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std::optional<T>::operator->, std::optional<T>::operator* - cppreference.com

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constexpr const T* operator->() const noexcept;

 (1) (since C++17)

constexpr T* operator->() noexcept;

 (2) (since C++17)

constexpr const T& operator*() const& noexcept;

 (3) (since C++17)

constexpr T& operator*() & noexcept;

 (4) (since C++17)

constexpr const 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

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

#include <iomanip>
#include <iostream>
#include <optional>
#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: " << std::quoted(*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: " << 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

returns the contained value
(public member function) [edit]
returns the contained value if available, another value otherwise
(public member function) [edit]