Objective C - getting line number or full stack trace from debugger error?

Question

Is it possible to get a line number for the source code (or anything that helps debug where the problem is) from the debugger, that shows where the problem is originating?

I am getting an error:

-[NSCFArray objectAtIndex:]: index (-1 (or possibly larger)) beyond bounds (9)

which obviously means that I am going out of bounds at some point, however if it possible I would like to get some more information to help me solve the problem.

I am placing a breakpoint and trying to go through the program line by line but it is a tedious process. Thanks!

Answer 1

When the debugger stops, go to the "Debug Navigator" and make sure the slider on the bottom is all the way to the right.

Scan your eye down from the point at which the exception is thrown and you should eventually come to your own code. Click on the appropriate method/function name and the code will be opened in the editor.

If you don't see any of your own methods in the stack trace, the exception may have been passed through a performSelector-style call in which case the stack trace is gone. If this is the case, you may get better information by adding an "On Throw" exception break point. First switch to the "Breakpoint navigator":

Then click on the plus and choose "Add Exception breakpoint..."

Create an "On Throw" break point:

This will stop the debugger at the exact point the exception is thrown, and you get a better stack trace. It's a good idea to have an exception break point like this enabled all the time, although you will occasionally get internal exceptions from Apple code (e.g. when using QLPreviewController, MPMoviePlayerController).

Answer 2

You should also consider using the NSSetUncaughtExceptionHandler. (You can save the crash log to the disk, check next startup if a new crash log was saved, attach it to an email, etc.)

put this into your didFinishLaunchingWithOptions method:

NSSetUncaughtExceptionHandler(&exceptionHandler);

and implement your exception handler:

void exceptionHandler(NSException *exception)
{        
    NSLog(@"%@",[exception name]);
    NSLog(@"%@",[exception reason]);
    NSLog(@"%@",[exception userInfo]);
    NSLog(@"%@",[exception callStackSymbols]);
    NSLog(@"%@",[exception callStackReturnAddresses]);
}