c++ - 仅包含第一个派生类

Question

我是 C++ 的新手，对于一项学校作业，我们必须创建一个基类并从中创建 2 个派生类，然后显示这两个派生类的所有关联函数的输出。

问题是，当我尝试在我的测试文件中包含这两个派生类时，只有我包含的派生类首先起作用。如果我颠倒我包含它们的顺序，那么现在包含的第一个有效，但第二个无效

知道为什么会发生这种情况吗？

这是我的测试文件:

#include "Payment.h"
#include "CashPayment.h" // This one will work
#include "CreditCardPayment.h" // This one won't. Unless you switch them
#include <iostream>
#include <string>
using namespace std;

// Tests the CashPayment and CreditCardPayment classes, derived from the Payment clas
int main() {

   CashPayment firstCash(420);
   cout << "First Cash Payment" << endl 
      << "Amount: " << firstCash.getAmount() << endl
      << firstCash.paymentDetails() << endl;

   CreditCardPayment firstCredit("Mingwu Chen", 123456789, 11, 2016, 100);
   cout << "Number: " << firstCredit.getNumber() << endl
      << "Month: " << firstCredit.getMonth() << endl
      << "Year: " << firstCredit.getYear() << endl
      << "Amount: " << firstCredit.getAmount() << endl
      << firstCredit.paymentDetails() << endl;
}

这是我的 CashPayment.h 文件:

#ifndef CASHPAYMENT_H
#define CASHPAYMENT_H

#include <string>
#include "Payment.h"
using namespace std;

class CashPayment: public Payment {

   public:

      // Creates a CashPayment with an amount of 0
      CashPayment();

      // Creates a CashPayment with the given amount
      CashPayment(double a);

      // Creates a string out of all the CashPayment details
      string paymentDetails();
};
#endif

这是 CreditCardPayment.h 文件:

#ifndef CASHPAYMENT_H
#define CASHPAYMENT_H

#include <string>
#include "Payment.h"
using namespace std;

class CreditCardPayment: public Payment {

   private:
      string name;
      int cardNumber;
      int expMonth;
      int expYear;

   public:

      // Creates a CreditCardPayment with an amount of 0
      CreditCardPayment();

      // Creates a CreditCardPayment with the given card holder name, card number, expiry month, expiry year, and amount
      CreditCardPayment(string n, int c, int m, int y, double a);

      // Creates a string out of all the CreditCardPayment details
      string paymentDetails();

      // Returns the card holder name
      string getName();

      // Returns the card number
      int getNumber();

      // Returns the expiry month
      int getMonth();

      // Returns the expiry year
      int getYear();

      // Sets the card holder name t0 the given name
      void setName(string n);

      // Sets the card number to the given number
      void setNumber(int c);

      // Sets the expiry month to the given month
      void setMonth(int m);

      // Sets the expiry year to the given year
      void setYear(int y);
};
#endif

这是 Payment.h 文件:

#ifndef PAYMENT_H
#define PAYMENT_H

#include <string>
using namespace std;

class Payment {

   private:
      double amount;

   public:
      // Creates a Payment with an amount of 0
      Payment();

      // Creates a Payment with the given amount
      Payment(double a);

      // Returns the amount
      double getAmount();

      // Sets the amount to the given value
      void setAmount(int a);

      // Creates a string out of all the Payment details
      string paymentDetails();
};
#endif

我整晚都在试图解决这个问题，但我真的被难住了。任何想法或建议都将不胜感激。

(PS:这里很多人似乎不喜欢使用namespace std，但这正是我老师想要的)

Answer 1

两个头文件都有:

#ifndef CASHPAYMENT_H
#define CASHPAYMENT_H

因此，无论哪个先包含，其内容实际得到编译。