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cast of Objective-C pointer type 'NSString *' to C pointer type 'CFStringRef' (aka 'const struct __C

2017-05-20 10:58 831 查看

第一步：

第二步：

http://stackoverflow.com/questions/6725558/cast-of-objective-c-pointer-type-nsstring-to-c-pointer-type-cfstringref-a

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?

objective-c casting automatic-ref-counting

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edited Oct
8 '14 at 5:31

Jayprakash
Dubey

12.5k28188

asked Jul 17 '11 at 17:37

Michael
Rowe

2671518

You can use '_bridge' or 'CFBridgingRetain' to resolve this error. – Jayprakash
Dubey Oct
8 '14 at 4:57

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3 Answers

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up
vote56down
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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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this answer

edited Jul
17 '11 at 18:57

answered Jul 17 '11 at 17:52

jtbandes

75.7k25162197

Thanks, understand.. and the link ont he ARC Documentation was very helpful on
the type of __bridge cast to use. – Michael
Rowe Jul
17 '11 at 21:55

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up
vote18down
vote

Here is a
nice ARC tutorial that I found to be easier to understand than Apple's documentation that @jtbandes references.

Take a look at the section titled "Toll free bridging" in particular.

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this answer

answered Oct 2 '11 at 4:15

benvolioT

3,82312629

Awesome ARC explanation with clear

__bridge

examples. – dontangg Jun
8 '12 at 22:37

Mike's posts are always awesome. – orange80 Dec
29 '12 at 5:34

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I know this is an old thread, I came across this issue while I need to use

- (NSString *)URLEncodedString
{
NSString *result = (NSString *)CFURLCreateStringByAddingPercentEscapes(kCFAllocatorDefault,
(CFStringRef)self,
NULL, CFSTR("!*'();:@&=+$,/?%#[]"),
kCFStringEncodingUTF8);
[result autorelease];
return result;
}

So what I did is go to Target > Build phase > Compile sources. There is your file listed, double
click on that and add following lines next to your file.

-fno-objc-arc

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