std::optional<T>::value (3) - Linux Man Pages

std::optional<T>::value: std::optional<T>::value

NAME

std::optional<T>::value - std::optional<T>::value

Synopsis


constexpr T& value() &; (1) (since C++17)
constexpr const T & value() const &;
constexpr T&& value() &&; (2) (since C++17)
constexpr const T&& value() const &&;


If *this contains a value, returns a reference to the contained value.
Otherwise, throws a std::bad_optional_access exception.

Parameters


(none)

Return value


A reference to the contained value.

Exceptions


std::bad_optional_access if *this does not contain a value.

Notes


The dereference operator operator*() does not check if this optional contains a value, which may be more efficient than value().

Example


// Run this code


  #include <optional>
  #include <iostream>
  int main()
  {
      std::optional<int> opt = {};


      try {
          int n = opt.value();
      } catch(const std::bad_optional_access& e) {
          std::cout << e.what() << '\n';
      }
  }

Possible output:


  bad optional access

See also


                    returns the contained value if available, another value otherwise
value_or (public member function)
                    accesses the contained value
operator-> (public member function)
operator*


bad_optional_access exception indicating checked access to an optional that doesn't contain a value
                    (class)
(C++17)