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From: rchen@m.cs.uiuc.edu
Newsgroups: comp.lang.c++
Subject: another Zortech bug?
Message-ID: <4800083@m.cs.uiuc.edu>
Date: 9 Feb 90 22:58:00 GMT
Lines: 86
Nf-ID: #N:m.cs.uiuc.edu:4800083:000:2848
Nf-From: m.cs.uiuc.edu!rchen    Feb  9 16:58:00 1990


I am posting for a friend who has only "read-only" access
to this news group.

/*-------------------- cut here --------------------------*/ 
 
I'm running Zortech 2.0, and possibly the problem is in the
compiler, but since the details of how to do this don't seem
to be discussed anywhere, I'm not yet ready to point the
finger in Walter's direction.
 
The problem is to do with static members in a class, where
the static member is 1) an array; and 2) a user-defined
class with a single constructor which takes no parameters.
 
So we have a class which is defined along the lines of:
 
class class_with_constructor
 { int dummy1, dummy2, /* ...*/ ;
 
public:
  class_with_constructor(void);
  ~class_with_constructor(void); };
 
and then another one which uses the first, as in:
 
class class_with_problem
{ static class_with_constructor array_name[ARRAY_SIZE];
 
public:
  class_with_problem(void);
  ~class_with_problem(void); };
 
finally, let's specify a global instance of the latter
class:
 
class_with_problem global_variable;
 
Now, what I want to happen is to have the constructors for
each element in the array "array_name" be called before the
call to the constructor to class_with_problem, since the
instantiation "global_variable" calls the latter construc-
tor, which in turn uses information stored in the array
"array_name". This information is intialised in the con-
structor for "class_with_constructor".
 
The 2.0 Ref manual merely says, in section 9.4, that "The
declaration of a static member in its class declaration is
*not* a definition. A definition is required elsewhere".
Fine, but where, and how?? Lippman gives an example for a
class with a static double member, but it isn't obvious to
me how to extrapolate the example to handle arrays; nor is
it obvious when or even if a constructor for a user-defined
type would be called.
 
I spent about three hours mucking
about with various combinations of things yesterday; most of
them compiled, but none of them worked. What actually hap-
pened in every reasonable case was that
class_with_constructor() *was* called ARRAY_SIZE times, but
with a "this" defined incorrectly each time; the first call
was with this == &global_variable; after that the value of
this increased with each call by some amount, probably
sizeof(class_with_constructor), although I didn't check
that.
 
This behavious is obviously designed to crash a program
rapidly...as it did.
 
So, how do I get the constructor called the right number of
times and with the first this == &array_name??
 
Hope this is an easy one for you...
 
All the best
 
  Doc Evans
 
 
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