如何重载 + 运算符以便可以编写 newVacation = oldVacation + 5，// 将 numDays 加 5，同时仅复制 numPeople

Question

我正在尝试编写一个重载 + 运算符的程序。当我输入 7 和 3 时，它会正确打印：第一个假期：天数：7，人数：3 但错误地打印：第二个假期：天数：-158458720，人数：32764 它应该输出：第二次假期：天数：12，人数：3

#include <iostream>
using namespace std;

class FamilyVacation {
 public:
  void  SetNumDays(int dayCount);
  void  SetNumPeople(int peopleCount);
  void  Print() const;
  FamilyVacation operator+(int moreDays);
 private:
  int   numDays;
  int   numPeople;
};

void FamilyVacation::SetNumDays(int dayCount) {
numDays = dayCount;
}

void FamilyVacation::SetNumPeople(int peopleCount) {
numPeople = peopleCount;
}

// FIXME: Overload + operator so can write newVacation = oldVacation + 5,
//        which adds 5 to numDays, while just copying numPeople.

FamilyVacation FamilyVacation::operator+(int moreDays) {
numDays = moreDays + 5;  
}


void FamilyVacation::Print() const {
cout << "Days: " << numDays << ", People: " << numPeople << endl;
}

 int main() {
 FamilyVacation firstVacation;
 FamilyVacation secondVacation;
 int userDays;
 int userPeople;

 cin >> userDays;
 cin >> userPeople;

 cout << "First vacation: ";
 firstVacation.SetNumDays(userDays);
 firstVacation.SetNumPeople(userPeople);
 firstVacation.Print();

 cout << "Second vacation: ";
 secondVacation = firstVacation + 5;
 secondVacation.Print();

  return 0;
 }

Answer 1

您的操作员有 未定义的行为。

它被声明为返回一个新的 FamilyVacation 对象，但实际上根本没有返回任何东西。这就是 secondVacation.Print() 打印垃圾的原因。

更糟糕的是，您的操作员正在修改被调用的对象（甚至没有使用 正确的 值修改它！），这是此操作员的错误行为实行。参见 What are the basic rules and idioms for operator overloading?

试试这个：

FamilyVacation FamilyVacation::operator+(int moreDays)
{
    FamilyVacation ret;
    ret.SetNumDays(numDays + moreDays);
    ret.SetNumPeople(numPeople);
    return ret;
}

如何重载 + 运算符以便可以编写 newVacation = oldVacation + 5，// 将 numDays 加 5，同时仅复制 numPeople

How to overload + operator so can write newVacation = oldVacation + 5, // which adds 5 to numDays, while just copying numPeople

c++

overloading