std:: cout, std:: wcout

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 with ordered initialization (as long as <iostream> is included before the object is defined).

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

By specification of std::cin , std:: cin . tie ( ) returns & std :: cout . This means that any input operation on std::cin executes std :: cout . flush ( ) (via std::basic_istream::sentry 's constructor). Similarly, std:: wcin . tie ( ) returns & std :: wcout .

By specification of std::cerr , std:: cerr . tie ( ) returns & std :: cout . This means that any output operation on std::cerr executes std :: cout . flush ( ) (via std::basic_ostream::sentry 's constructor). Similarly, std:: wcerr . tie ( ) returns & std :: wcout . (since C++11)

Notes

The 'c' in the name refers to "character" ( stroustrup.com FAQ ); cout means "character output" and wcout means "wide character output".

Because dynamic initialization of templated variables are unordered, it is not guaranteed that std::cout has been initialized to a usable state before the initialization of such variables begins, unless an object of type std::ios_base::Init has been constructed.

Example

#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";
}

static constructor
main function
static destructor

See also