#include <iostream>


#include <streambuf>
#include <locale>
#include <cstdio>

class outbuf : public std::streambuf
{
  protected:
    /* central output function
     * - print characters in uppercase mode
     */
    virtual int_type overflow (int_type c) {
        if (c != EOF) {
            // convert lowercase to uppercase
            c = std::toupper(c,getloc());

            // and write the character to the standard output
            if (putchar(c) == EOF) {
                return EOF;
            }
        }
        return c;
    }
};


int main()
{
    outbuf ob;                // create special output buffer
    std::ostream out(&ob);    // initialize output stream with that output buffer

    out << "31 hexadecimal: " << std::hex << 31 << std::endl;
}