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Hi ,
Here is what Stroutstroup had suggested on the same thing you want to achieve:
Can I stop people deriving from my class?
Bjarne Stroustrup :Yes, but why do you want to? There are two common answers:
* for efficiency: to avoid my function calls being virtual
* for safety: to ensure that my class is not used as a base class (for example, to be sure that I can copy objects without fear of slicing)
In my experience, the efficiency reason is usually misplaced fear. In C++, virtual function calls are so fast that their real-world use for a class designed with virtual functions does not to produce measurable run-time overheads compared to alternative solutions using ordinary function calls. Note that the virtual function call mechanism is typically used only when calling through a pointer or a reference. When calling a function directly for a named object, the virtual function class overhead is easily optimized away.
If there is a genuine need for "capping" a class hierarchy to avoid virtual function calls, one might ask why those functions are virtual in the first place. I have seen examples where performance-critical functions had been made virtual for no good reason, just because "that's the way we usually do it".
The other variant of this problem, how to prevent derivation for logical reasons, has a solution. Unfortunately, that solution is not pretty. It relies on the fact that the most derived class in a hierarchy must construct a virtual base. For example:
class Usable;
class Usable_lock {
friend class Usable;
private:
Usable_lock() {}
Usable_lock(const Usable_lock&) {}
};
class Usable : public virtual Usable_lock {
// ...
public:
Usable();
Usable(char*);
// ...
};
Usable a;
class DD : public Usable { };
DD dd; // error: DD::DD() cannot access
// Usable_lock::Usable_lock(): private member
I thinks This solves your problem , If yes rate the answer as Good and close the thread.
Regards,
Kushagra
I hate to code but I luv to Develop 
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G Haranadh wrote: can we make class cant be derived at all? if yes how to make it. please let meknow?
Actually there is an article on CodeProject which can help you. -> Sealing Classes in C++[^]
Personally I like this[^] handy macro, which is generalized version of Stroustrop's solution [^].
Regards,
Nuri Ismail
modified on Saturday, October 24, 2009 12:12 PM
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Hi all , i want to add the FilePath+FileName to the Scanner Driver so that the User App will Print :
Current File Name :MyCurrentFile.txt * for example *
you can download ( scanner *Driver +User App *) from here :http://www.box.net/shared/zm2d7cuyrm[^]
I tried with scanuk.h as follows :
typedef struct _SCANNER_NOTIFICATION {
ULONG BytesToScan;
ULONG Reserved;
UCHAR Contents[SCANNER_READ_BUFFER_SIZE];
PWSTR FileName;
} SCANNER_NOTIFICATION, *PSCANNER_NOTIFICATION;
many thanks
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you provide a link for source code for scanner driver & applications well so nw give me workable link for that i need it so much ....please help me to get it otherwise i will b in trouble ..pls pls frnd..pls contact me on my email if u can bcoz i m nt using this forum to communicate.
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I am attempting to write an application in VC 2008 under Vista 64. In the application, I create a Class and a pointer; the pointer is cast (void) and held in a map.
<CMap<int, int, void*, void*> myMap
m_pClassXYZ = new ClassXYZ;
m_pClassXYZ->Create(NULL, NULL, WS_CHILD, CRect(0, 0, 0, 0), this, nClsID, NULL);
p_vPtr = (void*)m_pClassXYZ;
//Note: Map holds pointers to multiple classes of different types and hence is cast void.
pmyMap->SetAt(n, p_vPtr);
When I want to use the pointer, it is cast back:
m_pClassXYZ = (ClassXYZ*)p_vPtr;
This seems to compile, link and execute without incident. On exit the application I want to destroy the Class(es) and free the memory:
m_pClassXYZ->DestroyWindow();
delete m_pClassXYZ;
The appropriate DLL's are part of the project and allow memory leak checking. I get the following in the Output pane when the application exits:
c:\..................\MyApp.cpp(164) : {192} client block at 0x00098F60, subtype c0,
88 bytes long. a ClassXYZ object at $00098F60, 88 bytes long
When I click on the leak statement, it takes me to the line with the "new" operator.
I understand the leak statement, just not why. I think that this worked in previous versions of Visual Studio.
Am I not destroying the class and freeing memory properly? If not, can someone please give me an idea of what I am doing wrong?
Thanks,
Barry
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This how I would do the allocation into CMap.
