Pointer changing after function call

Question

Here is some simple points about my problem;

• Using XCode 6.0.1 if that matters, llvm 6.0 with no optimizations (DEBUG)

• This is happening on a separate thread launched with;

  self.ioThread = [NSThread.alloc initWithTarget:self selector:@selector(initData) object:nil].autorelease;
  

• Not using ARC (should not matter)

• First code;

  if (_updatedAt) // A simple C function call
      data[@"updatedAt"] = RFC3339DateString(_updatedAt);
  

• RFC3339DateString function;

  NSString* RFC3339DateString(NSDate* date) {
      if (!date || ![date isKindOfClass:NSDate.class]) return nil;
      NSDateFormatter *rfc3339DateFormatter = NSDateFormatter.new.autorelease;
      NSLocale *enUSPOSIXLocale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"].autorelease;
  
      [rfc3339DateFormatter setLocale:enUSPOSIXLocale];
      [rfc3339DateFormatter setDateFormat:@"yyyy'-'MM'-'dd'T'HH':'mm':'ss'Z'"];
      [rfc3339DateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0]];
      return [rfc3339DateFormatter stringFromDate:date]; // point of crash.
  }
  

So, on the line I marked "point of crash", It says;

-[__NSCFString timeIntervalSinceReferenceDate]: unrecognized selector sent to instance 0x7fdc2870

There are couple strange things in this situration I cannot solve;

• On the first line of the function, I'm already type-checking date object.

• On debugger, when I say po date and p date, these are the results are I get;

  (lldb) po date
  stamp
  
  (lldb) p date
  (NSDate *) $11 = 0x7fdc2870 @"stamp"
  

• And when I go to the function calling RFC3339DateString function and say p _updatedAt and po updatedAt;

  (lldb) p _updatedAt
  (NSDate *) $12 = 0x7fd88a10 class name = __NSDate
  (lldb) po _updatedAt
  2014-09-27 06:37:33 +0000
  

I cannot understand how did the pointers changed in the middle of the way. Does anybody understand the situation?

Screenshot 1; http://cl.ly/image/1n1l1E1i2a3y

Screenshot 2; http://cl.ly/image/2A0s3S2J0S1P

Assembly Code around the code I'm calling RFC3339DateString function; http://pastie.org/private/e7xzc3ntfz0p0d95g5hzw

Answer 1

I would suspect _updatedAt is being overwritten. Sometimes it contains an NSDate and sometimes an NSString. Add a watchpoint to see where it's being written to.

Also, you should never return nil from RFC3339DateString() as that will cause an exception within [NSMutableDictionary addObject:forKey:].

Lastly you don't need so many quotes in that date formatting string, just around 'T' and 'Z'.