C / C++ / MFC

Prasanth M V wrote:

But when i ma using this in amy application , it is showing an error
error LNK2001: unresolved external symbol "public: static int CMyClass::nValue" (?nValue@CMyClass@@2HA)

Prasanth M V wrote:

I have already given the import lib file to the project.
And i could access all the class members expect the Static member of the class.
Then ???

#ifdef CPPDLL_EXPORTS
#define CPPDLL_API __declspec(dllexport)
#else
#define CPPDLL_API __declspec(dllimport)
#endif

// This class is exported from the CppDll.dll
class CPPDLL_API CCppDll {
public:
	CCppDll(void);
	~CCppDll(void);
	// TODO: add your methods here.

	static int nValue;
};

// DLLMain stuff
// ...
CCppDll::CCppDll()
{
	return;
}
CCppDll::~CCppDll()
{
	return;
}
int CCppDll::nValue = 0;

#include "stdafx.h"
#include "..\\..\\CppDLL\\CppDLL\CppDLL.h"

int _tmain(int argc, _TCHAR* argv[])
{
	CCppDll::nValue =5;
}

[uuid(B6127C55-AC5F-4ba0-AFF6-7220C95EEF4D), dual, oleautomation, hidden, nonextensible]

George_George wrote:

Good link!! Now my confusion is, to implement an interface for OLE automation, once we inherit from IDispatch interface, then it is always a dual interface, right?

George_George wrote:

What type of implementation in C++ for a component is not a dual interface?

CPallini wrote:

For instance, a component that does not support automation.

George_George wrote:

In the context of supporting automation, when in implement a component in C++, are there any ways to implement it not as a dual interface?

George_George wrote:

I have this confusion is because, if I remember clearly, if a component supports automation, it must inherit from IDispatch interface, then it must be a dual interface.

George_George wrote:

1. What is the purpose of doing so "in practice"? Force user to use IDispatch other than efficient vtable?

George_George wrote:

2. Could we use vtable even if dual property is not added to interface? For example, using QueryInterface to get some interface other than IUnknown and IDispatch, then invoke its member function just the same as invoking through vtable?

CPallini wrote:

In practice you use IDispatch on VTABLE capable client only if you need late binding.

CPallini wrote:

You can always use VTABLE on all of the COM Interfaces. what dual really means is that the same functionalities that you can access via IDispatch mechanism are also available as standard COM methods (i.e. are part of the interface itself).

George_George wrote:

You mean QueryInterface for IDispatch interface? What mean later binding?

Dim objSer as Object
set objSer = CreateObject("MSCOMMLib.MSComm")

George_George wrote:

So you mean even if we do not explicitly add dual to the property, we can still use dual (by vtable and by IDispatch.invoke()) functions if underlying component support it?

If yes, what is the function of dual keyword? It does not enforce anything strictly, right?

CPallini wrote:

For instance (maybe syntax is not correct, I havent VB6 at hand)

Dim objSer as Objectset objSer = CreateObject("MSCOMMLib.MSComm")

is late binding, i.e. MSComm object is ignored at compile time and you can only access objSer functionality through IDispatch. Late binding is often useful.

George_George wrote:

If I remember correctly (I am not VB expert), in VB to access some object in COM, we have to program in the way above, does it mean VB always use later binding?

2.

Do you mean there are any other ways to access VB in COM, that is not later binding?

George_George wrote:

3.

Later binding means runtime binding, right? In runtime, using invoke method on the IDispatch interface of the component?

George_George wrote:

1.

For the later binding case (suppose client will use invoke, other than vtabke), I am wondering during compile/build phase, how will the client (C++, VB, VBScript, etc.) utilize the TLB file? Does the contained interface function information be read and checked?

(I think the answer is no)

George_George wrote:

So, all the interface/function/parameter checking work in done during runtime?

Dim objSer as Objectset
objSer = CreateObject("MSCOMMLib.MSComm")

Private Sub Command1_Click()
    Dim obj As Object
    Set obj = CreateObject("George.George")
End Sub