关于#二进制文件输入输出#的问题，如何解决？

Question

本人计算机专业新生，麻烦各位帮忙看一下这段c++代码的文件输入输出部分问题在哪

在定义的file_input函数中，通过传入一个类，以二进制的形式存入文件。
在主函数中，我根据输入的信息动态生成类，用以存储这些信息，并将该类通过调用file_input函数以二进制存入文件中，如此循环直到输入为-1
在file_output函数中，从二进制文件中提取类并调用函数输出信息

但是这样无法将类正确地存入文件中，且输出为乱码，想问一下为什么会出现这种情况，以及如何修正

#include <iostream>
#include <fstream>
#include <cstring>
#include <cstdlib>
using namespace std;

class student
{
    public:
        student();
        student(int id, string name, float grade);
        student(const student &s);
        void print_stu();
        //friend void delete_stu(student *s);
        //friend void modify_stu(student *s);
    private:
        int id;
        string name;
        float grade;
};


student::student()
{
    
}
student::student(int id, string name, float grade)
{
    this -> id = id;
    this -> name = name;
    this -> grade = grade;
}
student::student(const student &s)
{
    id = s.id;
    name = s.name;
    grade = s.grade;
}

void student::print_stu()
{
    cout << "ID: " << id << " " << "Name: " << name << " " << "Grade: " << grade << endl; 
}


void file_input(student s)
{
    s.print_stu();
    fstream file1;
    file1.open("student.dat", ios::out | ios::binary | ios::app);
    
    if(!file1)
    {
        cout << "Cannot open the file" << endl;
        abort();
    }
    
    file1.write((char *)&s, sizeof(s));
    file1.close();
}

void file_output()
{
    fstream file1;
    file1.open("student.dat", ios::in | ios::binary);
    
    if(!file1)
    {
        cout << "Cannot open the file" << endl;
        abort();
    }
    
    student s;
    while(file1.read((char *)&s, sizeof(s)))
    {        
        s.print_stu(); 
    } 
    file1.close();
}


int main()
{
    while(1)
    {
        cout << "1: 输入学生信息" << endl << "2: 显示学生信息" << endl;
    
        int control = -1;
        cin >> control;
        
        if(control == 1)
        {    
            cout << "请输入学生id, 以-1停止输入" << endl;
        
            int id = 0;
            cin >> id;
            while(id != -1)
            {
                cout << "请输入学生姓名，成绩" << endl;
            
                string name;
                float grade;
                cin >> name >> grade;
            
                student *s_ptr = new student(id, name, grade);

                file_input(*s_ptr);
                delete s_ptr;
                s_ptr = NULL;
                
                cout << "请输入学生id, 以-1停止输入" << endl;
                cin >> id;
            }
        
            cout << "输入成功！" << endl;
        }
    
        if(control == 2)
        {
            file_output();
        }
    }
}

Answer 1

name是string类型，保存到文件时只是保存了一个指向堆中的地址，实际的姓名字符串并没有保存到文件中，将name改成以字符数组存储就行了。
运行截图：

代码：

#include <iostream>
#include <fstream>
#include <cstring>
#include <cstdlib>
using namespace std;
class student
{
    public:
        student();
        student(int id, char name[], float grade);
        student(const student &s);
        void print_stu();
        //friend void delete_stu(student *s);
        //friend void modify_stu(student *s);
    private:
        int id;
        char name[128];
        float grade;
};
 
student::student()
{
    id=0;
    strcpy(name,"noname");
    grade=0;
}
student::student(int id, char name[], float grade)
{
    this -> id = id;
    strcpy(this->name,name);
    this -> grade = grade;
}
student::student(const student &s)
{
    id = s.id;
    strcpy(this->name,s.name);
    grade = s.grade;
}
void student::print_stu()
{
    cout << "ID: " << id << " " << "Name: " << name << " " << "Grade: " << grade << endl; 
}
 
