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

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

#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 a 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