What does the Asterisk * mean in Objective-C?

Question

Is it true, that the Asterisk always means "Hey, that is a pointer!" And an Pointer always holds an memory adress?

(Yes I know for the exception that a * is used for math operation)

For Example:

NSString* myString;

or

SomeClass* thatClass;

or

(*somePointerToAStruct).myStructComponent = 5;

I feel that there is more I need to know about the Asterirsk (*) than that I use it when defining an Variable that is a pointer to a class.

Because sometimes I already say in the declaration of an parameter that the Parameter variable is a pointer, and still I have to use the Asterisk in front of the Variable in order to access the value. That recently happened after I wanted to pass a pointer of an struct to a method in a way like [myObj myMethod:&myStruct], I could not access a component value from that structure even though my method declaration already said that there is a parameter (DemoStruct*)myVar which indeed should be already known as a pointer to that demostruct, still I had always to say: "Man, compiler. Listen! It IIISSS a pointer:" and write: (*myVar).myStructComponentX = 5;

I really really really do not understand why I have to say that twice. And only in this case.

When I use the Asterisk in context of an NSString* myString then I can just access myString however I like, without telling the compiler each time that it's a pointer. i.e. like using *myString = @"yep".

It just makes no sense to me.

Answer 1

As I said in my answer of your previous question, @"yep" is already a pointer, so there is no need of * before myString which is also a pointer. In this case, you assign pointers not values.

Answer 2

mmattax well covered the distinction between declaration (as a pointer) and dereferencing.

However, as to your point about:

  (*myVar).myStructComponentX = 5;

to access a member of an instance of a C struct (as this is) you can do what you did , or more commonly you use the -> notation:

  myVar->myStructComponentX = 5;

Objective-C is a little confusing here because it recently (in ObjC 2.0) introduced property syntax, which is a short cut for:

  int val = [myObject someIntProperty];

and can now be written as:

  int val = myObject.someIntProperty;

This is Objective C (2.0) syntax for accessing a property which you have declared (not an actual member variable), whereas your example was accessing a member of a C struct.

Make sure you are clear on the difference.

Answer 3

Not an answer, but a question: .h file:

...
UIWebView *sections;
UIWebView *feature;
UIWebView *teasers;
...

.m file:

...
UIWebView *webView = nil
...
if([section isEqualToString:@"Feature"]) {
    // Do I use
    webView = feature;
    // Or do I use
    webView = &feature;
    // Or do I use
    webView = *feature;
}
...

So in the above fragments, if I want to interact with webView as if it were feature, anything done to webView affects feature, which one do I do?: feature, *feature, or &feature?