这是怎么一回事？

http://pan.baidu.com/s/1sjICkHJ

保存了吗？你用的是相对地址，错误确实是在头文件的第一行

/*
Sales_item.h
*/
#include <iostream>
#include <string>
class Sales_item {
friend bool compare(const Sales_item&, const Sales_item&);
friend bool operator==(const Sales_item&, const 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:
// operations on Sales_item objects
Sales_item& operator+=(const Sales_item&);
double avg_price() const;
bool same_isbn(const Sales_item &rhs) const
{ return isbn == rhs.isbn; }
// default constructor needed to initialize members of built-in type
Sales_item(): units_sold(0), revenue(0.0) { }
std::string book() const { return isbn; }
private:
std::string isbn;
unsigned units_sold;
double revenue;
};
// nonmember binary operator: must declare a parameter for each operand
Sales_item operator+(const Sales_item&, const Sales_item&);
inline bool
operator==(const Sales_item &lhs, const Sales_item &rhs)
{
// must be made a friend of Sales_item
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); // != defined in terms of operator==
}
inline bool
compare(const Sales_item &lhs, const Sales_item &rhs)
{
return lhs.book() < rhs.book();
}