Static member object initialization

Question

I'm trying to implement a template for states machines in C++, but I'm not sure how to handle static object members. Each state machine would be defined by its state variables and its transitions (which are structs). For instance:

// stm.h template <class T> struct transition { ... transition relevant data depending on state variables T ... }; template <class T> class stm { T *stv; // state variables static struct transition<T> *transitions; // I would like to have only one copy of transitions for stm's of type T ... etc ... };

Now, suppose I'm trying to implement the stm foo:

// foo_defs.h struct foo_stv { char a; int b; }; // foo_transitions.h // Note that I'm using a different file to keep everything in order #include "stm.h" #include "foo_defs.h" struct transition<struct foo_stv> foo_transitions[] = { { ... trans1 ... }, ..., { ... transN ... } }; // foo_stm.h #include "stm.h" #include "foo_defs.h" #include "foo_transitions.h" class foo_stm { stm<struct foo_stv> stm; struct foo_stv stv; ... other data ... };

Ok. So each instance of foo_stm should have a different set of state variables, but all instances should use the same transitions. The question is, how should I define/declare stm<struct foo_stv> in order to use foo_transitions as its class level transitions member?

Also any advice about C++ coding customs is welcome, since I come from the C coding world and just getting started with some C++ mechanics.

EDIT: Just to make clear my question, I guess you should forget about the stm logic and focus on the following: What's the correct way of doing something like...

foo_stm::stm.transitions = foo_transitions;

why not a singleton pattern ? The problem will be that you can not initialize the static member except in the cpp, OR if you use recent c++. — dzada
– dzada, Commented Sep 1, 2013 at 21:48
"Also any advice about C++ coding customs is welcome, since I come from the C coding world and just getting started with some C++ mechanics" OK: struct keyword is not needed in C++ (Im talking about the sentences like stm<struct foo_stv>. The only difference between class and struct is that the default scope of class members is private, in struct is public. — Manu343726
– Manu343726, Commented Sep 1, 2013 at 22:11
"each instance of foo_stm should have a different set of state variables, but all instances should use the same transitions." How can you have different state variables and the same transitions? — BartoszKP
– BartoszKP, Commented Sep 1, 2013 at 23:24
@BartoszKP Because the transition struct is composed of call back functions that use as one of its arguments the state vars of the instance stm. — user2553780
– user2553780, Commented Sep 2, 2013 at 2:44
@dzada Not sure if I could apply that to my particular problem, but I'll search info about it. Thanks. — user2553780
– user2553780, Commented Sep 2, 2013 at 2:45

BartoszKP · Accepted Answer · 2013-09-11 22:23:55Z

2

All right, I think that what you want to do is:

template <class T> class stm { T *stv; static transition<T> *transitions; }; template<class T> transition<T>* stm<T>::transitions; //define static template member

And then:

//define static member for particular template instantiation template<> transition<foo_stv>* stm<foo_stv>::transitions = foo_transitions; class foo_stm { stm<struct foo_stv> stm; struct foo_stv stv; ... other data ... };

edited Sep 11, 2013 at 22:23

answered Sep 3, 2013 at 11:58

BartoszKP

36k15 gold badges109 silver badges135 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

user2553780 Over a year ago

Interesting, I'll try this when I get home. I'm trying to desing in the context of OOP, but not used to it. Where am I failing?

BartoszKP Over a year ago

I'll try to give you a more detailed answer soon, sorry for the delay.

BartoszKP Over a year ago

All right, I've analysed your solution more thoroughly and I think it's quite OK, in the context template programming. What I saw wrong the last time, was the fact that you're abusing a bit the "struct" keyword (C-style), and it blurred my vision a bit :-) Assuming that your transition structure contains a pair of states, and optionally some additional transition data all seems to be OK. Sorry for the misleading comment in my previous answer.

Collectives™ on Stack Overflow

Static member object initialization

1 Answer 1

3 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Linked

Related