hash_map woes
Author
I'm creating a skeletal animation system, and I want to create a map between a point in its initial position and a point in its transformed position.
So, I have:
struct mikepoint {
float x, y, z;
public:
BOOL operator==(mikepoint &p1) {return (x==p1.x && y==p1.y && z==p1.z);}
};
I've never really used a hash_map in C++ before, but I thought I'd try it:
hash_map<mikepoint,mikepoint> allpointsmap;
Then, I have a mikepoint called v0. Just for testing, I tried:
allpointsmap[v0] = v0;
The compiler got mad, and said:
200 C:\Dev-Cpp\include\c++\3.4.2\bits\stl_function.h no match for 'operator==' in '__x == __y'
note C:\Dev-Cpp\linedraw.cpp:25 candidates are: BOOL mikepoint::operator==(mikepoint&)
note C:\Dev-Cpp\linedraw.cpp:25 BOOL operator==(const GUID&, const GUID&)
What's up with this? I added the operator== function to try to make it work, but that didn't seem to do it.
Mike C.
http://www.coolgroups.com/zoomer
Not only that it should be a constant member function. Also you will need to define a hashing function for user-defined key types. Which compiler are using? because not all hash_map are equal as its a library extension and not currently part of the standard.
Oh don't use BOOL use bool, BOOL is an MS type alias, your declaration should like this:
Oh don't use BOOL use bool, BOOL is an MS type alias, your declaration should like this:
bool operator==(const mikepoint&) const;
Author
Ok, thanks. Can you help me define the hash function? I can't figure out how to make the prototype even. I guess it's something like
int hash(mikepoint m)
but that doesn't quite work.
Mike C.
http://www.coolgroups.com/zoomer
int hash(mikepoint m)
but that doesn't quite work.
Mike C.
http://www.coolgroups.com/zoomer
Quote:Original post by snk_kid
Not only that it should be a constant member function. Also you will need to define a hashing function for user-defined key types. Which compiler are using? because not all hash_map are equal as its a library extension and not currently part of the standard.
Oh don't use BOOL use bool, BOOL is an MS type alias, your declaration should like this:bool operator==(const mikepoint&) const;
Quote:Original post by mike74
Ok, thanks. Can you help me define the hash function? I can't figure out how to make the prototype even. I guess it's something like
int hash(mikepoint m)
but that doesn't quite work.
which compiler are you using?
okay looking at the error messages its GCC [grin], you can either do a full specialization of hash or provide your own hash type.
To do a specialization of hash:
#include <ext/hash_map>namespace __gnu_cxx { template <> struct hash< const mikepoint > { size_t operator()(const mikepoint& m_ref) const { /* insert hashing code */ } }; template <> struct hash< mikepoint > : hash< const mikepoint > {};};To provide a custom hash type, just write a functor which takes a constant reference to mikepoint and returns std::size_t.
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