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std::optional::value

From cppreference.com
< cpp‎ | utility‎ | optional
constexpr T& value() &;
constexpr const T & value() const &;
(1) (since C++17)
constexpr T&& value() &&;
constexpr const T&& value() const &&;
(2) (since C++17)

If *this contains a value, returns a reference to the contained value.

Otherwise, throws a std::bad_optional_access exception.

Contents

[edit] Parameters

(none)

[edit] Return value

A reference to the contained value.

[edit] Exceptions

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

[edit] Notes

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

[edit] Example

#include <optional>
#include <iostream>
int main()
{
    std::optional<int> opt = {};
 
    try {
        int n = opt.value();
    } catch(const std::logic_error& e) {
        std::cout << e.what() << '\n';
    }
}

Possible output:

optional<T>::value: not engaged

[edit] See also

returns the contained value if available, another value otherwise
(public member function) [edit]
accesses the contained value
(public member function) [edit]
exception indicating checked access to an optional that doesn't contain a value
(class) [edit]