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文件I/O与异常处理

news 2026/6/15 2:33:30

##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;
}