# std::optional<T>::value

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< 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.

### 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 {
            [[maybe_unused]] int n = opt.value();
        } catch(const std::bad_optional_access& e) {
            std::cout << e.what() << '\n';
        }
        try {
            opt.value() = 42;
        } catch(const std::bad_optional_access& e) {
            std::cout << e.what() << '\n';
        }

        opt = 43;
        std::cout << *opt << '\n';

        opt.value() = 44;
        std::cout << opt.value() << '\n';
    }

Output:

    bad optional access
    bad optional access
    43
    44

### See also

value_or | returns the contained value if available, another value otherwise (public member function)
operator->operator* | accesses the contained value (public member function)
bad_optional_access (C++17) | exception indicating checked access to an optional that doesn't contain a value (class)

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