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In the first function you passed a pointer, not a reference, and you passed that pointer by value. Passing a parameter of type X by value is the same as passing the same parameter as type const X - at least from the point of view of the caller - therefore the declaration of your second function is syntactically the same as the first (again, from the point of view of the caller). The compiler cannot disambiguate any calls to this function into one of the two versions, therefore it does not allow you to overload like that. Follow the link to GOTW I've posted above, IIRC that this was also covered there. In short, if you pass a parameter by value, you cannot overload it only by adding const to that type.
If you meant to pass your pointer by reference, do it this way (using underscore to highlight the change):
void GetBlah2(Blah const *& blah) { } void GetBlah2(Blah const * const blah) { }
This should work.
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I see. Your reply makes sense. It's like trying to declare a const reference (Blah & const). It's redundant.
If your actions inspire others to dream more, learn more, do more and become more, you are a leader." - John Quincy Adams You must accept one of two basic premises: Either we are alone in the universe, or we are not alone in the universe. And either way, the implications are staggering” - Wernher von Braun
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Not quite. In case of a reference there really is no difference as there is no such thing as a non-const reference. In your example however there would be a difference, but it would only be visible within the code of your function: there, if you defined the parameter const , you could not modify it (locally), whereas if you didn't define it const you could. Of course, since you pass it by value the caller wouldn't notice the difference, basically you gain an additional local variable by not declaring it const .
const Blah* GetBlah1(const Blah*& const b) {
b = 0; return b;
}
const Blah* GetBlah2(const Blah*& b) {
b = 0; return b;
}
const Blah* GetBlah3(const Blah* const b) {
b = 0; return b;
}
const Blah* GetBlah4(const Blah* b) {
b = 0; return b;
}
int main() {
Blah* a = new Blah;
Blah* b = GetBlah4(a); assert(b==0);
assert(a!=0);
delete a;
return 0;
}
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I copied your code into VC++ 2010 and the first two errors do not occur.
Stefan_Lang wrote:
const Blah* GetBlah1(const Blah*& const b) {
b = 0;
return b;
}
const Blah* GetBlah2(const Blah*& b) {
b = 0;
return b;
}
Also, this line gets an error because you can't assign a const value to a non-const value:
Stefan_Lang wrote:
Blah* b = GetBlah4(a);
Anyway, thanks for your help. I understand I think.
If your actions inspire others to dream more, learn more, do more and become more, you are a leader." - John Quincy Adams You must accept one of two basic premises: Either we are alone in the universe, or we are not alone in the universe. And either way, the implications are staggering” - Wernher von Braun
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Ah, my bad, you are right in all three cases: in the first functions the assignments don't change the reference, only the value they reference. So these examples were not valid for the purpose I wanted to demonstrate. Also, when I tried to compile GetBlah1() I got the warning warning C4227: anachronism used : qualifiers on reference are ignored. This leads me to believe that it is not actually possible to pass a parameter by const reference, and the rightmost const in the signature is ignored, therefore b is not const and may be modified. I wasn't aware of that restriction before.
The function call to GetBlah4() doesn't work because it tries to assign the (const) return value to a non-const variable. Add a const at the start of the line and it should work.
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In the case of pointers, the following 2 lines are the same, where the contents cannot be changed while the pointer can be made to point to another object.
const Blah* p = GetMyBlahPtr();
Blah const* p = GetMyBlahPtr();
Whereas in the following line, the contents can be changed, but the pointer itself cannot be pointed to another object.
Blah* const p = GetMyBlahPtr();
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I can do this in my code
PostMessage(WM_KEYDOWN);
The message gets properly intercepted, no problem.
I need to detect right arrow so I add wParam like this
PostMessage(WM_KEYDOWN,VK_RIGHT,0);
The message is nowhere to be found.
WindowProc does not even detects WM_KEYDOWN.
All this in MFC.
What am I missing?
Thanks for your help.
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You may need to add some detail in your LPARAM variable as described here[^]. Also check the status returned from your PostMessage() call.
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I have changed to SendMessage and get expected results.
Also adding GetLastError processing AFTER the PostMessage I get expected results.
Can anybody explain why is this happening?
Especialy when it works when only WM_KEYDOWN is used without the wParam.
The lParam should specify number of repeats of the keyboard, right arrow in my case and should be 0.
I am not using any other language, only US English.
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I just dropped the following code into a program to test the interpretation of "Specifies the repeat count. The value is the number of times the keystroke is repeated as a result of the user holding down the key."
case WM_KEYDOWN:
sprintf(szText, "repeat count = %d", lParam & 0xFF);
MessageBox(NULL, szText, "Guess What?", MB_OK|MB_ICONQUESTION);
return 1;
While I agree with your interpretation, the message box says that the repeat count is 1.
I'd suppose that when you send WM_KEYDOWN without the wParam, the helper-function that you're calling sets up an appropriate one before calling the 'real' SendMessage, as defined by:
LRESULT SendMessage(
HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam );
?
