std::optional<T>::operator->,std::optional<T>::operator* (3) - Linux Manuals

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

NAME

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

Synopsis

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

Exceptions

(none)

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 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