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实验06

news 2026/4/9 12:22:20

任务1

代码

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();
}

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;
}

运行截图

问题回答

问题1

（1）因为多态性，std::cout 的类型是 std::ostream，std::ofstream 继承自 std::ostream，子类对象可以隐式转换为父类引用，通过基类指针或引用可以操作派生类对象。

（2）不需要改动。

问题2

异常：

if (!os) throw std::runtime_error("fail to open " + filename);

if (!is) throw std::runtime_error("fail to open " + filename);

（1）save()函数std::ofstream打开失败时触发，可能的具体原因有输出文件无写权限、路径错误、磁盘满了等；load()函数std::ifstream打开失败，具体可能是输入文件不存在、无读权限等。

（2）异常被task1.cpp 中 app() 函数的 try-catch 块捕获。处理：

catch (const std::exception& e) {std::cerr << e.what() << '\n';  // 打印错误信息到标准错误流return;                          // 正常退出，不中断程序
}

问题3

可以。功能完全相同，性能几乎相同，结果一致。

问题4

（1）结果

问题：注意到学号跑到最后去了，说明数据错位了，getline()跳过标题后，遇到空行时 is >> seq >> t 会失败，某些数据未被读取或读取错误。

任务2

代码

student.cpp

#include "student.hpp"
#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 << "\t" << s.name << "\t" << s.major << "\t" << 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 <fstream>
#include <algorithm>
#include <stdexcept>void StuMgr::load(const std::string& file) {std::ifstream in(file);if (!in.is_open()) {throw std::runtime_error("无法打开文件: " + file);}// 跳过标题行std::string line;std::getline(in, line);students.clear();Student s;while (in >> s) {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();}return a.get_grade() > b.get_grade();});
}void StuMgr::print() const {std::cout << "学号\t姓名\t专业\t成绩\n";for (const auto& s : students) {std::cout << s << "\n";}
}void StuMgr::save(const std::string& file) const {std::ofstream out(file);if (!out.is_open()) {throw std::runtime_error("无法打开文件: " + file);}write(out);
}void StuMgr::write(std::ostream& os) const {os << "学号\t姓名\t专业\t成绩\n";for (const auto& s : students) {os << s << "\n";}
}

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();
}