Re: C++ altering the wrong class members
From: Thomas Wintschel (thomas_at_portal.ca)
Date: 01/02/04
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Date: Fri, 02 Jan 2004 00:28:22 GMT
<fake@reply-address.com> wrote in message
news:bt2ank$jb8$1@news6.svr.pol.co.uk...
> What exactly does the line:
> rGfxOptionsWnd* m_pGfxOptionsWnd;
> do?
>
> I have chased this bug and narrowed it down to something that I
believe
> should not happen and I don't even know what could possibly cause it
to
> happen.
>
> My basic application structure is simple.
>
> An Application Class,
> An App Class derived from the Application Class
>
> The application class has a member varible which is a Paramater
class
>
> e.g.
> Application {
>
> Public:
> Param_class m_Params;
>
> };
>
> In it's constructor Application instalises m_Params values.
> m_Params.Window.bWindowed = false;
> m_Params.Window.width = 500;
> m_Params.Window.height = 500;
> m_Params.Window.icon = NULL;
> m_Params.Window.title = "rDirectXApp Default Window Title";
> m_Params.Window.wnd_type = RJM_WNDT2;
> m_Params.Window.res_x = 0;
> m_Params.Window.res_y = 0;
> m_Params.Window.esc_to_quit = true;
>
> In it's Constructor, App (Derived from Application) then alters some
of the
> values as nessecary.
>
> m_Params.Window.icon = (const char *) IDI_ICON1;
> m_Params.Window.title = "Super Game in this window!!!";
> m_Params.Window.bWindowed = true;
>
> m_Params.Window.wnd_type = RJM_WNDT5;
> m_Params.Window.width = 600;
> m_Params.Window.height = 300;
> m_Params.Window.bWindowed = true;
> m_Params.Window.res_x = 100;
> m_Params.Window.res_y = 100;
>
> Now I can compile and run this code perfectly. I have set break
points on
> each line shown here and I can watch the values as they go through
this
> process and change.
>
> I have another completely empty class, just an empty constructor and
> destructor.
> RGfxOptions. I add the following line into Applications private
section:
>
> rGfxOptionsWnd* m_pGfxOptionsWnd;
>
> With this line in the program I run the debug version of the
program.
>
> The Application constructor sets up m_Param exactly as it's supposed
to.
>
> Control then passes to App's constructor.
> When: m_Params.Window.icon = (const char *) IDI_ICON1;
> executes, m_Param.Height changes (nothing else)
>
> when m_Params.Window.title = "Super Game in this window!!!";
> executes, m_Params.title changes but the new value is corrupt
>
> when m_Params.Window.bWindowed = true;
> executes, nothing in m_Params alters
>
> when m_Params.Window.wnd_type = RJM_WNDT5;
> executes, nothing
>
> when m_Params.Window.width = 600;
> executes bWindowed alters
>
> when m_Params.Window.height = 300;
> executes, width alters
>
> when m_Params.Window.bWindowed = true;
> executes, nothing
>
> when m_Params.Window.res_x = 100;
> executes, wndtype alters but to an invalid value
>
> and after m_Params.Window.res_y = 100;
> the program crashes because of the invalid data.
>
> But with the line:
> rGfxOptionsWnd* m_pGfxOptionsWnd;
> remmed out it all works perfectly.
>
> Can anyone help? What does that line do? How is it possible that the
> statement altering the height actually alters the width member
variables? I
> havn't used or refered to m_pGrgOptionsWnd anywhere at all in my
code. How
> can simply adding a pointer member varible to my class have this
effect?
>
> Thanks in advance for any suggestions. I have absoultly no ideas at
the
> moment at all!
It is as though the changes to 'Application' are not triggering a
fresh compilation of 'App'. If this is the case then the constructor
code
(in App) could be using the wrong offsets into the objects storage
location. You can try doing a clean build (or at least verifying that
the
App source code is recompiled each time you make changes to your
declaration of Application).
Tom
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