Set/Unset unitbuf format flag
  unitbuf sets the format flag to flush the output buffer after each insertion operation.
  noskipws unsets this flag.

Parameters.

str

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

Return Value.
  A reference to the stream object.

Example.

// modify unitbuf flag
#include <fstream>
using namespace std;

int main () {
  ofstream outfile ("test.txt");
  outfile << unitbuf <<  "Test " << "file" << endl;
  outfile << nounitbuf;
  outfile.close();
  return 0;
}

See also.
  flags, setf, unsetf
  ios_base class