Asterisk sometimes on variable type, sometimes on variable name. Why?

Question

In Objective-C, I've seen, for example:

UIPickerView *tweetPicker

and

UIPickerView* tweetPicker

What does the asterisk mean (I know, the first part is a dupe...) and why does it go on different parts of the deceleration in different contexts?

Answer 1

The asterisk indicates that the variable is a pointer. In objective-C all objects are represented through pointers.

As far as where it is put, this is a style thing. My personal style is actually with spaces around the asterisk.

UIPickerView * tweetPicker

In all three cases they mean the same thing, but with different styles.

Edit: Spacing does not matter, but position does in corner cases dealing with keywords such as if const refers to a constant pointer or a pointer to a constant value. But your question was related to spacing, which does not matter.

Answer 2

In the exact case you're showing, there is no difference. Some people like to think of tweetPicker being of type UIPickerView *, that is, a pointer to a UIPickerView. These people usually write it as

UIPickerView* tweetPicker;

Other people prefer to think of it like *tweetPicker is a UIPickerView, that is, dereferencing the pointer gives a UIPickerView. Those people usually write:

UIPickerView *tweetPicker;

I prefer the latter, because the C (and Objective-C because of that) syntax supports it better. Take, for example, the following variable declarations:

int* a, b, c;
int  *a, *b, *c;

At first glance, the novice C (or Objective-C) programmer might say "those are the same", but they're not. In the first case, b and c are regular integers, in the second case, they're pointers. a is a pointer in both cases.

From my perspective, the concept of a "type" is so weak in C anyway (what with the behaviour of typecasting and the like) that extending that concept one step further to pointer variables is crazy - especially with the automatic & silent conversions to and from void * or id that you get.