Re: polymorphic sorting functors

#include <iostream>
#include <vector>

using namespace std;

class cmp_base : public std::binary_function<int, int, bool> {
   public:
   virtual bool operator()(int i, int j) { return i>j; }};

class cmp_inc : public cmp_base {
   public:
   virtual bool operator()(int i, int j) { return i<j; }};

void sort_it(vector<int> *v, cmp_base *cmp) {
   sort(v->begin(), v->end(), *cmp);}

int main(void) {
   vector<int> v;
   v.push_back(10);v.push_back(1);v.push_back(20);
   cmp_inc cmp;
   sort_it(&v, &cmp);
   for (unsigned int i=0; i<v.size(); ++i) { cout << v.at(i) << end=

   return 0;

}

It should be clear what I am trying to implement here: function sort_it s=

sort the given vector according to the comparison functor passed in the
second argument. The base class 'cmp_base' would usually be implemented
purely virtual, but is here given with an implementation for sorting the
vector in decreasing order, for demonstration purposes.

The problem is that although I create an object of type 'cmp_inc', the ve=

is sorted in decreasing order. If 'cmp_base' is implemented as an ABC, th=

program won't even compile.

As far as I understood, I am following a standard approach here: having a
base class and functions taking pointers to the base class, but in fact
handing pointers to objects of derived classes to these functions. Howeve=

the sort function from the STL expects an object, not a pointer, and so I
pass *cmp to it. This seems to be the cause of all the trouble.

Is there still a way to do this without using templates?