Standard library header <iostream>

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C++
Standard library headers

This header is part of the Input/output library.

Including <iostream> behaves as if it defines a static storage duration object of type std::ios_base::Init , whose constructor initializes the standard stream objects if it is the first std::ios_base::Init object to be constructed, and whose destructor flushes those objects (except for cin and wcin ) if it is the last std::ios_base::Init object to be destroyed.

Includes

(C++11)
std::ios_base class, std::basic_ios class template and typedefs
(C++11)
std::basic_streambuf class template
(C++11)
std::basic_istream class template and typedefs
(C++11)
std::basic_ostream , std::basic_iostream class templates and typedefs

Objects

reads from the standard C input stream stdin
(global object)
writes to the standard C output stream stdout
(global object)
writes to the standard C error stream stderr , unbuffered
(global object)
writes to the standard C error stream stderr
(global object)

Synopsis 

#include <ios>
#include <streambuf>
#include <istream>
#include <ostream>
 
namespace std {
  extern istream cin;
  extern ostream cout;
  extern ostream cerr;
  extern ostream clog;
 
  extern wistream wcin;
  extern wostream wcout;
  extern wostream wcerr;
  extern wostream wclog;
}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 155 C++98 the type of the static object was std::basic_ios::Init
(not strictly wrong, but the wording was misleading) 		corrected to std::ios_base::Init
LWG 1123 C++98 including <iostream> did not guarantee the
construction of std::ios_base::Init objects 		guarantees
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