std::cout,std::wcout(3)

NAME
std::cout,std::wcout - std::cout,std::wcout

Synopsis
   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 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
// Run this code
 #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
   Init initializes standard stream objects
          (public member class of std::ios_base)
   cerr writes to the standard C error stream stderr, unbuffered
   wcerr (global object)
   clog writes to the standard C error stream stderr
   wclog (global object)
   stdin expression of type FILE* associated with the input stream
   stdout expression of type FILE* associated with the output stream
   stderr expression of type FILE* associated with the error output stream
          (macro constant)