std::optional<T>::value

Since C++17

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

# Declarations

constexpr T& value() &;
constexpr const T& value() const &;

(since C++17)

constexpr T&& value() &&;
constexpr const T&& value() const &&;

(since C++17)

# Return value

A reference to the contained value.

# Notes

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

# Example

#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';
}

# See also