File handling using classes c++ - c++

Question

I'm doing an assignment which requires file handling in C++.Assignment is long enough to be posted here, but i have made a similar simple code to elaborate my question.The following code is not read all data from file it only read the last record
please help me to make it correct.
#include <iostream>
#include <conio.h>
#include <fstream>
#include <string.h>
//class
class medicine{
int id;
char med_name[50];
int price;
int quantity;
char date[50];
public:
void data_entery(){
//int i;char na[50];int p;int q;char da[50];
cout<<"Enter id: ";
cin>>id;
cout<<"Enter name: ";
cin>>med_name;
cout<<"Enter price: ";
cin>>price;
cout<<"Enter quantity: ";
cin>>quantity;
cout<<"Enter exp_date: ";
cin>>date;
}
void display(){
cout<<this->id<<"\t "<<this->med_name<<"\t "<<this->price<<"\t"<<this- >quantity<<"\t "<<this->date;
}
}med[10];
using namespace std;
int main (){
//writing in file
ofstream wfile("medicines.txt",ios::app|ios::binary);
wfile.seekp(0,ios::end);
int rec=wfile.tellp()/sizeof(medicine);
cout<<"there are "<<rec<<" records";
med[rec].data_entery();
wfile.write(reinterpret_cast<char *>(&med),sizeof(medicine));
wfile.close();
//reading in file
ifstream rfile("medicines.txt",ios::in|ios::binary);
rfile.seekg(0,ios::end);
rec=rfile.tellg()/sizeof(medicine);
rfile.seekg(0,ios::beg);
cout<<"there are "<<rec<<" records";
for (int k=0;k<rec;k++){
med[k].display();
}
rfile.read(reinterpret_cast<char *>(&med),sizeof(med)*rec);
rfile.close();
getch();
return 0;
}

Answer 1

I am assuming that your file medicines.txt is initially empty.
What you have done wrong is that you have made 10 objects of the medicine class, but you are writing only one object to the file.
What you need to do here is:
for (int i=0; i < 10; i++) {
med[i].data_entery();
wfile.write(reinterpret_cast<char *>(&med),sizeof(medicine));
}
wfile.close();
Now you'll need to add 10 medicines, after details of each medicine has been added, that medicine will be written to the file.
I hope this helps.

Answer 2

Here is a better version of your code
#include <iostream>
#include <conio.h>
#include <fstream>
#include <string.h>
using namespace std;
//class
class medicine
{
int id;
char med_name[50];
int price;
int quantity;
char date[50];
public:
void data_entery()
{
//int i;char na[50];int p;int q;char da[50];
cout<<"\nEnter id: ";
cin>>id;
cout<<"Enter name: ";
cin>>med_name;
cout<<"Enter price: ";
cin>>price;
cout<<"Enter quantity: ";
cin>>quantity;
cout<<"Enter exp_date: ";
cin>>date;
}
void display()
{
cout<<"\nID :"<<this->id<<"\nName :"<<this->med_name<<"\nPrice :"<<this->price<<"\nQuantity :"<<this->quantity<<"\nExp Date :"<<this->date<<"\n";
}
}med;
int main ()
{
//writing in file
ofstream wfile("medicines.txt",ios::app|ios::binary);
wfile.seekp(0,ios::end);
int rec=wfile.tellp()/sizeof(medicine);
cout<<"\nthere are "<<rec<<" records";
med.data_entery();
wfile.write(reinterpret_cast<char *>(&med),sizeof(medicine));
wfile.close();
//reading in file
ifstream rfile("medicines.txt",ios::in|ios::binary);
rfile.seekg(0,ios::end);
rec=rfile.tellg()/sizeof(medicine);
rfile.seekg(0,ios::beg);
cout<<"\nthere are "<<rec<<" records";
while(rfile.read(reinterpret_cast<char *>(&med),sizeof(med)))
{
med.display();
}
rfile.close();
getch();
return 0;
}
Now, when you are using files, you do not need to create an array of objects. Once you store the object into the file, you can just reuse that object. The data can be accessed from the File. That is what I have done in this code. I have edited this code in such a manner as to not change your method, instead just corrected the problems and also made your code a little better. In each run of this code, you enter the details of one record, and then the details of all the records are shown.
The good thing about this code is, you can enter as many records as you want. You are not restricted to 10 records like your original code.