Dynamic array implementaion c++ , Overloading assignment operator - c++

Question

vector<int> a = {1,2,3};
a[1] = 54; // I want to achieve this in my Darray implementation
int i = 0;
a[i] = 10 // This also
I am trying to implement dynamic arrays in c++. Below is my code :
//-------- means it has not been defined yet
// custom Exception class for handling bizzare situations
#include <iostream>
using namespace std;
class MyException {
public:
MyException() {
cout << "\nException occured !! Program will terminate...\n";
exit(0);
}
MyException(string message) {
cout << "\nException occured : " << message
<< ".\nProgram will terminate...\n";
exit(0);
}
};
//================================================================================
// class for Dyanamic array
template <typename T> //
class Darray {
T *arr; // Dyanamic array
size_t len, cap; // length and capacity
/*
len : number of elements currently Darray contains
cap : number of elements Darray can hold without resizing
*/
public:
Darray();
Darray(size_t);
Darray(Darray<T> &);
// Darray(T *); //---------------
size_t capacity();
size_t length();
void resize(size_t);
bool empty();
T operator[](int);
T operator[](T);
void operator=(T); //-------------
void operator=(Darray);
void push(T);
T pop();
T back();
T elemAt(int);
T front();
T *data();
void assign(Darray); //---------------
void assign(T *); //--------------
void insertAt(T, int); //--------------
void erase(); //-------------
void clear(); //---------------
void swap(Darray, Darray); //---------
};
//================================================================================
// default constructor for 0 capacity
template <typename T> //
Darray<T>::Darray() {
arr = new T[0];
len = 0;
cap = 0;
}
//================================================================================
// parameterized constructor with given cap
template <typename T> //
Darray<T>::Darray(size_t cap) {
arr = new T[cap];
this->cap = cap;
len = 0; // no elements initially
}
//================================================================================
// copy constructor with given Darray
template <typename T> //
Darray<T>::Darray(Darray<T> &temp) {
cap = temp.capacity();
len = 0;
arr = new T[cap];
while (len < temp.length()) {
arr[len] = temp[len];
len++;
}
}
//================================================================================
// operator[] for getting elements
template <typename T> //
T Darray<T>::operator[](int index) {
if (empty())
throw MyException("Darray is empty");
if (index < 0 || index > len - 1)
throw MyException("Invalid index. Index should be in range 0 to length-1");
return arr[index];
}
//================================================================================
// to check if Darray is empty
template <typename T> //
bool Darray<T>::empty() {
return len < 1;
}
//================================================================================
// push elements at the end
template <typename T> //
void Darray<T>::push(T element) {
if (len == cap)
resize(cap + (cap / 2) + 1); // resizing the array
// +1 to ensure arrays of size 0 or 1 are also resized ;-)
arr[len] = element;
len++;
}
//================================================================================
// remove and gives the last element of Darray
template <typename T> //
T Darray<T>::pop() {
if (empty())
throw MyException("Darray is empty");
return arr[--len];
}
//================================================================================
// gives the last element of Darray
template <typename T> //
T Darray<T>::back() {
if (empty())
throw MyException("Darray is empty");
return arr[len - 1];
}
//================================================================================
// gives the first element of Darray
template <typename T> //
T Darray<T>::front() {
if (empty())
throw MyException("Darray is empty");
return arr[0];
}
//================================================================================
// gives element at pos
template <typename T> //
T Darray<T>::elemAt(int index) {
if (empty())
throw MyException("Darray is empty");
if (index < 0 || index > len - 1)
throw MyException("Invalid index. Index should be in range 0 to length-1");
return arr[index];
}
//================================================================================
// length gives number of elements currently present in the array
template <typename T> //
size_t Darray<T>::length() {
return len;
}
//================================================================================
// capacity gives total capacity of the array
template <typename T> //
size_t Darray<T>::capacity() {
return cap;
}
//================================================================================
// returns a pointer to first element of Darray
template <typename T> //
T *Darray<T>::data() {
if (empty())
return NULL;
return arr;
}
//================================================================================
// resize the array to given size
template <typename T> //
void Darray<T>::resize(size_t newSize) {
if (newSize < 0)
throw MyException("Size cannot be negative");
if (newSize == cap) // no need to resize
return;
T *temp; // temp array to hold the elements temporarily
size_t t; // t holds the number of elements to be copied in the resized Darray
if (newSize < len) {
t = newSize;
temp = new T[newSize];
// copying to temp,new size is less, some elements will be lost
for (int i = 0; i < t; i++) {
temp[i] = arr[i];
}
} else {
t = len;
temp = new T[len];
// copying all the elements from original array to temp
for (int i = 0; i < t; i++) {
temp[i] = arr[i];
}
}
arr = new T[newSize]; // resizing the Darray
// copying elements from temp to original Darray
for (int i = 0; i < t; i++) {
arr[i] = temp[i];
}
cap = newSize;
len = t;
}
int main()
{
Darray<char> a(0);
a.push('A');
a.push('B');
a.push('C');
a.push('D');
a.push('E');
// a.push('F');
// a.push('G');
// a.push('H');
for (int i = 0; i < a.length(); i++) {
cout << a[i] << " ";
}
cout << a.length() << " " << a.capacity() << endl;
return 0;
}
Is overloading the assignment operator to assign elements at given index of my dynamic array possible?
Something like:
Darray<int> a(5);
a[1] = 26;
Also if I overload the constructor to take array as T* and create a Darray(0) it becomes ambiguous (null pointer and Darray of size 0).
How to overcome this?

Answer 1

Your subscript operator returns by value. That means it returns a brand new copy.
Assigning to this copy will not change the original inside your "array".
You should return by reference instead:
T& operator[](int);
And you should probably add a "constant" overload as well:
T const& operator[](int) const;