void file_input(student s)
{
    s.print_stu();
    fstream file1;
    file1.open("student.dat", ios::out | ios::binary | ios::app);
    if(!file1)
    {
        cout << "Cannot open the file" << endl;
        abort();
    }
    file1.write((char *)&s, sizeof(s));
    file1.close();
}
void file_output()
{
    fstream file1;
    file1.open("student.dat", ios::in | ios::binary);
    if(!file1)
    {
        cout << "Cannot open the file" << endl;
        abort();
    }
    student s;
    while(file1.read((char *)&s, sizeof(s)))
    {        
        s.print_stu(); 
    } 
    file1.close();
}
 
int main()
{
    while(1)
    {
        cout << "1: 输入学生信息" << endl << "2: 显示学生信息" << endl;
        int control = -1;
        cin >> control;
        if(control == 1)
        {    
            cout << "请输入学生id, 以-1停止输入" << endl;
            int id = 0;
            cin >> id;
            while(id != -1)
            {
                cout << "请输入学生姓名，成绩" << endl;
                char name[128];
                float grade;
                cin >> name >> grade;
                student *s_ptr = new student(id, name, grade);
                file_input(*s_ptr);
                delete s_ptr;
                s_ptr = NULL;
                cout << "请输入学生id, 以-1停止输入" << endl;
                cin >> id;
            }
            cout << "输入成功！" << endl;
        }
        if(control == 2)
        {
            file_output();
        }
    }
    return 0;
}

名字用string类型也是可以的，但代码得改成这样：

#include <iostream>
#include <fstream>
#include <cstring>
#include <cstdlib>
using namespace std;
class student
{
    public:
        student();
        student(int id, string name, float grade);
        student(const student &s);
        void print_stu();
        string& get_name();
        void set_name(string name);
        //friend void delete_stu(student *s);
        //friend void modify_stu(student *s);
    private:
        int id;
        string name;
        float grade;
};
 
student::student()
{
    this->id=0;
    this->name="noname";
    this->grade=0;
}
student::student(int id, string name, float grade)
{
    this -> id = id;
    this -> name = name;
    this -> grade = grade;
}

student::student(const student &s)
{
    id = s.id;
    name = s.name;
    grade = s.grade;
}
void student::print_stu()
{
    cout << "ID: " << id << " " << "Name: " << name << " " << "Grade: " << grade << endl; 
}

string& student::get_name()
{
    return name;
}

void student::set_name(string name)
{
    this->name=name;
}

void file_input(student s)
{
    int len;
    string name;
    
    s.print_stu();
    fstream file1;
    file1.open("student2.dat", ios::out | ios::binary | ios::app);
    if(!file1)
    {
        cout << "Cannot open the file" << endl;
        abort();
    }
    file1.write((char *)&s, sizeof(s));
    name=s.get_name();
    len=name.length();
    //写入名字长度
    file1.write((char*)&len,sizeof(len));
    //写入名字
    file1.write(name.c_str(),len);
    file1.close();
}
void file_output()
{
    int len;
    char name[128];
    
    fstream file1;
    file1.open("student2.dat", ios::in | ios::binary);
    if(!file1)
    {
        cout << "Cannot open the file" << endl;
        abort();
    }
    student s;
    while(file1.read((char *)&s, sizeof(s)) && file1.read((char *)&len, sizeof(len)) && file1.read(name, len))
    {        
        name[len]=0;
        s.set_name(name);
        s.print_stu(); 
    } 
    file1.close();
}
 
int main()
{
    while(1)
    {
        cout << "1: 输入学生信息" << endl << "2: 显示学生信息" << endl;
        int control = -1;
        cin >> control;
        if(control == 1)
        {    
            cout << "请输入学生id, 以-1停止输入" << endl;
            int id = 0;
            cin >> id;
            while(id != -1)
            {
                cout << "请输入学生姓名，成绩" << endl;
                string name;
                float grade;
                cin >> name >> grade;
                student *s_ptr = new student(id, name, grade);
                file_input(*s_ptr);
                delete s_ptr;
                s_ptr = NULL;
                cout << "请输入学生id, 以-1停止输入" << endl;
                cin >> id;
            }
            cout << "输入成功！" << endl;
        }
        if(control == 2)
        {
            file_output();
        }
    }
    return 0;
}