std::cout, std::wcout
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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 constructed before the first constructor of a static object is called and they are guaranteed to outlive the last destructor of a static object, so that it is always possible to write to std::cout in user code.
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)
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
