C++程序  |  26行  |  718 B

//===----------------------------------------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++98, c++03, c++11, c++14
// <optional>

// struct nullopt_t{see below};
// inline constexpr nullopt_t nullopt(unspecified);

// [optional.nullopt]/2:
//   Type nullopt_t shall not have a default constructor or an initializer-list
//   constructor, and shall not be an aggregate.

#include <optional>

int main()
{
    std::nullopt_t n = {};
}