Standard library header <iostream>

 

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Language support <cfloat> <climits> <compare>(C++20) <contracts>(C++26) <coroutine>(C++20) <csetjmp> <csignal> <cstdarg> <cstddef> <cstdint>(C++11) <cstdlib> <exception> <initializer_list>(C++11)    <limits> <new> <source_location>(C++20) <stdfloat>(C++23) <typeinfo> <version>(C++20) Concepts <concepts>(C++20) Diagnostics <cassert> <cerrno> <debugging>(C++26) <stacktrace>(C++23) <stdexcept> <system_error>(C++11) Memory management <memory> <memory_resource>(C++17) <scoped_allocator>(C++11) Metaprogramming <type_traits>(C++11) <ratio>(C++11)

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Input/output <cinttypes>(C++11) <cstdio> <filesystem>(C++17) <fstream> <iomanip> <iosfwd> <iostream> <ios> <istream> <ostream> <print>(C++23) <spanstream>(C++23) <sstream> <streambuf> <strstream>(C++98/26*) <syncstream>(C++20) Concurrency support <atomic>(C++11) <barrier>(C++20) <condition_variable>(C++11) <future>(C++11) <hazard_pointer>(C++26) <latch>(C++20) <mutex>(C++11) <rcu>(C++26) <semaphore>(C++20) <shared_mutex>(C++14) <stdatomic.h>(C++23) <stop_token>(C++20) <thread>(C++11) Execution support <execution>(C++17)

 

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
<ios> (C++11)	std::ios_base class, std::basic_ios class template and typedefs
<streambuf> (C++11)	std::basic_streambuf class template
<istream> (C++11)	std::basic_istream class template and typedefs
<ostream> (C++11)	std::basic_ostream, std::basic_iostream class templates and typedefs
Objects
cinwcin	reads from the standard C input stream stdin (global object)
coutwcout	writes to the standard C output stream stdout (global object)
cerrwcerr	writes to the standard C error stream stderr, unbuffered (global object)
clogwclog	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