I need a hash table implementation for Cygwin

From:

Jim Cobban <jcobban@magma.ca>

Newsgroups:

comp.lang.c++

Date:

Sat, 12 Apr 2008 15:14:04 -0400

Message-ID:

<ae945$480105ff$cebf3893$27544@PRIMUS.CA>

I am writing a program in which I need a hash table implementation of a
Map. The version of g++ available for Windo$e does not yet include the
TR1 support for this. It just has the original SGI implementation.
However the SGI implementation is so old that it predates the STL, so it
does not, among other things, include hash support for std::basic_string.

So I tried implementing the hash map from Stroustrup 3rd edition. At
the least I thought this would be a useful learning experience about
template programming. However even after I correct all of the typos I
can identify or which are described in postings I still cannot get it to
compile. Of course template error messages never provide much guidance
on how to resolve the issues so I am getting a little frustrated.

For example I have succeeded in getting a specialization for the hash
functor for std::string to compile, but I cannot get the more general
specialization for std::basic_string<C> to compile.

// this compiles
size_t hash<string>:: operator() (string const & key) const
{
    size_t res = 0;
    string:: const_iterator p = key.begin();
    string:: const_iterator end = key.end();
    while (p != end)
        res = (res << 1)^*p++;
    return res;
} // hash(string)

// this doesn't
template <class C>
size_t hash<basic_string<C> >:: operator() (basic_string<C> const & key)
const
{
    size_t res = 0;
    basic_string<C>:: const_iterator p = key.begin();
    basic_string<C>:: const_iterator end = key.end();
    while (p != end)
        res = (res << 1)^*p++;
    return res;
} // hash(basic_string<C>)

But even if I skip over that, since my specific application does not
need the more general case, as soon as I instantiate an instance I get a
flood of errors. Including:

If in my implementation of the hash table I code:

    hash(key)

I get an error that I have to specify the class instance, which I did
not expect, but if I try to make the compiler happy by coding:

    hash<Key>(key)

I get: error: no matching function for call to `GedCom::
hash<std::string>:: hash(std::string&)'

All I really would prefer to do is invoke the TR1 implementation which
Cygnus hasn't gotten around to incorporating yet. So what is your
advice on how to get this to work?

Specifically is there some place where I can get a pre-built Windo$e
implementation of g++ that includes TR1?