Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!unmvax!polyslo!ttwang
From: ttwang@polyslo.CalPoly.EDU (Thomas Wang)
Newsgroups: comp.lang.c++
Subject: Re: Global Variable Constructors, Language design
Message-ID: <14243@polyslo.CalPoly.EDU>
Date: 7 Sep 89 20:38:40 GMT
References: <6487@columbia.edu>
Reply-To: ttwang@polyslo.CalPoly.EDU (Thomas Wang)
Distribution: usa
Organization: Cal Poly State University -- San Luis Obispo
Lines: 45

kearns@cs.columbia.edu writes:
>In C++, classes often do some initialization before the program
>starts. It has been pointed out often in this newsgroup that C++ 
>suffers because one cannot predict the order in which the various files
>will be initialized.  However, one of the most serious ramifications
>just hit me:

>If a class, say class List, needs to do some initialization, then it
>is UNSAFE to declare any global variable of type List, or any global
>variable containing a List.  The global may be initialized before the 
>List class is, probably causing serious problems.  

This is not quite it, but you came close.  Eg.

a::a()
{
  cout << "initing...\n";
}

static a an_object;

Now you are in trouble; 'cout' might be initialized after 'an_object' is
initialized.

>Yech.  Anybody have any other suggestions?

The solution is really complicated.  Say that you have a class caled
'type_car'.  Basically you want to get a list of global variables and static
variables one could ever use during type_car's construction phase.  Remove
from the list those variables that do not have constructors.  A global
variable of 'type_car' must be created after all those variables left in
the list are created.

The same operation goes for destructors too.  You want to get a list of
global variables and static variables one could ever use during type_car's
destruction phase.  Remove from the list those variables that do not have
destructors.  A global variable of 'type_car' must be destroyed after all
those variables in the list are destroyed.

>-steve

 -Thomas Wang ("I am, therefore I am."
                 - Akira               )

                                                     ttwang@polyslo.calpoly.edu