实验6

实验6

task1

utils.hpp

#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;
}

task1.cpp

#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();
}

contestand.cpp

#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;
}

问题1

std::ostream是std::cout（屏幕输出）和std::ofstream（文件输出）的基类，基类引用可接收派生类对象，实现write()函数复用。 无需修改

问题2

调用load()时，指定的文件（如in_file）不存在时，调用load()时，指定的文件（如in_file）不存在时。

app()中通过try-catch块捕获std::exception类型的异常；

e.what()输出异常信息，然后return终止app()函数的执行。

问题3

可以替换，功能、结果一致。

 

 

task2

student.hpp

#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
};

stumgr.hpp

#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;
};

task2.cpp

#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();
}

student.cpp

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

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<<s.id<<" "<<s.name<<" "<<s.major<<" "<<s.grade;
    return os;
}

std::istream& operator>>(std::istream& is, Student& s) {
    is>>s.id>>s.name>>s.major>>s.grade;
    return is;
}

stumgr.cpp

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


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

    students.clear(); 
    Student s;
    std::string title_line;
    std::getline(is, title_line);
    while (is>>s) {
        students.push_back(s);
    }
    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& s : students) {
        os<<s<<'\n'; 
    }
}