Issue with array index out of bounds assignment - c++

Question

I have seen several articles regarding something similar but none of them seem to help me. I would appreciate if someone could look at my code and tell me what I am doing wrong here. My teacher is not helping much. I commented out lines 65 - 75 in the driver because i couldn't get it to compile with these, will need help with this as well
ArrayDriver.cpp
#include <iostream>
#include "myArray.h"
using namespace std;
int main()
{
myArray<int> list1(5);
myArray<int> list2(5);
int i;
cout << "list1 : ";
for (i = 0 ; i < 5; i++)
cout << list1[i] <<" ";
cout << endl;
cout << "Enter 5 integers: ";
for (i = 0 ; i < 5; i++)
cin >> list1[i];
cout << endl;
cout << "After filling list1: ";
for (i = 0 ; i < 5; i++)
cout << list1[i] <<" ";
cout<< endl;
list2 = list1;
cout << "list2 : ";
for (i = 0 ; i < 5; i++)
cout << list2[i] <<" ";
cout<< endl;
cout << "Enter 3 elements: ";
for (i = 0; i < 3; i++)
cin >> list1[i];
cout << endl;
cout << "First three elements of list1: ";
for (i = 0; i < 3; i++)
cout << list1[i] << " ";
cout << endl;
myArray<int> list3(-2, 6);
cout << "list3: ";
for (i = -2 ; i < 6; i++)
cout << list3[i] <<" ";
cout<< endl;
list3[-2] = 7;
list3[4] = 8;
list3[0] = 54;
list3[2] = list3[4] + list3[-2];
cout << "list3: ";
for (i = -2 ; i < 6; i++)
cout << list3[i] <<" ";
cout<< endl;
/*
if (list1 == list2)
cout << " list 1 is equal to list2 " << endl;
else
cout << " list 1 is not equal to list2" << endl;
if (list1 != list2)
cout << " list 1 is not equal to list2 " << endl;
else
cout << " list 1 is equal to list2" << endl;
*/
//10% EXTRA CREDIT: UNCOMMENT CODE IF YOU'VE SUCCESSFULLY IMPLEMENTED THE FOLLOWING:
//cout << list1<< (list1 == list2 ? " is equal to" : " not equal to ") << list2 << endl;
//cout << list1<< (list1 != list2 ? " not equal to" : " is equal to ") << list2 << endl;
return 0;
}
myArray.h
#ifndef MYARRAY_H
#define MYARRAY_H
//#pragma once
#include <iostream>
//#include <assert.h>
//#include <iomanip>
//#include <string>
using namespace std;
template <class DataType>
class myArray
{
//overload for <<
//friend ostream& operator<<(ostream& out, myArray<DataType>& arr);
//overload for >>
friend istream& operator>>(istream& in, myArray<DataType>& arr);
public:
//myArray();
myArray(int size);
myArray(int start, int end);
//~myArray();
//overload []
DataType& operator[](int i);
//overload == operator
friend bool operator==(myArray<DataType> &arr1, myArray<DataType> &arr2);
//overload != operator
friend bool operator!=(myArray<DataType> &arr1, myArray<DataType> &arr2);
//overload = opertator
myArray<DataType> &operator=(const myArray<DataType> &rhs)
{
if (myDataType != NULL)
delete[]myDataType;
myDataType = new DataType[rhs.arraySize];
arraySize = rhs.arraySize;
for (int i = 0; i < arraySize; i++)
myDataType[i] = rhs.myDataType[i];
return *this;
}
//function
void SetNULL();
protected:
int startIndex;
int endIndex;
int arraySize;
//template
DataType *myDataType;
};
#endif
template <class DataType>
DataType& myArray<DataType>::operator[](int i)
{
if (i > arraySize)
{
cout << "Array out of bounds: " << endl;
}
else if (startIndex == 0)
{
return myDataType[i];
}
else
{
return myDataType[(startIndex + (i - 1))];
}
}
template <class DataType>
myArray<DataType>::myArray(int size) :
arraySize(size), startIndex(0), endIndex(size)
{
myDataType = new DataType[arraySize];
SetNULL();
}
template <class DataType>
myArray<DataType>::myArray(int start, int end) :
startIndex(start), endIndex(end)
{
if (start > end)
{
cout << "Invalid start position: " << endl;
}
else
{
arraySize = end - start;
}
myDataType = new DataType[arraySize];
SetNULL();
}
template <class DataType>
void myArray<DataType>::SetNULL()
{
for (int i = startIndex; i < endIndex; i++)
{
myDataType[i] = (DataType)0;
}
}
//overload == operator
template <class DataType>
bool operator==(myArray<DataType> &arr1, myArray<DataType> &arr2)
{
bool testBool = true;
for (int i = 0; i < arraySize; i++)
{
if (arr1[i] != arr2[i])
{
testBool = false;
}
}
return testBool;
}
//overload != operator
template <class DataType>
bool operator!=(myArray<DataType> &arr1, myArray<DataType> &arr2)
{
bool testBool = true;
for (int i = 0; i < arraySize; i++)
{
if (arr1[i] == arr2[i])
{
testBool = false;
}
}
return testBool;
}
//overload >> operator
template <class DataType>
istream& operator>> (istream &in, myArray<DataType> &aList)
{
for (int i = 0; i < aList.arraySize; i++)
in >> aList.list[i];
return in;
}

