C++ Primer——Sales_item.h头文件源码及相关问题解决

在C++ Primer 第五版中有一个小练习要将网站上的头文件源码“拷贝到工作目录中”，首先，似乎并没有那个网站，源码也是百度资源上找的。其次，拷贝到工作目录中，添加头文件有个小细节。
源码如下：

#ifndef SALESITEM_H
#define SALESITEM_H
#include 
#include 

class Sales_item
{
public:
	Sales_item(const std::string &book) :isbn(book), units_sold(0), revenue(0.0) {}
	Sales_item(std::istream &is) { is >> *this; }
	friend std::istream& operator>>(std::istream &, Sales_item &);
	friend std::ostream& operator<<(std::ostream &, const Sales_item &);
public:
	Sales_item & operator+=(const Sales_item&);
public:
	double avg_price() const;
	bool same_isbn(const Sales_item &rhs)const
	{
		return isbn == rhs.isbn;
	}
	Sales_item() :units_sold(0), revenue(0.0) {}
public:
	std::string isbn;
	unsigned units_sold;
	double revenue;
};

using std::istream;
using std::ostream;
Sales_item operator+(const Sales_item &, const Sales_item &);
inline bool operator==(const Sales_item &lhs, const Sales_item &rhs)
{
	return lhs.units_sold == rhs.units_sold && lhs.revenue == rhs.revenue && lhs.same_isbn(rhs);
}
inline bool operator!=(const Sales_item &lhs, const Sales_item &rhs)
{
	return !(lhs == rhs);
}

inline Sales_item & Sales_item::operator +=(const Sales_item &rhs)
{
	units_sold += rhs.units_sold;
	revenue += rhs.revenue;
	return *this;
}
inline Sales_item operator+(const Sales_item &lhs, const Sales_item &rhs)
{
	Sales_item ret(lhs);
	ret += rhs;
	return ret;
}
inline istream& operator>>(istream &in, Sales_item &s)
{
	double price;
	in >> s.isbn >> s.units_sold >> price;
	if (in)
		s.revenue = s.units_sold * price;
	else
		s = Sales_item();
	return in;
}
inline ostream& operator<<(ostream &out, const Sales_item &s)
{
	out << s.isbn << "\t" << s.units_sold << "\t" << s.revenue << "\t" << s.avg_price();
	return out;
}
inline double Sales_item::avg_price() const
{
	if (units_sold)
		return revenue / units_sold;
	else
		return 0;
}
#endif

后续操作：
1.打开VS，新建空项目后，在如图位置右键点击头文件，添加新建项。
2.会跳出如图所示的对话框，注意：选择头文件而不是C++文件。将名字修改为Sales_item.h 不修改也可以，但写头文件代码时就需写成默认名#include"标头.h"

3.将源码复制上去即可。

完成后变可添加源文件写代码了，此时写头文件代码行#include"Sales_item.h"便不会报错
比如1.6的例题书店程序代码如下：

#include
#include"Sales_item.h"
using namespace std;
int main()
{
	Sales_item total;
	if (cin >> total)
	{
		Sales_item trans;
		while (cin >> trans)
		{
			if (total.isbn == trans.isbn)
				total += trans;
			else
			{
				cout << total << endl;
				total = trans;
			}
		}
		cout << total << endl;
	}
	else
	{
		cerr << "No data?!" << endl;
		return-1;
	}
	system("pause");
}

欢迎交流探讨。
谢谢。