CODEWITHSUNDEEP
objective-c
lamvanduong
lamvanduong

Reputation: 31

Can someone explain . and -> in objective c?

Help me :( i dont know why?

    @interface RootViewController : UITableViewController {
        BOOL isSearchOn; 
    }

    self->isSearchOn = NO; ( no error)
    self.isSearchOn = NO; ( error)

Upvotes: 0

Views: 89

Answers (4)

Alexis King
Alexis King

Reputation: 43842

There are essentially three operators here, two of which are inherited from C and the third which is from Objective-C.

In C, . and -> do the same thing—they retrieve a value from a struct—but - automatically dereferences a pointer to a struct, so the following two expressions are equivalent:

(*a).b
a->b

The second operator is simply syntactic sugar. Importantly, however, . doesn't make any sense when applied to a pointer—you have to use ->.

Objective-C allows the use of . with an object pointer (and only with a pointer, since all Objective-C objects are pointers) to reference a property value, a much higher level construct than the C operators provide.

Therefore, you may use . on objects to retrieve properties defined in the interface with @property, but you will need to use -> to retrieve ivars (instance variables) directly, which isSearchOn is in your example. However, it is usually better practice to expose variables using properties in Objective-C rather than refer to them directly using C's -> operator.

Upvotes: 0

Dharmbir Singh
Dharmbir Singh

Reputation: 17535

-> is the traditional C operator to access a member of a structure referenced by a pointer. Since Objective-C objects are (usually) used as pointers and an Objective-C class is a structure, you can use -> to access its members, which (usually) correspond to instance variables.

or

When applied to pointer arrow operator is equivalent to applying dot operator to pointee (ptr->field is equivalent to (*ptr).field)

or

pSomething->someMember

is equivalent to

(*pSomething).someMember

Upvotes: 2

Anoop Vaidya
Anoop Vaidya

Reputation: 46533

Dot operator . is used to access property.

Arrow operator -> is used to acces instance variable.

So you use

    self->isSearchOn = NO; // which is an instance not  a property

You can also use this way by skipping self->

    isSearchOn = NO;

Upvotes: 2

Theolodis
Theolodis

Reputation: 5102

. is used when you have a object and want to reference a attribute or a method, while you must use -> when holding the pointer only. instead of using -> you could aswell go for *. but I guess that you should in any case read about pointers in C.

Upvotes: 0

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