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_p
    return 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;
}

运行结果显示如下