C / C++ / MFC Discussion Boards

CPallini3-Feb-08 22:35

3-Feb-08 22:35

OK, It seems I missed the diamod issue of multiple inheritance.
BTW you can simply fix it choosing a derivation path, for instance:

Base* pb = (Derived1 *)&f;

hence my suggestion, on the OP becomes

IUnknown* pI = static_cast<iunknown*>(static_cast <ix*> (new CA));
</ix*></iunknown*>

Weird, I know, but descriptive.

BTW diamond inheritance scheme is evil and should be avoided.

Smile | :)

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.

[my articles]

Re: CreateInstance

George_George3-Feb-08 22:40

George_George

3-Feb-08 22:40

Thanks CPallini,

I am confused why there is ambiguity issue. In my knowledge, class instance is different by the data members, but common (share) in executable code.

In my sample, IUnknown, IX and IY are all classes which do not have data members, they should share the common executable code. Could you explain in more details why compiler complaint ambiguity issue and what blocks compiler from type conversion?

regards,
George

Re: CreateInstance

CPallini3-Feb-08 22:52

CPallini

3-Feb-08 22:52

Since C++ hasn't special syntax for interfaces, I think the compiler isn't allowed to make special assumptions on them. I mean the compiler probably behaves as it was dealing with standard classes (that can have data members), hence finds ambiguities on derivation path.
Smile | :)

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.

[my articles]

Re: CreateInstance

George_George3-Feb-08 23:01

George_George

3-Feb-08 23:01

Hi CPallini,

We can discuss in the situation of class other than interface. Smile | :)

Ambiguity means more than one different values could be selected. The different values in class is data members, not functions.

You can see there is no data members in IUnknown, IX and IY. Why there is ambiguity (I am not sure whether I have made myself understood about why in my context there is ambiguity)? I think the ambiguity occurs because of the data members are different.

regards,
George

Re: CreateInstance

CPallini3-Feb-08 23:33

CPallini

3-Feb-08 23:33

George_George wrote:
We can discuss in the situation of class other than interface.

Actually the OOP term to designate a C++ abstract class is interface.

George_George wrote:
Ambiguity means more than one different values could be selected. The different values in class is data members, not functions.

I know that. But, as I suggested before, since C++ syntax has no special syntax to designate interfaces (i.e. abstract classes) then probably the compiler cannot make assumptions on them and remains stuck to the more general case, thus finding (inexisting) ambiguities on the derivation path.
However, there is another reason I missed before: suppose, for instance, both IX and IY classes override one IUnknown member, say AddRef, due to polymorphism, how can the compiler resolve between IX::AddRef or IY::AddRef if it cannot make assumptions on the abstract nature of IX and IY classes?
Smile | :)

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.

[my articles]

Re: CreateInstance

George_George3-Feb-08 23:53

George_George

3-Feb-08 23:53

Thanks for your great reply, CPallini!

1.

CPallini wrote:
know that. But, as I suggested before, since C++ syntax has no special syntax to designate interfaces (i.e. abstract classes) then probably the compiler cannot make assumptions on them and remains stuck to the more general case, thus finding (inexisting) ambiguities on the derivation path.

No matter whether they contain data member, right?

2.

CPallini wrote:
how can the compiler resolve between IX::AddRef or IY::AddRef if it cannot make assumptions on the abstract nature of IX and IY classes?

I do not quite understand your statement above. Could you show some pseudo code please?

regards,
George

Re: CreateInstance

CPallini4-Feb-08 0:13

CPallini

4-Feb-08 0:13

George_George wrote:
No matter whether they contain data member, right?

Yes, if compiler cannot exploit abstract nature of classes.

George_George wrote:
I do not quite understand your statement above. Could you show some pseudo code please?

