CODEWITHSUNDEEP
objective-cmemory-management
Rahul Singh
Rahul Singh

Reputation: 1229

memory menagement in ios

Can anybody explain me why does the case1 and case2 crashes while the others does not in case of non-ARC?

Case1:
    NSString *rr = [[NSString alloc] initWithString:@"AB"];
    [rr release];
    [rr autorelease];

Case2:
    NSString *rrr = [[NSString alloc] initWithString:@"AB"];
    [rrr autorelease];
    [rrr release];

Case3:
    NSMutableString *rr1 = [[NSMutableString alloc] initWithString:@"AB"];
    [rr1 release];
    [rr1 autorelease];

Case4:
    NSMutableString *rrr1 = [[NSMutableString alloc] initWithString:@"AB"];
    [rrr1 autorelease];
    [rrr1 release];

Case5:
    NSArray *rr3 = [[NSArray alloc] initWithObjects:@"jj", nil];
    [rr3 release];
    [rr3 autorelease];

Case6:
    NSArray *rrr3 = [[NSArray alloc] initWithObjects:@"jj", nil];
    [rrr3 autorelease];
    [rrr3 release];

Case7:
    NSMutableArray *rr2 = [[NSMutableArray alloc] initWithObjects:@"jj", nil];
    [rr2 release];
    [rr2 autorelease];

Case8:
    NSMutableArray *rr2 = [[NSMutableArray alloc] initWithObjects:@"jj", nil];
    [rr2 autorelease];
    [rr2 release];

Upvotes: 0

Views: 64

Answers (1)

zaph
zaph

Reputation: 112855

All are are incorrect because eventually all will be released twice, but some may coincidentally not crash.

The alloc allocates the object with a retain count of 1. release decreases the retain count 1. autorelease eventually decreases the retain count 1. That means that all are over released.

But as @Chuck mentions some instances are constants, are created at compile time and never released so release and autorelease can be called to many tines with no crash.

String constants are one instance of this this where over-releasing will not cause a crash:
NSString *s = @"aa";
Even over-releasing this is OK because the compiler is smart enough:
NSString *s = [NSString stringWithString:@"aa"];
But you will get a warning from the current LLVM compiler that using stringWithString with a literal is redundant.

Upvotes: 3

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