Effective C++ 條款12：複製物件時勿忘其每一個成分

<textarea readonly="readonly" nam ="code" class="c++">
void logCall(const string& funcName);
class Customer{
public:
    Customer(string b):name(b){}
    Customer(const Customer& rhs);
    Customer& operator = (const Customer& rhs);
    string name;//將成員變數宣告為public便於實驗觀察
};

void logCall(const string &funcName){
    cout << "funcName = " << funcName << endl;
}

Customer::Customer(const Customer &rhs):name(rhs.name){
    logCall("Customer copy constructor.");
}

Customer& Customer::operator = (const Customer& rhs){
    logCall("Customer copy assignment operator.");
    name = rhs.name;
    return *this;
}

class PriorityCustomer:public Customer{
public:
    PriorityCustomer(int a, string b):Customer(b),priority(a){}
    PriorityCustomer(const PriorityCustomer& rhs);
    PriorityCustomer& operator = (const PriorityCustomer& rhs);
    int priority;//將成員變數宣告為public便於實驗觀察
};
// 拷貝建構函式中 Customer(rhs) 編譯器強制要求加上，在拷貝賦值函式中沒有向基類傳遞資訊，作為對比
PriorityCustomer::PriorityCustomer(const PriorityCustomer& rhs)
    :Customer(rhs), priority(rhs.priority){
    logCall("PriorityCustomer copy constructor.");
}

PriorityCustomer& PriorityCustomer::operator =(const PriorityCustomer& rhs){
    logCall("PriorityCustomer assignment operator.");
    priority = rhs.priority;
    return *this;
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    PriorityCustomer pc1(10,"Hello");
    PriorityCustomer pc2(100,"World");
    PriorityCustomer pc3(pc2);
    pc1 = pc2;
    cout<<"pc3.priority = "<<pc3.priority<<endl;
    cout<<"pc3.name = "<<pc3.name<<endl;
    cout<<"pc1.priority = "<<pc1.priority<<endl; 
    cout<<"pc1.name = "<<pc1.name<<endl;
    return a.exec();
}
</textarea>
 

此時得到的結果是

可見拷貝建構函式複製了每一個成員，而拷貝賦值函式並沒有全部複製。對拷貝賦值函式進行修改，加入基類的拷貝賦值函式：

<textarea readonly="readonly" nam ="code" class="c++">
PriorityCustomer& PriorityCustomer::operator =(const PriorityCustomer& rhs){
    logCall("PriorityCustomer assignment operator.");
    Customer::operator =(rhs);
    priority = rhs.priority;
    return *this;
}
</textarea>