How to get original string from the int generated by gethashcode

Question

I have generate a hash code as

string textBoxVal="Naresh";
int code =textBoxVal.GetHashCode();
textBox2.Text=code.ToString();

It has generated a integer value as -1078339947;

Now I want to get the Original name Naresh with this(-1078339947) hashcode. How can I do this.

If you want to take a string and generate a unique `int` identifier for it, what you're looking for is a database (of some sort, whether it be something that lives in memory for just the lifetime or your application to a full-blown database system), not a hash code. — Damien_The_Unbeliever, Apr 18 '13 at 07:32
Would it be possible for you to use a `string instead of an `int` for this purpose? Since you can't do this using a standard hashcode, perhaps you can create an algorithm to generate a unique string code to use instead? (I guess this basically amounts to some form of encryption of the original data, instead of creating a hash from it) — Kjartan, Apr 18 '13 at 09:10

Dan Puzey · Accepted Answer · 2013-04-18T10:55:52.020

5

For all practical purposes, you can't: there are lot less hash codes than there are strings, so there is more than one original value that would give your same hash code.

Hashing is, in reality, a one-way operation. If someone refers to a reversible hash, this isn't a true hash (because a hash by definition reduces an input set into one of a smaller number of output values). The closest operation to what you describe might be an encryption function - this would allow you to reverse the operation - but this is unlikely to generate as small a number as the 10-digit output in your question.

edited Apr 18 '13 at 10:55

answered Apr 18 '13 at 07:26

Dan Puzey

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Then in what way I can convert string to int vice versa – Learner Apr 18 '13 at 07:31
For what purpose do you need to do this? – Dan Puzey Apr 18 '13 at 07:35
I want to give a number to a customer based on his name and date of birth. and I want get the name back with that number. – Learner Apr 18 '13 at 07:36
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An `int` has 2^32 possible values. A string longer than 4 unicode characters has way more than 2^32 possible characters. So it's not even possible to turn strings of 5 characters into unique ints, let alone longer strings. – Matthew Watson Apr 18 '13 at 07:37
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Is there a reason that you can't simply use an auto-incremented number? – Dan Puzey Apr 18 '13 at 07:38

score 3 · Answer 2 · edited May 23 '17 at 11:50

3

You just can't do that! A hash code doesn't contains all the necessary informations to convert it back to a string.

There is no even guarantee that GetHashCode() will return the same thing in different environments.

Check out Eric Lippert's blog post Guidelines and rules for GetHashCode

edited May 23 '17 at 11:50

Community

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answered Apr 18 '13 at 07:27

Soner Gönül

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Then in what way I can convert string to int vice versa – Learner Apr 18 '13 at 07:31

How to get original string from the int generated by gethashcode

2 Answers2