Re: objc_msgSend problems on x86
Re: objc_msgSend problems on x86
- Subject: Re: objc_msgSend problems on x86
- From: Rosyna <email@hidden>
- Date: Thu, 9 Feb 2006 05:18:00 -0700
Ack, at 2/9/06, Nicko van Someren said:
On 9 Feb 2006, at 10:25, Rosyna wrote:
I've noticed when running code like:
bool isEqual=objc_msgSend(string,
NSSelectorFromString(CFSTR("isEqualToString:")), otherString);
On the PPC will work just fine 100% of the time. If I run the same
code on the ICBMs it'll return true even when the strings weren't
equal at all in some rare cases. It also shows an error in GCC
The error might be conveying useful information. Would you like to
tell us what it says?
If I had typed BOOL instead of bool it would have said something
about casting to a smaller size. But it's bool so it won't (on PPC).
Even worse was trying something like:
if (objc_msgSend(string,
NSSelectorFromString(CFSTR("isEqualToString:")), otherString))
which returns true the far majority of the time even when it the
strings are not equal. However, if I change the code to read:
if ((signed char(*)(id, SEL, id)objc_msgSend)(string,
NSSelectorFromString(CFSTR("isEqualToString:")), otherString))
it always returns the correct value. Is there a reason for this
change between the PPC and the x86?
In your old code you were taking the result of objc_msgSend as a
BOOL; it fails and gives you an error. In the later case you
explicitly tell the compiler that it is something else and it works.
Two things to note: firstly, the function objc_msgSend returns an
id, not a BOOL, which is probably what your error is about.
Secondly, in the Universal Binary Programming Guidelines [1] you'll
find that the BOOL type is represented differently on the Intel
processors compared to how it was on the PPC. The first observation
means that your original code was making an assumption about how
something works and the second observations means that how things
work with respect to BOOL types has changed, so I'm guessing your
code fails because your assumption is no longer correct.
Where are you seeing this in the universal programming guidelines?
BOOL and bool are two distinct types. bool has changed on the ICBMs
but I don't see any indication that the behaviour of BOOL has.
if (objc_msgSend(string,
NSSelectorFromString(CFSTR("isEqualToString:")), otherString))
The above code produces no error. But it does not work 100% of the
time on the ICBMs. It works 100% of the time on the PPCs. Whether it
works or not on the ICBMs seems to be a total crapshoot.
--
Sincerely,
Rosyna Keller
Technical Support/Holy Knight/Always needs a hug
Unsanity: Unsane Tools for Insanely Great People
It's either this, or imagining Phil Schiller in a thong.
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