Re: Can some one please explain this code

From:

Joe Greer <jgreer@doubletake.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 14 Nov 2007 18:43:59 +0100 (CET)

Message-ID:

<Xns99E88187671C9jgreerdoubletakecom@194.177.96.78>

raghukumar <raghukumar.rags@gmail.com> wrote in news:1195059799.037952.79770
@t8g2000prg.googlegroups.com:

I was thinking on the same line as mentioned above, and this is what i
realized. Just for testing,
i changed j variable's initial value to 3 in class B. Then ran the
program, as you mentioned instead of getting 1,1,1,1 or 1,2,1,2, it
gave 1,3,1,3(sum ). This indicates to me that the value which i am
getting as an output, which is 20, is completely depend on how the
internal class structure is stored in memory. But, i don't know what
does standard say anything about this. So, this means can i assume
this behavior is not undefined, as any one at given point in time can
detect the value of the output. If it's really has undefined
behavior, can somebody please show me the right direction, so that i
can get some proof(code), which makes me believe.

The standard says this is undefined behavior. The object layout is compiler
dependent and there is no guarantees about much of anything. It just happens
give something sensible in your case.

Well, if you want proof that what you are doing is a bad idea, change your j
variable to a double with the value of 30000 and then see what you get.

What you need to do is iterate through B's and that will give you the right answer.
QED.

joe