I got them as a gift , and i dont know if they're the real ones or no.
tip number one: dont buy them from some guy in the street for $20
tip number two: only buy from a dior retailer or their website
tip number three: if the price anywhere else seems to good to be true, it is.
That's a good tip from Phil. And to add, Christian Dior sunglasses are expensive and I guess you can tell the difference from that and of course the quality of the sunglasses itself.
You can have a look at the logo and the frame itself. Most fake ones have a slightly different logo on them and are made of inferior materials. Authentic sunglasses always have a certificate, product labels attacted to them, and an original case. If, at this point, the sunglasses look authentic to you, but you are not certain, you can always take them to a local optician. You can compare it with the models at there store, or ask the optician about his/her opinion. Usually they are very experienced in recognizing real ones from the fake ones (and they do it probably for free if you indicate it was a gift).
Hope this helps!