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

 

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std::optional

Member functions

optional::optional (C++17)

optional::~optional (C++17)

optional::operator= (C++17)

Observers

optional::operator->optional::operator* (C++17)(C++17)

optional::operator booloptional::has_value (C++17)(C++17)

optional::value (C++17)

optional::value_or (C++17)

Monadic operations

optional::and_then (C++23)

optional::transform (C++23)

optional::or_else (C++23)

Modifiers

optional::emplace (C++17)

optional::swap (C++17)

optional::reset (C++17)

Non-member functions

operator==operator!=operator<operator<=operator>operator>=operator<=> (C++17)(C++17)(C++17)(C++17)(C++17)(C++17)(C++20)

make_optional (C++17)

swap (C++17)

Deduction guides

Helper classes

hash (C++17)

nullopt_t (C++17)

in_place_t (C++17)

bad_optional_access (C++17)

Helper objects

nullopt (C++17)

in_place (C++17)

 

constexpr const T* operator->() const noexcept;	(1)	(since C++17)
constexpr T* operator->() noexcept;	(1)	(since C++17)
constexpr const T& operator*() const& noexcept;	(2)	(since C++17)
constexpr T& operator*() & noexcept;	(2)	(since C++17)
constexpr const T&& operator*() const&& noexcept;	(2)	(since C++17)
constexpr T&& operator*() && noexcept;	(2)	(since C++17)

Accesses the contained value.

1) Returns a pointer to the contained value.

2) Returns a reference to the contained value.

The behavior is undefined if *this does not contain a value.

Parameters

(none)

Return value

Pointer or reference to the contained value.

Notes

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

Example

Run this code

#include <optional>
#include <iostream>
#include <string>
 
int main()
{
    using namespace 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: " << *opt2 << " size: " << opt2->size() << '\n';
 
    // You can "take" the contained value by calling operator* on an rvalue to optional
 
    auto taken = *std::move(opt2);
    std::cout << "taken: " << taken << " opt2: " << *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)