std::cout, std::wcout
<iostream>
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"; }
Output:
static constructor main function static destructor
See also
expression of type FILE* associated with the output stream
expression of type FILE* associated with the error output stream
(macro constant) [edit]