bar.cpp

#include "bar.h"

bar::bar(): 
  reader(14)
{}

bar.h

#pragma once

#include "cardreader.h"

class bar
{
public:
    bar();

protected:
    CardReader reader;
};

foo.cpp

#include "foo.h"

foo::foo(): 
  reader(x)
{}

foo.h

#pragma once

#include "cardreader.h"

class foo
{
public:
    foo();

protected:
    CardReader reader;
    const uint8_t x = 14;
};