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Re: how to set NavDialogCreationOptions strings

on 7/29/04 5:37 PM, Frederick Cheung <email@hidden> wrote:

>
> On 30 Jul 2004, at 02:05, Scott Thompson wrote:
>>>> Why isn't that a memory leak?
>>>>
>>> Well it's not a memory leak if you don't own those strings.
>>
>> It could, potentially, be a memory leak, but there's no way for you to
>> know.
>>
>> I strongly suspect, however, that it is not.
>>
>> At the very least, the operating system is probably expecting to use
>> the same strings every time you create default dialog options. If you
>> were to free those strings out from under the Navigation Services
>> framework, that would be a Bad Thing
>>
>> If I had to guess at how Navigation services is implemented, however, I
>> would say that you couldn't really "free" those strings even if you
>> tried. The operating system is probably creating a CFString from a
>> static string somewhere using the same technology that sits behind the
>> CFSTR macro. With such objects you can pretty much think of the string
>> as being created at compile-time and stored in the program's global
>> data.
>>
> Well it's more likely to be a CFCopyLocalizedString type thing.
>> As I understand, these strings can actually participate in
>> retain-release semantics. Since the memory can't actually be freed,
>> however, releasing them enough that they should be freed is actually
>> an unsupported operation with undefined behavior (at least according to
>> engineers at Apple).
>>
> I seem to recall that conceptually CFSTR(foo) actually calls through to
> cfstringcreatewithcstring (cacheing results of course), although that
> is of course an implementation detail that may have changed, i note
> that gcc has an fconstant-cfstrings switch. Whatever they are, they do
> behave as you would expect any cftype to: releaseing them more times
> than you have retained/copied/created them is definitely bad mojo.
>
> Anyway, i got bored and had a quick look, as i had guessed earlier, all
> the strings are set to NULL, so there's no leaking whatever you do.

Yes, that makes sense. But I hate to depend on observed undocumented
behavior as the source of information used in defining best practices.

-Kurt
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References: 
 >Re: how to set NavDialogCreationOptions strings (From: Frederick Cheung <email@hidden>)



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