Set/Unset showbase format flag
  showbase sets the format flag to represent values with its C++ base format prefix. That is 0x for hexadecimal values, 0 for octal values and no prefix for decimal values.
  noshowbase unsets this flag, representing values in its corresponding base without base prefix.

Parameters.

str

Stream object where to apply. This is a manipulator parameter.

Return Value.
  A reference to the stream object.

Example.

// modify showbase flag
#include <iostream>
using namespace std;

int main () {
  int n;
  n=20;
  cout << hex << showbase << n << endl;
  cout << hex << noshowbase << n << endl;
  return 0;
}

See also.
  flags, setf, unsetf
  ios_base class