Get 32-bit hash value from boost::hash

Question

I am using boost::hash to get hash value for a string. But it is giving different hash values for same string on Windows 32-bit and Debian 64-bit systems.

So how can I get same hash value (32-bit or 64-bit) using boost::hash irrespective of platform?

Answer 1

What is the guarantee concerning boost::hash? I don't see any guarantees that a generated hash code is usable outside of the process which generates it. (This is frequently the case with hash functions.) If you need a hash value for external data, valid over different programs and different platforms (e.g. for a hashed access to data on disk), then you'll have to write your own. Something like:

uint32_t
hash( std::string const& key )
{
    uint32_t results = 12345;
    for ( auto current = key.begin(); current != key.end(); ++ current ) {
        results = 127 * results + static_cast<unsigned char>( *current );
    }
    return results;

}

should do the trick, as long as you don't have to worry about porting to some exotic mainframes (which might not support uint32_t).