实验6

task 1

Contestant.hpp

 1 #pragma once
 2 #include<iomanip>
 3 #include<iostream>
 4 #include<string>
 5 
 6 struct Contestant {
 7     long id;
 8     std::string name;
 9     std::string major;
10     int solved;
11     int penalty;
12 };
13 
14 inline std::ostream& operator<<(std::ostream& out, const Contestant& c) {
15     out << std::left;
16     out << std::setw(15) << c.id
17         << std::setw(15) << c.name
18         << std::setw(15) << c.major
19         << std::setw(10) << c.solved
20         << std::setw(10) << c.penalty;
21 
22     return out;
23 }
24 
25 inline std::istream& operator>>(std::istream& in, Contestant& c) {
26     in >> c.id >> c.name >> c.major >> c.solved >> c.penalty;
27 
28     return in;
29 }
Contestant.hpp

utils.hpp

 1 #pragma once
 2 #include <fstream>
 3 #include <iostream>
 4 #include <stdexcept>
 5 #include <string>
 6 #include <vector>
 7 #include "Contestant.hpp"
 8 
 9 inline bool cmp_by_solve(const Contestant& a, const Contestant& b) {
10     if (a.solved != b.solved)
11         return a.solved > b.solved;
12 
13     return a.penalty < b.penalty;
14 }
15 
16 inline void write(std::ostream& os, const std::vector<Contestant>& v) {
17     for (const auto& x : v) 
18         os << x << '\n';
19 }
20 
21 inline void print(const std::vector<Contestant>& v) {
22     write(std::cout, v);
23 }
24 
25 inline void save(const std::string& filename, const std::vector<Contestant>& v) {
26     std::ofstream os(filename);
27     if (!os)
28         throw std::runtime_error("fail to open" + filename);
29 
30     write(os, v);
31 }
32 
33 inline std::vector<Contestant> load(const std::string &filename ){
34     std::ifstream is(filename);
35     if (!is)
36         throw std::runtime_error("fail to open" + filename);
37 
38     std::string line;
39     std::getline(is, line);
40 
41     std::vector<Contestant> v;
42     Contestant t;
43     int seq;
44     while (is >> seq >> t)
45         v.push_back(t);
46 
47     return v;
48 }
utils.hpp

task1.cpp

 1 #include<algorithm>
 2 #include<iostream>
 3 #include<stdexcept>
 4 #include<vector>
 5 #include"Contestant.hpp"
 6 #include"utils.hpp"
 7 
 8 const std::string in_file = "./data.txt";
 9 const std::string out_file = "./ans.txt";
10 
11 void app() {
12     std::vector<Contestant> contestants;
13 
14     try {
15         contestants = load(in_file);
16         std::sort(contestants.begin(), contestants.end(), cmp_by_solve);
17         print(contestants);
18         save(out_file, contestants);
19     }
20     catch (const std::exception& e) {
21         std::cerr << e.what() << '\n';
22         return;
23     }
24 }
25 
26 int main() {
27     app();
28 }
task1.cpp

image

Q1：

（1）std::ostream是所有输出流的基类，std::cout是std::ostream类的对象，std::ofstream是std::ostream的派生类对象

（2）不需要改动writr()。write()只需要std::ostream类的接口。

Q2：

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

（1）尝试打开指定文件失败的时候会抛出异常

（2）

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;
}

异常被app()中的try-catch捕获，若打开文件失败，会抛出runtime_error并且跳出该函数，回到app的tyr函数，e.what()会返回throw传入的字符串，然后结束整个程序。

Q3：可以替换。sort利用迭代器实现了按照解题数的降序排序，原代码在utils.hpp中定义了cmp_by_slove函数来实现这个功能，改写的lamba表达式把cmp_by_slove实现的功能就地解决

Q4：

image

 load函数的读取时通过重载的>>(is>>seq>>t)，>>会跳过空白字符；Contestant重载中的>>读取到缺失的数据时会读取失败，导致类的对象没有被初始化

 

