Passing Null Values and a variable in to NSMutableArray/NSArray. Why is there a difference in output?

Question

My question is how to pass Null values in to NSMutableArray/NSArray.

But by searching google and going through different sites, i think that i have achieved my purpose. But, while trying i got a new doubt.

See the below code to understand my question

I am declaring a mutable array and initializing it with some objects initially and also i am passing a null in to it at the time of declaration itself.

Now when i run this code below

NSMutableArray * mar = [[NSMutableArray alloc]initWithObjects:@"first",@"last", nil];

[ar addObject:[NSNull null]];

NSLog(@"%@",mar); 

The o/p is :

(
    first,
    last,
    "<null>"
)

But my actual doubt is when i initialize the NSMutableArray as below

NSString *str;

NSMutableArray * mar = [[NSMutableArray alloc]initWithObjects:@"first",str,@"last", nil];

[ar addObject:[NSNull null]];

NSLog(@"%@",mar); 

The o/p is :

(
    first,
    "<null>"
)

The 2nd element in the array is "null", i understand that as i have passed a variable without assigning any value to it. It is printing null. But why are the remaining elements not printed.

According to what i know, the array will stop adding elements whenever it overcomes nil while initializing. But here, in this case. The o/p shows that the 2nd element is also null.(But not nil.)

Then why does the remaining elements are not printed.

UPDATING QUESTION

NSString* str;
NSLog(@"%@",str); 
NSMutableArray * mar = [[NSMutableArray alloc]initWithObjects:@"first",str,@"last", nil];

NSLog(@"%@",mar);

and the o/p for the above code is

(null) // for str an uninitialised NSString variable.


(
    first // first element in the array
)

If the value present in str is (null), how come the array encountered nil and stopped adding elements to array and printing them.

Now, someone answer this?

Answer 1

initWithObjects uses nil as the marker for the last item. If you pass a nil (the unitialized str variable) to it as the 2nd item out of 4, only the first one is actually added.

[[NSMutableArray alloc]initWithObjects:@"first",str ?: [NSNull null],@"last", nil];

will fix your problem by replacing the nil with a [NSNull null] .

Also see NSArray creation with variable argument lists

Answer 2

in objective-C, when iterating through Array if nil/null encountered then it gets treated as end of array.

this is the reason it is not printing remaining values.

in case you want clear diff between nil/null/Nil then check Difference between nil, NIL and, null in Objective-C