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Seems like it shouldn't work because of circular references, but the fact is that this little trick compiles fine (and what's more, it does not incur in any run-time penalty, everything is resolved on compilation). To the best of my knowledge, it was the ATL guys the first who used this idiom.
Templates are a constant source of enjoyment and productivity. I feel sorry about C# & Java users with its "single hierarchy"/"no hassles"/"type-unsafe containers" languages!
Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo
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Thanx again Joaquín.
Not only does it work, but it works great!
This totally simplifies the everything in my classes, instead of throwing it all into one big class I've seperated them, which is what was wanted. The 2-3 ideas i originally had required so much more overhead and some redudant code. This is great.
Only one question remains. Is this an example of downcasting sort of...? Also, doesn't this break the rules of OOP...? I'm positive this is the best solution for my particular problem, however if used improperly or too often this could cause spaghetti code correct...?
Thanx again!
"An expert is someone who has made all the mistakes in thier field" - Niels Bohr
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Is this an example of downcasting sort of...?
Yes, downcasting is the process of going from a Base * to a Derived *.
Also, doesn't this break the rules of OOP...?
I don't think so; after all, its semantics strongly mimic that of virtual functions mechanisms (although in compile-time).
however if used improperly or too often this could cause spaghetti code correct...?
The main defect of this idiom, IMHO, is that it's little known among C++ programmers, which find it hard to understand at first. If it ever goes commonplace in the C++ community, the technique is as sound as many others. Think about this: 20 years ago, this idiom was probably seen as clumsy and tricky:
while(*dst++=*src++); Now it is only one of those gadgets people are accostumed to use in C/C++ code.
Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo
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hi,
what about this approach:
class CBuffer
{
public:
virtual void Set() = 0;
virtual void Get() = 0;
...
};
template<class TBuffer>
class CUndoBuffer
{
public:
...
void SomeFunc()
{
m_theBuffer.Set( whatever );
m_theBuffer.Get( whatever );
}
private:
TBuffer m_theBuffer;
};
class CConcreteBuffer : public CBuffer
{
public:
virtual void Set();
virtual void Get();
...
};
CUndoBuffer<CConcreteBuffer> AConcreteUndoBuffer;
etc..
..have fun..
jk 
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Don't pure virtual functions make it a ABC...?
CBuffer is not the base class it's the child which contains most of the functionality and would be much easier and I thought OOD friendly if it shared some of it's functionality with it's parent class. Which made me realize I don't understand inheritence, up/downcasting or MI as well as i thought;P
The template solution given by Joaquín seems most confusing but has no RT penalties.
right now as we speak Joaquín has me convinced, however perhaps you feel another solution is more appropriate.
Opinions...?
thanx again.
"An expert is someone who has made all the mistakes in thier field" - Niels Bohr
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Who have seen the project ICONIZER in codeproject.com??? You can get it by http://codeguru.earthweb.com/shell/iconizer.zip
It is a great code. But I have found a big bug in it.
CASE: Open notepad.exe program -> run ICONIZER -> Open ABOUT DIALOG of notepad.exe -> exit ICONIZER -> press OK button in ABOUT DIALOG, finally, the notepad.exe crashed....
who can anwser this question???????
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If I don't open taht ABOUT DIALOG, this bug will never appear...
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Hi, everybody,
This may be a stupid question, but I really hope somebody to help me...
I got some trouble about the "unit" and "unit conversion" for rendering an image.
I have read some people's share codes on this web site. Those codes are all for image rendering with the COM interface IPicture. Here are my questions.
1. IPicture::get_Width: Returns the current width of the picture in the picture object. (from MSDN), the API is as follows:
HRESULT get_Width( OLE_XSIZE_HIMETRIC* pwidth //Receives a pointer to width );
My question is, what kind of unit we get from pwidth ? I mean, is pwidth in inch ? or in mini-meter ? or anything else ? Does this IPicture use MM_HIMETRIC coordinate system ?
2. If there are some code segment related to calculate the dimension (in pixels) of an image,
HIMETRIC_INCH is 2540
long hmWidth;
long hmHeight;
m_pPicture->get_Width(&hmWidth); /// m_pPicture is of type pointer to ///IPicture
m_pPicture->get_Height(&hmHeight);
rcResult.cx = MulDiv(hmWidth, pDC->GetDeviceCaps(LOGPIXELSX), HIMETRIC_INCH);
rcResult.cy = MulDiv(hmHeight, pDC->GetDeviceCaps(LOGPIXELSY), HIMETRIC_INCH);
Could anybody explain why HIMETRIC_INCH (2540) is used above ? And explain more about the above formula ? Is hmWidth (or hmHeight) in mini-meter ?