CMap<int, int, void*, void*> myMap;
m_pClassXYZ = new ClassXYZ;
m_pClassXYZ->Create(NULL, NULL, WS_CHILD, CRect(0, 0, 0, 0), this, nClsID, NULL);
p_vPtr = (void*)m_pClassXYZ;
myMap.SetAt(n, p_vPtr);
The deallocation would be done as follows -
int nKey;
void* pValue;
POSITION pos = myMap.GetStartPosition();
while (pos)
{
myMap.GetNextAssoc(&pos, &nKey, &pValue);
myMap.RemoveKey(nKey);
m_pClassXYZ = (ClassXYZ*)pValue;
delete m_pClassXYZ;
}
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Superman, you came to the rescue. Your reply cleared out all of those pesky client blocks. Thanks. I do have some normal blocks left, but I will start another thread to address them.
Barry
BTW - I too love work; I can lie down next to it all day long. 
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You say you are using DLLs. Is the memory allocated in one module and deleted in another? You have to keep the allocation and deletion of objects in the same module.
You may be right
I may be crazy
-- Billy Joel --
Within you lies the power for good - Use it!
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My mistake. I was refering to the header files MS supplies that allow the memory leak detail in the output pane. The project does not have any DLL's as of this stage in the writing. Again, sorry for misleading you.
Thanks,
Barry
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void CaDlg::OnBnClickedBrefreshdevices()
{
m_ctlStatus.SetString(_T("Not Functional"));
UpdateData(FALSE);
unsigned int field0 = 0, field1 = 0, field2 = 0, field3 = 0;
CString ips = _T("");
char a[4] = "";
int t=0,c=0;
for(field0 = 192; field0 <= 192; field0++)
{
for(field1 = 168; field1 <= 168; field1++)
{
for(field2 = 0; field2 <= 255; field2++)
{
for(field3 = 0; field3 <= 255; field3++)
{
_itoa_s(field0, a, 4, 10);
ips += a;
ips += '.';
_itoa_s(field1, a, 4, 10);
ips += a;
ips += '.';
_itoa_s(field2, a, 4, 10);
ips += a;
ips += '.';
_itoa_s(field3, a, 4, 10);
ips += a;
t = LCDevices.InsertItem(c, ips);
c++;
LCDevices.SetItemText(c, 1, _T("Testing"));
ips = _T("");
}
}
}
}
}
In this code I am getting a bug when the value of t reaches 9. When InsertItem(c, ips); increases the
value to 10 (ten) it becomes 2 (i.e. 10 is treated as binary nos. 1 0).
Why is it so?
the integer c is not treated as binary no.
Future Lies in Present.
Manmohan Bishnoi
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Manmohan29 wrote: _itoa_s(field0, a, 4, 10);
ips += a;
You could change this to:
ips = a; and eliminate the "reset" at the bottom of the loop.
Manmohan29 wrote: LCDevices.SetItemText(c, 1, _T("Testing"));
This should probably be:
LCDevices.SetItemText(t, 1, _T("Testing"));
"Old age is like a bank account. You withdraw later in life what you have deposited along the way." - Unknown
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
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I did what you told but
values after inserting a breakpoint after
c++;
ips "192.168.0.9"
t 9
c 10
ips "192.168.0.10"
t 2
c 11
the problem is still there.
Future Lies in Present.
Manmohan Bishnoi
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I'm not sure what you are asking or showing. When you call InsertItem(), it will return the index of the item that was added. This index is used in subsequent calls to SetItemText(). If you have anything other than that, your code will not work correctly.
Feel free to show the updated code.
"Old age is like a bank account. You withdraw later in life what you have deposited along the way." - Unknown
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
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void CaDlg::OnBnClickedBrefreshdevices()
{
m_ctlStatus.SetString(_T("Not Functional"));
UpdateData(FALSE);
unsigned int field0 = 0, field1 = 0, field2 = 0, field3 = 0;
CString ips = _T("");
char a[4] = "";
int t=0,c=0;
for(field0 = 192; field0 <= 192; field0++)
{
for(field1 = 168; field1 <= 168; field1++)
{
for(field2 = 0; field2 <= 255; field2++)
{
for(field3 = 0; field3 <= 255; field3++)
{
_itoa_s(field0, a, 4, 10);
ips = a;
ips += '.';
_itoa_s(field1, a, 4, 10);
ips += a;
ips += '.';
_itoa_s(field2, a, 4, 10);
ips += a;
ips += '.';
_itoa_s(field3, a, 4, 10);
ips += a;
t = LCDevices.InsertItem(c, ips);
c++;
LCDevices.SetItemText(t, 1, _T("Testing"));
}
}
}
}
}
I am using index in subsequent calls to SetItemText().
but still when t = 10 then it becomes t = 2 (binary 10).
one more thing the counting is like this:-
ips "192.168.0.0" t = 0
.