Answer 1

That's why not ignoring warnings (or using debugger) is helpful. My compiler showed the issue (via warnings), which should be the culprit of your problem.
In function:
myArray<DataType> &operator=(const myArray<DataType> &rhs)
{
if (myDataType = NULL)
delete[]myDataType;
myDataType = new DataType[rhs.arraySize];
arraySize = rhs.arraySize;
for (int i = 0; i < arraySize; i++)
myDataType[i] = rhs.arraySize;
return *this;
}
UPDATE: You are also assigning the array size as elements of your newly created copy. Copy actual elements.
UPDATE #2: As pointed out by fellow commenters, you also forgot to check for self-assignment. Check if the array pointer of your current array is equal to the one you are assigning.
you are doing an assignment instead of comparison in the first if statement. Consider doing this:
myArray<DataType> &operator=(const myArray<DataType> &rhs)
{
if (myDataType == rhs.myDataType) //CHECK IF THE ARRAY IS THE SAME (self-assignment case).
return *this;
// Missing '!' character here!!!
if (myDataType != NULL)
delete[]myDataType;
myDataType = new DataType[rhs.arraySize];
arraySize = rhs.arraySize;
for (int i = 0; i < arraySize; i++)
myDataType[i] = rhs.myDataType[i]; // COPY ACTUAL ELEMENTS INSTEAD OF WRITTING ARRAY SIZE.
return *this;
}
And, to avoid such issues in the future (if your compiler doesn't pick up on issues like this, consider doing comparisons, with constant values, like this:
if (NULL != myDataType)
delete[]myDataType;
And then your compiler will, no matter what, pick up on the issue, since it can't assign to a constant value.
UPDATE #3: Also, as I noticed, you are also allowing for arrays to have user defined start/end indexes. But, you would need to rethink your current approach of calculating the index at which to get the elements in such a case (where startIndex != 0). You are getting the position of element with formula: 'startIndex + (i - 1)'. But in your test case, in list3, where the range of indexes is [-2; 6), and you start your for loop, the initial index equates to -2 + (-2 - 1) = -2 - 3 = -5. I am not sure why your code isn't crashing here, but it should.
Also, to implement the comparisons operators, check if the size is the same at first, since if one of the arrays is smaller, and you are iterating through the indexes of the larger one, it should crash, when you will access the non-existing index (and to be honest, if sizes of arrays differ - they are not equal, are they?).