Thanks in advance ! Any reponse will be appreciated !
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marouane miftah el kheir wrote:
C:\Windows\Desktop\mCpp2.cpp(8) : error C2146: syntax error : missing ';' before identifier 's'
Check your syntax. Are you missing a semicolon on one of your lines? Perhaps you're missing a semicolon after one of your "class {...};" definitions.
Jon Sagara
What about ![Green Alien | [Alien]](https://www.codeproject.com/script/Forums/Images/alien.gif) ?
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LOL
He deleted all his posts
Nish
Sonork ID 100.9786 voidmain
www.busterboy.org
If you don't find me on CP, I'll be at Bob's HungOut
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Too bad, I was willing to help him. 
Jon Sagara
What about ?
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Where do i find the exception-declaration info for try-catch statements...?
I'm currently using catch(...) but i'd like to be a little more specific.
Do i have to use (CException* e) with MFC apps?
I can't much on try/catch in the online docs...any ideas?
TIA
"An expert is someone who has made all the mistakes in thier field" - Niels Bohr
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I have some problems with windows messaging
I create a Custom control with the create funtion in my InitDialog function:
m_pGrid = new CGridCtrl(22,9,0,0);
m_pGrid->Create(rect,this,1);
How can I set my dialog up to receive notification messages?
I would use:
ON_NOTIFY(GVN_ENDLABELEDIT, ???, OnGridStartSelChange)
but I do not have the ID of the control.
Thank You
LP
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By specifying the ID in the Create Function.
Sometimes you just search in the wrong spot.
LP
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Hi,
Just wondering if anyone has any ideas on the following.
I have a largish memory mapped file (~80Mb) to which data is being consistantly written to and read from. The problem lays in the once part of the MM file has been written to on Win 9x (the problem doesn't exist on NT) memory is used, the only way to free this memory is to completely close the MM file and re-open it. This is a large hit to take, ie 70-80% of CPU for approx 2 seconds when flushing every 30 seconds. Is there any way I can consistantly flush the data out of memory when it hasn't been used for a specified time?
Thanks
Stuart 
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in a MFC dialog based app, i got my previous app to work finally but i also need the edit box to be checked for entered text, if nothing is entered it has to generate a message box stating so when the show button is clicked.
like i said i got it all working, i can enter some text and click the button and have a box pop up displaying what i typed. but i'm not sure how to make the button check the edit box for text and display my error message.
also it's not important but where would i put the updatdata to clear the edit box once ok is clicked on the message box.
here's the part of code i'm referring to:
void CProgEx3Dlg::OnShow()
{
GetDlgItemText(IDC_TEXT,m_sText);
MessageBox(m_sText,"Sample Dialog Box",NULL);
}
thnx again in advance
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I am writing a program.
In this program I wanna know whether the CD-ROM's door is Opened or Closed?
How I can write code?
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hi there,
a good starting point is to search the MSDN for MCI. Another (but much harder) way is the function DeviceIoControl().
..have fun..
jk 
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I wanna know which Function I can use ?
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mciSendCommand() or DeviceIOControl().
There's no Function like Is_Drive_A_CDRom_And_If_Its_So_Is_The_Tray_Open(LPCTSTR pszDrive).
RTFM 
..have fun..
jk
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Try (file-)reading-routines on the CD, if it fails drive is open, if it doesn't fail, drive is closed
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Does anyone know of a good UNICODE Registry, or INI file class? If you do could you let me know? Thanks.
- Matt Newman
-Sonork ID: 100.11179:BestSnowman
Frankly AOL should stick to what it does best: Fooling millions of americans into believing that it, AOL, is the web. -Paul Watson
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Hi,
Can some one post me a good example of a plugin based application. I would like to implement an app with a plugin structure like photoshop., I guess an expert with this must write a small plugin based example app with some good explanation. This I think is one of the difficult areas but still very useful 
Any links, source code, articles welcome
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I wrote an artical which does document/view plugins. Heres the URL:
http://www.codeproject.com/docview/docviewfromdll.asp
It may be useful for what you are doing.
Roger Allen
Sonork 100.10016
If I'm not breathing, I'm either dead or holding my breath.
A fool jabbers, while a wise man listens. But is he so wise to listen to the fool?
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What are they, and why do they plague me so when creating ActiveX controls dynamically
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