Question

In my app i get a memory leak in

first

-(void)connectionDidFinishLoading:(NSURLConnection *)connection {  
    result = [[NSString alloc] initWithBytes:[webData mutableBytes]
                                      length:[webData length]
                                    encoding:NSUTF8StringEncoding];  
    [webData release];  
}

second

-(void)connectionDidFinishLoading:(NSURLConnection *)connection {  
    NSString * result = [[NSString alloc] initWithBytes:[webData mutableBytes]
                                                 length:[webData length]
                                               encoding:NSUTF8StringEncoding];
    [webData release];
}

in my first process I didn’t get a memory leak(Declare a string object globally and I didn’t release it)

In my second process i get a memory leak in string object.

1. Value stored to ‘result’ during its initialization is never read

2. Method returns an Objective-C object with a +1 retain count (owning reference)

3. Object allocated on line 124 and stored into ‘result’ is no longer referenced after this point and has a retain count of +1 (object leaked)

what is the difference?

Answer 1

In first case analyzer expects you to release your initted result string in, say, - (void)dealloc method of the class. If you don’t – you’ll get a leak as well (you’ll see the leak if you run your app with via Instruments app with Leaks instrument added.

In second case you’re creating a local variable in method scope where it should be released as well since you won’t have a reference of it in any other method (i.e. if you try access result variable in other method you’ll get unknown identifier error).