Question about C++ inheritence - Overclock.net

icyblizard · 11-22-07

#ifndef PERSON_H
#define PERSON_H

class person
{
string name;
string NRIC;
int age;
public:
void GetName(string n);
void GetNRIC(string nric);
void GetAge(int a);
string ReturnName() const;
string ReturnNRIC() const;
int ReturnAge() const;
virtual void printName() const=0;
virtual void PrintNRIC() const=0;
virtual void printAge() const=0;

person(string n="person",string nric="S1234567Z",int a=100);
};

#include "person.h"
#ifndef STUDENT_H
#define STUDENT_H

class student

ublic person
{
string AdminNo;
public:
void GetAdminNo(string a);
string ReturnAdminNo() const;
void printName() const;
void PrintNRIC() const;
void printAge() const;
void PrintAdminNo() const;

student(string n="student",string nric="S8954443C",int a=10,string admin="071234Z");
};
#endif

I want to make a database that can store 5 sets of data from either person class or student class, is that possible?

brightemo · 11-22-07

Define database in this case?

kdbolt70 · 11-22-07

I'm not quite sure what you mean by database, but I'm assuming you want to store objects, or pointer to objects to both people and students. You could do this by making all objects of type person. (I don't know if you know all this, so I'll go through it a little bit anyways). You could do something like:

Code:

Person *studentPtr = new Student("John", "nric12345", 15, "123456789");
Person *personPtr = new Person();

add_to_database(studentPtr);
add_to_database(personPtr);

This basically outlines the fact that a subclass can be initilized in a base class pointer. This then can be handed around like a base class without really knowing it is an inherited class type. The problem comes whenever you want to access a member function from a student pointer. In the example above, your studentPtr will be thought of as a person, and will therefore have no idea what do do when you do:

Code:

studentPtr->PrintAdminNo();

this is because a person object has no access to any subclass functions not defined in the base class. To solve this you either need a fat interface (i.e virtualize all the methods in the subclass in the baseclass) or cast the pointer to a student pointer if you KNOW it is a student. You also could store them separately (some as people and some as students) but this kinda defeats the purpose.

In terms of making a database that can store it... Basically you'll need to store pointers to objects of type person, and load it with ptrs to persons and students. Other than that I don't know what you mean by database.

icyblizard · 11-23-07

Woot! Problem solved, the correct way was to do it using polymorphism (pointers to class), like kdbolt70 had said

crazydj · 11-23-07

icyblizard, are you taking A-Levels computing?

icyblizard · 11-23-07

No, im taking a diploma in Digital Entertainment Technology. It involves alot of programming for either CG or games. 3 of my current subjects are C++ related

crazydj · 11-24-07

I see. When i was doing my A-Levels practical using C++, i had like only 2 hours of sleep everyday for 3 and and half months! Anyway, just keep on practicing man! Good luck!

icyblizard · 11-24-07

Ooh, thanks

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Question about C++ inheritence

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