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From: mikem@otc.OZ (Mike Mowbray)
Newsgroups: comp.lang.c++
Subject: Re: Static class members
Message-ID: <118@otc.OZ>
Date: Thu, 7-May-87 02:09:42 EDT
Article-I.D.: otc.118
Posted: Thu May  7 02:09:42 1987
Date-Received: Sat, 9-May-87 02:53:52 EDT
References: <722@apple.UUCP>
Organization: O.T.C. Systems Development, Australia
Lines: 57

In article <722@apple.UUCP>, kanner@apple.UUCP (Herbert Kanner) says:

>     Section 8.5.1 of the C++ Reference Manual (page 275) states: "A
>     data member of a class may be *static*.  ...  No initializer can be
>     specified for a static member, and it cannot be of a class with a
>     constructor."
> 
>     [ ... ] With respect to initializers:  I have been unable to find
>     an instance of a (non-static) class data member with an
>     initializer; [...]  So, what would an explicit initializer do?

Nothing, it would be illegal.  One initialises non-static data members
by passing arguments to their constructors from the constructor of the
class.

>     With respect to a static member of a class that has a constructor:
>     what could be wrong with that as long as the constructor does not
>     assign to the static member?

As posted sometime ago, the reason is as follows: class definitions
appearing in header files will appear in multiple .c files. But static
members have to be one and the same for ALL instances of the class. The
mechanism by which static instances is initialised is to call a
compiler-generated function at the start of main(). However, this
function will be inserted in every .o file that used the .h file, and
so the initialisation would happen lots of times. There are ways around
this, of course, but they are not yet implemented. So there is nothing
"wrong with it" as such. Personally, I would like to see it happen, but
I understand that other more important things are being worked on. And
after all, you can achieve the same effect (almost) by having a static
pointer member and using a first-time switch in the constructor, e.g:

    class SomeClass {
	    ....
	public:
	    SomeClass();
    };

    class MyClass {
	    static SomeClass  *statmbr;
	public:
	    MyClass();
    };

    MyClass::MyClass()
    {
	if (statmbr == NULL)
	    statmbr = new SomeClass;

	//  ...etc
    }

			Mike Mowbray
			Systems Development
			Overseas Telecommunications Commission (Australia)

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