Masalah saat membaca objek dari file di c ++

Question

Saya melakukan proyek kuliah kecil di mana saya harus menambah, mengedit, dan mencari catatan di / dari file menggunakan konsep OOP. Menambahkan ke file berfungsi dengan baik tetapi setiap kali saya mencoba membaca dari file itu mencetak dalam teks yang tidak dapat dibaca. Berikut kode lengkap dan keluarannya. main.cpp

#include <iostream>
#include <cstdlib>
#include <fstream>
#define MIN 20
#define MAX 100
#include "student.h"

using namespace std;

void add_student();
void edit_student();
void search_student();
void addToFile(const Student&);
Student* fetchFromFile();
int getFileSize();
void updateFile(Student*);

// Student stud[MAX];
int main()
{
  int choice;
  system("cls");                                                  
  system("Color B0");
  while(1)
  {                                                                                            
    cout<<"\n\t\tWhat do you want to do?"<<endl;
    cout<<"\t\t----------------------"<<endl;                                                 
    cout<<"\t\t1-Add student"<<endl;                                                       
    cout<<"\t\t2-Edit student"<<endl;                                                         
    cout<<"\t\t3-Search student"<<endl;                                                   
    cout<<"\t\t4-Quit Program"<<endl;                                                              
    cout<<"\t\t----------------------"<<endl;            
    cout<<"Enter your choice: ";                           
    cin>>choice;                                           
    switch(choice)                                         
    {
      case 1:
        add_student(); //calling add_student function to add records.
        break;
      case 2:
        edit_student();
        break;
      case 3:
        search_student();
        break;
      case 4:
        return 0;
        break;
      default:
        cout<<"Invalid choice";
        break;
    }
}
  return 0;
}

int Student::id = getFileSize() - 1; //Initialize id equals to size of file

// setData function of class Student definition
void Student :: setData()
{
  // taking input from user
  cout<<"Enter student roll no in format(1XXX): ";
  cin>>roll;
  cout<<"Enter student name: ";
  cin>>name;
  cout<<"Enter stduent date of birth(dd/mm/yy): ";
  cin>>dob;
  cout<<"Enter stduent phone no: ";
  cin>>phone;
  cout<<"Enter student address: ";
  cin>>address;
  stdId = Student::id;
}

void Student :: showData()
{
  cout<<stdId<<"  ";
  cout<<roll<<"   ";
  cout<<name<<"     ";
  cout<<dob<<"\t";
  cout<<phone<<"   ";
  cout<<address<<"\n\n";
}

const int Student :: getRoll()
{
  return roll;
}

Student& Student::operator = (const Student& newObj)
{
  stdId = newObj.stdId;
  roll = newObj.roll;
  name = newObj.name;
  dob = newObj.dob;
  phone = newObj.phone;
  address = newObj.address;
  return *this;
}

void add_student()
{
  Student stud;
  Student::incrementId();
  stud.setData();
  addToFile(stud); //adding records to file
  system("CLS");
  cout<<endl;
  cout<<"--------------------------------------------------------------------------------"<<endl;
  cout<<"---------------------------Student updated record Table---------------------------------"<<endl;
  cout<<"--------------------------------------------------------------------------------"<<endl;
  cout<<"ID      "<<"Roll      "<<"Name      "<<"DOB      "<<"Phone no         "<<"Address\n\n";
  cout<<"--------------------------------------------------------------------------------"<<endl;

