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Hi
Suppose I have following:
class A
{
}
class B : public class A
{
}
I have an instance of class A "pClassA". can I cast it to class B?
I want an instance of class B from the existing instance class A. How can I get it?
Thanks,
modified on Thursday, January 14, 2010 5:41 PM
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Assuming the inheritance is public (in your sample it is private), you can do something like:
A* a = new B;
B* b = dynamic_cast<B*>(a);
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I have following:
A* a = new A;
B* b = dynamic_cast<B*>(a);; ??????
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Since it is a dynamic cast, a type safety check is incurred at runtime: Add a try catch block and you will know. Alternative answer, if you want an instance of class B you might need to create a new object (if class B has more member variables than class A), a good way to do this could be a specific constructor/assignment operator.
Hope this helps,
M
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You cannot do that: a tiger is an animal, an animal (usually...  ) isn't a tiger.
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke
[My articles]
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CODEPC wrote: I have an instance of class A "pClassA". can I cast it to class B?
No, you can only cast back from derived to base class. In your example a B object is always also an A object, but an A object may not be a B object.
MVP 2010 - are they mad?
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Hi,
I am debugging a C app using Visual Studio would anyone know what is
the best approach
Is there an add on for this
Thankx
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Set break points and step through? You don't need any addons for that. Just the debugger will do.
What sort of specific debugging issue are you having? Is the app multi-threaded? Are there DLLs involved? If so, do you have the source? Ask something more specific.
“Follow your bliss.” – Joseph Campbell
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There are pretty big macros
It also multi threaded
Guess there are no easy answers to this
would be nice if I could make a breakpoint
in the macro However I know there is no code associated
with macros variables are just substitued
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Macros? I feel your pain.
The only approach that works for me is to open the Dissasembly windows (Alt+8 with VC++ keyboard setting) and look there. The macros are expanded into real lines of C code and if you are not comfortable with assembly you can simply ignore that part.
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Ok
here is the deal I am stepping thru
HERCULES the mainframe emulator
I wrote a Windows MFC front end
to the DOS C program
There is a CPU_STEPPING macro
which I am trying to debug
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Again, use the dissasembly window. It looks like this: A jpeg screenshot from cprogramming.com[^]. As you can see, the *preprocessed* C++ code is still visible among the assembly instructions. You can step, set a breakpoint, whatever you want. The only downside is that you will see a lot of assembly instructions between the C source code.
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Just a silly idea (I've no means to test it now): why don't you run the preprocessor (compile with /E option) then use the output as your source file?
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke
[My articles]
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Used the /P option and cut and paste the output and commented the macro
thankx
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Hi.
I have a little problem's (I hope!).
I must call a VC++ (6.0) DLL with a dialog from a VB program.
I have try to call a MFC Extension DLL (create in vc++ 6.0) but when the VB program call my DLL crash.
Can you help me??
Thank's a lot from everybody.
Patrizio
Hi! I'm very happy to talk with everybody about VC++.
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Lazzari Patrizio wrote: but when the VB program call my DLL crash
does it give you any error messages ?
also note that VB6 requires that DLLs use the 'stdcall' calling convention. if your functions aren't exported using stdcall, you will get an error.
modified on Thursday, January 14, 2010 11:51 PM
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Lazzari Patrizio wrote: I have try to call a MFC Extension DLL (create in vc++ 6.0) but when the VB program call my DLL crash.
I don't think you can use an MFC extension DLL from a VB program. You could build an use an MFC extension DLL only if the client program (the one that loads and executes code from the dll) is also an MFC program.
I recommend that you rebuild the DLL as a regular DLL (MFC can be used within, but the DLL should not be built as an extension DLL) and try using it from your VB program.
“Follow your bliss.” – Joseph Campbell
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Can i change my project from MFC Extension DLL to regular DLL or i must create a new project? Thank's
Hi! I'm very happy to talk with everybody about VC++.
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As long as you are not throwing around MFC objects between functions (back and forth the DLL and client), just changing the settings should suffice. Because that would be possible only when an MFC extension DLL loaded by an MFC program.
Also, remember what the other responder said about calling conventions while exporting functions from the DLL.
“Follow your bliss.” – Joseph Campbell
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Hi All,
I am developing an application which uses directx apis to render a 3d image.
I want to use .Net framework.Which one of the below languages is good for doing that.I am pretty new to .net.I may seek some coding help from internet.
1.)VC++.Net(Form based application)
2.)Vb.net(Form based application)
3.)C#.net(Form based application)
Please adivce,
Ashwath.
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you've already posted this under [.Net Framework] which since you say you want to use .Net is likely the best forum. Dont cross post please, its bad form and you'll get snarled at and possibly not even an answer to your question in any forum
'g'
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Hi all,
I have made a SDI application in that application i have made a tree ctrl and its class derived from CTreeView. But my problem is when in OnInitialUpdate i write this piece of code
HRESULT hres;
hres = CoInitializeEx(0, COINIT_MULTITHREADED);
if (FAILED(hres))
{
AfxMessageBox(_T("Failed to initialize COM library") );
return ;
}
it returns a error
hres 0x80010106 Cannot change thread mode after it is set.
how can i resolve this
thanks in advance
To accomplish great things, we must not only act, but also dream;
not only plan, but also believe.
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Looking at the documentation here[^] may help. I think your CoInitializeEx() call is occurring more than once, in which case calls after the first will receive S_FALSE even though the call is valid. It may be better to move the call to the beginning of your application.
MVP 2010 - are they mad?
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Actually he is getting RPC_E_CHANGED_MODE, probably one of the loaded DLLs of his application already called the function specifying a different threading model.
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke
[My articles]
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Once again, foolishly, I assumed he had already checked the return code and determined this was not the case.
MVP 2010 - are they mad?
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