sales_items.h
#ifndef INCLUDE_SALES_DATA_H
#define INCLUDE_SALES_DATA_H
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
//程序用途:每次从cin读取一个Sales_item对象,如果读取的isbn和上一次的相同,那么读取的
//对象加到前一个中,如果读取的isbn和前一次不一样,那么把前一次的结果输出,把新读入的元素存入
//
#include <iostream>
#include <string>
#include "sales_data.h"
#include <iterator>
using namespace std;
int main()
{
//新建一个istream的iterator,读取元素类型是Sales_item对象,该istream_iterator关联到
//流cin,同时创建一个空流eof,当读取元素时候遇到流错误或者文件末尾时候,in_iter 就会等于eof
istream_iterator<Sales_item> in_iter(cin),eof;
//创建一个ostream_iterator,输出元素类型是Sales_item,关联到流cout,且每次输出时候在末尾
//加上"\n"
ostream_iterator<Sales_item> out_iter(cout,"\n");
//创建Sales_item对象sum,并且用in_iter内的元素初始化,接着in_iter读取下一个值
Sales_item sum =*in_iter ++;
//创建while循环,当in_iter关联的流没有遇到错误,并且没有到达文件末尾的时候,循环继续
while(in_iter != eof)
{
//如果刚才读取的元素的isbn和sum中的Sales_data的isbn相等,那么把这个元素加到sum中,且
//in_iter读取下一个值
if(in_iter -> isbn == sum.isbn)
{
sum += *in_iter ++;
}
//如果新读取的对象的isbn不等于sum中元素的isbn,那先输出sum中的对象,然后把新*in_iter
//赋值给sum,然后in_iter再读取下一个值
else
{
*out_iter++ = sum;
sum = *in_iter ++;
}
}
return 0;
}
注意几点用途:
1.istream_iterator对象关联到一个istream或者调用++运算符的时候,就会是的istream_iterator对象读取新值,例如:
istream_iterator<Sales_item> in_iter(cin); 这句in_iter关联到cin的同时就会从流cin读取一个值。
in_iter ++; //这句的意思是in_iter从cin读取一个新值
我自己的理解就是,istream_iterator读取新值也就是用和他关联的流读取新值
2.ostrem_iterator的流迭代器如何输出呢?只要把对象赋值给它就可以用它输出,例如:
out_iter = sum;
因为对ostream_iterator的流迭代器调用*,前自增++,后自增++,都对ostream_iterator不执行任何操作,所以也可以写成
*out_iter ++ = sum; //等价于out_iter = sum
3.输入流迭代器(就是istream_iterator类型,输入流迭代器是我自己取的名字),读取元素只需要调用前自增或者后自增++,而输出流迭代器要输出元素
就赋值就可以了,为了可读性以及以后好更改成其他流,可以加上一些诸如: ++ ,* 运算符。