How to create unique pointers in a loop C++?

Question

I am reading a double from the standard input and saving it into a variable d . I want to be able to do this an unspecified amount of times. I use the following code to create a pointer to d .

double *pd = new double;
pd = &d;

I then push this pointer into a constructed stack (list) class. But whenever I push more than one double it changes all of them (the pointer is the same).

Ex. push 2 and get an array [2]. push 3 and get array [3, 3] instead of [3, 2].

Answer 1

Why are you using pointers at all?

std::vector<double> v;

double d;
while (std::cin >> d)
    v.push_back(d);

Or as chris points out:

std::copy(std::istream_iterator<double>(std::cin),
          std::istream_iterator<double>(),
          std::back_inserter(v));

Answer 2

*pd = d

instead of

pd = &d;

What you do is:

• you have double d variable on stack
• you create double and save its pointer in pd variable
• then you save address to d variable in pd
• and then you save address from pd on list

This means you have list of addresses to variable d (every single object on list is pointer to d variable).