NAME¶

std::optional::value - std::optional::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 <iostream>
#include <optional>

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¶

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