Class pointer and vector problem

[po0ky]

As the title shows, I find it hard to come up for a good description of the problem I encountered.

Please can some of you guru's help me?

#include <vector>

class sD
{
private:
   float* _d;
public:
    sD(){};
    ~sD(){ delete _d; }
   sD(const sD & D):_d(new float((*D._d))){}
   sD(float d){ _d = new float(d); }
   operator float(){ return *_d;
};

class tst{
private:
   std::vector<sD> vec;
public:
   tst(){};
   void insert(float sD){ vec.insert(vec.begin(), sD); }
   float operator[](std::vector<sD>::size_type i){ return vec[i]; }
};

int main(){
    tst t;
    t.insert(10);
    t.insert(20);
    float tmp1 = t[1];// tmp1 holds 10
    float tmp2 = t[0];// tmp2 holds ?
}

This is a distilled segment of the code. The actual code is much bigger.

I would expect tmp2 to be 20.
If I replace "vec.insert(vec.begin(), sD);" with "vec.push_back(sD);" than as expected; tmp2 holds 10 and tmp1 holds 20.

Why doesn’t the tmp2 of my code hold 20? How can I remedy this behaviour?