index 0 beyond bounds for empty array error - iphone

Question

I don't understand on how to debug this error message:
2011-02-01 20:45:56.151 NeMe[3206:207] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[NSMutableArray objectAtIndex:]: index 0 beyond bounds for empty array'
*** Call stack at first throw:
(
0 CoreFoundation 0x027deb99 __exceptionPreprocess + 185
1 libobjc.A.dylib 0x0292e40e objc_exception_throw + 47
2 CoreFoundation 0x027d4695 -[__NSArrayM objectAtIndex:] + 261
3 NeighborMe 0x0000f617 -[NeighborMapViewController regionFromLocations] + 65
4 NeighborMe 0x0001047b -[NeighborMapViewController locationManager:didUpdateToLocation:fromLocation:] + 94
5 CoreLocation 0x02393870 -[CLLocationManager onClientEventLocation:] + 793
6 CoreLocation 0x0239218b OnClientEvent + 49
7 CoreLocation 0x023a8a83 _Z22CLClientInvokeCallbackP10__CLClient13CLClientEventPK14__CFDictionary + 47
8 CoreLocation 0x023a9b2c _Z27CLClientHandleDaemonDataFixP10__CLClientPK23CLDaemonCommToClientFixPK14__CFDictionary + 290
9 CoreLocation 0x023acb30 _Z24CLClientHandleDaemonDataP12__CFMachPortPvlS1_ + 1125
10 CoreFoundation 0x02720982 __CFMachPortPerform + 338
11 CoreFoundation 0x027bfff4 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 52
12 CoreFoundation 0x02720807 __CFRunLoopDoSource1 + 215
13 CoreFoundation 0x0271da93 __CFRunLoopRun + 979
14 CoreFoundation 0x0271d350 CFRunLoopRunSpecific + 208
15 CoreFoundation 0x0271d271 CFRunLoopRunInMode + 97
16 GraphicsServices 0x030bd00c GSEventRunModal + 217
17 GraphicsServices 0x030bd0d1 GSEventRun + 115
18 UIKit 0x002eeaf2 UIApplicationMain + 1160
19 NeighborMe 0x00002818 main + 102
20 NeighborMe 0x000027a9 start + 53
21 ??? 0x00000001 0x0 + 1
)
terminate called after throwing an instance of 'NSException'
There is NSMutableArray in this code... so how is this possible?

Answer 1

You have an empty array. You tried to call [array objectAtIndex:0]. 0 is beyond the bounds of an empty array (not surprising – anything is beyond the bounds for an empty array).

Answer 2

It means that early in [NeighborMapViewController regionFromLocations] you are attempting to index an NSMutableArray object. That array has zero elements in it -- it's empty. But you're apparently trying to access index 0, which would be the first element. Since there is no first element, you get an exception.
Probably the code that you expect to have executed to add items to the array has not yet executed, or you simply need to check the length of the array prior to trying to access the element at index 0. It's hard to say without knowing more about what you're doing.
gdb reports the offset as 65 bytes in to the function, so it's likely in one of the first few lines. You could probably manually inspect the code of the function to see, or set a breakpoint on the first line of the function and step through it.

Answer 3

I was seeing this error, however, not as an exception but only in the Issue Navigator. The solution was to simply restart XCode, then the error was gone.

Answer 4

As Kevin Ballard said, this error is thrown when you ask for the element at index X that is beyond array bounds, in addition to looking for [array objectAtIndex: X], this error may be even caused from the modern syntax array[X]