iOS sigbart abort crash - ios

Question

I am experiencing a random crash in the following method:
- (void) addLineToVCard:(NSMutableString **)vCard forKey:(NSString *)key setValue:(NSString *)value
{
[*vCard appendString:[NSString stringWithFormat:#"%#:%#\r\n", key, value]];
}
and I'm calling this as:
NSMutableString* vCard = [NSMutableString string];
[self addLineToVCard:&vCard forKey:#"BEGIN" setValue:#"VCARD"];
[self addLineToVCard:&vCard forKey:#"VERSION" setValue:#"3.0"];
What am I doing wrong ? I could avoid this by passing a reference instead of a pointer object. But I would like to know the reason of crash here.
The crash log:
Crashed: com.apple.main-thread
0 libsystem_kernel.dylib 0x251e6c5c __pthread_kill + 8
1 libsystem_pthread.dylib 0x25290733 pthread_kill + 62
2 libsystem_c.dylib 0x2517b0ad abort + 108
3 libsystem_malloc.dylib 0x252180ad free_list_checksum_botch + 362
4 libsystem_malloc.dylib 0x252181db free_tiny_botch + 66
5 CoreFoundation 0x255332d3 __CFStringChangeSizeMultiple + 1838
6 CoreFoundation 0x2553178b __CFStringCheckAndReplace + 554
7 CoreFoundation 0x25491557 -[__NSCFString appendString:] + 26
8 iPhoneHandheldACT 0x1ae7cf -[ContactDetailViewController addLineToVCard:forKey:setValue:] (ContactDetailViewController.m:3009)
9 iPhoneHandheldACT 0x1ae515 -[ContactDetailViewController assembleVCard:] (ContactDetailViewController.m:2987)
10 iPhoneHandheldACT 0x1adcbd -[ContactDetailViewController shareVCard:] (ContactDetailViewController.m:2927)
11 iPhoneHandheldACT 0x1ad351 __47-[ContactDetailViewController btnSharePressed:]_block_invoke (ContactDetailViewController.m:2813)
12 UIKit 0x29f2cbd9 -[UIAlertController _fireOffActionOnTargetIfValidForAction:] + 68
13 UIKit 0x29f2d283 __85-[UIAlertController _dismissAnimated:triggeringAction:triggeredByPopoverDimmingView:]_block_invoke + 30
14 UIKit 0x29e237e3 -[UIPresentationController transitionDidFinish:] + 1230
15 UIKit 0x29e26a85 __56-[UIPresentationController runTransitionForCurrentState]_block_invoke_2 + 192
16 UIKit 0x29c04157 -[_UIViewControllerTransitionContext completeTransition:] + 90
17 UIKit 0x29b11ba5 -[UIViewAnimationBlockDelegate _didEndBlockAnimation:finished:context:] + 540
18 UIKit 0x29b11685 -[UIViewAnimationState sendDelegateAnimationDidStop:finished:] + 204
19 UIKit 0x29b1157f -[UIViewAnimationState animationDidStop:finished:] + 78
20 QuartzCore 0x27b71689 CA::Layer::run_animation_callbacks(void*) + 252
21 libdispatch.dylib 0x250c980f _dispatch_client_callout + 22
22 libdispatch.dylib 0x250d7ba9 _dispatch_main_queue_callback_4CF$VARIANT$mp + 1524
23 CoreFoundation 0x2551db6d __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 8
24 CoreFoundation 0x2551c067 __CFRunLoopRun + 1574
25 CoreFoundation 0x2546b229 CFRunLoopRunSpecific + 520
26 CoreFoundation 0x2546b015 CFRunLoopRunInMode + 108
27 GraphicsServices 0x26a5bac9 GSEventRunModal + 160
28 UIKit 0x29b3f189 UIApplicationMain + 144
29 iPhoneHandheldACT 0xcbe21 main (main.m:16)
30 libdispatch.dylib 0x25113873 (Missing)

Answer 1

The pointer's pointer is not necessary, just like this:
- (void)addLineToVCard:(NSMutableString *)vCard forKey:(NSString *)key setValue:(NSString *)value
{
[vCard appendFormat:#"%#:%#\r\n", key, value];
}
Then use it:
NSMutableString* vCard = [NSMutableString string];
[self addLineToVCard:vCard forKey:#"BEGIN" setValue:#"VCARD"];
[self addLineToVCard:vCard forKey:#"VERSION" setValue:#"3.0"];
The result:
(lldb) po vCard
BEGIN:VCARD
VERSION:3.0