Question

I want to output an integer to a std::stringstream with the equivalent format of printf‘s %02d. Is there an easier way to achieve this than:

std::stringstream stream;
stream.setfill('0');
stream.setw(2);
stream << value;

Is it possible to stream some sort of format flags to the stringstream, something like (pseudocode):

stream << flags("%02d") << value;

Answer 1

You can use the standard manipulators from <iomanip> but there isn’t a neat one that does both fill and width at once:

stream << std::setfill('0') << std::setw(2) << value;

It wouldn’t be hard to write your own object that when inserted into the stream performed both functions:

stream << myfillandw( '0', 2 ) << value;

E.g.

struct myfillandw
{
    myfillandw( char f, int w )
        : fill(f), width(w) {}

    char fill;
    int width;
};

std::ostream& operator<<( std::ostream& o, const myfillandw& a )
{
    o.fill( a.fill );
    o.width( a.width );
    return o;
}