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.
The 'c' in the name refers to "character" (stroustrup.com FAQ); cin
means "character input" and wcin
means "wide character input"
#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
initializes standard stream objects (public member class of std::ios_base ) |
|
writes to the standard C output stream stdout (global object) |
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