Apple did not post any alternative code for this on the Apple Developer site.
The equivalent code to
// C way
UInt32 category = kAudioSessionCategory_MediaPlayback ;
OSStatus result = AudioSessionSetProperty(
kAudioSessionProperty_AudioCategory, sizeof(category), &category ) ;
if( result ) // handle the error
Is
// Objective-C way
NSError *nsError;
[[AVAudioSession sharedInstance]
setCategory:AVAudioSessionCategoryPlayback error:&nsError];
if( nsError != nil ) // handle the error