std::ios_base:: Init
|
class
Init
;
|
||
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).
|
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) |