Pointers to classes

It is perfectly valid to create pointers that point to classes. We simply have to consider that once declared, a class becomes a valid type, so we can use the class name as the type for the pointer. For example:

CRectangle * prect;

is a pointer to an object of class CRectangle.

As it happened with data structures, in order to refer directly to a member of an object pointed by a pointer we can use the arrow operator (->) of indirection. Here is an example with some possible combinations:

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// pointer to classes example #include using namespace std; class CRectangle { int width, height; public: void set_values (int, int); int area (void) {return (width * height);} }; void CRectangle::set_values (int a, int b) { width = a; height = b; } int main () { CRectangle a, *b, *c; CRectangle * d = new CRectangle[2]; b= new CRectangle; c= &a; a.set_values (1,2); b->set_values (3,4); d->set_values (5,6); d[1].set_values (7,8); cout << "a area: " << a.area() << endl; cout << "*b area: " << b->area() << endl; cout << "*c area: " << c->area() << endl; cout << "d[0] area: " << d[0].area() << endl; cout << "d[1] area: " << d[1].area() << endl; delete[] d; delete b; return 0; }

a area: 2 *b area: 12 *c area: 2 d[0] area: 30 d[1] area: 56

Next you have a summary on how can you read some pointer and class operators (*, &, ., ->, [ ]) that appear in the previous example:

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

Be sure that you understand the logic under all of these expressions before proceeding with the next sections. If you have doubts, read again this section and/or consult the previous sections about pointers and data structures.