实验6

实验任务1：

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"
#include "windows.h"

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()
{
    SetConsoleOutputCP(CP_UTF8);
    app();
}

运行结果：

数据文件ans.txt：

问题回答：

1.（1）std::cout 是 std::ostream 的直接实例，std::ofstream 继承自 std::ostream，

            std::ostream& 作为参数类型时，能接收任何 std::ostream 派生类的对象，因此write()能同时接受 std::cout 和 std::ofstream 对象作为实参。

   （2）不需要。只要该设备也提供 std::ostream 接口就能调用write()。

2.（1）

第一处：

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);
}

抛出异常情况：打开指定文件（out_file）失败时。

第二处：

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;
}

抛出异常情况：打开指定输入文件（in_file）失败时。

   （2）被try{}catch{}捕获，通过std::cerr << e.what() << '\n';进行输出，并终止程序。

3.可以，功能、性能、结果一致，都无额外开销。

4.（1）

问题：读取不完整，输出产生乱码；

原因：is >> seq >> t 读取时，solved和penalty 无值，会导致读取失败，导致while循环终止，无法继续读取。

   （2）

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;
    int line_num = 1;
    while(getline(is, line))
    {
        line_num++;
        std::istringstream iss(line);
        if(line.empty()||line.find_first_not_of(" \t\n\r") == std::string::npos) continue; 
        if (!(iss >> seq >> t.id >> t.name >> t.major >> t.solved >> t.penalty))
        {
            std::cerr <<"Warning: invalid data format at line " << line_num << ", skipped.\n";
            continue;
        }
        v.push_back(t);
    }
    return v;
}

 

实验任务2：

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
};

student.cpp：

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

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(15) << s.grade;
    return os;
}

std::istream &operator>>(std::istream &is, Student &s)
{
    int temp_id;
    std::string temp_name;
    std::string temp_major;
    int temp_grade;
    if(!(is >> temp_id >> temp_name >> temp_major >> temp_grade))
        throw std::runtime_error("Invalid input format for Student");
    if(temp_grade < 0 || temp_grade > 100)
        throw std::runtime_error("Grade must be between 0 and 100");
    s.id = temp_id;
    s.name = temp_name;
    s.major = temp_major;
    s.grade = temp_grade;
    return is;
}

const std::string Student::get_major() const
{
    return major;
}

int Student::get_grade() const
{
    return grade;
}

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;
};

stumgr.cpp：

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

void StuMgr::load(const std::string &filename)
{
    std::ifstream is(filename);
    if (!is)
        throw std::runtime_error("fail to open " + filename);

    std::string line;
    getline(is, line);

    int line_num = 1;
    while (getline(is, line))
    {
        std::istringstream iss(line);
        line_num++;
        if (line.empty() || line.find_first_not_of(" \t\n\r") == std::string::npos)
        {
            std::cerr << "[Warning] line " << line_num << " format error, skipped: ";
            std::cout << line << '\n';
            continue;
        }
        else
        {
            int temp_id;
            std::string temp_name;
            std::string temp_major;
            int temp_grade;
            if (!(iss >> temp_id >> temp_name >> temp_major >> temp_grade))
            {
                std::cerr << "[Warning] line " << line_num << " format error, skipped: ";
                std::cout << line << '\n';
                continue;
            }
            else if (temp_grade < 0 || temp_grade > 100)
            {
                std::cerr << "[Warning] line " << line_num << " grade invalid, skipped: ";
                std::cout << line << '\n';
                continue;
            }
            else
            {
                {
                    Student s;
                    std::istringstream line_iss(line);
                    try
                    {
                        line_iss >> s; 
                    }
                    catch (const std::runtime_error &e)
                    {
                        std::cerr << "[Warning] line " << line_num << " " << e.what() << ", skipped: ";
                        std::cout << line << '\n';
                        continue;
                    }
                    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();
        else
            return a.get_grade() > b.get_grade(); });
}

void StuMgr::print() const
{
    write(std::cout);
}

void StuMgr::save(const std::string &filename) const
{
    std::ofstream os(filename);
    if (!os)
        throw std::runtime_error("fail to open " + filename);

    write(os);
}

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

task2.cpp：

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

const std::string in_file = "./data_bad.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()
{
    SetConsoleOutputCP(CP_UTF8);
    app();
}

运行结果：