Re: Framework Weak Linking Weirdness
Re: Framework Weak Linking Weirdness
- Subject: Re: Framework Weak Linking Weirdness
- From: David Aames <email@hidden>
- Date: Sat, 7 Jul 2007 12:50:55 +0100
Hi,
Why do you think I'm comparing the return value of the function? The
function is never called (I have no () after the function name) so
I'm always comparing the address of the function.
Thanks,
David
On 7 Jul 2007, at 12:40, Dominik Pich wrote:
Well in the first case you compare the return value of the function
(a BOOL) while in the second case you compare the function pointer
to nil.
I dont think C specifies 'ret = BOOL from Null Pointer Function'
....
so comparing ret doesnt do it.
Regards,
Dominik
Am 07.07.2007 um 13:18 schrieb David Aames:
Hi all,
I've been experimenting with weak linking a simple framework. To
strip out all the unnecessary parts, my framework only contains
one C function. The function signature is BOOL isFrameworkAvailable
(void); The purpose of this function is for the user of the
framework to determine whether the framework is available because
if it is the linker will assign it a valid address.
Now here comes the tricky part. Because I'm weakly linking the
whole framework I pass "-weak_framework MyFrameworkName" as Other
Linker Flags. This works as expected. If I run the application and
the framework is in place and I do a comparison like if
(isFrameworkAvailable == NULL) - it evaluates to false. Here's the
problem. If I delete the framework and re-run the app it still
doesn't equal NULL (here's the catch). But if I do something like:
void* ptr = isFrameworkAvailable;
if(ptr == NULL)
Now this comparison returns true as supposed. The question is why
do I have to go through that intermediate stage? Is this a bug or
I'm not doing things properly? I should note that if I print out
isFrameworkAvailable using NSLog it prints the value as 0x0 but
compared to 0x0 doesn't return true (I find this weird).
The solution which I found is to apply __attribute__
((weak_import)) to the function signature. But I thought that if I
link to the whole framework weakly (-weak_framework) then the
compiler adds this declaration to all symbols.
On a side note, there is no way to apply the weak link attribute
to a ObjC class because really when it's compiled it's a call to
objC_msgSend. So all classes are kind of weakly linked by default,
am I right? Or not?
Many thanks,
David
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