实验6 文件I/O与异常处理

实验任务1

实验代码：
contestant.hpp:

#pragma once
#include <iomanip>
#include <iostream>
#include <string>
struct Contestant {
	long id;
	std::string name; 
	std::string major;
	int solved; 
	int penalty; 
};
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;
}

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"

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;
}
inline void write(std::ostream& os, const std::vector<Contestant>& v) {
	for (const auto& x : v)
		os << x << '\n';
}
inline void print(const std::vector<Contestant>& v) {
	write(std::cout, v);
}
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);
}
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);
	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();
}

运行测试截图：

回答问题：
问题1：
(1) ostream 是所以输出流的基类
(2) 不需要
问题2：
（1）文件无法打开，可能是文件和代码文件不在同一目录下；
（2）在app()函数中被捕获，输出异常提示；
问题3：
功能结果一致
问题4：
（1）运行结果出错，项目中没有对脏数据进行处理

实验任务2

实验代码：
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; 
};

student.cpp:

#include"student.hpp"

#include<stdexcept>
#include<iostream>
#include <string>
#include <iomanip>

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 << std::left;
	 os << std::setw(15) << s.id
		<< std::setw(15) << s.name
		<< std::setw(15) << s.major
		<< std::setw(10) << s.grade;
		
	return os;
}

std::istream& operator>>(std::istream& is, Student& s)
{
	is>>s.id>>s.name>>s.major>>s.grade;

	return is;
}

stumgr.hpp:

#pragma once
#include <string>
#include <vector>
#include "student.hpp"
class StuMgr {
public:
	void load(const std::string& file);
	void sort();
	void print() const;
	void save(const std::string& file) const;
private:
	void write(std::ostream& os) const; 
private:
	std::vector<Student> students;
};

stumgr.cpp:

#include"stumgr.hpp"

#include<stdexcept>
#include<fstream>
#include<iostream>
#include<string>
#include<vector>
#include<algorithm>

void StuMgr::load(const std::string& file)
{
	std::ifstream is(file);
	if(!is)
	{
		throw std::runtime_error("Error:cannot open file："+file);
	}
	std::string line;
	std::getline(is,line);
	Student t;
	while(is>>t)
	{
		students.push_back(t);
	}
}

void StuMgr::sort()
{
	std::sort(students.begin(), students.end(), [](const Student& a, const Student& b) {return a.get_major()!= b.get_major() ? a.get_major() < b.get_major(): a.get_grade() > b.get_grade();});
}

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

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

void StuMgr::save(const std::string& file) const
{
	std::ofstream os(file);
	if(!os)
	{
		throw std::runtime_error("Error:cannot open file："+file);
	}
	write(os);
}

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();
}

运行测试截图：