std::multiset<classA , classA ::SortClass> mydata;

    class SortClass
        {
        public:
            bool operator() (const classA &pt1, const classA &pt2)
                {
                if(pt1.a < pt2.a)
                    {
                    if(abs(pt1.a-pt2.a) < 0.01)
                        {
                        if(pt1.b > pt2.b)
                            return true;
                        else
                            return false;
                        }
                    else
                        return true;
                    }
                else
                    return false;
                }
        };

#include <iostream>
#include <set>
using namespace std;


class classA
    {
    protected:
        double m_b;
        double m_a;

    public:
        double get_b() {return m_b;}
        double get_a() {return m_a;}
        void set_b(double b) {m_b = b;}
        void set_a(double a) {m_a = a;}

        class SortClass
            {
            public:
                bool operator() (const classA &pt1, const classA &pt2)
                    {
                    if(pt1.m_a < pt2.m_a)
                        {
                        if(pt2.m_a - pt1.m_a == 0)
                            return (pt1.m_b > pt2.m_b);
                        else
                            return (pt1.m_a < pt2.m_a);
                        }
                    else
                        return false;
                    }
            };
    };
int main()
    {

    std::multiset<classA, classA::SortClass> mydata;
    classA objA;
    for(int i=0; i<100;i++)
        {
        objA.set_a(rand() %100);
        objA.set_b(rand() %10);
        mydata.insert(objA);
        }

    return 0;
    }

bool sortClassA (const classA &pt1, const classA &pt2)
    {
        if(pt2.m_a == pt1.m_a) {
            return pt1.m_b > pt2.m_b;
        }
        return pt1.m_a > pt2.m_a;
    };