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It looks like Opera does just that.... Is opera MDI app?
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I would like to write an application, having MANY classes. Each class needs access to a common (application-wide) global variable, say, int nVAR.
One of the classes would "set" nVAR, the rest of the classes would "get" nVAR.
Could someone please provide a simple sample code showing how to do this (or provide references to applicable samples).
Also, according to several sources I read "global variables" should NOT be used. Then WHAT should be used?
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look for the singleton pattern, it's a class that can be instanciated only once, and can live everywhere,
for example ( taken from Design Patter, by Gamma, Helm, Johnson and Vlissides):
class Singleton {
public:
static Singleton* Instance();
protected:
Singleton();
private:
static Singleton* _instance;
};
The corresponding implementation is
Singleton* Singleton::_instance = 0;
Singleton* Singleton::Instance () {
if (_instance == 0) {
_instance = new Singleton;
}
return _instance;
}
Maximilien Lincourt
For success one must aquire one's self
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There are no iron-cast, inviolable laws of programming.
Every program usually has at least a few things that are global and creating global variables for them is fine. It's the excessive, unnecessary use of global variables that causes problems.
Using a Singleton class is fine in itself but you want to be careful not to put a whole lot of stuff in place that ends up with you having a really complicated global variable 
The situation you describe is a good case for *not* using a global variable since it introduces a coupling between your classes that can be hard to detect. Better if you make it a static member variable of the setting class and provide a static "get" method. That way, the coupling is obvious.
Software is everything. It also sucks. Charles Fishman [^]
Awasu 1.0.3 (beta)[^]: A free RSS reader with support for Code Project.
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Gabor Kalman wrote:
Then WHAT should be used?
Static variables inside a class visible to everywhere, or inside a namespace, or globals in an unnamed namespace. Anything else is a nightmare, although obviously one global is not going to bring your project to your knees, I usually regard a long list of glabals as evidence that people have elsewhere used bad practices out of ignorance or laziness. It's better to do things right ALL the time than to make allowances where you can't be bothered.
Christian
NO MATTER HOW MUCH BIG IS THE WORD SIZE ,THE DATA MUCT BE TRANSPORTED INTO THE CPU. - Vinod Sharma
Anonymous wrote:
OK. I read a c++ book. Or...a bit of it anyway. I'm sick of that evil looking console window.
I think you are a good candidate for Visual Basic. - Nemanja Trifunovic
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Hi there,
I just finished compiling a static library with Dev-C++ 5.0. I tried to use the library in VC++ 6.0, but this brings up the error LNK1136 while trying to link...How can I get that to work? Does anybody have an idea? Is there a free compiler which can be used to produce static libraries that are compatible to VC++ 6.0 ??
thanks in advance...
jason
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I experienced the most bizzare thing with SetPaneText
Some application of mine has a CStatusBar with 3 panes.
It's created properly, and SetPaneText() calls are successful for pane 1, but not for pane 2.
My indicators were declared as follows :
static UINT indicators[] =
{
ID_SEPARATOR,
ID_PANE1,
ID_PANE2
}
If I swap positions of ID_PANE1 and ID_PANE2 in indicators declaration, then SetPaneText works for pane 2, but not 1.
So I checked the declaration of ID_PANE1 and ID_PANE2 in the resource header file. Nothing unsual, besides ID_PANE1 shows up as hexadecimal when all other strings are decimal.
Deleting ID_PANE2 and re-inserting it from the string resources did the trick. But I'm still confused about why a simple string declaration has been able to block SetPaneText.
JC
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Ok, I have a class called CComboBox2. Lets assume there's not much to it other than the declaration. It is derived from CComboBox(public)
I put the CComboBox2 in my afx message map.
Windows is not dunningmy dialog-level handler.
It does call the class's own OnSelchange():
void CComboBox2::OnSelchange()
{
m_bChanged = true;
CEdit2::SetChange(true);
}
It is used on a dialog where a CMyDialog::OnSelchangeCombo1() is defined.
