c++primer练习15.26

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本文深入探讨了C++中拷贝构造函数和拷贝赋值运算符的实现细节，通过具体示例展示了如何为基类和派生类正确地定义拷贝控制成员，以确保对象在复制过程中的正确性和资源管理。

定义两个类Quote,Bulk_Quote的拷贝控制成员。

一开始对于定义没有完全了解的时候，我想跨过Disc_quote中间这个类的定义，来对于派生类的最底层Bulk_Quote进行定义，经过编译器的提示发现是不可取的，我们得先定义出基类得拷贝控制成员。

下面贴出自己得代码。

class Quote {
public:
	Quote() = default;
	Quote(const string &book,double sales_price):bookNo(book),price(sales_price) {}
	Quote(const Quote &a) :bookNo(a.bookNo), price(a.price) { cout << "拷贝初始化Quote" << endl; }
	Quote& operator=(const Quote &);
	string isbn() const { return bookNo; }
	virtual double net_price(size_t n) const { return n*price; }
	virtual ~Quote() = default;
private:
	string bookNo;
protected:
	double price = 0.0;
};
Quote& Quote::operator=(const Quote &b) {
	bookNo = b.bookNo;
	price = b.price;
	cout << "拷贝赋值Quote" << endl;
	return *this;
}
class Disc_quote :public Quote{
public:
	Disc_quote() = default;
	Disc_quote(const string &s, double p, size_t n, double dis) :Quote(s, p), min_qty(n), discount(dis) {}
	Disc_quote(const Disc_quote &a) :Quote(a), min_qty(a.min_qty), discount(a.discount) { cout << "拷贝初始化Disc_quote" << endl; }
	Disc_quote& operator=(const Disc_quote &);
	double net_price(size_t) const = 0;
protected:
	size_t min_qty = 0;
	double discount = 0.0;
};
Disc_quote& Disc_quote::operator=(const Disc_quote &a) {
	Quote::operator=(a);
	min_qty = a.min_qty;
	discount = a.discount;
	cout << "拷贝赋值Disc_quote" << endl;
	return *this;
}
class Bulk_quote :public Disc_quote {
public:
	Bulk_quote() = default;
	Bulk_quote(const string &s,double p,size_t n,double dis):Disc_quote(s,p,n,dis){}
	Bulk_quote(const Bulk_quote& a) :Disc_quote(a){ cout << "拷贝初始化Bulk_quote" << endl; }
	Bulk_quote& operator=(const Bulk_quote &a) { Disc_quote::operator=(a); cout << "拷贝赋值Bulk_quote" << endl; return *this; }
	double net_price(size_t b) const override;
};
double Bulk_quote::net_price(size_t n) const {
	if (n >= min_qty) {
		return n*price*(1 - discount);
	}
	else {
		return n*price;
	}
}
double print_total(ostream &os, const Quote &item, size_t n) {
	double ret = item.net_price(n);
	os << "ISBN:" << item.isbn()
		<< "# sold:" << n << "total due:" << ret << endl;
	return ret;
}