std::cout, std::wcout

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< cpp‎ | io
 
C++
 
Input/output library
 
std::basic_ostream
 
Defined in header <iostream>
extern std::ostream cout;
 (1)
extern std::wostream wcout;
 (2)

The global objects std::cout and std::wcout control output to a stream buffer of implementation-defined type (derived from std::streambuf), associated with the standard C output stream stdout.

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 (as long as <iostream> is included).

Unless sync_with_stdio(false) has been issued, it is safe to concurrently access these objects from multiple threads for both formatted and unformatted output.

Once initialized, std::cout is tie()'d to std::cin and std::wcout is tie()'d to std::wcin, meaning that any input operation on std::cin executes std::cout.flush() (via std::basic_istream::sentry's constructor).

Once initialized, std::cout is also tie()'d to std::cerr and std::wcout is tie()'d to std::wcerr, meaning that any output operation on std::cerr executes std::cout.flush() (via std::basic_ostream::sentry's constructor) (since C++11)

[edit] Example

Run this code
#include <iostream>
struct Foo {
    int n;
    Foo() {
       std::cout << "static constructor\n";
    }
    ~Foo() {
       std::cout << "static destructor\n";
    }
};
Foo f; // static object
int main()
{
    std::cout << "main function\n";
}

Output: 

static constructor
main function
static destructor

[edit] See also

initializes standard stream objects
(public member class of std::ios_base)
writes to the standard C error stream stderr
(global object)
coutwcout
 writes to the standard C output stream stdout
(global object)
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