std::optional::reset - cppreference.com (original) (raw)

| 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.

[edit] Notes

[edit] Example

#include #include   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 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

[edit] Defect reports

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

[edit] See also