Break on EXC_BAD_ACCESS in Xcode?

Question

I\'m new to iPhone development and Xcode in general and have no idea how to begin troubleshooting an EXC_BAD_ACCESS signal. How can I get Xcode to break at the

Answer 1

For any EXC_BAD_ACCESS errors, you are usually trying to send a message to a released object. The BEST way to track these down is use NSZombieEnabled.

This works by never actually releasing an object, but by wrapping it up as a "zombie" and setting a flag inside it that says it normally would have been released. This way, if you try to access it again, it still know what it was before you made the error, and with this little bit of information, you can usually backtrack to see what the issue was.

It especially helps in background threads when the Debugger sometimes craps out on any useful information.

VERY IMPORTANT TO NOTE however, is that you need to 100% make sure this is only in your debug code and not your distribution code. Because nothing is ever released, your app will leak and leak and leak. To remind me to do this, I put this log in my appdelegate:

if(getenv("NSZombieEnabled") || getenv("NSAutoreleaseFreedObjectCheckEnabled"))
  NSLog(@"NSZombieEnabled/NSAutoreleaseFreedObjectCheckEnabled enabled!");

If you need help finding the exact line, Do a Build-and-Debug (CMD-Y) instead of a Build-and-Run (CMD-R). When the app crashes, the debugger will show you exactly which line and in combination with NSZombieEnabled, you should be able to find out exactly why.

Answer 2

A new answer to an old thread... in XCode 4 the most effective way to diagnose EXC_BAD_ACCESS exceptions is to use Instruments to profile your app (from XCode click Product/Profile and choose Zombies). This will help you identify messages sent to deallocated objects.

Answer 3

Before enabling zombies I recommend first get rid of all warnings (if you have any). Simple things like a non void function without a returncan cause this error. If you don't have warnings proceed as the other answers suggest.

Answer 4

I hope I didn't miss an identical answer, but I've found that it's possible for some projects to throw this error due to running on simulators for older iOS versions that may be incompatible with a project dependency or framework. I was chasing one of these down for too long before realizing it was just happening in the -older- simulator versions, like iPhone 4S, the app wasn't even supposed to try to support.

Would have been nice to have gotten a more verbose error message, but I would imagine that's the responsibility of the framework where it originated... At any rate, this is a fairly common search landing and maybe this will help someone goofing up as badly as I found myself.