Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!apollo!vasta
From: vasta@apollo.COM (John Vasta)
Newsgroups: comp.lang.c++
Subject: Re: Help!
Summary: static object construction order undefined
Keywords: constructors, C++ i/o, extern
Message-ID: <4443be62.1ad5a@apollo.COM>
Date: 6 Jul 89 21:30:00 GMT
References: <2774@ssc-vax.UUCP>
Reply-To: vasta@apollo.COM (John Vasta)
Organization: Apollo Computer, Chelmsford, MA
Lines: 41

In article <2774@ssc-vax.UUCP> dmg@ssc-vax.UUCP (David Geary) writes:
>
>  Here's something interesting:
>  [ ... ]
>The file noworks.cxx:
>----------------------------------------------------------------------
>#include "//ernie/user/geary/c++/include/stream.hxx"        // c++ i/o
>
>class junk { public: junk() { cout << "Constructing Link\n"; } };
>
>junk myjunk;
>
>main() { }
>----------------------------------------------------------------------
>
>When I compile and run, I get:
>
>$ noworks
>Segmentation Fault
>
>  Can anybody provide an explanation as to why this is happening?

The cout object from the stream library must be initialized when the
program starts up. So does your myjunk object. The order of execution
of constructors for static objects in different modules is not defined.
It looks like your object is getting attention first in this case,
and its constructor is trying to use an uninitialized stream object.

Although some people have found ways of determining or even controlling
the execution order of static constructors/destructors, these techniques
are not portable, so I'd advise you not to count on them. Making the
object automatic (e.g. local to main) makes sure that all static objects
are initialized first. If you need global visibility for an object which
depends on other static objects being initialized, you can create
the object dynamically (using new) and put a pointer to it in file scope.

-- 
John Vasta                Apollo Computer (division of Hewlett Packard)
vasta@apollo.com          M.S. CHA-01-LT
(508) 256-6600 x6362      330 Billerica Road, Chelmsford, MA 01824
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