Re: extern "C" DllExport Function crashing - COM Discussion Boards

Re: Passing HWND from a MDI app to a activeX control

Abhishek Srivastava28-Dec-03 21:34

28-Dec-03 21:34

Hi ,

Actually HWND data type cannot be used for automation, as it is not supported.

so what you can do is simply use long data type, make "HWND hwnd" as "long hwnd" and when u recieve handle in ur activeX object typecast again into HWND

Init(LPTSTR lpstrCmdLine, int nCmdShow,long hwnd)
{

HWND wHandle =(HWND)hwnd;

// now you can use this wHandle for your purpose Smile | :)

-----
-----
}

Regards

Abhishek Srivastava
Software Engg (VC++)
India ,Noida
Mobile no 9891492921 Smile | :)

COM interface: EnumFormatEtc

Tristan Rhodes23-Dec-03 8:46

Tristan Rhodes

23-Dec-03 8:46

I have found the EnumFORMATETC method for IDataObject in COM, and the C# verion, and they appear to have nothing in common. How does this:

HRESULT EnumFormatEtc(
DWORD dwDirection, //Specifies a value from the enumeration
// DATADIR
IEnumFORMATETC ** ppenumFormatetc
//Address of output variable that receives the
// IEnumFORMATETC interface pointer
);

Get turned into this:

IEnumFORMATETC OleEnumFormatEtc([in] int dwDirection);

i'm very fuzzy on this, as from what I understand, it should get turned into this:

<br />
int EnumFormatEtc(<br />
int dwDirection,<br />
out IEnumFORMATETC[] ppenumFormatetc<br />
)

If anyone could explain to me, why this is the case, I would be a very happy dude! Smile | :)

Cheers

Cata

Re: COM interface: EnumFormatEtc

Stefan Pedersen27-Dec-03 10:59

Stefan Pedersen

27-Dec-03 10:59

I don't have much experience with C# but it seems that it respects the retval keyword (treating "failed" HRESULTs as exceptions).

And by the way... the ppenumFormatetc is an INTERFACE pointer, not an array.

And if the paths that I have followed/have tread against the flow/there is no need for sorrow
I am coming home
Return, Crüxshadows

Re: COM interface: EnumFormatEtc

Jörgen Sigvardsson6-Jan-04 6:25

Jörgen Sigvardsson

6-Jan-04 6:25

As Stefan points out, HRESULTS are translated as exceptions in .NET. More specifically, they're translated into System.Runtime.InteropServices.COMException's.

If you look up the IDL definition for EnumFormatEtc it'll look something like this:

HRESULT EnumFormatEtc([in] DWORD dwDirection, [out, retval] IEnumFORMATETC)

All [in] parameters are treated as normal copy by value parameters. [in, out] are treated as ref parameters, and [out] are treated as out parameters in C# lingo. [out, retval] is a special kind of parameter (which must always be the last parameter by the way), which is mapped as the return type in languages which are not "C like".

The .NET framework will call the method something like this (pseudo code):

IEnumFORMATETC* EnumFormatEtc(DWORD dwDirection) {
   IEnumFORMATETC* res = 0;
   HRESULT hr = itf_ptr->EnumFormatEtc(dwDirection, &res);
   if(FAILED(hr)) throw COMException(hr);
   return res;
}

--
You're entertaining at least.

User 78226222-Dec-03 22:58

User 782262

22-Dec-03 22:58

hi,

i have created an exe com seerver with Visual C++ 7 & WinXP SP1.
on my system ans my testing machine, my server register successfully.
But my client can't register it !
he seems he doesn't have any MFC70XX.dll on it system, thus an error appear during registration.
How can i update it system in order to add the MFC70 dll series ??

thanks.

modified 14-Jun-22 21:01pm.

Re: Register an exe COM server

valikac26-Dec-03 5:39

valikac

26-Dec-03 5:39

Include a copy of the MFC 7.0 DLL with setup.

Kuphryn

extern "C" DllExport Function crashing

Kishor Morkhandikar22-Dec-03 19:56

Kishor Morkhandikar

22-Dec-03 19:56

I am exporting a function with a CString object as its parameter, as show below:
extern "C" DllExport const char* ActivatePlot(CString szPlot);

When I called this function from another DLL or module, the application crashes. From debug/call-stack I found that while returning from the function ActivatePlot() the control is in the destructor of CString object and is trying to free the memory.
When I changed the parameter type to const char* it worked fine.
Can you explain whether we can use CString object in a DllExport functions? If not why?

Re: extern "C" DllExport Function crashing

Sebastián Benítez23-Dec-03 0:24

Sebastián Benítez

23-Dec-03 0:24

You should check MSDN. Go to www.msdn.microsoft.com And type MFC DLL export in the search field. You will find enough information on how to export functions depending on what kind of DLL are you building.

-- Sebastián.

Re: extern "C" DllExport Function crashing

Lim Bio Liong26-Dec-03 20:17

Lim Bio Liong

26-Dec-03 20:17

Hello Kishor,

Usage of CStrings in an exported function is perfectly fine as far as I know. Your function is declared as :

extern "C" DllExport const char* ActivatePlot(CString szPlot);

This means that when your ActivatePlot() is called, MFC creates a temporary CString for szPlot to be used within the context of the ActivatePlot() function.

Now, if this input is another CString as in the following example :

CString cstr("Country road.");
ActivatePlot(cstr);

the temporary CString "szPlot" which is created and gets passed into ActivatePlot() will contain a pointer to the same string that "cstr" points to.

