How to copy a NSURL object to an array of CFURL structs

Question

I have an ivar that is a 'plain' C array of CFURLRef structs. I call this sourceURLArray. I initialize it to hold six elements.

Later on, in a function, I create (alloc/init) an NSURL* object. I call it fileURL and I want to save a copy of that object into the first element of the aforementioned array. I thought all I needed to do was this:

        sourceURLArray[0] = (__bridge CFURLRef)([fileURL copy]);

However when I execute the code I get message sent to deallocated instance messages the second time through the function. Upon inspection of the variables, after the line above executes, sourceURLArray[0] holds the same address as fileURL. Since fileURL goes out of scope when the function completes the address in sourceURLArray[0] is deallocated.

It seems I'm misunderstanding something fundamental about either copying, nuances with toll-free bridging, or both.

Could you provide more code? Where exactly (on which line) application fails? Do you have any global/static variables involved? I'm not sure that failure is related to the line you show — SergGr
– SergGr, Commented Dec 7, 2012 at 20:06
Alternatively, make the ivar a C array of NSURL* and ARC should do the right thing. — tc.
– tc., Commented Dec 7, 2012 at 20:24
Yeah, I considered that, but I have other functions already written that are expecting CFURLRefs out of this same array. — Nick
– Nick, Commented Dec 7, 2012 at 22:00

rmaddy · Accepted Answer · 2012-12-07 19:55:51Z

1

Try:

sourceURLArray[0] = (__bridge_retained CFURLRef)([fileURL copy]);

or:

sourceURLArray[0] = (CFURLRef)CFBridgingRetain([fileURL copy]);

This tells ARC that you are transferring ownership to the other array. You must now properly call CFRelease on the CFURLRef at some point.

answered Dec 7, 2012 at 19:55

rmaddy

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2 Comments

Nick Over a year ago

Thanks for the suggestion! When I try that the compiler complains that Cast of Obj-C pointer type id to C pointer type 'CFURLRef' cannot use __bridge_transfer. It suggests using CFBridgingRetain instead, which worked! Thanks so much for your help!

evanchin Over a year ago

__bridge_retained equals to CFBridgingRetain, which is correct in rmaddy's answer. You just have a typo in your code with "__bridge_transfer" which equals to CFBridgingRelease.

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