Accessing element in custom array wrapper via overloading operator []

Question

I am trying to implement my own array wrapper. I overloaded [] operators that returns address of element in array. However when I dynamically allocate the ArrayWrapper class in main, it is not working.

Why is it not working? Is it because variable arr is a pointer?

I get these errors:

Description Resource Path Location Type cannot bind 'std::ostream {aka std::basic_ostream}' lvalue to 'std::basic_ostream&&' Cviceni.cpp /Cviceni/src line 25 C/C++ Problem

Description Resource Path Location Type no match for 'operator<<' (operand types are 'std::ostream {aka std::basic_ostream}' and 'ArrayWrapper') Cviceni.cpp /Cviceni/src line 25 C/C++ Problem

Working code

    ArrayWrapper arr(250);

 try
 {
   for(int i = 0; i < arr.getSize(); i++)
   {
     arr[i] = i + 1;
     cout << arr[i] << endl;
   }
}
catch(std::range_error& e)
  {
      cout << e.what() << endl;
  }

  cout << "End..." << endl;

  return 0;
}

Not working code:

ArrayWrapper *arr = new ArrayWrapper(250);

  try
  {
    for(int i = 0; i < arr->getSize(); i++)
    {
      arr[i] = i + 1;
      cout << arr[i] << endl;
    }
  }

ArrayWrapper implementation:

class ArrayWrapper
{
private:
  int size;
  int *elements;

public:
  ArrayWrapper(int n) : size(n), elements(new int[n])
  {
    for(int i = 0; i < size; i++)
      elements[i] = 0;
  };

  ~ArrayWrapper(){delete []elements;};

  int& operator[](int i)
  {
    if(i >= size || i < 0)
      {
    throw range_error("Out of range");
      }
    return elements[i];
  };

  int getSize(){ return size;};
};

Just change `cout << arr[i] << endl;` to `cout << (*arr)[i] << endl;`. you should not mess around with a pointer for that case at all. — πάντα ῥεῖ, Jun 03 '17 at 09:49
Also [The Rule of Three](https://stackoverflow.com/questions/4172722/what-is-the-rule-of-three); *"I overloaded [] operators that returns address of element in array."* - no, it returns a reference. And you wouldn't need to check for negative numbers if you used `size_t` for indexing and sizes. — LogicStuff, Jun 03 '17 at 09:49

score 2 · Accepted Answer · answered Jun 03 '17 at 09:52

It's that you are using pointer in the second example arr[2] is not an operation on ArrayWrapper it's operation on pointer.

ArrayWrapper *arr = new ArrayWrapper(250);

  try
  {
    for(int i = 0; i < arr->getSize(); i++)
    {
      (*arr)[i] = i + 1;
      cout << (*arr)[i] << endl;
    }
  }

Accessing element in custom array wrapper via overloading operator []

1 Answers1