Yes, suppose (the example is naive, but you'll probably get the idea):

class IX: public IUnknown
{
...
virtual ULONG AddRef(){ return ++m_nRef;}
...
};

class IY: public IUnknown
{
...
virtual ULONG AddRef(){ return 1;}
...
};


void main()
{
  IUnknown *pUnk = new CA;

  int n = pUnk->AddRef();
}

what will be (if the above code compiles) n value?

Smile | :)

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.

[my articles]

Re: CreateInstance

George_George4-Feb-08 0:34

George_George

4-Feb-08 0:34

Thanks CPallini,

I think I have got your ideas.

You mean even if IUnknown *pUnk = new CA; can compile, then the statement int n = pUnk->AddRef(); will give ambiguity result -- call AddRef of IX or call AddRef of IY? My understanding correct? Smile | :)

regards,
George

Re: CreateInstance

CPallini4-Feb-08 1:47

CPallini

4-Feb-08 1:47

No, I mean that the sample does NOT compile because of the (call AddRef of IX or call AddRef of IY) ambiguity, i.e. the compiler prevents such weirdness.
Smile | :)

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.

[my articles]

Re: CreateInstance

George_George4-Feb-08 1:48

George_George

4-Feb-08 1:48

Thanks CPallini,

My question is answered. You are so knowledgeable. Smile | :)

regards,
George

Thanks

CPallini4-Feb-08 2:00

CPallini

4-Feb-08 2:00

George_George wrote:
My question is answered. You are so knowledgeable.

Thanks

, but it isn't true. There is a lot of people far more knowledgeable than me here at CP.
Anyway, thank you again.
Smile | :)

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.

[my articles]

Lost Helpfiles

Bram van Kampen3-Feb-08 13:22

Bram van Kampen

3-Feb-08 13:22

Last December I installed VC2008 Enterprise Edition on one of the Laptops. It clobbered my VC version 5 (VC 97) edition, all Online VC 97 Helpfiles became Unavailable. I decided that Managed Code is not for me, I prefer MFC, particularly because of the Code Base I have developped. I know that VC 97 is not really supported anymore, but for me it worked, and I decided to stay with it, at least untill I can afford an Upgrade.
I Uninstalled VC2008, and even re-installed VC 97. Still No Helpfiles. Anyone seen this before?

Regards, Mad | :mad:

Bram van Kampen

make an Mdiform transparent

diddy343-Feb-08 11:57

diddy34

3-Feb-08 11:57

I need help with the code for making an mdiform transparent

tony-yeyo

Transparent MDIform

diddy343-Feb-08 11:49

diddy34

3-Feb-08 11:49

code to make an Mdiform transparent

tony-yeyo

Re: Transparent MDIform

Mark Salsbery3-Feb-08 12:10

Mark Salsbery

3-Feb-08 12:10

Handle the WM_ERASEBKGND Notification[^] and do nothing in the handler code
except return a non-zero value.

Mark

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

2 Rows in CListCtrl Header

AnTri3-Feb-08 9:01

AnTri

3-Feb-08 9:01

Hey,

is there any way to wrap text in a CListCtrl Header? I know I can subclass and do some CustomDraw, but with this method I loose the XP style.

Thanks for your help!

binary to GdiPlus::Image

followait3-Feb-08 7:02

followait

3-Feb-08 7:02

BYTE *pBuf=GetBinaryOfOneJpegFileFromDatabase();

Need to construct a GdiPlus::Image object using the data pointed to by pBuf.

I found a way, but not so efficient

_variant_t varBLOB;
SafeArrayAccessData(varBLOB.parray,(void**)&pBuf);
SafeArrayUnaccessData (varBLOB.parray);
COleStreamFile stmFile;
stmFile.CreateMemoryStream();
stmFile.WriteHuge(pBuf,lDataSize);
IStream *pS=stmFile.GetStream();
m_pImg=::new Image(pS);

The data pointed to by pBuf is copied several times,
so is there an more efficient way?
Thanks.

