std::experimental::optional<T>::value

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Technical specifications
Filesystem library (filesystem TS)
Library fundamentals (library fundamentals TS)
Library fundamentals 2 (library fundamentals TS v2)
Library fundamentals 3 (library fundamentals TS v3)
Extensions for parallelism (parallelism TS)
Extensions for parallelism 2 (parallelism TS v2)
Extensions for concurrency (concurrency TS)
Extensions for concurrency 2 (concurrency TS v2)
Concepts (concepts TS)
Ranges (ranges TS)
Reflection (reflection TS)
Mathematical special functions (special functions TR)
 
 
 
constexpr T& value() &;
constexpr const T & value() const &;
(1) (library fundamentals TS)
constexpr T&& value() &&;
constexpr const T&& value() const &&;
(2) (library fundamentals TS)

Returns the contained value.

1) Equivalent to return bool(*this) ? *val : throw bad_optional_access();.
2) Equivalent to return bool(*this) ? std::move(*val) : throw bad_optional_access();.

Parameters

(none)

Return value

A reference to the contained value.

Exceptions

std::experimental::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 <experimental/optional>
#include <iostream>
 
int main()
{
    std::experimental::optional<int> opt = {};
 
    try
    {
        int n = opt.value();
    }
    catch (const std::logic_error& e)
    {
        std::cout << e.what() << '\n';
    }
}

Possible output:

optional<T>::value: not engaged

See also

returns the contained value if available, another value otherwise
(public member function)
accesses the contained value
(public member function)
(library fundamentals TS)
exception indicating checked access to an optional that doesn't contain a value
(class)