Data storage NSArray and NSMutableArray - Objective C

Data storage and its retrieval is one the most important in any program. In objective C, we generally won't depend on structures like linked list since it makes the work complex. Instead, we use the collection like NSArray , NSSet , NSDictionary and its mutable forms.

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NSArray  & NSMutableArray

NSArray is used to hold an immutable array of objects and the NSMutaableArray is used to hold an mutable array of object.

Mutability helps to change the array in runtime a preallocated array, but if we use NSArray , we only replace the existing array and cannot change the content of the existing array.

Important methods of NSArray are as follows:

• alloc/initWithObjcts: used to initalized array with objects.
• objectAtIndex: return the object at the specific index.
• count: return the number of objects.

 NSMutableArray is inherited from NSArray and hence all instance methods of NSArray is available in NSMutableArray.

Important methods of NSMutableArray are as follows:

• removeAllObjects : Empties the array
• addObject : inserts a given object at the end of the array
• removeObjectAtIndex : This is used to remove objectAt a specific index
• exchangeObjectAtIndex : withObjectAtIndex : Exchange the objects in the array at given indices.
• replaceObjectAtIndex : withObject : Replace the object at index with an object.

We have to remember that the above list is just the freuently used methods and we can jump into respective classes in our xCode to know more methods in these class. A simple example is shown below:

#import <Foundation/Foundation.h>
int main()
{
        NSArray *arrobj = [[NSArray alloc]initWithObjects : @"raj", @"ram",@"rahul",nil];
       NSString *strobj = [[arrobj objectAtIndex: 0];
       NSLog(@"The object in array at index 0 is %@", strobj);
  
       NSMutableArray *mutarrobj = [[NSMutableArray alloc]init];
      [mutarrobj addObject : @"sunena"];
       strobj = [ mutarrobj objectAtIndex : 0];
      NSLog(@"The object in array at index 0 is %@", strobj); 
     return 0;
}

In the above program , we have seen a simple differntiation between NSMutableArray and NSArray where we can insert a string after allocation in mutable array.

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NSMutableArray