I want to implement K nearest neighbor search using KD tree
For maintaining nearest points, I construct a priority queue where each element is of type double* (pointer to array). I have my custom comparator class to which I pass 2 parameters, double* query and int d (dimension):
priority_queue <double* , vector<double*>, comparator(query,d) > min_heap; My comparator class looks like this:
class comparator{ double* query; int d; public: int operator()( double* point1, double* point2) { double dist1 = 0,dist2 = 0; for(int i=0;i<d;i++){ dist1 += (point1[i] - query[i]) * (point1[i] - query[i]); dist2 += (point2[i] - query[i]) * (point2[i] - query[i]); } return dist1 < dist2; } comparator(double * query,int d) { this->query = query; this->d = d; } }; I get the following errors:
main.cpp:92:63: error: temporary of non-literal type ‘comparator’ in a constant expression
priority_queue , comparator(query,d) > min_heap;
main.cpp:20:7: note: ‘comparator’ is not literal because:
class comparator{main.cpp:20:7: note: ‘comparator’ is not an aggregate, does not have a trivial default constructor, and has no constexpr constructor that is not a copy or move constructor
main.cpp:92:65: error: type/value mismatch at argument 3 in template parameter list for ‘template class std::priority_queue’
priority_queue , comparator(query,d) > min_heap;
main.cpp:92:65: note: expected a type, got ‘comparator(query, d)’
I am not well versed with const and constexpr and their usage. I am stuck here for a while and can't understand the errors. Any help is appreciated.
