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Editorial Team
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Asked: 2026-05-13T13:27:11+00:00

I’ve gotten stung by a bug that I just can’t figure out how to

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I’ve gotten stung by a bug that I just can’t figure out how to debug. Basically I run my code on the simulator and everything is just fine.

When I go to the actual device however, I get a EXC_BAD_ACCESS error. Unfortunately, when running on the phone under the debugger the damned thing works just fine, so I have no way to judge where the error is occurring.

I did get one stack trace that I couldn’t reproduce, so I’m pretty sure that the line in my code that is causing the problem is this one (but I can’t for the life of me figure out how it could be):

[[NSNotificationCenter defaultCenter] postNotificationName:@"SubscriberChanged" object: nil];

The actual error was on an objc_msgSend about four frames below this line, but its in code that appears to be part of the iPhone SDK, so I don’t have the source to inspect it.

Can anyone give me a few pointers on how I might go about figuring out where this problem is? I have a deadline to ship this thing and I can’t let it go out like this…

I finally managed to reproduce this in the debugger. The stack trace I get is as follows:


#0  0x30011940 in objc_msgSend ()
#1  0x3054dc80 in _nsnote_callback ()
#2  0x3024ea58 in _CFXNotificationPostNotification ()
#3  0x3054b85a in -[NSNotificationCenter postNotificationName:object:userInfo:] ()
#4  0x3054dbc0 in -[NSNotificationCenter postNotificationName:object:] ()
#5  0x000027c6 in -[My2CentsAppDelegate handleMOCChange:] (self=0x1159d0, _cmd=0x2bf90, notification=0x147400) at /Users/sdussin/Desktop/UPOD Research LLC/Development/My2Cents/Classes/My2CentsAppDelegate.m:52
#6  0x3054dc80 in _nsnote_callback ()
#7  0x3024ea58 in _CFXNotificationPostNotification ()
#8  0x3054b85a in -[NSNotificationCenter postNotificationName:object:userInfo:] ()

Frame #5 in the stack trace corresponds to the line above.

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1 Answer

  1. Editorial Team

    If you can’t repeat your crash in the debugger, you might try other approaches to tackle it:

    • Review the code (perhaps ask a friend or coworker for a code review)
    • Add logging and assertions
    • Activate all (or at least most) compiler warnings and obey them
    • Make sure to use the [] clang2 static analyzer and obey its warnings

    Especially clang is quite good at finding memory management bugs. And EXC_BAD_ACCESS smells like one.

    Probably one of the observers that you registered with NSNotificationCenter was released. Remember,

    Important: The notification center
    does not retain its observers,
    therefore, you must ensure that you
    unregister observers (using
    removeObserver: or
    removeObserver:name:object:) before
    they are deallocated. (If you don’t,
    you will generate a runtime error if
    the center sends a message to a freed
    object.)

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