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)

Returns the contained value.

1) Equivalent to return bool(*this) ? *val : throw bad_optional_access();
2) Equivalent to return bool(*this) ? std::move(*val) : throw bad_optional_access();

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)
accesses the contained value
(public member function)
exception indicating checked access to an optional that doesn't contain a value
(class)