Question

What is wrong in the code?

What change should I make in the code to make it defensive?

Array.h

#ifndef _ARRAY_H_
#define _ARRAY_H_

class Array
{
private:
    int * m_ArrayContainer;

public:
    Array();
    void AllocateMemoryOfSize(int size);
    void DeallocateMemory();
    void SetElementsIntoTheIndex(int index, int value);
    int GetElementFromIndex(int index);
    int operator [] (int index);
    ~Array();
};

#endif

Array.cpp

#include "Array.h"
#include <iostream>

Array :: Array()
{
    this->m_ArrayContainer = NULL;
}

void Array :: AllocateMemoryOfSize(int size)
{
    this->m_ArrayContainer = new int[size];
}

void Array :: DeallocateMemory()
{
    delete [] this->m_ArrayContainer;
}

void Array :: SetElementsIntoTheIndex(int index, int value)
{
    this->m_ArrayContainer[index] = value;
}

int Array :: GetElementFromIndex(int index)
{
    return this->m_ArrayContainer[index];
}

int Array :: operator [] (int index)
{
    return this->m_ArrayContainer[index];
}

Array :: ~Array()
{
    this->DeallocateMemory();
}

Main.cpp

#include <iostream>
#include "Array.h"

int main()
{   
for(int i=0 ; i<250 ; i++)
{
    Array array1;
    array1.AllocateMemoryOfSize(3);
    array1.SetElementsIntoTheIndex(0, 10);
    array1.SetElementsIntoTheIndex(1, 10);
    array1.SetElementsIntoTheIndex(2, 10);

    /*array1.SetElementsIntoTheIndex(0, NULL);
    array1.SetElementsIntoTheIndex(1, NULL);
    array1.SetElementsIntoTheIndex(2, NULL);*/

    array1.DeallocateMemory();
}
}

Answer 1

The destructor calls DeallocateMemory() for the second time and that leads to delete[] being called for the second time with the same address which triggers undefined behavior. To guarg against this you should change

void Array::DeallocateMemory()
{
    delete [] this->m_ArrayContainer;
    this->m_ArrayContainer = 0;
}

so that when the destructor is called and it calls DeallocateMemory() a null pointer is delete[]d which is a no-op.

Btw you should at least prohibit copy constructor and operator= in your class by declaring them private and leaving unimplemented – your class doesn’t support memberwise copying.