How can I check what hardware my iPhone app is running on?

I'm writing an app that needs to fun开发者_JAVA技巧ction differently if it is running on different models of the iPhone/iPod Touch. How can I check if the app is running on 3GS, 3G or other?

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See here:

how do I detect whether I have iPhone 2G,3G,3GS

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The UIDevice class provides some information like this.

But you're probably much better off testing for capabilities ("does this device support compass headings?") than for specific models ("is this device a 3GS?"). What is it that you're trying to do?

Edit: for the specific example I presented above, see the headingAvailable property of CLLocationManager. It will be YES if and only if heading information can be obtained from the device.