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:

// 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() << '
';
  cout << "*foo's area: " << foo->area() << '
';
  cout << "*bar's area: " << bar->area() << '
';
  cout << "baz[0]'s area:" << baz[0].area() << '
';
  cout << "baz[1]'s area:" << baz[1].area() << '
';       
  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:

expression	can be read as
`*x`	pointed to by `x`
`&x`	address of `x`
`x.y`	member `y` of object `x`
`x->y`	member `y` of object pointed to by `x`
`(*x).y`	member `y` of object pointed to by `x` (equivalent to the previous one)
`x[0]`	first object pointed to by `x`
`x[1]`	second object pointed to by `x`
`x[n]`	(`n+1`)th object pointed to by `x`

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 (->).