On Jun 9, 2013, at 1:32 PM, Kyle Sluder <[email protected]> wrote: > On Jun 9, 2013, at 1:26 PM, Boyd Collier <[email protected]> wrote: >> Quite by chance, I stumbled on to what seems to be an error that ought to be >> caught by the compiler but wasn't. Here's an example: >> >> NSNumber *testNumber = [NSNumber numberWithInt:5]; >> int testInt = (int)testNumber; >> >> […snip…] >> >> Should I file a bug report or is this a well-known anomaly that I've just >> come across? > > Sitting on a runway right now, so I can't double-check the C spec, but I > believe this is a consequence of C's use of integers for truth types. > > A pointer must be convertible to integer type, because it can be used in the > form `if (expressionOfPointerType)`. It follows that casting to int must also > be allowed. I'm not sure what the spec says about the actual value of the > result.
Explicitly converting a pointer to an integer type (other than _Bool/bool) reinterprets the bit-representation of the pointer as an integer. There are a lot of low-level tricks you can then play with that. Of course, you need to use an integral type that's large enough to store the pointer value. Playing with the bit-representation of Objective-C pointers specifically is ill-advised because the implementation reserves the right to play its own games with object pointers (such as the optimized representation of integer values when boxed as NSNumbers on 64-bit platforms), but nonetheless this behavior is inherited from C and cannot really be changed. John. _______________________________________________ Cocoa-dev mailing list ([email protected]) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to [email protected]
