Suppress XCode Analyzer Potential leak of an object stored into a .. error

Question

I have a method that creates an returns an instance of a CoreGraphics object - CGPathRef.

When I run the app through Analyzer it complains that this method is leaking...it is , but it is deliberate. I do want to transfer the ownership to the caller and let them clean up.

What can I do to suppress this Analyzer warning?

- (CGPathRef) createSomePath:(CGPoint)center innerRadius:(CGFloat)innerRadius outerRadius:(CGFloat)outerRadius startAngle:(CGFloat)startAngle endAngle:(CGFloat)endAngle
{
  CGMutablePathRef slicePath = CGPathCreateMutable();

  ....

  return slicePath;  <--- Analyzer points to this line as a potential leak.
}

Assume this should be possible as lots of frameworks return these objects requiring the caller to clean up...

Thanks in advance !

P.S. Am afraid that this question is not a dup nor does not have a proper answer anywhere else...the 3 answers highlighted at the top of this page are not proper/complete...only the answer provided here by Matthias Bauch i.e. "new" rule is truly the right answer to the question I raised :) THANKS!

@moonwalker It isn't magic; `Create` is CF* nomenclature. `+new` is Objective-c nomenclature. `+create` means nothing in Objective-C. — bbum, Jun 25 '13 at 20:14
@bbum - of course I do realize it is the "create rule" -- magic is just a figure of speech..:) — Moonwalker, Jun 26 '13 at 07:23

score 10 · Accepted Answer · answered Jun 25 '13 at 19:06

CoreFoundation functions follow the "create rule". If the function has a "Create" in it it returns an object with a reference count of 1.

Unfortunately your method is not a c function.

So you should turn your Objective-C method into a C function. Something like this:

CGPathRef CreatePath(CGPoint center, CGFloat innerRadius, CGFloat outerRadius, CGFloat startAngle, CGFloat endAngle) {
    // your code here
}

This should please the analyzer and work correctly with ARC.

In a Objective-C method you can get similar behaviour by starting your method signature with new, alloc, copy or mutableCopy. Starting the method with new probably fits your case best.
Something like this should please the analyzer, but I am not sure if it works correctly with ARC. You have to profile this.

- (CGPathRef)newPath:(CGPoint)center innerRadius:(CGFloat)innerRadius outerRadius:(CGFloat)outerRadius startAngle:(CGFloat)startAngle endAngle:(CGFloat)endAngle {
    // your code here
}

Awesome - newPath worked for Analyzer. Assume ARC will not have a problem with it but will keep an eye on it.... Thank you Matt. Accept this answer — Moonwalker, Jun 25 '13 at 19:17

woz · Answer 2 · 2013-06-25T19:01:24.463

0

You should be able to do this:

#ifndef __clang_analyzer__
CGMutablePathRef slicePath = CGPathCreateMutable();
#endif

I can't say I recommend it though!

edited Jun 25 '13 at 19:01

answered Jun 25 '13 at 18:13

woz

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Did this not work? I just tested it myself and it's working for me. – woz Jun 25 '13 at 18:22
Oh, sorry! I wasn't sure who it was. Is this only when you run *Product > Analyze*? – woz Jun 25 '13 at 18:54
yes...and if you put the #ifndef around the assignment CGMutablePathRef slicePath = CGPathCreateMutable(); rather than return it does work...I already up voted your answer form -1 to 0... :) – Moonwalker Jun 25 '13 at 18:56
Oh, thanks! I edited my answer; does that look like what's working for you? It's also working for me when I do it that way. – woz Jun 25 '13 at 19:02
yes...it suppresses the warning with correction...however I do not understand the drawbacks of using this approach...can you share you thoughts ? – Moonwalker Jun 25 '13 at 19:03
If you work with other developers, they may not expect to have to manage memory whenever they call your method. Passing a CGRefPath by reference is a possible alternative. – woz Jun 25 '13 at 19:12

Suppress XCode Analyzer Potential leak of an object stored into a .. error

2 Answers2