Yesterday, I was messing around building shared NSLayoutConstraint code to be used across iOS and OS X. I put in a few #if TARGET_OS_MAC directives, assuming they'd just work.
They didn't.
Turns out that you should always check for TARGET_OS_IPHONE first, before TARGET_OS_MAC because the latter is true on the iPhone but the former is not on OS X.
Here are some of the most common checks suggested to me yesterday as I messed with this dilemma.
#if TARGET_OS_MAC
#if TARGET_OS_IPHONE
#if TARGET_IPHONE_SIMULATOR
#if TARGET_OS_EMBEDDED
#if defined(__MAC_OS_X_VERSION_MIN_REQUIRED)
#if defined(__IPHONE_OS_MIN_VERSION_REQUIRED)
And here are the results of running them on the Simulator,
