# std::optional<T>::reset

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< cpp‎ | utility‎ | optional

void reset() noexcept; |  | (since C++17) (constexpr since C++20)

If *this contains a value, destroy that value as if by value().T::~T(). Otherwise, there are no effects.

*this does not contain a value after this call.

### Notes

Feature-test macro | Value | Std | Feature
--- | --- | --- | ---
`__cpp_lib_optional` | `202106L` | (C++20) (DR20) | Fully constexpr

### Example

Run this code

    #include <iostream>
    #include <optional>

    struct A
    {
        std::string s;
        A(std::string str) : s(std::move(str)) { std::cout << " constructed\n"; }
        ~A() { std::cout << " destructed\n"; }
        A(const A& o) : s(o.s) { std::cout << " copy constructed\n"; }
        A(A&& o) : s(std::move(o.s)) { std::cout << " move constructed\n"; }

        A& operator=(const A& other)
        {
            s = other.s;
            std::cout << " copy assigned\n";
            return *this;
        }

        A& operator=(A&& other)
        {
            s = std::move(other.s);
            std::cout << " move assigned\n";
            return *this;
        }
    };

    int main()
    {
        std::cout << "Create empty optional:\n";
        std::optional<A> opt;

        std::cout << "Construct and assign value:\n";
        opt = A("Lorem ipsum dolor sit amet, consectetur adipiscing elit nec.");

        std::cout << "Reset optional:\n";
        opt.reset();
        std::cout << "End example\n";
    }

Output:

    Create empty optional:
    Construct and assign value:
     constructed
     move constructed
     destructed
    Reset optional:
     destructed
    End example

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
P2231R1 | C++20 | `reset` was not constexpr while non-trivial destruction is allowed in constexpr in C++20 | made constexpr

### See also

operator= | assigns contents (public member function)

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