Weak linking on iPhone refuses to work

Question

I\'ve got an iPhone app that\'s mainly targetting 3.0, but which takes advantage of newer APIs when they\'re available. Code goes something like this:

if (UI         


        

Answer 1

Here is what I had to do when checking for an external framework constant.

const CLLocationAccuracy * ptr = &kCLLocationAccuracyBestForNavigation;
BOOL frameworkSupports = (ptr != NULL);
if (frameworkSupports) {
    return kCLLocationAccuracyBestForNavigation;
} else {
    return kCLLocationAccuracyBest;
}

It would not work without the ptr variable.

Answer 2

Aaand I figured it out. For symbols that are not functions (extern const int foobar, for instance), you have to compare against the address of the symbol, not the symbol itself, so:

if (&UIApplicationWillEnterForegroundNotification != NULL)
    etc;

Which in retrospect is kind of obvious, but I still fault the entire universe around me for not ever mentioning the distinction.