实验六-文件I/O与异常处理

实验任务1源代码：

#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.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();
}

实验任务1运行结果：

　　实验任务1问题1：

　　（1）C++标准库中的流类之间存在继承关系

　　（2）不需要

　　实验任务1问题2：

　　（1）save函数中：打开输出文件失败时会抛出异常，load函数中：打开输入文件失败时会抛出异常

　　（2）被app函数中try-catch捕获

　　实验任务1问题3：可以，效果完全一致

　　实验任务1问题4：

　　（1）运行结果：

　　原因：程序运行可能会出现数据读取错误，读取不完整甚至中断

实验任务2源代码：

#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;
    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
};

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

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;
}

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

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

    students.clear();
    Student s;

    try {
        while (in_file >> s) {
            students.push_back(s);
        }
    }
    catch(const std::exception& e) {
        in_file.close();
        throw std::runtime_error("file is wrong：" + std::string(e.what()));
    }

    in_file.close();

    if (students.empty()) {
        throw std::runtime_error("file is null or data is wrong");
    }
}

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 << "暂无学生数据" << std::endl;
        return;
    }

    std::cout << "学号\t姓名\t专业\t成绩\t" << std::endl;
    
    write(std::cout);
}

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

    try {
        write(out_file);
    }
    catch(const std::exception& e) {
        out_file.close();
        throw;
    }

    out_file.close();
}

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

实验任务2运行结果：