 

task 2

Student.hpp

 1 #pragma once
 2 #include<iostream>
 3 #include<string>
 4 
 5 class Student {
 6 public:
 7     Student() = default;
 8     ~Student() = default;
 9 
10     const std::string get_major() const;
11     int get_grade() const;
12 
13     friend std::ostream& operator<<(std::ostream& os, const Student& s);
14     friend std::istream& operator>>(std::istream& is, Student& s);
15 
16 private:
17     int id;
18     std::string name;
19     std::string major;
20     int grade;
21 };
Student.hpp

Student.cpp

 1 #include "Student.hpp"
 2 
 3 const std::string Student::get_major() const {
 4     return major;
 5 }
 6 
 7 int Student::get_grade() const {
 8     return grade;
 9 }
10 
11 std::ostream& operator<<(std::ostream& os, const Student& s) {
12     os << s.id << '\t' << s.name << '\t' << s.major << '\t' << s.grade;
13 
14     return os;
15 }
16 
17 std::istream& operator>>(std::istream& is, Student& s) {
18     is >> s.id >> s.name >> s.major >> s.grade;
19 
20     return is;
21 }

StuMgr.hpp

 1 #pragma once
 2 #include <string>
 3 #include <vector>
 4 #include "Student.hpp"
 5 
 6 class StuMgr {
 7 public:
 8     void load(const std::string& file); 
 9     void sort(); 
10     void print() const; 
11     void save(const std::string& file) const; 
12 
13 private:
14     void write(std::ostream& os) const; 
15 
16 private:
17     std::vector<Student> students;
18 };
StuMgr.hpp

StuMgr.cpp

 1 #include "StuMgr.hpp"
 2 #include<fstream>
 3 #include<vector>
 4 #include<algorithm>
 5 
 6 void StuMgr::load(const std::string& file) {
 7     std::ifstream is(file);
 8     if (!is)
 9         throw std::runtime_error("fail to open" + file);
10 
11     std::string line;
12     std::getline(is, line);
13 
14     Student s;
15     while (is >> s)
16         students.push_back(s);
17 }
18 
19 bool cmp(const Student& s1, const Student& s2) {
20     if (s1.get_major() != s2.get_major())
21         return s1.get_major() < s2.get_major();
22 
23     return s1.get_grade() > s2.get_grade();
24 }
25 
26 void StuMgr::sort() {
27     std::sort(students.begin(), students.end(),cmp);
28 }
29 
30 void StuMgr::write(std::ostream& os) const {
31     for (const auto& x : students)
32         os << x << '\n';
33 }
34 
35 void StuMgr::print() const {
36     write(std::cout);
37 }
38 
39 void StuMgr::save(const std::string& file) const {
40     std::ofstream os(file);
41     if (!os)
42         throw std::runtime_error("fail to open " + file);
43 
44     write(os);
45 }

task2.cpp

 1 #include <iostream>
 2 #include <limits>
 3 #include <string>
 4 #include "StuMgr.hpp"
 5 
 6 const std::string in_file = "./data.txt";
 7 const std::string out_file = "./ans.txt";
 8 
 9 void menu() {
10     std::cout << "\n**********简易应用**********\n"
11         "1. 加载文件\n"
12         "2. 排序\n"
13         "3. 打印到屏幕\n"
14         "4. 保存到文件\n"
15         "5. 退出\n"
16         "请选择：";
17 }
18 
19 void app() {
20     StuMgr mgr;
21 
22     while (true) {
23         menu();
24         int choice;
25         std::cin >> choice;
26 
27         try {
28             switch (choice) {
29             case 1: mgr.load(in_file);
30                 std::cout << "加载成功\n"; break;
31             case 2: mgr.sort();
32                 std::cout << "排序已完成\n"; break;
33             case 3: mgr.print();
34                 std::cout << "打印已完成\n"; break;
35             case 4: mgr.save(out_file);
36                 std::cout << "导出成功\n"; break;
37             case 5: return;
38             default: std::cout << "不合法输入\n";
39             }
40         }
41         catch (const std::exception& e) {
42             std::cout << "Error: " << e.what() << '\n';
43         }
44     }
45 }
46 
47 int main() {
48     app();
49 }
task 2.cpp

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image

 找不到指定文件

image

 

posted @ 2025-12-24 00:37  璐Luzi  阅读(2)  评论(0)    收藏  举报