Objective-C Bitmask Enumeration Essentials

http://www.pumpmybicep.com/2014/05/22/objective-c-bitmask-enumeration-essentials

by pumpmybicep • 12 years ago

13 7 12 years ago

anon1385• 12 years ago

Use the bitwise AND operator & to check for a selected bitmask enumeration value.

You should take care if you store result of this in a BOOL (or pass it to a method or function that takes a BOOL). BOOL is only char big and plenty of common Cocoa bitmasks don't have any bits set in that range. For example NSEventMaskEndGesture is (1<<20).

  NSEventMask mask = NSEventMaskEndGesture;
  BOOL end = mask & NSEventMaskEndGesture;
  if (!end) NSLog(@"Oops");

MaxGabriel• 12 years ago

Is this the correct approach?

    BOOL end = mask & NSEventMaskEndGesture ? YES : NO;

al_gore2• 12 years ago

or just != 0

plorkyeran• 12 years ago

(mask & NSEventMaskEndGesture) == NSEventMaskEndGesture is the most correct, as it handles the case where NSEventMaskEndGesture has multiple bits set.

ridiculous_fish• 12 years ago

I think, not!!

   BOOL end = !! (mask & NSEventMaskEndGesture);

Like a little pair of surprised eyes.

Also works for pointers:

    BOOL hasError = !! errorObj;

al_gore2• 12 years ago

This is just plain old C (which, yes, Objective-C is a superset of).

tonysuper• 12 years ago

Isn't this applicable to any kind of bitmask, and not just Obj-C?

I suppose that Cocoa uses bitmasks fairly often, but this article could have been titled "Working With Bitmasks in C" and it would have been just as accurate.

Objective-C Bitmask Enumeration Essentials

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