std::optional::optional

 

C++

Language

Standard library headers

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Utilities library

Strings library

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Numerics library

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Regular expressions library (C++11)

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Utilities library

Type support (basic types, RTTI, type traits)

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Error handling

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Date and time

Function objects

initializer_list (C++11)

bitset

hash (C++11)

Relational operators

rel_ops::operator!= rel_ops::operator> rel_ops::operator<= rel_ops::operator>=

Pairs and tuples

pair

tuple (C++11)

piecewise_construct_t (C++11)

piecewise_construct (C++11)

Swap, forward and move

swap

forward (C++11)

move (C++11)

move_if_noexcept (C++11)

declval (C++11)

 

std::optional

Member functions

optional::optional

optional::~optional

optional::operator=

Observers

optional::operator-> optional::operator*

optional::operator bool

optional::value

optional::value_or

Modifiers

optional::emplace

optional::swap

Non-member functions

operator== operator<

make_optional

swap

Helper classes

hash

 

constexpr optional();	(1)	(since C++14)
constexpr optional( std::nullopt_t );	(1)	(since C++14)
optional( const optional& other);	(2)	(since C++14)
optional( optional&& other );	(3)	(since C++14)
constexpr optional( const T& value );	(4)	(since C++14)
constexpr optional( T&& value );	(5)	(since C++14)
template< class... Args > constexpr explicit optional( std::in_place_t, Args&&... args );	(6)	(since C++14)
template< class U, class... Args > constexpr explicit optional( std::in_place_t, std::initializer_list<U> ilist,                              Args&&... args );	(7)	(since C++14)

Constructs a new optional object.

1) Constructs the object without initializing the contained value. The object is in disengaged state after the call.

2-3) Initializes the contained value by copying (2) or moving(3) the contained value of other, but only if other is engaged. other is still in engaged state if it was in engaged state before the call.

4-7) Initializes the contained value from various sources. *this is in engaged state after the call.

4) Initializes the contained value by copying value.

5) Initializes the contained value by moving value.

6) Initializes the contained value by constructing it in-place and passing args... to the constructor.

7) Initializes the contained value by constructing it in-place and passing the initializer list ilist and arguments args... to the constructor. The function does not participate in the overload resolution if

std::is_constructible<T, std::initializer_list<U>&, Args&&...>::value != true

Parameters

other	-	another optional object whose contained value to copy
value	-	value to initialize the contained value with
args...	-	arguments to initialize the contained value with
ilist	-	initializer list to initialize the contained value with
Type requirements
- T must meet the requirements of CopyConstructible in order to use overloads (2,4).
- T must meet the requirements of MoveConstructible in order to use overloads (3,5).

Exceptions

1)

noexcept specification:  

noexcept

  (since C++11)

2) Throws any exception thrown by the constructor of T.

3) Throws any exception thrown by the constructor of T. Has the following noexcept declaration:

noexcept specification:  (since C++11)

noexcept(std::is_nothrow_move_constructible<T>::value)

.

4-5) Throws any exception thrown by the constructor of T.

See also

make_optional	creates an optional object (function template)