Thanks, I solved my problem by doing this: namespace boost { std::size_t hash_value(const GS_VECTOR2 &v2) { return ((std::size_t)v2.y*COLUMNS)+(std::size_t)v2.x; } }; Is it also ok? André. 2010/2/27 Daniel James

On 27 February 2010 19:21, André Santee wrote:

...

I know it has probably been asked a million times here, but I couldn't find any example that I could use. I want to create an unordered_map whose key is an object that I made (vector2), what's the best way of implementing a hash function to it? Can I have an example?

You need to implement 'hash_value' so that Boost.Hash can hash your custom type, take a look at the last example in:

http://www.boost.org/doc/html/unordered/hash_equality.html#unordered.hash_eq...

It's pretty much what you want. There's more info in the Boost.Hash documentation:

http://www.boost.org/doc/html/hash/custom.html

Daniel _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

On 27 February 2010 19:37, André Santee wrote:

Thanks, I solved my problem by doing this:

namespace boost {     std::size_t hash_value(const GS_VECTOR2 &v2)     {         return ((std::size_t)v2.y*COLUMNS)+(std::size_t)v2.x;     } };

Is it also ok?

Yes, but unless you're using a really old compiler that doesn't support argument dependent lookup (ADL), you should put the function in the same namespace as your vector. You can read about ADL at: http://en.wikipedia.org/wiki/Argument_dependent_name_lookup Daniel