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 (->).