std::optional<T>::operator->, std::optional<T>::operator*

 

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Language support Type support (basic types, RTTI) Library feature-test macros(C++20) Program utilities Variadic functions initializer_list (C++11) is_constant_evaluated (C++20) is_within_lifetime (C++26) source_location (C++20) Coroutine support(C++20) Contract support(C++26) Three-way comparison three_way_comparablethree_way_comparable_with (C++20)(C++20) strong_ordering (C++20) weak_ordering (C++20) partial_ordering (C++20) common_comparison_category (C++20) compare_three_way_result (C++20) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20)   is_eqis_ltis_lteq (C++20)(C++20)(C++20)   is_neqis_gtis_gteq (C++20)(C++20)(C++20)

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std::optional

Member functions

optional::optional

optional::~optional

optional::operator=

Observers

optional::operator->optional::operator*

optional::operator booloptional::has_value

optional::value

optional::value_or

Iterators

optional::begin (C++26)

optional::end (C++26)

Monadic operations

optional::and_then (C++23)

optional::transform (C++23)

optional::or_else (C++23)

Modifiers

optional::emplace

optional::swap

optional::reset

Non-member functions

operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20)

make_optional

swap(std::optional)

Deduction guides

Helper classes

hash<std::optional>

nullopt_t

in_place_t

bad_optional_access

Helper objects

nullopt

in_place

 

constexprconst T* operator->()constnoexcept;	(1)	(since C++17)
constexpr T* operator->()noexcept;	(2)	(since C++17)
constexprconst T& operator*()const&noexcept;	(3)	(since C++17)
constexpr T& operator*()&noexcept;	(4)	(since C++17)
constexprconst T&& operator*()const&&noexcept;	(5)	(since C++17)
constexpr T&& operator*()&&noexcept;	(6)	(since C++17)

Accesses the contained value.

1,2) Returns a pointer to the contained value.

3-6) Returns a reference to the contained value.

If has_value() is false, the behavior is undefined.	(until C++26)
If has_value() is false: If the implementation is hardened, a contract violation occurs. Moreover, if the contract-violation handler returns under “observe” evaluation semantic, the behavior is undefined. If the implementation is not hardened, the behavior is undefined.	(since C++26)

Return value

1,2)val

3,4)*val

5,6)std::move(*val )

Notes

This operator does not check whether *this contains a value, users can do so manually by using has_value() or operator bool(). Alternatively, if checked access is needed, value() or value_or() may be used.

Example

Run this code

#include <iomanip>#include <iostream>#include <optional>#include <string>   int main(){usingnamespace std::string_literals;   std::optional<int> opt1{1};std::cout<<"opt1: "<<*opt1 <<'\n';   *opt1 =2;std::cout<<"opt1: "<<*opt1 <<'\n';   std::optional<std::string> opt2{"abc"s};std::cout<<"opt2: "<<std::quoted(*opt2)<<", size: "<< opt2->size()<<'\n';   // You can “take” the contained value by calling operator* on an rvalue to optionalauto taken =*std::move(opt2);std::cout<<"taken: "<<std::quoted(taken)<<"\n""opt2: "<<std::quoted(*opt2)<<", size: "<< opt2->size()<<'\n';}

Output:

opt1: 1 opt1: 2 opt2: "abc", size: 3 taken: "abc" opt2: "", size: 0

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 2762	C++17	operator-> and operator* might be potentially-throwing	made noexcept

See also

value	returns the contained value (public member function)
value_or	returns the contained value if available, another value otherwise (public member function)