EXC_BAD_ACCESS signal received

Question

When deploying the application to the device, the program will quit after a few cycles with the following error:

Program received signal: \"EXC_BAD_ACCESS\".         


        

Answer 1

A major cause of EXC_BAD_ACCESS is from trying to access released objects.

To find out how to troubleshoot this, read this document: DebuggingAutoReleasePool

Even if you don't think you are "releasing auto-released objects", this will apply to you.

This method works extremely well. I use it all the time with great success!!

In summary, this explains how to use Cocoa's NSZombie debugging class and the command line "malloc_history" tool to find exactly what released object has been accessed in your code.

Sidenote:

Running Instruments and checking for leaks will not help troubleshoot EXC_BAD_ACCESS. I'm pretty sure memory leaks have nothing to do with EXC_BAD_ACCESS. The definition of a leak is an object that you no longer have access to, and you therefore cannot call it.

UPDATE: I now use Instruments to debug Leaks. From Xcode 4.2, choose Product->Profile and when Instruments launches, choose "Zombies".

Answer 2

Not a complete answer, but one specific situation where I've received this is when trying to access an object that 'died' because I tried to use autorelease:

netObjectDefinedInMyHeader = [[[MyNetObject alloc] init] autorelease];

So for example, I was actually passing this as an object to 'notify' (registered it as a listener, observer, whatever idiom you like) but it had already died once the notification was sent and I'd get the EXC_BAD_ACCESS. Changing it to [[MyNetObject alloc] init] and releasing it later as appropriate solved the error.

Another reason this may happen is for example if you pass in an object and try to store it:

myObjectDefinedInHeader = aParameterObjectPassedIn;

Later when trying to access myObjectDefinedInHeader you may get into trouble. Using:

myObjectDefinedInHeader = [aParameterObjectPassedIn retain];

may be what you need. Of course these are just a couple of examples of what I've ran into and there are other reasons, but these can prove elusive so I mention them. Good luck!

Answer 3

Just to add another situation where this can happen:

I had the code:

NSMutableString *string;
[string   appendWithFormat:@"foo"];

Obviously I had forgotten to allocate memory for the string:

NSMutableString *string = [[NSMutableString alloc] init];
[string   appendWithFormat:@"foo"];

fixes the problem.

Answer 4

Don't forget the @ symbol when creating strings, treating C-strings as NSStrings will cause EXC_BAD_ACCESS.

Use this:

@"Some String"

Rather than this:

"Some String"

PS - typically when populating contents of an array with lots of records.

Answer 5

I've been debuging, and refactoring code to solve this error for the last four hours. A post above led me to see the problem:

Property before: startPoint = [[DataPoint alloc] init] ; startPoint= [DataPointList objectAtIndex: 0];
. . . x = startPoint.x - 10; // EXC_BAD_ACCESS

Property after: startPoint = [[DataPoint alloc] init] ; startPoint = [[DataPointList objectAtIndex: 0] retain];

Goodbye EXC_BAD_ACCESS

Answer 6

NSAssert() calls to validate method parameters is pretty handy for tracking down and avoiding passing nils as well.