My program sometimes crashes when the following code is called and I can’t figure out why. I get a sigbus error from NSIntersectionRange(). When I break on my method and try to step through it everything is fine, the program doesn’t crash. Can someone with a better understanding of pointers help me figure this out?

The code below is supposed to remove the NSLinkTextAttribute from an NSAttributedString in my textView.

• (IBAction)removeAnnotation:(id)sender {

  if ( [textView selectedRange].length == 0) { return; }

  // if it’s the whole range remove it from the annotations array NSRangePointer annotationRange; // if this returns nil the selected text is not linked // this also fills annotationRange id attribute = textView textStorage] attribute:[[NSLinkAttributeName atIndex:[textView selectedRange].location longestEffectiveRange:annotationRange inRange:NSMakeRange(0,textView textStorage] length])];

  if (attribute == nil) { // should never happen return; } else {

    if ([[NSEqualRanges([textView selectedRange], *annotationRange)) {
        AVNRannotation *thisNote = textView textStorage] 
            attribute: [[NSLinkAttributeName
            atIndex: [textView selectedRange].location
            effectiveRange:NULL];
  		
        [self willChangeValueForKey:@"annotationList"];
        [self document] annotations] removeObject: thisNote];
        [self didChangeValueForKey:@"annotationList"];
    }   }
  

  [[textView textStorage] removeAttribute:[[NSLinkAttributeName range:[textView selectedRange]]; self document] updateChangeCount:[[NSChangeDone]; }

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Both the original post and the reply above belie a horrible misunderstanding of the situation. (No offense, it’s just the kind of thing that will make horrible, hard-to-find bugs.)

The attribute:… method asks for an NSRangePointer because it’s returning an NSRange. Thus, you should not be passing it a variable NSRangePointer, initialized to nil or otherwise. What you should be doing is passing it a pointer to an existing NSRange, like this:

NSRange annotationRange; id attribute = textView textStorage] attribute:[[NSLinkAttributeName atIndex:[textView selectedRange].location effectiveRange:&annotationRange];

The range will be returned to the range variable.

When something asks for a pointer, you must always give it a pointer that is either nil or points to something interesting. If the pointer is used to return information, it must point to some space for that information.

To whom:

Thanks for the info. That worked perfectly. I have been able to get along with very little knowledge of C so far but this one bit me. I edited your post for clarity. Thanks for correcting my laziness, it’s much easier to read now.

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Pointers are the most important thing you could possibly know about C. If you don’t know about them, that will be the cause of about 70% of your problems.