< cpp‎ | utility‎ | optional
Utilities library
Language support
Type support (basic types, RTTI)
Library feature-test macros (C++20)
Dynamic memory management
Program utilities
Coroutine support (C++20)
Variadic functions
Debugging support
Three-way comparison
General utilities
Date and time
Function objects
Formatting library (C++20)
Relational operators (deprecated in C++20)
Integer comparison functions
Swap and type operations
Common vocabulary types
Elementary string conversions

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] Example

#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";
    std::cout << "End example\n";


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

[edit] 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

[edit] See also

assigns contents
(public member function) [edit]