Re: how to set NavDialogCreationOptions strings

• Subject: Re: how to set NavDialogCreationOptions strings
• From: OL&L Lists <email@hidden>
• Date: Thu, 29 Jul 2004 17:40:25 -0700

On Jul 29, 2004, at 6:17 PM, Frederick Cheung wrote:

On 30 Jul 2004, at 00:37, Kurt Bigler wrote:

gs just replace
the ones that are there with your own CFStringRefs.

First I thought these strings must be mutable else it would be
unsafe to
modify the strings in NavDialogCreationOptions. But maybe I am
expected to
dispose the old strings and create new ones to assign to the fields?
Otherwise--I could not find an API to reassign the value of a
mutable string.
Doing a replace operation seems like overkill.

They are not mutable (if they were they would be
CFMutableStringRefs).
I wouldn't release the strings either (you didn't create them so you
shouldn't release them). Just assign your own CFStringRefs into the
fields and ignore the default values.

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.

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).

The thing to keep in mind here, however, is that you didn't allocate
those strings so you are not responsible for releasing them. If it is
a memory leak... it's the OSes fault and not yours.

--
Macintosh Software Engineering Consulting Services
Visit my resume at <http://homepage.mac.com/easco/RSTResume.html>

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