior to printing them out like so (works for C and C++):

cout << (int)data1 << endl;

Or more C++ style would be:

cout << static_cast<int>(data1) << endl;

If you want to display the numbers in hexadecimal, you need to change the default output base using the hex IO manipulator. Afterwards all output is done in hexadecimal. If you want to switch back to decimal output, use dec. See cppreference.com for details.

cout << hex << static_cast<int>(data1) << endl;

How to plus hex( No output)?

What I understand is that you want to retrieve the result in an hexadecimal specific format XXXX.

Computing the addition is the same as any number base, you only need to use (here I display) the result in your format.

You can do this, for instance:

#include <iostream>
#include <iomanip>


std::string displayInPersonalizedHexa(unsigned int a)
{
    std::stringstream ss;
    ss << std::uppercase<<  std::setfill('0') << std::setw(4) << std::hex<< a;
    std::string x;
    ss >>x;
    //std::cout << x;
    return x;
}
int main() {
    unsigned int  a = 0x0009, b = 0x0002;
    unsigned int  c = a + b;
    // displays 000B
    std::cout << displayInPersonalizedHexa(c) << std::endl;

    // adds c=c+1
    c=c+1;
    // displays 000C
    std::cout << displayInPersonalizedHexa(c) <<  std::endl;
    
   //0xC+5 = 0x11
    c=c+5;
    // displays 0011
    std::cout << displayInPersonalizedHexa(c) <<  std::endl;
}

This will output

000B
000C
0011

How do you convert a `std::string` hex value to an `unsigned char`

As a very simple solution, you can use a istringstream, which allows parsing hex strings:

#include <cstdio>
#include <iterator>
#include <sstream>
#include <string>
#include <vector>

std::vector<unsigned char> cipher_as_chars(std::string const& cipher) {
    std::istringstream strm{cipher};
    strm >> std::hex;

    return {std::istream_iterator<int>{strm}, {}};
}

int main() {
    auto const cipher = "a8 49 7f ac 24 77 c3 6e 70 ca 99 ca fc e2 c5 7b";
    auto const sep = cipher_as_chars(cipher);
    for (auto elm : sep) {
        std::printf("%hhx ", elm);
    }
    std::putchar('\n');
}