C++ class design coding question

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In effective c++ Item 22, Scott Meyers say data member must be in private.

My question is, if there is class A, which is parent of class B and C, and A has data member "int id".

if A put "int id" in private, class B and C should use A's getter and setter, which cause reduction in performance.

example code in below.

C++

class A
{
public:
  int getId() { return id; }
  void setId(int id) { id_ = id; }
private:
  int id_;
};

class B : public A
{
public:
  int getId() { return A::getId(); }
  void setId(int id) { A::setId(id); }
}

class C : public A
{
public:
  int getId() { return A::getId(); }
  void setId(int id) { A::setId(id); }
};

I'm confused. Anybody help me what I should do?

Posted 2-Feb-14 21:33pm

Young Hyun Yoo

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2 solutions

Solution 2

First, see solution 1, it explains the issue pretty well.

In addition to that, the getId and setId functions (in your case) are implicitly inline, so you don't have to bother with reduction in performance in this case.

Posted 2-Feb-14 22:09pm

Shmuel Zang

Updated 2-Feb-14 22:18pm

v2

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Raul Iloc · Accepted Answer · 2014-02-02T21:47:00

Solution 1

1)First note, the classes B and C inherits getID() and setID() from class A (that is the parent for both) so you should delete them from class B and class C!

2)In generally the performance lost by using of get or set methods can be ignored, and it is recommended to use get() and set() in place of direct access.

3)If you want to access directly the id__ directly from class B or C you could change its access from private to protected.

Posted 2-Feb-14 21:47pm

Raul Iloc

Comments

Young Hyun Yoo 3-Feb-14 4:03am

Thanks

Shmuel Zang 3-Feb-14 4:10am

5'ed. See my addition.

Raul Iloc 3-Feb-14 9:14am

Yes, your right, there are inline methods.

CPallini 3-Feb-14 4:26am

5.

Raul Iloc 3-Feb-14 9:13am

Thank you for your vote!