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Re: static CFSTR in C

On Wed, 27 Aug 2003, Laurence Harris wrote:

> >> A while back, Steve Zellers posted the following:
> >>
> >>> CFSTR, when compiled on 10.2 or later with GCC 3.x with
> >>> -fconstant-cfstrings will lay out a memory object with your CFString in
> >>> your TEXT section; it'll be as efficient as possible.
> >>
> >> So in this case, using a macro as Jim suggested will do essentially what you
> >> want.
> >>
> >> Otherwise, CFSTR is actually a function which takes a key and returns a
> >> CFStringRef, and you can't do that with a global (outside a function)
> >> variable. Or at least I've never figured out a way to do it.
> >
> > You can with C++.
>
> Well, I don't know how do it with CFSTR(), and I'd like to for improved
> efficiency (see below).

No, it works fine with C++, different rules for initializing global
variables. You can have this outside of any function definition in a C++
source file and it will build and work just fine:

static const CFString yoop = CFSTR("woof");


> Common practice is to use a macro, but with the exception of the above,
> people should understand that CFSTR() really is a function. Basically what's
> going on here is that the system maintains a dictionary of CFStringRefs for
> you. The first time you call CFSTR with a particular key, the system does a
> lookup in that dictionary for an entry with that key, and not finding one,
> it creates a CFStringRef containing the text in the key, adds the
> CFStringRef to the dictionary, and then returns the CFStringRef. Future
> calls to CFSTR() result in the system searching the dictionary and returning
> the CFStringRef corresponding to the key. So there is a performance hit
> here, especially if you're using a CFSTR() call in a loop, for example. I
> don't honestly know how efficient those lookups are, but given all the
> strings you could be defining with CFSTR(), the dictionary could have
> hundreds of entries.
>
> It also explains why you should never release the results of a call to
> CFSTR().

Thanks for the info.

Marc
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 >Re: static CFSTR in C (From: Laurence Harris <email@hidden>)



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