14.3.1.3 Flushing

As with most I/O libraries, iostream often accumulates output and sends it on in larger and generally more efficient chunks. If you want to flush the buffer, you simply insert the special value flush. For example:

cout << "This needs to get out immediately." << flush;
 

flush is an example of a kind of object known as a manipulator, which is a value that can be inserted into an iostream to have some effect other than causing output of its value. It is really a function that takes an ostream& or istream& argument and returns its argument after performing some actions on it (see 14.7 Manipulators).