The global objects std::cin and std::wcin control input from a stream buffer of implementation-defined type (derived from std::streambuf), associated with the standard C input stream stdin.

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.

Once initialized:

1) std::cin.tie() returns &std::cout. This means that any input operation on std::cin forces a call to std::cout.flush() if any characters are pending for output..

2) std::wcin.tie() returns &std::wcout. This means that any input operation on std::wcin forces a call to std::wcout.flush() if any characters are pending for output.

Notes

The “c” in the name refers to “character” (stroustrup.com FAQ); cin means “character input” and wcin means “wide character input”.

Example

#include <iostream>

struct Foo
{
    int n;
    Foo()
    {
        std::cout << "Enter n: "; // no flush needed
        std::cin >> n;
    }
};

Foo f; // static object

int main()
{
    std::cout << "f.n is " << f.n << '\n';
}

See also