NAME¶

std::optional::reset - std::optional::reset

Synopsis¶

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.

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 made constexpr
destruction is allowed in constexpr in C++20

See also¶

operator= assigns contents
(public member function)