  Student* student = fetchFromFile(); //getting records from file in array of objects
  int length = getFileSize(); //getting length of array of objects

  for(int i=0; i<(length-1); i++)
  {
    student[i].showData(); //showing all the data
  }

  cout<<"--------------------------------------------------------------------------------"<<endl;
  cout<<"---------------------------------FINISH-----------------------------------------"<<endl;
  cout<<"--------------------------------------------------------------------------------"<<endl;
  cout<<"You want to add more?(Y/n):  ";
  char c;
  cin>>c;
  if(c=='y' || c=='Y')
  {
    add_student();
  }
  else{
    system("pause");
  }
}

void edit_student(){
  //Showing existing record first before editing
  cout<<endl;
  cout<<"--------------------------------------------------------------------------------"<<endl;
  cout<<"---------------------------Student Existing record Table---------------------------------"<<endl;
  cout<<"--------------------------------------------------------------------------------"<<endl;
  cout<<"ID   "<<"Roll   "<<"Name      "<<"DOB      "<<"Phone no         "<<"Address\n\n";
  cout<<"--------------------------------------------------------------------------------"<<endl;

  Student* student = fetchFromFile(); //fetching all records from file
  int length = getFileSize();

  for(int i=0; i<(length-1); i++)
  {
    student[i].showData();
  }
  int idnumber;
  cout<<"--------------------------------------------------------------------------------"<<endl;
  cout<<"Which ID number your want to edit: ";

  cin>>idnumber;            //Asking the user at which ID he wants to make a change.
  //checking for valid id number
  if(idnumber>length || idnumber<0)
  {
    cout<<"\nInvalid ID Number."<<endl;
  }
  //showing existing information about that specific record
  cout<<"\nExisted information about this record.\n\n";
  cout<<"--------------------------------------------------------------------------------"<<endl;
  cout<<"ID   "<<"Roll   "<<"Name      "<<"Father\tCell no.      "<<"DOB          "<<"Address\n\n";
  cout<<"--------------------------------------------------------------------------------"<<endl;
  student[idnumber].showData();
  cout<<"\n\nEnter new data for above shown record.\n\n";
  student[idnumber].setData();         //Inputting data for that specific record.
  updateFile(student);
  cout<<"\n\nRecord updated successfully."<<endl;
  cout<<endl;
  cout<<"--------------------------------------------------------------------------------"<<endl;
  cout<<"---------------------------Updated record Table---------------------------------"<<endl;
  cout<<"--------------------------------------------------------------------------------"<<endl;
  cout<<"ID   "<<"Roll   "<<"Name      "<<"DOB      "<<"Phone no         "<<"Address\n\n";
  cout<<"--------------------------------------------------------------------------------"<<endl;
  for(int i=0; i<(length-1); i++) //Showing updated record Table
  {
    student[i].showData();
  }
}

void search_student(){
  Student* student = fetchFromFile();
  int fileLenth = getFileSize() - 1;
  int searchkey;
  cout<<"Enter roll_no of student you want to search: ";
  cin>>searchkey;     //roll_no as the search key can be entered by user.
  for(int i=1; i<fileLenth; i++)
  {
    if(searchkey==student[i].getRoll()) //checking for roll no
    {
      student[i].showData();
    }
  }
  cout<<"--------------------------------------------------------------------------------"<<endl;
  cout<<"---------------------------------FINISH-----------------------------------------"<<endl;
  cout<<"--------------------------------------------------------------------------------"<<endl;
  system("pause");
}

//FILE HANDLING

void addToFile(const Student& obj)
{
  ofstream fout;
  fout.open("records.txt", std::ofstream::app | std::ofstream::binary);
  fout.write((char*)&obj, sizeof(obj));
  cout<<"Added to file successfully!"<<endl;
  fout.close();
}

Student* fetchFromFile()
{
  int i=0;
  Student obj;
  Student* returnObj = new Student[MAX];
  ifstream fin;
  fin.open("records.txt", std::ifstream::binary);
  while(!fin.eof())
  {
    fin.read((char*)&obj, sizeof(obj));
    returnObj[i] = obj;
    i++;
  }
  fin.close();
  delete[] returnObj;
  return returnObj;
}

int getFileSize()
{
  int i=0;
  Student obj;
  ifstream fin;
  fin.open("records.txt", std::ifstream::binary);
  while(!fin.eof())
  {
    fin.read((char*)&obj, sizeof(obj));
    i++;
  }
  fin.close();
  return i;
}

