Conversion base

Integers are normally inserted and extracted in decimal notation, but this is controlled by flag bits. If none of ios::dec, ios::hex, or ios::oct are set the insertion is done in decimal but extractions are interpreted according to the C++ lexical conventions for integral constants. If ios::showbase is set then insertions will convert to an external form that can be read according to these conventions.

For example,

   int x = 64;
   cout << dec << x << " "
        << hex << x << " "
        << oct << x << endl ;
   cout.setf(ios::showbase,ios::showbase) ;
   cout << dec << x << " "
        << hex << x << " "
        << oct << x << endl ;

   64 40 100
   64 0x40 0100

setf() with only one argument turns the specified bits on, but doesn't turn any bits off.

Reading the lines shown above could be done by:

   cin >> dec >> x
       >> hex >> x
       >> oct >> x
       >> resetiosflags(ios::basefield)
       >> x >> x >> x ;