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);

Use setw and setfill from iomanip

#include  <iostream>
#include  <iomanip>

using std::cout;  
using std::endl;  
using std::hex;

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

Personally, the stateful nature of iostreams always annoys me. I think boost format is a better option, so I'd recommended the other answer.