怎样把fsort函数的cmp改成可选参数：

#include <bits/stdc++.h>
using namespace std;
template <class iter, class comp>
void fsort(iter l, iter r, comp cmp)
{
	for (iter i = l; i != r; i++)
		for (iter j = i; j != r; j++)
			if (not cmp(*i, *j))
				swap(*i, *j);
}
int main()
{
	vector<int> v({5, 4, 3, 2, 1});
	fsort(v.begin(), v.end());
	for (vector<int>::iterator it=v.begin();it!=v.end();it++)
		cout << *it << "\n";
	return 0;
}