std::optional<T>:: value

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

#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';
}

bad optional access
bad optional access
43
44

See also