实验6

task1

(1)

#pragma once
#include <iomanip>
#include <iostream>
#include <string>

struct Contestant {
    long   id;              // 学号
    std::string name;       // 姓名
    std::string major;      // 专业
    int    solved;          // 解题数
    int    penalty;         // 总罚时
};

// 重载<<
// 要求：姓名/专业里不含空白符
inline std::ostream& operator<<(std::ostream& out, const Contestant& c) {
    out << std::left;
    out << std::setw(15) << c.id
        << std::setw(15) << c.name
        << std::setw(15) << c.major
        << std::setw(10) << c.solved
        << std::setw(10) << c.penalty;

    return out;
}

// 重载>>
inline std::istream& operator>>(std::istream& in, Contestant& c) {
    in >> c.id >> c.name >> c.major >> c.solved >> c.penalty;

    return in;
}

#pragma once
#include <fstream>
#include <iostream>
#include <stdexcept>
#include <string>
#include <vector>
#include "contestant.hpp"

// ACM 排序规则：先按解题数降序，再按罚时升序
inline bool cmp_by_solve(const Contestant& a, const Contestant& b) {
    if(a.solved != b.solved)
        return a.solved > b.solved;
    
    return a.penalty < b.penalty;
}

// 将结果写至任意输出流
inline void write(std::ostream& os, const std::vector<Contestant>& v) {
    for (const auto& x : v) 
        os << x << '\n';
}

// 将结果打印到屏幕
inline void print(const std::vector<Contestant>& v) {
    write(std::cout, v);
}

// 将结果保存到文件
inline void save(const std::string& filename, const std::vector<Contestant>& v) {
    std::ofstream os(filename);
    if (!os) 
        throw std::runtime_error("fail to open " + filename);

    write(os, v);
}

// 从文件读取信息（跳过标题行）
inline std::vector<Contestant> load(const std::string& filename) {
    std::ifstream is(filename);
    if (!is) 
        throw std::runtime_error("fail to open " + filename);

    std::string line;
    std::getline(is, line);          // 跳过标题

    std::vector<Contestant> v;
    Contestant t;
    int seq;
    while (is >> seq >> t) 
        v.push_back(t);
        
    return v;
}

#include <algorithm>
#include <iostream>
#include <stdexcept>
#include <vector>
#include "contestant.hpp"
#include "utils.hpp"

const std::string in_file = "./data.txt";
const std::string out_file = "./ans.txt";

void app() {
    std::vector<Contestant> contestants;

    try {
        contestants = load(in_file);                                      
        std::sort(contestants.begin(), contestants.end(), cmp_by_solve); 
        print(contestants);      
        save(out_file, contestants);                         
    } catch (const std::exception& e) {
        std::cerr << e.what() << '\n';
        return;
    }
}

int main() {
    app();
}

(2)运行结果

（3）回答问题

1.1）std::ofstream是std::ostream的派生类，而std::cout是std::ostream的一个具体实现。

2）不需要改动。

2.1）没有打开对应文件时会抛出异常。

2）打印错误信息。

3. 可以，功能，性能，结果均一致。

4.1）输出的内容有误。

 task 2

(1)

#pragma once

#include <iostream>
#include <string>

class Student {
public:
    Student() = default;
    ~Student() = default;
    
    const std::string get_major() const;
    int get_grade() const;

    friend std::ostream& operator<<(std::ostream& os, const Student& s);
    friend std::istream& operator>>(std::istream& is, Student& s);

private:
    int id;   
    std::string  name;
    std::string  major;
    int          grade;  // 0-100
};

#include"student.hpp"
#include<iostream>      
#include <iomanip>
const std::string Student::get_major() const 
{
    return major; 
}
 int Student::get_grade() const
 {
     return grade;
 }
 std::ostream& operator<<(std::ostream& os, const Student& s)
 {
      os << std::left;
     os << std::setw(15) << s.id   
        << std::setw(15) << s.name
        << std::setw(15) << s.major
        << std::setw(10) << s.grade;
        return os; 
 }
 
std::istream& operator>>(std::istream& is, Student& s)
 {
     is>>s.id>>s.name>>s.major>>s.grade;
     return is;
 }

#pragma once
#include <string>
#include <vector>
#include "student.hpp"

class StuMgr {
public:
    void load(const std::string& file);  // 加载数据文件（空格分隔）
    void sort();                         // 排序: 按专业字典序升序、同专业分数降序
    void print() const;                  // 打印到屏幕
    void save(const std::string& file) const; // 保存到文件

private:
    void write(std::ostream &os) const;  // 把数据写到任意输出流

private:
    std::vector<Student> students;
};  

#include"stumgr.hpp"
#include<iostream>
#include<fstream>
#include<stdexcept>
#include<algorithm>

void StuMgr::write(std::ostream &os) const
{
    for (const auto& x : students)
      os<<x<<'\n';    
}

void StuMgr::load(const std::string& file)
{
    std::ifstream ifs(file);
    if (!ifs) 
        throw std::runtime_error("fail to open " + file);
    std::string line;
    std::getline(ifs, line);          // 跳过标题
    students.clear();
    Student s;
    while (ifs >>s) 
        students.push_back(s);
        
}
void StuMgr::sort()
{
      std::sort(students.begin(), students.end(),
       [](const Student& a,const Student& b)
       {
               if(a.get_major()!=b.get_major())
                   return a.get_major()<b.get_major();
               return a.get_grade()>b.get_grade();
       }
       ); 
}

 void StuMgr::print() const
 {
     if(students.empty())
     {
         std::cout<<"(empty)"<<std::endl;
         return;
     }
     write(std::cout);
 }
 void StuMgr::save(const std::string& file) const
 {
     std::ofstream os(file);
    if (!os) 
        throw std::runtime_error("fail to open " + file);
    write(os);
 }

#include <iostream>
#include <limits>
#include <string>
#include "stumgr.hpp"

const std::string in_file = "./data.txt";
const std::string out_file = "./ans.txt";

void menu() {
    std::cout << "\n**********简易应用**********\n"
                 "1. 加载文件\n"
                 "2. 排序\n"
                 "3. 打印到屏幕\n"
                 "4. 保存到文件\n"
                 "5. 退出\n"
                 "请选择：";
}

void app() {
    StuMgr mgr;

    while(true) {
        menu();
        int choice;
        std::cin >> choice;

        try {
            switch (choice) {
            case 1: mgr.load(in_file); 
                    std::cout << "加载成功\n"; break;
            case 2: mgr.sort(); 
                    std::cout << "排序已完成\n"; break;
            case 3: mgr.print(); 
                    std::cout << "打印已完成\n"; break;
            case 4: mgr.save(out_file); 
                    std::cout << "导出成功\n"; break;
            case 5: return;
            default: std::cout << "不合法输入\n";
            }
        }
        catch (const std::exception& e) {
            std::cout << "Error: " << e.what() << '\n';
        }
    }
}

int main() {
    app();
}

 

(2)运行结果