0

模板问题；第一个是包含模板及其定义的头文件，Visual Studio 2019 没有显示 /C++lastest 功能（c++20）的警告

#ifndef PAIR_H
#define PAIR_H

#include <compare>
#include <iostream>

template <typename First, typename Second>
class Pair
{
public:
  // Public members + no m_ prefix analogous to std::pair<> (see <utility> module)
  First first;    
  Second second;

  Pair() = default;
  Pair(const First& f, const Second& s);
  
  // Note: not all compiler may fully support this generation yet (C++20)...
  // (replacing auto with std::strong_ordering may make Soln17_02.cpp compile then,
  // but in general auto is better because First and/or Second could be types 
  // that are not strongly ordered, such as a floating-point types)
  auto operator<=>(const Pair& other) const = default;
};

// Constructor
template <typename First, typename Second>
Pair<First, Second>::Pair(const First& f, const Second& s)
  : first{f}, second{s}
{}

template <typename First, typename Second>
std::ostream& operator<<(std::ostream& out, const Pair<First, Second>& pair)
{
  return out << '(' << pair.first << ", " << pair.second << ')';
}

#endif

波纹管只是解决方案

#include "Pair.h"
#include <iostream>
#include <string>

int main()
{
  // To make the s string literal suffix work 
  // (facilitates creation of Pairs using CTAD, or Constructor Template Argument Deduction).
  // This syntactic sugar for creating std::string objects is not really covered in the book.
  using namespace std::string_literals;

  auto my_pair{ Pair{122, "abc"s} };
  ++my_pair.first;
  std::cout << "my_pair equals " << my_pair << std::endl;

  auto pair1{ Pair{  0, "def"s} };
  auto pair2{ Pair{123, "abc"s} };
  auto pair3{ Pair{123, "def"s} };

  std::cout << (pair1 < pair2 && pair2 < pair3? "operator< seems to be working" : "oops") << std::endl;
  std::cout << (pair1 == pair2? "oops" : "operator== works as well") << std::endl;
}

我只是无法编译，它显示了这个“错误 C2098 数据成员 '<=' 后的意外令牌”，它指向这一行“auto operator<=>(const Pair& other) const = default;”。我已经阅读了有关操作的 cpp++ 参考<<。是模板错误还是有什么问题？谢谢

4

0 回答 0