std::ios_base::Init - cppreference.com (original) (raw)
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 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 is included in the translation unit before these objects were defined).
| Each C++ library module in a hosted implementation behaves as if it contains an interface unit that defines an unexported std::ios_base::Init variable withordered initialization.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) |
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[edit] Member functions
| | initializes the default C++ streams if they have not been created yet (public member function) | | ---------------------------------------------------------------------------------------------------------- | | | flushes the default C++ streams if *this is the last instance to be destroyed (public member function) |
[edit] 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 destructordepend on an exposition-only static data member init_cnt | removed the dependency |