What must I do to get the dialog's OnSelchangeCombo1() to run?
Many thanks in advance!
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First of all, your question is confusing. It sounds as if you are trying to implement a custom message map, but not. If you used the class wizard, the message map is generated automagically. If not, you need to do it by hand. i.e.:
in your MyDialog.cpp:
BEGIN_MESSAGE_MAP(CMyDialog, CDialog)
ON_NOTIFY(NM_DBLCLK, IDC_SOMECONTROL, OnDblclkSomeControl)
END_MESSAGE_MAP()
void CMyDialog::OnDblclkSomeControl(NMHDR* pNMHDR, LRESULT* pResult)
{
NM_LISTVIEW* pNMListView = (NM_LISTVIEW*)pNMHDR;
int item_clicked = pNMListView->iItem;
if(item_clicked != -1)
{
DoSomething();
}
*pResult = 0;
}
and in MyDialog.h:
afx_msg void OnDblclkSomeControl(NMHDR* pNMHDR, LRESULT* pResult);
- Nitron
"Those that say a task is impossible shouldn't interrupt the ones who are doing it." - Chinese Proverb
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Ok. I have a Drop-List style combo box control. It is declared as a CComboBox2. CComboBox2's base class is CComboBox.
I want a CBN_SELCHANGE handler for a control IDC_COMBO1 in a dialog IDD_DIALOG1
When the control is a CComboBox2, the dialog never gets the message. It never calls the dialog's handler for that control for that message. It does run the CComnoBox2's CBN_SELCHANGE handler though.
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I'm working on an MFC project. When I went to add an MFC class via the wizard it tells me I can only add an MFC class to an MFC project. Anyone know how to tell it that it is an MFC project? Or how this information is kept so I can fix the project?
Cross posted on VS thread too..
ed
Regulation is the substitution of error for chance.
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Best way is probably to start a new fresh MFC project and transfer your files there.
Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo
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If you created an MFC application from the AppWizard (I'm assuming you are using VC6 and not VC7 since you mention Class Wizard), you shouldn't have any problems. Did you try to convert a console app to an MFC app or something like that? Have you ever had problems making MFC apps before?
-Matt
------------------------------------------
The 3 great virtues of a programmer:
Laziness, Impatience, and Hubris.
--Larry Wall
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Are you sure that it is an MFC project and not a console application, or just a simple application? Did you use the application wizard to create the project?
// Afterall I realized that even my comment lines have bugs
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I overrode the CBN_SELCHANGE event so I have a OnSelChangeControl event for my dialog. (In MFC, via ClassWizard)
When the user changes the selection, the code doesn't get called. If I do a close-up event on the same control it works, but I need it to run on selection change and not just close-up.
I'm using a break point in the debugger to see if it'd getting called.
What am I forgetting?
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This is odd. I made a new project, and did what I did above. It works. But it refuses to work on this project.
Does anyone have any ideas?
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Compare your message map calls between the two projects and see if they match. Your event may not have gotten hooked up for some reason. I've had issues with that before (though not usually on a combo box) that were fixed by hooking up the message map manually.
I did a test app to see if I could duplicate your problem and mine worked fine. Heres the code that classwizard generated.
void CSelChangeTestDlg::DoDataExchange(CDataExchange* pDX)
{
CDialog::DoDataExchange(pDX);
DDX_Control(pDX, IDC_STATIC_LABEL, m_label);
DDX_Control(pDX, IDC_COMBO1, m_combo1);
}
BEGIN_MESSAGE_MAP(CSelChangeTestDlg, CDialog)
ON_WM_SYSCOMMAND()
ON_WM_PAINT()
ON_WM_QUERYDRAGICON()
ON_CBN_SELCHANGE(IDC_COMBO1, OnSelchangeCombo1)
END_MESSAGE_MAP()
Best Regards.
