Pointers to classes (From the note of my firend)



Pointers to classes

Objects can also be pointed to by pointers: Once declared, a class becomes a valid type, so it can be used as the type pointed to by a pointer. For example:

Rectangle * prect;

is a pointer to an object of class Rectangle.

Similarly as with plain data structures, the members of an object can be accessed directly from a pointer by using the arrow operator (->). Here is an example with some possible combinations:

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// pointer to classes example
#include <iostream>
using namespace std;

class Rectangle {
  int width, height;
public:
  Rectangle(int x, int y) : width(x), height(y) {}
  int area(void) { return width * height; }
};

int main() {
  Rectangle obj (3, 4);
  Rectangle * foo, * bar, * baz;
  foo = &obj;
  bar = new Rectangle (5, 6);
  baz = new Rectangle[2] { {2,5}, {3,6} };
  cout << "obj‘s area: " << obj.area() << ‘\n‘;
  cout << "*foo‘s area: " << foo->area() << ‘\n‘;
  cout << "*bar‘s area: " << bar->area() << ‘\n‘;
  cout << "baz[0]‘s area:" << baz[0].area() << ‘\n‘;
  cout << "baz[1]‘s area:" << baz[1].area() << ‘\n‘;
  delete bar;
  delete[] baz;
  return 0;
}	

This example makes use of several operators to operate on objects and pointers (operators
*, &, ., ->, []). They can be interpreted as:

Most of these expressions have been introduced in earlier chapters. Most notably, the chapter about arrays introduced the offset operator ([]) and the chapter about plain data structures introduced the arrow operator (->).

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