Defined in header
extern std::istream cin;
extern std::wistream wcin;
These objects are guaranteed to be initialized during or before the first time an object of type std::ios_base::Init is constructed and are available for use in the constructors and destructors of static objects with ordered initialization (as long as
<iostream> is included before the object is defined).
Unless sync_with_stdio(false) has been issued, it is safe to concurrently access these objects from multiple threads for both formatted and unformatted input.
std::cin is constructed, std::cin.tie() returns &std::cout, and likewise, std::wcin.tie() returns &std::wcout. This means that any formatted input operation on
std::cin forces a call to std::cout.flush() if any characters are pending for output.
The 'c' in the name refers to "character" (stroustrup.com FAQ);
cin means "character input" and
wcin means "wide character input"
Enter n: 10 f.n is 10
| initializes standard stream objects |
(public member class of
| writes to the standard C output stream stdout|