How to initialize static members in derived classes?

Question

Well, apparently, I cannot. But that's my problem. Maybe it's a design issue and I'm getting the whole thing wrong.

I would like to have a class member initialized differently within each derived class. Imagine I have an object of type Device. This Device is just an interface used by the application code, because the actual devices are just one of two types, DeviceA or DeviceB. There are some features common to all devices, like, say, the name. That should be then a class member, shouldn't it? So I'd have:

class Device {
    static std::string sm_name;
}

But each family device has its own name. How could I initialize the name to a different value for each derived class? Is the design wrong? Should the name property not be a class member?

possible duplicate of [Are static variables in a base class shared by all derived classes?](http://stackoverflow.com/questions/1390913/are-static-variables-in-a-base-class-shared-by-all-derived-classes) — , Apr 04 '11 at 15:34

score 6 · Accepted Answer · answered Apr 04 '11 at 15:35

6

Should the name property not be a class member?

Each family device should, most likely, have it's own, private static member. You could use a virtual method to return the proper name on a device instance.

answered Apr 04 '11 at 15:35

Reed Copsey

554,122
78
1,158
1,373

Ok, I see then, no other choice than having each derived class define its own member. – José M. Benítez Apr 04 '11 at 15:55

score 2 · Answer 2 · edited Apr 04 '11 at 16:14

2

why not just have a virtual member function which returns the name, and implement it in the derived class to return the correct name?

e.g.

class A
{
public:
   virtual std::string name() = 0;
};

class B : public A
{
public:
virtual std::string name() { return "typeB"; }
};

class C : public A
{
public:
virtual std::string name() { return "typeC"; }
};

edited Apr 04 '11 at 16:14

José M. Benítez

435
3
13

answered Apr 04 '11 at 15:35

Chris Card

3,216
20
15

You'll want the function to be virtual, though. And for safety, `A`s destructor should be either virtual or protected. – Mike Seymour Apr 04 '11 at 16:10
sorry, I missed off the virtual in my haste :-( – Chris Card Apr 04 '11 at 16:14

How to initialize static members in derived classes?

2 Answers2

Linked