Re: binary to GdiPlus::Image

Mark Salsbery3-Feb-08 7:41

Mark Salsbery

3-Feb-08 7:41

followait wrote:
is there an more efficient way?

What about using GlobalAlloc() and CreateStreamOnHGlobal() to
create a stream to pass to the Image ctor?

Mark

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Re: binary to GdiPlus::Image [modified]

followait3-Feb-08 21:16

followait

3-Feb-08 21:16

It must be better,
but there is a problem when call GlobalUnlock

IStream *pStm=NULL;
::CreateStreamOnHGlobal(NULL,TRUE,&pStm);
ULARGE_INTEGER ui;
ui.LowPart=lDataSize+1;
ui.HighPart=0;
HRESULT hr=pStm->SetSize(ui);
HGLOBAL hGlobal=NULL;
::GetHGlobalFromStream(pStm,&hGlobal);
BYTE *pBuf=(BYTE*)::GlobalLock(hGlobal);
::SafeArrayAccessData(varBLOB.parray,(void**)&pBuf);
::SafeArrayUnaccessData (varBLOB.parray);
BOOL b=::GlobalUnlock(hGlobal);//b==FALSE (even without <code>SafeArrayAccessData</code> and <code>SafeArrayUnaccessData </code>)
DWORD dw=::GetLastError();//dw==0:confused:

modified on Monday, February 04, 2008 3:35:03 AM

I can't modify the former msg, the 'edit' button is out of the view

followait3-Feb-08 23:03

followait

3-Feb-08 23:03

I've solved it.

Thanks.

Re: binary to GdiPlus::Image

Mark Salsbery4-Feb-08 5:33

Mark Salsbery

4-Feb-08 5:33

I assume you found this already...

GlobalUnlock():

"If the memory object is still locked after decrementing the lock count,
the return value is a nonzero value. If the memory object is unlocked
after decrementing the lock count, the function returns zero and GetLastError
returns NO_ERROR.

If the function fails, the return value is zero and GetLastError returns a value other than NO_ERROR."

Smile | :)

Mark

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Re: binary to GdiPlus::Image

bob169723-Feb-08 9:05

bob16972

3-Feb-08 9:05

I would agree with Mr. Salsbery.

IStream* pStream=NULL;

then use
CreateStreamOnHGlobal(NULL,TRUE,&pStream);

then use the streams "Write" method to get the data from the buffer in,
pStream->Write(pBuf,nSize,NULL);

then use Image::FromStream or the constructor as you had been doing.

Re: binary to GdiPlus::Image

bob169723-Feb-08 9:13

bob16972

3-Feb-08 9:13

Don't forget to initialize COM for this technique.

DLL Function call

ginjikun3-Feb-08 1:09

ginjikun

3-Feb-08 1:09

Hi everyone!

Would like to ask...
if i have a DLL that implements a function.. this DLL is used by an EXE. can the call to the DLL function by the EXE be done in parallel? say the EXE implements several thread and each of these threads calls the DLL function. or is the call just 1 at a time?

Thanks for any help.

not so newbie Smile | :)

Re: DLL Function call

Gary R. Wheeler3-Feb-08 1:30

Gary R. Wheeler

3-Feb-08 1:30

The short answer is yes. Any number of threads can call a function in a DLL at the same time; the DLL calling mechanism allows this.

The real answer is it depends on the function in the DLL. The DLL function must be designed to be thread-safe. In other words, you must know that the function can be called from multiple threads safely. If the function uses a global resource, it must protect accesses to that resource so that its state isn't changed incorrectly by multiple threads.

If you don't know that the function is thread-safe, you can make it so by writing your own wrapper, something like this:

static CCriticalSection MyFunction_CS;
void Function(...);
void MyFunction(...)
{
  MyFunction_CS.Lock();
  Function(...);
  MyFunction_CS.Unlock();
}

Intead of calling Function(...) directly, you call MyFunction(...) which uses a critical section to ensure only a single thread at a time can call Function(...).

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