Re: slightly interresting derrived class problem

From:
"Alf P. Steinbach" <alfps@start.no>
Newsgroups:
comp.lang.c++
Date:
Tue, 30 May 2006 04:59:12 +0200
Message-ID:
<4e1qo4F1cf7t3U1@individual.net>
* easy:

I start off with an interface class that has no data members and a
handful of virtual functions.

First Question: is that allowed ?


Yes.

I then derived from this class and it gets included into a couple of
other classes that need that interface. The derived class had a number
of data members including a struct that allow it to do its dirty work.

When I directly access any data members (through pointers or through
public data members) in the derrived class hilarity ensues. I found
that the value returned is offset by 4 bytes( 32bits ).

for example, if I wanted:
    class1.public_struct.int0
I would get
   class1.public_struct.int1

more curiously this problem would only show up when i ran the release
version of the code. The debug version behaved correctly.


Post a minimal example that compiles.

For other requirements on posting example code, see the FAQ item "How do
I post a question about code that doesn't work correctly?", currently at
<url: http://www.parashift.com/c++-faq-lite/how-to-post.html#faq-5.8>.

After an entire wasted morning I added an unused data member to the
very first interface class and all problems dissapeared like a fart in
the wind.

Main Question: Is this a compiler error or did I violate the standard?


Probably the latter, but not in the way you indicated above.

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