C++在容器中放置有继承关系的对象和指针区别

《C++ Primer 5》15.28和15.29两题

1 .h头文件：包括父类Quote和子类Bulk_quote的定义

bookQuote.h：

#pragma once
#include<iostream>
#include<string>

using namespace std;

class Quote {
	//friend ostream& operator<<(ostream&, Quote&);
public:
	Quote() = default;
	Quote(const string& book = "", double sales_price = 0.0) :bookNo(book), price(sales_price) {}

	string isbn() const {
		return bookNo;
	}

	virtual double net_price(size_t n) const {
		return n * price;
	}

	virtual ~Quote(){}
private:
	string bookNo;
protected:
	double price = 0.0;
};

class Bulk_quote :public Quote {
public:
	Bulk_quote(const string& book = "", double sales_price = 0.0, size_t qty = 0, double disc = 0.0) :
		Quote(book, sales_price), min_qty(qty), discount(disc) {}

	double net_price(size_t cnt) const {
		if (cnt > min_qty) {
			return cnt * (1 - discount) * price;
		}
		else {
			return cnt * price;
		}
	}

	~Bulk_quote(){}
private:
	size_t min_qty;
	double discount;
};

2-1 .cpp文件：定义父类Quote对象的vector容器，存入子类Bulk_quote对象

#include<iostream>
#include<string>
#include<vector>
#include"bookQuote.h" //1中定义的.h头文件
#include<memory> //shared_ptr智能指针
using namespace std;

int main() {
	vector<Quote> itemVec;
	for (size_t i = 0;i != 10;++i) {
		Bulk_quote item("C++ Primer 5", 6, 5, 0.5);
		itemVec.push_back(item);
	}
	double sum = 0;
	for (auto iter = itemVec.begin();iter != itemVec.end();++iter) {
		sum += iter->net_price(10);
	}
	cout << sum << endl;
	return 0;
}

输出结果，600。

2-2 .cpp文件：定义指向父类Quote对象的智能指针的vector容器，存入指向子类Bulk_quote对象的智能指针

#include<iostream>
#include<string>
#include<vector>
#include"bookQuote.h"
#include<memory>
using namespace std;

int main() {
	vector<shared_ptr<Quote>> itemVec;
	for (size_t i = 0;i != 10;++i) {
		Bulk_quote item("C++ Primer 5", 6, 5, 0.5);
		itemVec.push_back(make_shared<Bulk_quote>(item));
	}
	double sum = 0;
	for (auto iter = itemVec.begin();iter != itemVec.end();++iter) {
		sum += (*iter)->net_price(10);
	}
	cout << sum << endl;
	return 0;
}

输出结果：300。