std::cout,std::wcout (3) - Linux Manuals
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 with ordered_initialization (as long as <iostream> is included before the object is defined).
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)
The 'c' in the name refers to "character" (stroustrup.com_FAQ); cout means "character output" and wcout means "wide character output"
// Run this code
Init (public member class of std::ios_base)
cerr (global object)
clog (global object)