Michael Rowe Michael Rowe - 2 months ago 12
Objective-C Question

cast of Objective-C pointer type 'NSString *' to C pointer type 'CFStringRef' (aka 'const struct __CFString *') requires a bridged cast

When converting an Objective-C program to a Objective-C ARC, I get the error:

"cast of Objective-C pointer type 'NSString *' to C pointer type 'CFStringRef' (aka 'const struct __CFString *') requires a bridged cast "


The code is as follows:

- (NSString *)_encodeString:(NSString *)string
{
NSString *result = (NSString *)CFURLCreateStringByAddingPercentEscapes(NULL,
(CFStringRef)string, // this is line in error
NULL,
(CFStringRef)@";/?:@&=$+{}<>,",
kCFStringEncodingUTF8);
return [result autorelease];
}


What is a bridged cast?

Screenshot for error

Answer

Have a look at the ARC documentation on the LLVM website. You'll have to use __bridge or one of the other keywords.

This is because Core Foundation objects (CF*Refs) are not controlled by ARC, only Obj-C objects are. So when you convert between them, you have to tell ARC about the object's ownership so it can properly clean them up. The simplest case is a __bridge cast, for which ARC will not do any extra work (it assumes you handle the object's memory yourself).

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