Question

I create a vector of pointers to double array. Are these pointers valid after function (i.e. InsertIntoVector) exits? If I later fetch the pointer as in GetVecElement, are the pointers still guaranteed to point to the same memory location they were assigned?

class A { 
   vector<double*> vec; 

   void insertIntoVector(double x, double y); 
   void GetVecElement(int i, double& x, double& y); 
}; 

A::insertIntoVector(double x, double y) { 
   double* xy = new double[2]; 
   xy[0] = x; xy[1] = y; 
   vec.push_back(xy);       
}

A::GetVecElement(int i, double& x, double& y)
{
    x = vec[i][0];       // will the reference to the double array still be valid? 
    y = vec[i][1];
}

Answer 1

Those are not references! Those are pointers…

If I later fetch the pointer as in GetVecElement, are the references still guaranteed to point to the same memory location they were assigned?

You are not deleting the pointer, and std::vector won’t do it for you, so yes the pointers will remain valid. It will also be leaked unless you manually delete each of them at A‘s destructor. But for that you will need a copy-constructor and an assign-operator as well, to clone the contents of the vector.