How to generate “random” but also “unique” numbers?

Question

How are random numbers generated.? How do languages such as java etc generate random numbers, especially how it is done for GUIDs.? i found that algorithms like Pseudorandomnumb

Answer 1

I understand that you are seeking a way to generate random number using C#. If yes, RNGCryptoServiceProvider is what you are looking for.

[EDIT]

If you generate a fairly long number of bytes using RNGCryptoServiceProvider, it is likely to be unique but there is no gurantee. In theory, true random numbers doesnt mean to be unique. You roll a dice 2 times and you may get head both the times but they are still random. TRUE RANDOM!

I guess to apply the check of being unique, you just have to roll out your own mechanism of keeping history of previously generated numbers.