复制对象时要把对象的每一部分都赋值到位，尤其在有基类的时候容易遗漏复制
#includeusing namespace std;class Date{public: Date(int d = 1, int m = 1, int w = 1) :day(d), month(m), weekday(w) { cout << "基类构造函数" << endl; } Date(const Date& rhs) { day = rhs.day; month = rhs.month; } Date& operator=(const Date& rhs) { day = rhs.day; month = rhs.month; return *this; } ~Date() { cout << "基类析构函数" << endl; } void printDay() { cout << month << "月" << day << "日" << "周" << weekday << endl; }private: int day; int month; int weekday;};int main(){ //忘记了赋值weekend Date day1; Date day2(2, 2, 2); day1 = day2; day1.printDay(); /* 基类构造函数 基类构造函数 2月2日周1 */ system("pause");}
在继承、派生体系中，对于派生类的复制控制函数，也要调用基类的复制控制，否则复制、赋值等操作只会作用于派生类特有的数据上：
#includeusing namespace std;class Date{public: Date(int d = 1, int m = 1, int w = 1) :day(d), month(m), weekday(w) { cout << "基类构造函数" << endl; } Date(const Date& rhs) { init(rhs); } Date& operator=(const Date& rhs) { if (&rhs != this) { init(rhs); } return *this; } ~Date() { cout << "基类析构函数" << endl; } void printDay() { cout << month << "月" << day << "日" << "周" << weekday << endl; }private: void init(const Date &rhs) { day = rhs.day; month = rhs.month; weekday = rhs.weekday; }public: int day; int month; int weekday;};class DetailDay :public Date{public: DetailDay(const DetailDay& rhs) :year(rhs.year), Date(rhs) { } DetailDay(int y, int m, int d, int w) :year(y), Date(m, d, w) {} DetailDay& operator=(const DetailDay& rhs) { Date::operator=(rhs); year = rhs.year; return *this; } void printDay() { cout << year<<"年"< << "月" << day << "日" << "周" << weekday << endl; }private: int year;};int main(){ DetailDay dt(2017, 5, 10, 3); dt.printDay(); system("pause");}
最后有一点需要注意：我们发现，复制构造函数和赋值构造函数里面很多内容是重复的。此时并不要用一个去调用另外一个，良好的编程习惯是定义一个init函数，让这两个函数都调用它，就想像程序中所做的那样。