Thread: File IO with polymorphism

I would imagine that the file will contain some way to indicate whether a record represents a dog or a cat. do you know how to read from files? do you understand polymorphism?

I know how to read from file and I know polymorphism but i do not know how to implement them together.
this is my virtual function readFromFile for localStudent.

Code:

void clsLocalStudent::readFromFile(vector <clsStudent*> &s)
{
   string name, IC_no,state, gender, accNumb, accName, nationality, progName, progCode;
   int accID, times;
   float GPA, discountedFees, principle, rate, years, CI, C_Amount, progFees;
   clsDate DOB, accStart, accDOB ;
   clsLocalStudent *stud;
   stud = new clsLocalStudent();


   ifstream in(filename);
   if(in)
   {
      in >> name ;
      in >> DOB;
      in >> gender ;
      in >> nationality;
      in >> GPA ;
      in >> progName ;
      in >> progCode ;
      in >> progFees;
      in >> accNumb;
      in >> accName;
      in >> accID ;
      in >> accDOB ;
      in >> accStart;
      in >> principle ;
      in >> rate;
      in >> years ;
      in >> times;
      in >> CI ;
      in >> C_Amount;
      in >> discountedFees ;
      in >> IC_no;
      in >> state;
      in.close();
   }
   else
      cerr << "\nCannot open " << filename << " for reading" << endl;


    clsUniversityProgram program(progName, progCode, progFees);
    clsAccount objAccount(accNumb,name,accID, accDOB, accStart, principle, rate, years, times);
    stud->setName(name);
    stud->setDateOfBirth(DOB);
    stud->setGender(gender);
    stud->setNationality(nationality);
    stud->setGPA(GPA);
    stud->setProgram(&program);
    stud->setAccounts(objAccount);
    stud->setIC(IC_no);
    stud->setState(state);




    s.push_back(stud);


}

my guess is that you're going to have a base class called animal, and derived classes called cat and dog, and when you read from the file, you will determine whether it's a cat or dog and use new to create the appropriate type, and assign to a pointer of animal type. I'm not going to write the code for you, but I'll be happy to help you out if you put some effort into it and ask more specific questions when you get stuck on something.

Well how do i determine if its a cat or a dog?
my print() function here is virtual. So in this case, the program determines itself which class it's in and calls the correct print function.

Code:

            for(int x = 0; x < student.size(); x++)
            {
                cout << " ============ Student " << x+1 << " Details ============";
                student[x]->printStudentDetails();
                student[x]->print();
                cout << endl;
            }

However, this cannot be use because the specific type has not yet been created. Unlike the one shown above.

Originally Posted by Alexius Lim

Well how do i determine if its a cat or a dog?

having not seen the format of the file, I have no idea. if I were developing this system, I would have the first field of the record indicate what type the record is.

if you positively can't tell, then whether you care or not is irrelevant.