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# std::cin, std::wcin

From cppreference.com
< cpp‎ | io

Defined in header `<iostream>` |  |
extern std::istream cin; | (1) |
extern std::wistream wcin; | (2) |

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 constructed before the first constructor of a static object is called and they are guaranteed to outlive the last destructor of a static object, so that it is always possible to read from std::cin in user code.

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 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.

### [edit] Example

Run this code

    #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';
    }

Output:

    Enter n: 10
    f.n is 10

### [edit] See also

Init | initializes standard stream objects (public member class of `std::ios_base`) [edit]
cout wcout | writes to the standard C output stream stdout (global object) [edit]

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