std::optional<T>::value

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

Possible output:

bad optional access

Language
Standard Library Headers
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Named requirements
Language support library
Concepts library (C++20)
Diagnostics library
Utilities library
Strings library
Containers library
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Ranges library (C++20)
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Technical Specifications

Member functions
optional::optional
optional::~optional
optional::operator=
Observers
optional::operator->optional::operator*
optional::operator booloptional::has_value
optional::value
optional::value_or
Modifiers
optional::emplace
optional::swap
optional::reset
Non-member functions
operator==operator!=operator<operator<=operator>operator>=
make_optional
swap
Deduction guides
Helper classes
hash
nullopt_t
in_place_t
bad_optional_access
Helper objects
nullopt
in_place