C++ an array of pointers to the base class [closed] - c++

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There are several classes which are made in different files.
Here are the class name: Hospital class and patient class.
Basically, for hospital class, it has array of pointers for patient which can store the information of patient based on their patient type. For patient class(base class) has four derived classes as follows: male, female, inpatient, outpatient. What I am trying to do is, in hospital class, I want to assign the object according to the patient type.
#include <iostream>
#include "Hospital.h"
#include "Female.h"
#include "Male.h"
#include "Inpatient.h"
#include "Outpatient.h"
using namespace std;
Hospital::Hospital(const char * name, int capacity)
{
hospitalName=name;
patientCapacity=capacity;
totalPatients=0;
}
void Hospital::determinePatientType()
{
int selection;
cout << "What is the patient type?" << endl;
cout << "1. Female" << endl;
cout << "2. Male" << endl;
cout << "3. Outpatient" << endl;
cout << "4. Inpatient" << endl;
cin >> selection;
if(selection==1)
{
patients = new Patient[totalPatients];
Female* female = new Female();
patients = female;
}
else if(selection==2)
{
patients = new Patient[totalPatients];
Male* male = new Male();
patients = male;
}
else if(selection==3)
{
patients = new Patient[totalPatients];
Outpatient* outpatient = new Outpatient();
patients = outpatient;
}
else
{
patients = new Patient[totalPatients];
Inpatient* inpatient = new Inpatient();
patients = inpatient;
}
totalPatients++;
}
This is my code, but I am not sure if it's correct or not.
And I will upload the class diagram for your understanding what I am doing.
Thank you for your assistance in advance.
enter image description here

Answer 1

No your code is not correct.
Lets take a look at this code snippet:
if(selection==1)
{
patients = new Patient[totalPatients];
Female* female = new Female();
patients = female;
}
With
patients = new Patient[totalPatients];
you allocate an array of totalPatients objects. You make patients point to the first element of that array.
Then two lines down you do
patients = female;
That reassigns the variable patients to point to the single object female.
You will lose the original memory from the first allocation, which will lead to a leak. It will most likely also lead to undefined behavior if you then use delete[] patients since patients no longer point to an array.
Unless your exercise is to lean how to use pointers and dynamic memory allocation, you should use std::vector.
There's also another potential issue, and that relates toobject slicing and polymorphism (if the classes are polymorphic, i.e. they have virtual member functions).
If you solve the first problem the natural way, by doing e.g.
patients[totalPatients] = female;
Or if you use a std::vector<Patient> and do a simple push_back(female).
Then you slice the female object, and lose all data specific for the Female class. And since you no longer have a Female objects, all virtual functions will think they are called on a Patient object, making polymprphism not working either.
To solve this problem you should have a vector (or array) of pointers to the base Patient class. Like e.g. std::vector<Patient*>.
Or better yet use a smart pointer like std::unique_ptr as in std::vector<std::unique_ptr<Patient>>.