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| Observers | ||||
| Iterators | ||||
(C++26) | ||||
(C++26) | ||||
| Monadic operations | ||||
(C++23) | ||||
(C++23) | ||||
(C++23) | ||||
| Modifiers | ||||
optional::reset | ||||
| Non-member functions | ||||
| Deduction guides | ||||
| Helper classes | ||||
| Helper objects | ||||
void reset()noexcept; | (since C++17) (constexpr since C++20) | |
If*this contains a value, destroy that value as if byvalue().T::~T(). Otherwise, there are no effects.
*this does not contain a value after this call.
Contents |
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_optional | 202106L | (C++20) (DR20) | Fullyconstexpr |
#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 destructedReset optional: destructedEnd example
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 inconstexpr in C++20 | madeconstexpr |
| assigns contents (public member function)[edit] |
