I am creating a min heap from stl priority queue. Here is my class which I am using.
class Plane
{
private :
int id ;
int fuel ;
public:
Plane():id(0), fuel(0){}
Plane(const int _id, const int _fuel):id(_id), fuel(_fuel) {}
bool operator > (const Plane &obj)
{
return ( this->fuel > obj.fuel ? true : false ) ;
}
} ;
In main I instantiate an object thus.
priority_queue<Plane*, vector<Plane*>, Plane> pq1 ;
pq1.push(new Plane(0, 0)) ;
I am getting an error from xutility
which I am unable to understand.
d:\microsoft visual studio 10.0\vc\include\xutility(674): error C2064: term does not evaluate to a function taking 2 arguments
Any help to its solution would be appreciated.
If you drop the use of pointers (which are overkill for your simple structures), then you can use std::greater
from the header functional
:
std::priority_queue<Plane, std::vector<Plane>, std::greater<Plane> > pq1;
pq1.push(Plane(0, 0));
Currently, you are feeding Plane
as the comparison type. That won't work since the comparison type must be a type of function object, i.e. it must have an operator()
that does the comparison. Plane
doesn't have such a member (and adding it just for this purpose would be a bad idea).
std::greater
has the appropriate method, implemented in terms of your operator>
. However, it doesn't work with pointers, because then it uses a pointer comparison (based on memory addresses).
Btw., note that your comparison function can be expressed more succinctly as
bool operator>(const Plane &other)
{
return fuel > other.fuel;
}