Re: [Boost-users] seed for hash

From: James Dennett (jdennett_at_[hidden])
Date: 2007-02-03 18:44:31

Rares Vernica wrote:
> Hi,
> 
> Does the hash function uses a seed?
> 
> If a call:
> boost::hash<std::string> string_hash;
> std::size_t h = string_hash("Hash me");
> 
> and then after a year I call again:
> string_hash("Hash me");
> 
> Does it return the same value?

Yes; a hash is a (pure, deterministic) function of its
input value, i.e., a function in the mathematical sense
as well as the C++ sense.  Any hash must satisfy that
property or algorithms using it will behave in rather
strange/unpredictable ways.

-- James