.
.
ips "192.168.0.9" t = 9
ips "192.168.0.10" t = 2
.
.
.
ips "192.168.0.20" t = 13
.
.
.
ips "192.168.0.99" t = 99
ips "192.168.0.100" t = 3
ips "192.168.0.101" t = 4
ips "192.168.0.102" t = 5
Future Lies in Present.
Manmohan Bishnoi
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While not related to your problem (at least I don't think so), you could shorten it down a bit to:
int c = 0;
for (unsigned int field2 = 0; field2 <= 255; field2++)
{
for (unsigned int field3 = 0; field3 <= 255; field3++)
{
CString ips;
ips.Format(_T("192.168.%u.%u"), field2, field3);
int nIndex = LCDevices.InsertItem(c, ips);
LCDevices.SetItemText(nIndex, 1, _T("Testing"));
c++;
}
}
"Old age is like a bank account. You withdraw later in life what you have deposited along the way." - Unknown
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
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Hi. Well... I have a trouble with scrollbars. In my (developer) computer it all looks great! BUT in any other computer it looks incorrectly. The first time, when i create the window scrollbars are painted on the border of the dialog instead of the inside of the window. And when i resize it, it repaints the window correctly with the scrollbars inside.
This i wrote in OnCreate
this->EnableScrollBar(SB_VERT);
this->EnableScrollBar(SB_HORZ);
And this is at OnInit
this->SetScrollRange(SB_HORZ,0,2*STARTPIXELX+MAPSQUARE*FIELDSIZE);
this->SetScrollRange(SB_VERT,0,2*STARTPIXELY+MAPSQUARE*FIELDSIZE);
SCROLLINFO info;
info.cbSize = sizeof(info);
info.fMask = SIF_ALL | SIF_DISABLENOSCROLL;
info.nMin = 0;
info.nMax = 2*STARTPIXELY+MAPSQUARE*FIELDSIZE;
CRect rr;
this->GetClientRect(&rr);
info.nPage = rr.bottom-rr.top;
info.nPos = 0;
info.nTrackPos = 0;
SetScrollInfo(SB_VERT,&info);
info.nPage = rr.right-rr.left;
info.nMax = 2*STARTPIXELX+MAPSQUARE*FIELDSIZE;
SetScrollInfo(SB_HORZ,&info);
this->ShowScrollBar(SB_VERT);
this->ShowScrollBar(SB_HORZ);
My dialog has application window, Overlapped, resizing border styles. Pls help!
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Well.. A found a solution.. I don't like it, but it works.
void MainDial::OnTimer(UINT_PTR nIDEvent)
{
if (theApp.First)
{
CRect rr;
this->GetWindowRect(&rr);
rr.right-=1;
rr.bottom-=1;
MainDial::MoveWindow(rr);
theApp.First=false;
}
}
modified on Friday, October 23, 2009 6:53 PM
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You could put this in OnSize and check.
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The problem is that after OnSize it shows all correct, that's why i use MoveWindow in my timer. But my problem is how to make that right after OnInit it draws correctly? I resolved it only with timer... And by the way.. WHY it's all working on MY computer and on any other not?!?! (I have VS2008 SP1 and Windows XP SP3)
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You can try another method.
Create a custom message and map it to a handler using ON_MESSAGE[^].
In the OnInitDialog function to a PostMessage[^] for your custom message.
In the message handler you could put the code that is in the timer.
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Solution found.
LRESULT MainDial::OnMyMsg(WPARAM, LPARAM)
{
CRect rr;
this->GetWindowRect(&rr);
rr.bottom-=1;
rr.right-=1;
MainDial::MoveWindow(rr);
return NULL;
}
with ON_MESSAGE use.
Big thnx.
modified on Friday, October 23, 2009 8:30 PM
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I'm looking for a MEE that can handle number expressed with factions.
Example: A user may use 3.5 * 4 7/8 or 3 1/2 * 4.875
I see a lot of MEE but do not want to go through each one.
Any help, pointers would be helpful
Thanks
Tony Teveris
Gerber Scientific Products
Senior Software Engineer
Phone: 860 648 8151
Fax: 860 648 8214
83 Gerber Road West
South Windsor, CT 06074
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Are you looking for a seriously advanced one (see this thread), or just one to handle 4-5 basic operators? The latter cab be done via a basic RPN calculator.
"Old age is like a bank account. You withdraw later in life what you have deposited along the way." - Unknown
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
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