It seems that the author thinks that Unix typically shows leap seconds to the application programmer? In fact, there aren't leap seconds there unless you intentionally turn that feature on. The seconds you get with the time() call will increment one by one. You will not have to care that leap second occurred. If you want to see leap seconds, then it is assumed that you know what you are doing. If you don't know the effects of that, please, please don't turn it on and don't write about how it's broken.

If you want to learn more about leap seconds read: http://www.cl.cam.ac.uk/~mgk25/time/leap/