Problema al leer objetos del archivo en c ++

Question

Estoy haciendo un pequeño proyecto universitario en el que tengo que agregar, editar y buscar registros en / desde archivos usando el concepto de programación orientada a objetos. La adición al archivo funciona bien, pero cada vez que intento leer un archivo, se imprime en textos ilegibles. Aquí está el código completo y la salida. 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();
}

archivo de encabezado 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&);
};

Salida de muestra 1

Cuando agrego un objeto de estudiante al archivo

Salida de muestra 2

Leer todos los registros del archivo

Problema 1: mostrando el valor de basura de id.

Salida de muestra 3

Agregar otro objeto al archivo

Salida de muestra 4

Leer todos los objetos del archivo

Salida de muestra 5

Ahora regresó y eligió editar el registro

Problemam2: Vea cómo se imprimen los registros en forma ilegible.

Por qué está pasando esto. Ahora, si cierro el programa y lo ejecuto de nuevo, todavía se muestra en texto ilegible. Espero que entiendas mi problema. Quiero tener una explicación detallada sobre esto. Además, si he cometido otros errores diversos, hágamelo saber. ¡Gracias!

Answer 1

Studentes demasiado complicado de leer con IO sin formato como ready write. En términos técnicos, no es trivialmente copiable porque contiene std::strings, y stringno es trivialmente copiable.

Lo más fácil de hacer es abandonar ready write. La mayoría de sus datos son datos de cadena, así que escriba <<y >>sobrecargue Studenty almacene todo como texto.

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

Volver a leer los datos es un poco más complicado

    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

Primero, un truco menor, agregue un constructor vacío para la clase para inicializar todos los miembros, enteros {0} y cadena {}, lo que eliminará algunas brechas no deseadas.

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

Su principal problema surgió de la función fetchfomrfile () donde elimina la matriz de Estudiantes obtenida, por lo tanto, la persona que llama recibió una matriz de datos no definida:

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
}

Dado que puede calcular el tamaño del archivo, sugiero en la función de llamada:

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

Reescribe fetchFromFile como:

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