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RecordsetPtr rsUrun;
rsUrun.CreateInstance(__uuidof(Recordset));
try{
_variant_t Holder;
CString cQry=_T("");
CString cTmp=_T("");
_stUrun stTmp;
vUrun.clear();
cQry=_T("Select * From urun order by adi");
rsUrun->Open(_variant_t(cQry),AdoTest.GetInterfacePtr(),adOpenDynamic,adLockOptimistic,adCmdText);
CStringArray caTmp;
int nPs=0;
while(!rsUrun->adoEOF)
{
stTmp.cUrunAd=_T("");
stTmp.dBirimf=0;
stTmp.nDBID=0;
Holder = rsUrun->GetCollect("urunid"); if(Holder.vt!=VT_NULL) stTmp.nDBID=atoi((char*)_bstr_t(Holder));
Holder = rsUrun->GetCollect("adi"); if(Holder.vt!=VT_NULL) stTmp.cUrunAd=(char*)_bstr_t(Holder);
Holder = rsUrun->GetCollect("birimf"); if(Holder.vt!=VT_NULL) stTmp.dBirimf=atof((char*)_bstr_t(Holder));
vUrun.push_back(stTmp);
CString adi = rsUrun->GetCollect("adi");
listbo1.AddString(_T(adi));
int gfujf = listbo1.GetItemData(listbo1.GetCount()-1);
rsUrun->MoveNext();
SO here is the code, could you please help me on how can I get the listbox item's id in order to use it in an update query?? Here is my button below, I did some work on it but seems no good
void CTestADSSQLDlg::OnBnClickedButton1()
{
_RecordsetPtr rsUrun;
rsUrun.CreateInstance(__uuidof(Recordset));
CString cQry=_T("Update urun set adi='%s' where urunid='%d'", editbo1;
rsUrun->Open(_variant_t(cQry),AdoTest.GetInterfacePtr(),adOpenDynamic,adLockOptimistic,adCmdText);
}
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symeramon wrote: CString cQry=_T("Update urun set adi='%s' where urunid='%d'", editbo1;
Seems a parenthesis has gone AWOL.
symeramon wrote: SO here is the code, could you please help me on how can I get the listbox item's id...
Umm, since you are using MFC, why not just assign it a CListBox member variable? Use ClassWizard (or equivalent).
"One man's wage rise is another man's price increase." - Harold Wilson
"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
"Show me a community that obeys the Ten Commandments and I'll show you a less crowded prison system." - Anonymous
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Thanks David, at least you answered my question... But the main problem is how can I get the id from vector to use it in the button click event?
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symeramon wrote: But the main problem is how can I get the id from vector...
What does a vector have to do with any of this?
symeramon wrote: ...use it in the button click event?
BEGIN_MESSAGE_MAP(CMyDialog, CDialog)
ON_BN_CLICKED(IDC_SOME_BUTTON, OnButtonClicked)
END_MESSAGE_MAP()
...
void CMyDialog::OnButtonClicked()
{
m_listbox.AddString(_T("Hello World!"));
}
"One man's wage rise is another man's price increase." - Harold Wilson
"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
"Show me a community that obeys the Ten Commandments and I'll show you a less crowded prison system." - Anonymous
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Thanks for your reply David... Finally I got it, by SetItemData!
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1, Window Design
2, Skining the Dialog
3, Other plug in usage
if any one have answers with simple snippets please refer me.
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Are you trying to ask how its used? MFC is basically an objected oriented layer around the WinAPI, but it's not just that, it provides a framework for development. As a framework, it provides base abstraction layers for creating objects, windows, threads, lists, arrays, strings, controls, and many more objects common in desktop development.
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Albert Holguin wrote: basically an objected oriented layer
Emphasis mine: Personally I always considered MFC (any version) to be version 1.0.x of Microsofts attempt to make an object oriented layer. Even the most recent versions still contain way too much remnants of C-style programming to be rightfully called 'object oriented'. To just name one example (or two): the WPARAM and LPARAM parameters widely used in functions all over the API are IMNSHO an abomination all by themselves. Or the 'type', HANDLE : Try to figure out what that type really is, and you'll find there are quite a few different variants, many of them incompatible with each other (as I've learned the hard way)
My hopes are on Windows 8: maybe Metro will provide the long-awaited 'Windows API 2.0' ...
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Do you really need to use bold text for a simple list of links?
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LOL.. i like to be dramatic. Just to put a little empasis on topics
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I am new into writing C++ providers.
Can anyoone let me know the basics of provider writing.
I mean I wanted to know about Provider types(Instance, Method, Indication) and why are they needed etc
What are properties, mof, cim, schema etc.
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Providers are used to provide dynamic data which are not stored in internal datastore for the CIMOM .
More details[^] can be found in the link.
Also if you could google with "C++ provider" keyword you can get more results and channels to start.
You talk about Being HUMAN. I have it in my name
AnsHUMAN
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Thanks Anshuman I will have a look at the link.
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