C++ //练习 8.7 修改上一节的书店程序，将结果保存到一个文件中。将输出文件名作为第二个参数传递给main函数。

C++ Primer（第5版）练习 8.7

练习 8.7 修改上一节的书店程序，将结果保存到一个文件中。将输出文件名作为第二个参数传递给main函数。

环境：Linux Ubuntu（云服务器）

工具：vim

代码块

/*************************************************************************> File Name: ex8.7.cpp> Author: > Mail: > Created Time: Sun 25 Feb 2024 12:26:50 PM CST************************************************************************/#include<iostream>
#include<fstream>
using namespace std;struct Sales_data{string isbn() const;Sales_data& combine(const Sales_data&);double avg_price() const;string bookNo;unsigned units_sold = 0;double price = 0.0;double revenue = 0.0;
};string Sales_data::isbn() const{return this->bookNo;
}Sales_data& Sales_data::combine(const Sales_data &rhs){units_sold += rhs.units_sold;revenue += rhs.revenue;return *this;
}double Sales_data::avg_price() const{if(units_sold){return revenue / units_sold;}else{return 0;}
}Sales_data add(const Sales_data &sd1, const Sales_data &sd2){Sales_data t = sd1;t.combine(sd2);return t;
}ostream &print(ostream &output, const Sales_data &sd){output<<sd.bookNo<<" "<<sd.units_sold<<" "<<sd.price<<" "<<sd.revenue<<" "<<sd.avg_preturn output;
}istream &read(istream &input, Sales_data &sd){input>>sd.bookNo>>sd.units_sold>>sd.price;sd.revenue = sd.price * sd.units_sold;return input;
}int main(int argc, char *argv[]){if(argc < 2){cerr<<"No File Name."<<endl;return -1;}ifstream in(argv[1]);ofstream out("8.7.txt");if(!in){cerr<<"Cannot open file!"<<endl;return -1;}Sales_data total;if(read(in, total)){Sales_data trans;while(read(in, trans)){if(total.isbn() == trans.isbn()){total.combine(trans);}else{print(out, total)<<endl;total = trans;}}print(out, total)<<endl;}else{cout<<"No data?!"<<endl;}return 0;
}