void updateFile(Student* student)
{
  ofstream fout;
  fout.open("records.txt", std::ofstream::binary);
  fout.write((char*)&student, sizeof(student));
  fout.close();
}

file header student.h

// A student class that hold students attributes like id, name, address and class
// Object of this class will be craeted to store student details
class Student
{
  int stdId;
  int roll;
  std::string name;
  std::string dob;
  std::string phone;
  std::string address;
public:
  static int id; //we will increase 'id' whenever student is added to the record
  //Member functions declaration
  void setData(); //this function will take input from user and set the data to attributes of class
  void showData(); //This function will give student data to user when called
  static void incrementId()
  {
    id++;
  }
  const int getRoll();
  Student& operator = (const Student&);
};

Keluaran sampel 1

Saat saya menambahkan objek siswa ke file

Keluaran sampel 2

Membaca semua catatan dari file

Masalah1: Menampilkan nilai sampah id.

Output sampel 3

Menambahkan objek lain ke file

Output sampel 4

Membaca semua objek dari file

Keluaran sampel 5

Sekarang kembali dan memilih untuk mengedit catatan

Masalah2: Lihat bagaimana catatan dicetak dalam bentuk yang tidak terbaca.

Mengapa ini terjadi. Sekarang jika saya menutup program dan menjalankannya lagi maka itu masih muncul dalam teks yang tidak dapat dibaca. Semoga Anda mengerti masalah saya. Saya ingin penjelasan rinci tentang ini. Juga, jika saya telah melakukan kesalahan lain-lain, beri tahu saya. Terima kasih!

Answer 1

Studentterlalu rumit untuk dibaca dengan IO yang tidak diformat seperti readdan write. Dalam istilah teknis, ini tidak dapat disalin secara sepele karena mengandung std::strings, dan stringtidak dapat disalin secara sepele.

Hal termudah untuk dilakukan adalah meninggalkan readdan write. Sebagian besar data Anda adalah data string, jadi tulis <<dan >>overload Studentdan simpan semuanya sebagai teks.

    friend std::ostream & operator<<(std::ostream & out, 
                                     const Student & stu) 
    { 
        out << stu.stdId << ',' <<stu.roll << ','<< stu.name... <<'\n'; 
        return out;
    } 

Membaca kembali data sedikit lebih rumit

    friend std::istream & operator>>(std::istream & in, 
                                     Student & stu) 
    { 
        std::string line;
        if (std::getline(in, line))
        {
            std::stringstream strm(line);
            if (!(strm >> stu.stdId >> comma >> stu.roll >> comma) ||
                !std::getline(strm, stu.name, ',') ||
                !std::getline(strm, stu.dob, ',') ||
                ...))
            { // If any read failed, mark the stream as failed so the caller knows.
                out.setstate(std::ios_base::failbit);
            }
        }
        return out;
    } 

Answer 2

Pertama, trik kecil, tambahkan konstruktor kosong untuk kelas ke initailial semua anggota, integer {0}, dan string {}, yang akan menghilangkan beberapa gabage yang tidak diinginkan.

 Student::Student() :stdId(0), roll(0), name{}, dob{}, phone{}, address{} {;}

Masalah utama Anda muncul dari fungsi fetchfomrfile () tempat Anda menghapus larik Student yang diambil, oleh karena itu pemanggil menerima larik data yang tidak ditentukan:

Student* fetchFromFile()
{
  int i=0;
  Student obj;
  Student* returnObj = new Student[MAX];

  //reading records from file
  fin.close();
  delete[] returnObj;// <<<< youe deleted
  return returnObj; // and return it as undefined
}

Karena Anda dapat menghitung ukuran file, saya sarankan di fungsi pemanggil:

void search_student(){
 // Student* student = fetchFromFile();
    Student *student = new Stduent [getFileSize()];
     fecchFromFile(student); // use this array in fetch_file 
  // other things
 }

Tulis ulang fetchFromFile sebagai:

viod fetchFromFile(Stduent *ss)
{
  // read file data to array ss[i];
}