object as a key of unordered map
I am having problem in putting object of a class in an unordered map as key here is a simple example:
class first
{
string name;
public:
first(){}
first(string nam):name(nam){}
string get_name() const
{
return name;
}
};
struct SampleTraits
{
size_t operator()(const first &that) const
{
return tr1::hash<const char*>()(that.get_name().c_str());
}
bool operator()(const first &t1,const first &t2) const
{
return t1.get_name()==t2.get_name();
}
};
typedef tr1::unordered_set<unsigned short> uset;
typedef tr1::unordered_map<first,uset,SampleTraits,SampleTraits> umap;
ostream& operator <<(ostream& out, uset &ust)
{
for(uset::iterator it=ust.begin开发者_C百科();it!=ust.end();++it)
out<<" "<<*it;
}
int main()
{
umap *mymap= new umap;
string names,nm,n;
cout<<"\nEnter 1st name: ";
cin>>names;
first obj(names);
(*mymap)[obj].insert(100);
(*mymap)[obj].insert(120);
(*mymap)[obj].insert(112);
cout<<"\nEnter 2nd name:";
cin>>nm;
first obj2(nm);
(*mymap)[obj2].insert(201);
(*mymap)[obj2].insert(202);
cout<<"\nEnter name which u want to search:";
cin>>n;
first obj1(n);
umap::iterator it=mymap->find(obj1);
cout<<it->first.get_name();
cout<<it->second;
//delete mymap;
/*
for(umap::iterator it=mymap->begin();it!=mymap->end();it++)
{
cout<<it->first.get_name()<<" ";
cout<<it->second<<endl;
}
*/
return 0;
}
My problem is when iam tryin to insert two different objects and trying to display it is shows segmentation fault.. again if i try to use find() then also it shows segmentation fault.. Its quite hard for me to understand why unordered_map is showing this behavior.
Any help will be appreciated!! This will be a great help for my project...
The problem is with hash function. It does not work as you have expected with pointer types, since it uses a pointer to calculate a hash value instead of its content. Using the std::string fixes the problem.
return tr1::hash<string>()(that.get_name());
Looks like you forgot to return out from operator<< for the uset. Although, most compilers will issue warning for such functions they still have to compile them and running such program will result in undefined behaviour.
ostream& operator <<(ostream & out, uset & ust)
{
for(uset::iterator it=ust.begin();it!=ust.end();++it)
out<<" "<<*it;
return out;
}
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