Generally (by default), the iostream standard stream objects - cin, cout, cerr, clog, and their wide character alternatives wcin, wcout, wcerr and wclog, are synchronized with C standard streams : stdin, stdout and stderr.
This synchronisation is an performance overhead for pure C++ modules.
With stdio synchronization turned off, iostream stream objects may operate independently of the standard C streams.
To control this behavior C++ provides below static method -
public static member function
ios_base::sync_with_stdio
bool sync_with_stdio ( bool sync = true );
---- Toggles on or off synchronization of the iostream standard streams with the standard C streams.
Notice that this is a static member function, therefore a call to this function using the member of any object (or of any related class) toggles on or off synchronization for all standard iostream objects.
std::ios_base::sync_with_stdio(false);
This will increase program speed in linux not much difference in windows.
One can also consider untie cin with cout (after calling sync_with_stdio with false).
std::cin.tie(0);
cin is usually tied with cout to provide a intuitive way to code cli like program, where the cin prompt is preceded with some text which suggest what to input.
for e.g.
std::string name;
cout << "Enter Name: ";
cin >> name;
(for further reading)
