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Re: [OT] Retain count riddle
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Re: [OT] Retain count riddle


  • Subject: Re: [OT] Retain count riddle
  • From: Stéphane Sudre <email@hidden>
  • Date: Tue, 30 Mar 2004 22:10:33 +0200

On mardi, mars 30, 2004, at 09:49 PM, Sailesh Agrawal wrote:

So I had this bug the other day that I thought would make an interesting
riddle.

The code looked like this:

#define SAFE_SET(old, new) [new retain]; [old release]; old = new;

...

- (void) foo : (NSString*)path {
SAFE_SET(m_Path, [path lastPathComponent]);
}

Now the problem was any time I accessed m_Path my app would crash. This
isn't cocoa specific, I'm just dumb for using macros where I should have
been using a function. Can anyone guess what the problem is ?

Too easy.

Your Macro leads to:

old = [path lastPathComponent];

so old points to an autoreleased object.

So next time you try to access the object, the object points to nothing particular.
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References: 
 >[OT] Retain count riddle (From: "Sailesh Agrawal" <email@hidden>)

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