C ++中抽象类的问题

Question

main:

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

int main()
{
    serviceChargeChecking newAccount("Crim", 111222, 50.00, 100, 1.00); 


    system("PAUSE");
    return 0;
}

serviceChargeChecking.h:

#ifndef H_serviceChargeChecking
#define H_serviceChargeChecking

#include "checkingaccount.h"
#include <string>


class serviceChargeChecking: public checkingAccount
{
public:
    void setMonthlyFee(double);
    void writeCheck(int);
    void getMonthlyStatement() const;
    serviceChargeChecking(std::string =" ",int = 0, double = 0.00, int= 0, double =     0.00);
private:
    double serviceCharge;

};
#endif

serviceChargeChecking.cpp:

#include "serviceChargeChecking.h"
#include <iostream>

using std::string;


void serviceChargeChecking::setMonthlyFee(double fee)
{
    serviceCharge=fee;
}
void serviceChargeChecking::getMonthlyStatement() const
{
    checkingAccount::getMonthlyStatement();
    std::cout<< "Service Charge: " << serviceCharge << std::endl;
}
void serviceChargeChecking::writeCheck(int ammount)
{
    if(checkingAccount::getChecks()>0)
    {
        checkingAccount::setChecks(checkingAccount::getChecks()-ammount);
    }
    else
    {
        std::cout<<"No checks available." << std::endl;
    }
}
serviceChargeChecking::serviceChargeChecking(string name, int acct, double bal, int numCheck, double sCharge)
{
    bankAccount::setAcctOwnersName(name);
    bankAccount::setAcctNum(acct);
    bankAccount::setBalance(bal);
    checkingAccount::setChecks(numCheck);
    serviceCharge=sCharge;
}

checkingAccount.h:

#ifndef H_checkingAccount
#define H_checkingAccount
#include "bankAccount.h"
#include <iostream>

class checkingAccount: public bankAccount
{
public:
    virtual void writeCheck()=0;
    void deposit(double);
    void withdraw(double);
    void getMonthlyStatement() const;
    int getChecks();
    void setChecks(int);

private:
    int numChecks;
};
#endif

checkingAccount.cpp:

#include "checkingAccount.h"
#include <iostream>

int checkingAccount::getChecks()
{
    return numChecks;
}
void checkingAccount::setChecks(int c)
{
    numChecks=c;
}
void checkingAccount::deposit(double d)
{
    bankAccount::setBalance(bankAccount::getBalance()+d);
}
void checkingAccount::withdraw(double w)
{
    bankAccount::setBalance(bankAccount::getBalance()-w);
}
void checkingAccount::getMonthlyStatement() const
{ 
    bankAccount::getMonthlyStatement();
}

bankAccount.h:

#ifndef H_bankAccount
#define H_bankAccount
#include <string>

class bankAccount
{
public:
    std::string getAcctOwnersName() const;
    int getAcctNum() const;
    double getBalance() const;
    void getMonthlyStatement() const;

    void setAcctOwnersName(std::string);
    void setAcctNum(int);
    void setBalance(double);

    virtual void withdraw(double)=0;
    virtual void deposit(double)=0;
private:
    std::string acctOwnersName;
    int acctNum;
    double acctBalance;
};
#endif

bankAccount.cpp:

#include "bankAccount.h"
#include <iostream>
using std::string;


string bankAccount::getAcctOwnersName() const
{
    return acctOwnersName;
}
int bankAccount::getAcctNum() const
{
    return acctNum;
}
double bankAccount::getBalance() const
{
    return acctBalance;
}
void bankAccount::setAcctOwnersName(string name)
{
    acctOwnersName=name;
}
void bankAccount::setAcctNum(int num)
{
    acctNum=num;
}
void bankAccount::setBalance(double b)
{
    acctBalance=b;
}
void bankAccount::getMonthlyStatement() const
{
    std::cout << "Name on Account: " << getAcctOwnersName() << std::endl;
    std::cout << "Account Id: " << getAcctNum() << std::endl;
    std::cout << "Balance: " << getBalance() << std::endl;
}

I know this is a lot of code to go through but can anyone help me understand why i cannot create an object from the class serviceChargeChecking the error is telling me that i cannot create an object from the abstract class but it doesn't seem to be abstract to me.

Answer 1

serviceChargeChecking实现了void writeCheck(int) ，但是来自checkingAccount的纯虚函数的类型为void writeCheck() ，因此在serviceChargeChecking它仍然是纯净的，这使类成为了抽象。

Answer 2

You have this in the abstract class checkingAccount :

virtual void writeCheck()=0;

but implement this in the derived class serviceChargeChecking :

void writeCheck(int);

The signature must be the same.

Answer 3

The writeCheck() method has different signatures in serviceChargeChecking and checkingAccount .

If you use C++11, use override in order to avoid this kind of error.

Answer 4

这是因为您的CheckingAcount具有writeCheck（）而serviceChargeChecking具有writeCheck（int）;

Answer 5

This probably due to the fact that you failed to Override checkingAccount's, writeCheck method, the abstract prototype was was

in checkingAccount class

virtual void writeCheck()=0;

and in serviceChargeChecking class

 void writeCheck(int);

note the parameters, you didn't override checkingAccount's writeCheck you probably inherited it (implicitly), the serviceChargeChecking made a new writeCheck with an int parameter.