How to generate a list of unique random strings? How would you generate a list of distinct random strings, where all strings are alphanumeric and have a fixed length?
There are three general solutions to the non-duplicate random number problem:


If you want a few numbers from a large range then pick one and reject it if it is a duplicate. If the range is large, then this won't cause too many repeated attempts.
If you want a lot of numbers from a small range, then set out all the numbers in an array and shuffle the array. The Fisher-Yates algorithm is standard for array shuffling. Take the random numbers in sequence from the shuffled array.
If you want a lot of numbers from a large range then use an appropriately sized encryption algorithm. E.g. for 64 bit numbers use DES and encrypt 0, 1, 2, 3, ... in sequence. The output is guaranteed unique because encryption is reversible. The Hasty Pudding Cipher can be set for any convenient range of numbers.