The following code example is taken from the book
The C++ Standard Library - A Tutorial and Reference, 2nd Edition
by Nicolai M. Josuttis, Addison Wesley Longman, 2012
Copyright © 2012 by Pearson Education, Inc. and Nicolai M. Josuttis
#include <iostream>
#include "outbuf2.hpp"
int main()
{
fdostream out(1); // stream with buffer writing to file descriptor 1
out << "31 hexadecimal: " << std::hex << 31 << std::endl;
}