std::cin,std::wcin (3) Linux Manual Page

std::cin,std::wcin – std::cin,std::wcin

Synopsis

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 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 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.

Notes

The ‘c’ in the name refers to "character" (stroustrup.com_FAQ); cin means "character input" and wcin means "wide character input"

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

See also

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