CODEWITHSUNDEEP
iphoneiosobjective-cxcodememory-leaks
Balram Tiwari
Balram Tiwari

Reputation: 5667

Need to understand the difference in behavior for the below code interms of memory leak

I have gone through objective-C literals & class methods, but I am not clear from Memory point of View. I am confused to use which version of the code. I have two piece of code & I would like to understand the difference between them from Memory Leak point of View.

Assuming that "returnArray" is Array to be returned

Version 1

if([tempArray count] > 0) {
    for(NSDictionary *dict in tempArray) {

        NSDictionary *tempDict = [
                                  [NSDictionary alloc]initWithObjectsAndKeys:
                                  [dict objectForKey:@"verifiedEmail"],@"verifiedEmail",
                                  [dict objectForKey:@"identifier"], @"identifier",
                                  nil
                                  ];

        [returnArray addObject:tempDict];
    }
}

Version2

if([tempArray count] > 0) {
    for(NSDictionary *dict in tempArray) {
        NSDictionary *tempDict = @{
                                 @"verifiedEmail" : [dict objectForKey:@"verifiedEmail"],
                                 @"identifier" : [dict objectForKey:@"identifier"],
                                 };
        [returnArray addObject:tempDict];
    }
}

Upvotes: 0

Views: 105

Answers (4)

Anil Varghese
Anil Varghese

Reputation: 42977

In manual memory management when you alloc an object such as [NSDictionary alloc]initWithObjectsAndKeys: you are getting a retained object. means you are responsible to release that object. Where as [NSDictionary dictionaryWithObjectsAndKeys] giving you a autoreleased object. Your second version of code is modern objective c style creating dictionary same as [NSDictionary dictionaryWithObjectsAndKeys](in particular replacement for +[NSDictionary dictionaryWithObjects:forKeys:count:]) . In memory concern second one is autoreleased. If you are not sure about memory management use ARC

Upvotes: 0

mjswan
mjswan

Reputation: 91

You will leak memory using Version 1. You're allocating an NSDictionary but then overwriting its pointer (the local tempDict) so have no way to release it. Version 2 will not leak memory since the creation of the NSDictionary object creates an auto-released object. (All of this assumes you are using Manual Retain/Release, rather than ARC.)

Upvotes: 0

Andrea
Andrea

Reputation: 26385

Supposing that you are NOT using ARC:

  • Version 1, the rule states that object with alloc, new or copy give object a retain count of 1. So you are creating tempdict without releasing it in the future, that's a leak
  • Version 2, since you are not using none of the words above you are creating an autoreleased object, that goes into the autorelease pool, this object in the future if none will take its ownership will be released. In that particular case the array will take the ownership.

Upvotes: 2

Nareshkumar
Nareshkumar

Reputation: 2351

Version 1 is creating a dictionary everytime and version two is giving out an autoreleased version of dictionary. Version 2 is equivalent to [NSDictionary dictionaryWithObjectsAndKeys] method.

Upvotes: 0

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