-Matt
------------------------------------------
The 3 great virtues of a programmer:
Laziness, Impatience, and Hubris.
--Larry Wall
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I did verify that I have:
ON_CBN_SELCHANGE(IDC_COMBO1, OnSelchangeCombo1)
So it is wired up right.
I also checked for duplicate nmumonics and control IDs. No such luck. It's like windows isn't sending (or is swallowing) the event.
I even went into PreTranslateMessage() and did:
if (m_cmbCombo1.m_hWnd==pMsg->hWnd) {
TRACE ("%d %d %d\n",pMsg->message,pMsg->wParam,pMsg->lParam);
}
and no CBN_SELCHANGE messages are comming in!
Arg!
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Someone (not me) made it a CComboBox2
CComboBox2 publicly inherits CCombobox, be it looks like this isn't good enough.
How do I use a derived class like this, while still being able to use the CComboBox's events?
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The message for Combo box you handled in the parent dialog
i.e. CBN_SELCHANGE is called notification. In your project this notification message from child i.e. ComboBox to parent dialog is handled by the parent (Dialog which has the message handler). But when you derive the a class publically from the CComboBox class then you define the message handler in this new derive class for the notification message from the ComboBox and this method is called Message Reflection.
Now you will have to map your combo box with your newly
derived class through wizard which will defined an instance
of derive class to the parent dialog like...
class CSelChangeTestDlg:public CDialog<br />
{<br />
...<br />
private:<br />
CDerivedCombo m_MyCombo;<br />
....<br />
}<br />
<br />
void CSelChangeTestDlg::DoDataExchange(CDataExchange* pDX)<br />
{ <br />
CDialog::DoDataExchange(pDX);<br />
DDX_Control(pDX, IDC_COMBO1, m_MyCombo); <br />
...... <br />
}
Now the newly derivered class is self contained and you can this class for the customized behaviour in any project. You dont have to define the message handler again in the parent class/Window of the ComboBox because this defined in the derived class. you only need to map it with the Combo Box. If you need further help plz .....
![Rose | [Rose]](https://codeproject.freetls.fastly.net/script/Forums/Images/rose.gif) Regard,
Nasir Maan
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I have a Class (XClass) which has a private variable (Dialog*). It references to main dialog. So, the main dialog has same variables which were initializated before.
In the dialog I do something like that: varibleX.setParnert(this)
The problem is when I call one method, from the XClass, the Dialog´s variables lost their values.
it is an example how i do: ((CMyDlg*)pWnd)->NuevaTarea(strRecvd);
Which is my error?
el hombre arriesga su vida cada vez que elige y eso es lo que lo hace libre
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I don't know exactly what's your problem, but since you're accessing the variables through a pointer (Dialog*) you can modify them in any way. What you can do is making the parameters of your member-functions in XClass "const". That way you won't be able to change the dialog variables directly. You can change e.g. definition of NuevaTarea() to something like that:
NuevaTarea(const CString& strRecvd);
regards
modified 12-Sep-18 21:01pm.
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I´ll try to explain
I have a dialog(CSurSpoolerDialog) which has a public variable(server).
So, the Server has a private variable pWnd as CDialog* (which is a reference to parnert dialog (CSurSpoolerDialog))
I initilized the Server, Then I call server.setParnert(this)
So, The Server has a event (OnMessage)where I want to call a Dialog´s method ( ((CSpoolerSurDlg*)pWnd)->NuevaTarea(strmessage) )
All work fine, but when i debug the NuevaTarea all the dialod´s variables have lost them values. they have NULL (???)
it is more clearer?
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I found the solution thanks you the any way
el hombre arriesga su vida cada vez que elige y eso es lo que lo hace libre
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I try to make an active X calling an other active X, but I dont know how to do to make the active X I'm calling to be visible.
I don't know if I explain it as clearly as I should, but who can help me?
Thank you
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