Question

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what is hashCode use for? is it unique?

I am generating a lot of strings, then my question is:

Can 2 different string have the same hash code in C# ?

By hash code I mean:

string s = "Hello";
s.GetHashCode();

My question is more about of the algorithm that C# follow to geneate the strings, maybe the
collisions come when all the other hash code are generated already or maybe not.
Is possible that somebody have this answer.

Answer 1

Yes. Hash codes are not unique. There are 2^32 (4,294,967,296) possible hash codes (one for each integer value in a 32 bit integer). There are effectively an infinite number of possible strings. Clearly it’s impossible for each of an infinite number of strings to have a different number of finite numbers.

Two different strings (or any values for that matter) having the same hash code is called a “collision”. A good hashing algorithm will attempt to ensure that collisions are minimized to the greatest extent possible (although they can’t be eliminated). Often this will be dependent on the actual types of data in practice; in this case of strings this means that strings that are similar, or of a similar size, should (ideally) be less prone to collisions.

I assume that you’re asking because you’re considering using a string’s hash code as a unique identifier for a string. Don’t do that.

Here is a link that goes into more detail about hash codes in general, if you’re interested.