实验六

实验五

#任务1

##代码

#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_bad.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(), [](const Contestant& a, const Contestant& b) {
return a.solved != b.solved ? a.solved > b.solved
 : a.penalty < b.penalty;}); 
        print(contestants);      
        save(out_file, contestants);                         
    } catch (const std::exception& e) {
        std::cerr << e.what() << '\n';
        return;
    }
}

int main() {
    app();
}

##运行测试截图

 

##问题回答

问题1：(1)多态,cout和ofstream都是osteam的派生类

             (2)不需要

问题2：save () 函数：打开输出文件失败时抛出异常；load()函数：打开输入文件失败时抛出异常

             (1)若文件打开失败，抛出std::runtime_error异常

             (2)捕获异常后，通过e.what()获取异常描述信息，将其输出到标准错误流（std::cerr），然后直接返回，终止后续的数据处理操作，避免程序在文件未正常打开的情况下继续执行导致非法访问。

问题3：可以，都一致

问题4：输出不完整并提前终止。部分行缺少解题数或罚

 

#任务2

##代码

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

class StuMgr {
public:
    void load(const std::string& file);  // ????????????????????
    void sort();                         // ????: ????????????????????????
    void print() const;                  // ????????
    void save(const std::string& file) const; // ???浽???

private:
    void write(std::ostream &os) const;  // ??????д???????????

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

#include <string>
#include <vector>
#include <fstream>
#include <algorithm>
#include <stdexcept>
#include <sstream>
#include <iostream>
#include "student.hpp"
#include "stumgr.hpp"

void StuMgr::load(const std::string& file) {
    std::ifstream is(file);
    if (!is.is_open()) {
        throw std::runtime_error("cannot open file: " + file);
    }

    std::string line;
    std::getline(is, line);
    
    Student stu;
    int num;
    while(is>>num>>stu){
        students.push_back(stu);
    }
    is.close();
}

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 {
    write(std::cout);
}

void StuMgr::save(const std::string& file) const {
    std::ofstream os(file);
    if (!os.is_open()) {
        throw std::runtime_error("cannot open file: " + file);
    }
    write(os);
    os.close();
}


void StuMgr::write(std::ostream& os) const {
    for (const auto& stu : students) {
        os << stu;
    }
}

#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();
}

#pragma once

#include <iostream>
#include <string>

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

    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 <iostream>
#include <string>
#include "student.hpp"

std::ostream& operator<<(std::ostream& os, const Student& s){
    os<<s.name<<'\t'<<s.major<<'\t'<<s.grade<<'\n';
    return os;
}
std::istream& operator>>(std::istream& is, Student& s){
    is>>s.name>>s.major>>s.grade;
    return is;
}

##运行测试截图