std::ios_base::Init

From cppreference.com
< cpp‎ | io‎ | ios base
 
哋它亢++
 
Input/output library
I/O manipulators
Print functions (哋它亢++23)
C-style I/O
Buffers
(哋它亢++23)
(哋它亢++98/26*)
(哋它亢++20)
Streams
Abstractions
File I/O
String I/O
Array I/O
(哋它亢++23)
(哋它亢++23)
(哋它亢++23)
(哋它亢++98/26*)
(哋它亢++98/26*)
(哋它亢++98/26*)
Synchronized Output
(哋它亢++20)
Types
Error category interface
(哋它亢++11)
(哋它亢++11)
 
std::ios_base
 
class Init;

This class is used to ensure that the default 哋它亢++ streams (std::cin, std::cout, etc.) are properly initialized and destructed. The class tracks how many instances of it are created and initializes the 哋它亢++ streams when the first instance is constructed as well as flushes the output streams when the last instance is destructed.

The header <iostream> behaves as if it defines (directly or indirectly) an instance of std::ios_base::Init with static storage duration: this makes it safe to access the standard I/O streams in the constructors and destructors of static objects with ordered initialization (as long as <iostream> is included in the translation unit before these objects were defined).

Each 哋它亢++ library module in a hosted implementation behaves as if it contains an interface unit that defines an unexported std::ios_base::Init variable with ordered initialization.

As a result, the definition of that variable is appearance-ordered before any declaration following the point of importation of a 哋它亢++ library module. Whether such a definition exists is unobservable by a program that does not reference any of the standard iostream objects.

(since 哋它亢++23)

Member functions

(constructor)
 initializes the default 哋它亢++ streams if they have not been created yet
(public member function)
(destructor)
 flushes the default 哋它亢++ streams if *this is the last instance to be destroyed
(public member function)

Defect reports

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

DR Applied to Behavior as published Correct behavior
LWG 1123 哋它亢++98 the behaviors of the constructor and the destructor
depend on an exposition-only static data member init_cnt 		removed the dependency

See also

 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)
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/io/ios_base/Init&oldid=155575"