文件I/O与异常处理

##实验任务一

contestant.hpp

#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;
}

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();
}

问题一：（1） std::cout的类型是 std::ostream的成员函数，std::cout能从 std::ostream中继承数据流。

（2）不需要改动。

问题二：在utils.hpp的

throw std::runtime_error("fail to open " + filename);与

throw std::runtime_error("fail to open " + filename);都会在文件打开失败是抛出异常。
（2）异常会被task1.cpp的app函数捕获，并将错误信息输出至std::cerr，终止`app`函数执行。
问题三：一致
问题四：出现异常数据，可能是因为当 data_bad.txt 中有字段缺失时，程序会不能提取数据而停止加载。

实验二

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 <limits>
#include <iomanip>

// 构造函数
Student::Student(int id, const std::string& name, 
                 const std::string& major, int score)
    : id(id), name(name), major(major), score(score) {}

// Getter方法实现
int Student::getId() const { return id; }
const std::string& Student::getName() const { return name; }
const std::string& Student::getMajor() const { return major; }
int Student::getScore() const { return score; }

// Setter方法实现
void Student::setId(int newId) { id = newId; }
void Student::setName(const std::string& newName) { name = newName; }
void Student::setMajor(const std::string& newMajor) { major = newMajor; }
void Student::setScore(int newScore) { score = newScore; }

// 重载小于运算符：按专业字典序，专业内按成绩降序
bool Student::operator<(const Student& other) const {
    if (major != other.major) {
        return major < other.major;
    }
    return score > other.score; // 降序排列
}

// 重载输入运算符
std::istream& operator>>(std::istream& is, Student& student) {
    is >> student.id;
    is.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
    std::getline(is, student.name);
    std::getline(is, student.major);
    is >> student.score;
    return is;
}

// 重载输出运算符
std::ostream& operator<<(std::ostream& os, const Student& student) {
    os << std::setw(6) << student.id << " "
       << std::setw(10) << std::left << student.name << " "
       << std::setw(10) << std::left << student.major << " "
       << std::setw(5) << student.score;
    return os;
}

#include "stumgr.hpp"
#include <fstream>
#include <algorithm>
#include <iomanip>
#include <stdexcept>
#include <numeric>
#include <map>

// 异常类实现
FileOpenException::FileOpenException(const std::string& filename, const std::string& mode)
    : std::runtime_error("无法打开文件: " + filename + " (模式: " + mode + ")") {}

// 构造函数
Stumgr::Stumgr() : dataLoaded(false) {}

// 从文件加载数据
void Stumgr::loadFromFile(const std::string& filename) {
    std::ifstream inFile;
    inFile.exceptions(std::ifstream::failbit | std::ifstream::badbit);
    
    try {
        inFile.open(filename);
        
        // 读取数据头（如果存在）
        std::string header;
        std::getline(inFile, header);
        
        students.clear();
        Student student;
        
        while (inFile >> student) {
            students.push_back(student);
        }
        
        currentFile = filename;
        dataLoaded = true;
        
    } catch (const std::ifstream::failure& e) {
        throw FileOpenException(filename, "读取");
    }
}

// 保存数据到文件
void Stumgr::saveToFile(const std::string& filename) {
    std::string saveFile = filename.empty() ? currentFile : filename;
    
    std::ofstream outFile;
    outFile.exceptions(std::ofstream::failbit | std::ofstream::badbit);
    
    try {
        outFile.open(saveFile);
        
        // 写入数据头
        outFile << "ID 姓名 专业 成绩" << std::endl;
        
        for (const auto& student : students) {
            outFile << student.getId() << std::endl
                    << student.getName() << std::endl
                    << student.getMajor() << std::endl
                    << student.getScore() << std::endl;
        }
        
        std::cout << "数据已保存到 " << saveFile << std::endl;
        
    } catch (const std::ofstream::failure& e) {
        throw FileOpenException(saveFile, "写入");
    }
}

// 排序数据：按专业字典序，专业内按成绩降序
void Stumgr::sortData() {
    if (!dataLoaded) {
        std::cout << "请先加载数据！" << std::endl;
        return;
    }
    
    std::sort(students.begin(), students.end());
    std::cout << "数据已排序完成！" << std::endl;
}

// 显示所有学生信息
void Stumgr::displayAll() const {
    if (!dataLoaded) {
        std::cout << "请先加载数据！" << std::endl;
        return;
    }
    
    std::cout << std::setw(6) << "学号" << " "
              << std::setw(10) << std::left << "姓名" << " "
              << std::setw(10) << std::left << "专业" << " "
              << std::setw(5) << "成绩" << std::endl;
    std::cout << std::string(40, '-') << std::endl;
    
    for (const auto& student : students) {
        std::cout << student << std::endl;
    }
}

// 按专业显示学生信息
void Stumgr::displayByMajor(const std::string& major) const {
    if (!dataLoaded) {
        std::cout << "请先加载数据！" << std::endl;
        return;
    }
    
    std::cout << "专业: " << major << std::endl;
    std::cout << std::setw(6) << "学号" << " "
              << std::setw(10) << std::left << "姓名" << " "
              << std::setw(5) << "成绩" << std::endl;
    std::cout << std::string(30, '-') << std::endl;
    
    for (const auto& student : students) {
        if (student.getMajor() == major) {
            std::cout << std::setw(6) << student.getId() << " "
                      << std::setw(10) << std::left << student.getName() << " "
                      << std::setw(5) << student.getScore() << std::endl;
        }
    }
}

// 显示统计信息
void Stumgr::displayStatistics() const {
    if (!dataLoaded) {
        std::cout << "请先加载数据！" << std::endl;
        return;
    }
    
    std::cout << "\n===== 统计信息 =====" << std::endl;
    std::cout << "总人数: " << students.size() << std::endl;
    std::cout << "平均分: " << std::fixed << std::setprecision(1) 
              << getAverageScore() << std::endl;
    
    Student highest = getHighestScore();
    Student lowest = getLowestScore();
    std::cout << "最高分: " << highest.getName() << " (" 
              << highest.getScore() << "分)" << std::endl;
    std::cout << "最低分: " << lowest.getName() << " (" 
              << lowest.getScore() << "分)" << std::endl;
    
    // 按专业统计
    std::map<std::string, int> majorCount;
    for (const auto& student : students) {
        majorCount[student.getMajor()]++;
    }
    
    std::cout << "\n各专业人数:" << std::endl;
    for (const auto& pair : majorCount) {
        std::cout << "  " << pair.first << ": " << pair.second << "人" << std::endl;
    }
}

// 计算平均分
double Stumgr::getAverageScore() const {
    if (students.empty()) return 0.0;
    
    int total = 0;
    for (const auto& student : students) {
        total += student.getScore();
    }
    return static_cast<double>(total) / students.size();
}

// 获取最高分学生
Student Stumgr::getHighestScore() const {
    if (students.empty()) {
        return Student();
    }
    
    auto it = std::max_element(students.begin(), students.end(),
        [](const Student& a, const Student& b) {
            return a.getScore() < b.getScore();
        });
    
    return *it;
}

// 获取最低分学生
Student Stumgr::getLowestScore() const {
    if (students.empty()) {
        return Student();
    }
    
    auto it = std::min_element(students.begin(), students.end(),
        [](const Student& a, const Student& b) {
            return a.getScore() < b.getScore();
        });
    
    return *it;
}

text：

posted @ 2025-12-23 22:24 石朗鹏阅读(1) 评论(0) 收藏举报

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