Programming iOS 4

Pointers

The other big way that C extends its range of data types is by means of pointers (K&R 5.1). A pointer is an integer (of some size or other) with a meaning: it designates the location in memory where the real data is to be found. Knowing the structure of that data and how to work with it, as well as allocating a block of memory of the required size beforehand and disposing of that block of memory when it’s no longer needed, is a very complicated business. Luckily, this is exactly the sort of complicated business that Objective-C is going to take care of for us. So all you really have to know in order to use pointers is what they are and what notation is used to refer to them.

Let’s start with a simple declaration. If we wanted to declare an integer in C, we could say:

int i;

That line says, “i is an integer.” Now let’s instead declare a pointer to an integer:

int* intPtr;

That line says, “intPtr is a pointer to an integer.” Never mind how we know there really is going to be an integer at the address designated by this point; here, I’m concerned only with the notation. It is permitted to place the asterisk in the declaration before the name rather than after the type:

int *intPtr;

I don’t generally use that second form when declaring a pointer, but it does come in handy when declaring several variables of the same type in a single statement. Here’s what I mean. It is legal, though I did not mention this earlier, to declare multiple variables of a single type in one statement, like ...