Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!taumet!steve
From: steve@taumet.com (Stephen Clamage)
Newsgroups: comp.lang.c++
Subject: Re: Initializing Global Objects
Message-ID: <750@taumet.com>
Date: 27 May 91 15:41:25 GMT
References: <76813@brunix.UUCP> <1991May27.060310.16757@mathcs.sjsu.edu>
Organization: Taumetric Corporation, San Diego
Lines: 47

horstman@mathcs.sjsu.edu (Cay Horstmann) writes:

>In article <76813@brunix.UUCP> sdm@cs.brown.edu (Scott Meyers) writes:

>>    class nifty_counter {
>>      static count;
>>    public:
>>      nifty_counter()
>>      {
>>        if (count++ == 0)
>>          // initialize global objects (i.e., X)
>>      }
>>    };

>	int nifty_counter::count = 0;

>>Prior to this statement is the declaration of the static nifty_counter
>>object, so we know that the nifty_counter constructor will have been called
>>by the time that nifty_counter::count is explicitly initialized...

>I think you have the wrong conception of the initialization of static
>integers. They are just set to 0 in the load image, so it is guaranteed
>that they are zero before any constructors of static objects are executed.

Cay's analysis reflects current implementations, but not anything in the
language definition.  The language definition makes no distinction between
the initialization of
	int i = 1;	// value can be part of load image
and
	extern int j, k;
	class C { C(int, int); ... };
	C c(j, k);	// value cannot be part of load image

The requirement is merely that both initializations be complete before
the first statement of main() is executed.

In an embedded system, for example, non-const variables cannot be
initialized in the "load image" (ROM) because they then could not be
changed.  All variables must be initialized at program startup, including
nifty_counter::count.

Thus, Scott's concern is not fanciful.  The ANSI C++ committee (X3J16) is
addressing the issue of static initialization, and in particular, how, if
at all, initialization order can be specified.
-- 

Steve Clamage, TauMetric Corp, steve@taumet.com