Suggestion regarding Good Hash Function

Question

I want to create a hash table in c++ for storing strings. I am willing to write a good hash function to avoid collisions as much as possible. As a sample hash function I have used the following method:

function Hash(string)

return (summation of the ASCII values of the characters in the string) mod PrimeNumber

end

Is this function good enough to avoid collisions or is there any other good function ? please help :)

N.B: No STL is allowed

Did you search for existing hash functions? Do they not do what you need? — Neil Kirk, Mar 13 '15 at 15:15
I am just searching for a function which will avoid collision as much as possible. Do u have any idea? @Neil — user4667841, Mar 13 '15 at 15:17
using summation of the ASCII values of the characters. @interjay — user4667841, Mar 13 '15 at 15:18
Just use `std::hash` wherever possible. If you have multiple values to hash, use `boost::hash_combine` or `boost::hash_range`. — Baum mit Augen, Mar 13 '15 at 15:20
All anagrams will hash to the same value, that doesn't seem optimal. — Paul Rubel, Mar 13 '15 at 15:22
I am sure the built-in hash code function for C++ strings is more than adequate for most uses. If you are curious about how to compute hash codes for strings, check out [this SO](http://stackoverflow.com/questions/299304/why-does-javas-hashcode-in-string-use-31-as-a-multiplier) about java's string hash code. — Giovanni Botta, Mar 13 '15 at 15:31
Any reason not to use `std::unordered_map`? Or the Boost or TR1 `unordered_map`, or even the old STL `hash_map`, if you can't use C++11 for some reason? — Mike Seymour, Mar 13 '15 at 15:32

score 2 · Answer 1 · answered Mar 13 '15 at 15:22

2

c++11 already comes with a good hash function for string you don't need to introduce one. See: http://www.cplusplus.com/reference/unordered_map/unordered_map/operator[]/

answered Mar 13 '15 at 15:22

W.F.

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Suggestion regarding Good Hash Function

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