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)
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.
#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 destructorSee also initializes standard stream objects
std::ios_base) [edit] writes to the standard C error stream stderr, unbuffered
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