std::ios_base::Init
| class Init; |
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This class is used to ensure that the default C++ streams (std::cin, std::cout, etc.) are properly initialized and destructed. The class tracks how many instances of it are created and initializes the C++ 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).
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Each C++ library module in a hosted implementation behaves as if it contains an interface unit that defines an unexported As a result, the definition of that variable is appearance-ordered before any declaration following the point of importation of a C++ library module. Whether such a definition exists is unobservable by a program that does not reference any of the standard iostream objects. |
(since C++23) |
Member functions
| (constructor) |
initializes the default C++ streams if they have not been created yet (public member function) |
| (destructor) |
flushes the default C++ 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 C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 1123 | C++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) |