#include "my_class.hh"

int main()
{
    My_Class my_class(NULL);

    my_class.perform_tasks();

    return 0;
}

#include "device.hh"

class My_Class
{
public:
    My_Class(Device* device = NULL);

    void perform_tasks();

private:

    Device* m_device;
};

#include "my_class.hh"

My_Class::My_Class(Device* device)
: m_device(device)
{

}

void My_Class::perform_tasks()
{
    if(m_device != NULL)
    {
        m_device->use();
    }

    // perform other tasks
}