How to call a specific function from all instances of a class in C++?

I'm making a game in C++ using GLUT, and I have a function that is called in a loop to draw cubes, spheres, etc. I made a few classes that represent these different shapes for example: (objects.hpp)

namespace Objects
{
    class SelectionInstance
    {
        public:
            Vector3 Position;
            void Draw();
    };
    class CubeInstance
    {
        public:
            Vector3 Position;
            void Draw();
    };
};

(objects.cpp)

void Objects::SelectionInstance::Draw()
{
    drawSelection(Objects::SelectionInstance::Position.X, 
    Objects::SelectionInstance::Position.Y, 
    Objects::SelectionInstance::Position.Z);
}

void Objects::CubeInstance::Draw()
{
    drawCube(Objects::SelectionInstance::Position.X, Objects::SelectionInstance::Position.Y, Objects::SelectionInstance::Position.Z);
}

void drawSelection(float x_position, float y_position, float z_position)
{
    glScalef(1.0, 1.0, 1.0);
    glTranslatef(x_position, y_position, z_position);
    glColor3f(255, 0, 0);
    glutWireCube(1.0);
}

void drawCube(float x_position, float y_position, float z_position)
{
    glScalef(1.0, 1.0, 1.0);
    glTranslatef(x_position, y_position, z_position);
    glColor3f(255, 0, 0);
    glutSolidCube(1.0);
}

How can I call the draw functions of all the instances of these two classes? I want to call them inside the function that is called to render objects...