From:	Michael Bukin <bukinm AT sunkedr30 DOT inp DOT nsk DOT su>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Solution(?) to STRANGE PROBLEM
Date:	20 Oct 1997 11:50:32 +0600
Organization:	Budker Institute of Nuclear Physics
Lines:	94
Message-ID:	<m3u3edgezb.fsf@H-Bukin.inp.nsk.su>
References:	<34495247 DOT 8960CC82 AT nbnet DOT nb DOT ca>
NNTP-Posting-Host:	aster.inp.nsk.su
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Jason Nye <jnye AT nbnet DOT nb DOT ca> writes:

> I have figured out what was going on with my SIGSEGV!!!
>
> I created a class, say A, which had a helper class, say B.  B was
> basically a singleton (except its
> members were not static), which means that there would only ever be one
> instance of this class.  This
> class, B, would be hidden to the user of class A, therefore, I decided
> to put it in the cpp file.  I also
> instantiated the class in the cpp file like so:
> 
> #include <A.hpp>
> 
> // B's interface is of no interest to the user of A
> class B {
> public:
>     B(int size);
>     ...
> };
> 
> // B's functions...
> B::B(int size)
> {
>     ...
> }
> ...
> 
> // Create a static instance of B.
> static B workerB(100);
> 
> // A's interface is defined in A.hpp
> A::A(char c)
> {
>     //
>     // Start using workerB as a helper here...
> }
> 

Are you sure that A's constructor is not called before constructor
of workerB?  Say, by having "static A someobject;" somewhere.

Suggestion: place    cerr << __PRETTY_FUNCTION__ << endl;
in constructors of A and B and see which one comes first.

> ---------------------------------------------------------------------
> 
> Now, I would think that this would work absolutely fine, but what
> actually happens is once the execution has gone past the construction of
> workerB, all Hell breaks loose.  This, apparently is a bug and a damn
> hard to find bug at that.  I also tried declaring workerB without the
> static storage class and it crashed that way too.
> 
> This is how I got around the bug:
> ---------------------------------------------------------------------
> 
> // Header:
> #ifndef A_HPP
> #define A_HPP
> 
> class B;
> 
> class A {
> public:
>     A::A(char c);
> private:
>     static B *workerB;
>     static bool setup;
> };
> 
> #endif
> ---------------------------------------------------------------------
>
> // Cpp:
> #include <A.hpp>
>
  B* A::workerB = 0;
> bool A::setup = false;
> 
> // B's declaration as above...
> ...
> 
> A::A(char c)
> {
>     if (!setup) {
>         workerB = new B(100);
>         setup = true;
>     }
> }
> ----------------------------------------------------------------------
> 
> This works with no crashes.  Why did the other way not work?  I have no
> Idea.  Maybe someone could help me out on why the static initialization
> did not work.

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