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iOS

Posted by Alex Atwater
Alex Atwater
2,624 Points

Question with "*" in code and ()

@interface Sphere : NSObject {

NSArray *_center;
float _radius;

}

-(void)setCenter:(NSArray *)center; -(NSArray *)center; -(void)setCenter:(NSArray *)center radius:(float)radius;

-(void)setRadius:(float)radius; -(float)radius;

@end

There is some code from the video. Questions:

  1. Why is _center being declared as NSArray *_center with a *? Why isn't float _radius have one? What's the purpose of it being there?

  2. In the declarations of methods for center, why is the return type (NSArray )? does that mean the return type is going to be a pointer of an NSArray? or a location of an NSArray? and why is there space? could it be (NSArray)?

christo
christo
3,525 Points

I'm no expert at this yet, but I'll have a go based on my understanding. Someone please correct me if I'm wrong!

  1. Justin in right, but I'll expand a little more:

an * can have a few different functions. For example, an * is actually an operator to de-reference a pointer. Only during variable declaration does * mean, "Look at me, I'm a pointer!!"

```Foo *foo // foo in this case is a pointer to a Foo object

  1. The method you reference in your question: objectivec -(NSArray *)center; This method does not have a space, it has an *. The code would not compile without an *, so no, (NSArray) would not work, but to answer you question, yes, what will be returned is a pointer to an NSArray that was created in the "center" method in the Sphere class. You asked, "or a location of NSArray"...sort of. It's pointing to a particular memory address location. So if you have code like:
Sphere *mySphere = [[Sphere alloc] init];    // creates a Sphere object (assuming it's initialized properly)
NSArray *objectCenter = [mySphere center];

you have a Sphere object called "mySphere." You can then perform the class method "center" that will return an NSArray with something in it. In this case, "objectCenter" is an NSArray pointing to the same memory address that's storing the NSArray that was created in the "center" method. But overall only on NSArray was created, but we have two pointers to it:

  1. [mySphere center]
  2. objectCenter

You could just do [mySphere center] every time you wanted to access that NSArray, but it kind of looks funny to do that all the time. By assigning [mySphere center] to another pointer (in this case objectCenter), you can do things like:

[objectCenter objectAtIndex: 0];

rather than

[[mySphere center] objectAtIndex:0];

Hope what I said made sense. Good luck!

-Christo

3 Answers

Justin Johnson
PLUS
Justin Johnson
Courses Plus Student 24,793 Points
Justin Johnson
Justin Johnson
Courses Plus Student 24,793 Points

I don't know if anyone can answer better but... to my knowledge _center has a pointer because NSArray is an object where as float _radius is a C primitive data type so it doesn't require a pointer ( because it is not an object );

Justin Johnson
Justin Johnson
Courses Plus Student 24,793 Points

oh man I ended a sentence with a semi-colon. I'm literally turning into a robot.

christo
christo
3,525 Points
christo
christo
3,525 Points

(meant to post this as an answer, not a comment, but can't edit/delete the comment)

I'm no expert at this yet, but I'll have a go based on my understanding. Someone please correct me if I'm wrong!

  1. Justin is right, but I'll expand a little more: an * can have a few different functions. For example, an * is actually an operator to de-reference a pointer. Only during variable declaration does * mean, "Look at me, I'm a pointer!!"
Foo *foo // foo in this case is a pointer to a Foo object
  1. The method you reference in your question:
- (NSArray *) center;

This method does not have a space, it has an *. The code would not compile without an *, so no, (NSArray) would not work, but to answer you question, yes, what will be returned is a pointer to an NSArray that was created in the "center" method in the Sphere class. You asked, "or a location of NSArray"...sort of. It's pointing to a particular memory address location. So if you have code like:

Sphere *mySphere = [[Sphere alloc] init];    // creates a Sphere object (assuming it's initialized properly)
NSArray *objectCenter = [mySphere center];

you have a Sphere object called "mySphere." You can then perform the instance method "center" that will return an NSArray with something in it. In this case, "objectCenter" is an NSArray pointing to the same memory address that's storing the NSArray that was created in the "center" method. But overall, only one NSArray was created, but we have two pointers to it:

  1. [mySphere center]
  2. objectCenter

You could just do [mySphere center] every time you wanted to access that NSArray, but it kind of looks funny to do that all the time and doesn't do much for readability. By assigning [mySphere center] to another NSArray pointer (in this case objectCenter), you can do things like:

[objectCenter objectAtIndex: 0];

rather than

[[mySphere center] objectAtIndex:0];

Hope what I said made sense. Good luck!

-Christo

Scott Magdalein
Scott Magdalein
1,667 Points
Scott Magdalein
Scott Magdalein
1,667 Points

Testing something in the forum again. Please disregard.