c++ - 如何重载 + 运算符，以便可以编写 newVacation = oldVacation + 5,//将 5 添加到 numDays，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，它正确打印: 第一个假期:天数:7，人数:3 但打印错误: 第二个假期:天数:-158458720，人数:32764 它应该输出: 第二个假期: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

您的运算符(operator)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内容。这就是为什么 secondVacation.Print() 打印垃圾。

更糟糕的是，您的运算符正在修改正在调用的对象(甚至没有使用正确的值来修改它!)，这是该运算符实现的错误行为。请参阅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;
}