The reference count of the actual string ("Country road.") is incremented and "cstr" and the "szPlot" both share the same string.

It is true that when the ActivatePlot() function exits, the CString destructor is called. This is done to free the temporary CString object "szPlot".

Let's take a look at the actual source codes of the CString destructor :

CString::~CString()
// free any attached data
{
if (GetData() != _afxDataNil)
{
if (InterlockedDecrement(&GetData()->nRefs) <= 0)
FreeData(GetData());
}
}

What happens here is that the szPlot's string pointer's reference count is decremented and only if this reference count drops to zero (or negative) will the actual string be released.

In our example, if szPlot still points to the same string "Country road.", the reference count of this string in memory is decremented but the ref count will not be zero yet (cstr still holds a ref count) and no freeing is actually performed.

I believe no harm is actually done by the destructor in this sense.

Please provide more info on how you call the ActivatePlot() function as well what actually takes place in the function ActivatePlot() so that we can have a better picture of the nature of your crash.

Thanks,
Bio.

Problems passing a DISPPARAMS structure to IDispatch::Invoke

Dark Magus22-Dec-03 17:39

Dark Magus

22-Dec-03 17:39

I desesperatly need help for passing a DISPPARAMS strucutre to IDispatch::Invoke.

Here is the calling code, in C++:

<br />
	HRESULT hr;<br />
	OLECHAR FAR* szMember = L"MyFunction";<br />
	DISPID DispatchID;<br />
<br />
	int i = 10; // The variable I use for testing<br />
<br />
	DISPPARAMS DispatchParams;<br />
	DispatchParams.cArgs=1;<br />
	DispatchParams.rgvarg = new VARIANTARG[1];<br />
	DispatchParams.rgvarg[0].vt = VT_BYREF|VT_INT;<br />
	DispatchParams.rgvarg[0].pintVal = &i;<br />
	DispatchParams.rgdispidNamedArgs=NULL;<br />
	DispatchParams.cNamedArgs=0;<br />
<br />
	CoInitialize(NULL);<br />
<br />
	if (FAILED(hr = CoCreateInstance(MyCLSID, NULL, CLSCTX_SERVER, IID_IUnknown, (void FAR* FAR*)&pUnknown))) return hr;<br />
	if (FAILED(hr = pUnknown->QueryInterface(IID_IDispatch, (void FAR* FAR*)&pDispatch))) return hr;<br />
	if (FAILED(hr = pDispatch->GetIDsOfNames(IID_NULL, &szMember, 1, LOCALE_USER_DEFAULT, &DispatchID))) return hr;<br />
<br />
<br />
	hr = pDispatch->Invoke(DispatchID, IID_NULL, LOCALE_SYSTEM_DEFAULT, DISPATCH_METHOD, &DispatchParams, NULL, NULL, NULL);<br />
<br />

And this is the function I'm trying to call, in VB:

<br />
	Public Function MyFunction(ByRef Parameter As Integer)<br />
		MsgBox Str(Parameter), , "Parameter:"<br />
	End Function<br />

When I run the calling code, IDispatch::Invoke returns a type mismatch error. However, if I enlarge the rgvarg field of the DispatchParams structure and write the parameter into rgvarg[1] instead of rgvarg[0] (while cArg is still 1), it does not return any error and MyFunction does show the message box, but it shows the value is 0, while it is supposed to be 10. I would add that I have no problems when using IDispatch::Invoke for calling functions that have no parameters.

I've spent hours trying to figure out what was wrong but it went nowhere. Would someone please help me ?

Re: Problems passing a DISPPARAMS structure to IDispatch::Invoke

Vi223-Dec-03 23:36

Vi2

23-Dec-03 23:36

You have to use the VT_I2 or VT_I4 instead of VT_INT, because VT_INT is not OLE-compatible type at all.

Also the VB type "Integer" is the C/C++ type "short int". Therefore, you have to write

short int i = 10; // The variable I use for testing<br />
...<br />
DispatchParams.rgvarg[0].vt = VT_BYREF|VT_I2;<br />
DispatchParams.rgvarg[0].piVal = &i;

With best wishes,
Vita

Re: Problems passing a DISPPARAMS structure to IDispatch::Invoke

Dark Magus25-Dec-03 11:34

Dark Magus

25-Dec-03 11:34

Thank you so much, it helped a lot. Now I'm going to be careful with data types. However I have another question. I was wondering if it was possible to pass an array containing pointers to variables, these variables being either long integers or BSTR. I was thinking I could pass an array of variant, but I'm not sure about the result.

Re: Problems passing a DISPPARAMS structure to IDispatch::Invoke

Vi225-Dec-03 19:21

Vi2

25-Dec-03 19:21

[quote]I was wondering if it was possible to pass an array containing pointers to variables, these variables being either long integers or BSTR. I was thinking I could pass an array of variant, but I'm not sure about the result. [/quote]

I think that this has no sense.

There is no array with reference data. Because the VARIANT with vt==VT_BYREF|VT_ARRAY|VT_?SIMPLETYPE? means the "pointer to SAFEARRAY with SIMPLETYPE members" (aka "SAFEARRAY(SIMPLETYPE)*") instead of the "SAFEARRAY with pointers to SIMPLETYPE data" (aka "SAFEARRAY(SIMPLETYPE*)").

Therefore, there is only SAFEARRAY(VARIANT) way, but the VB can use (or get) the VARIANT with VT_BYREF|VT_?SIMPLETYPE?, but cannot set such type. So I think that you can use only SAFEARRAY(VARIANT) with VT_?SIMPLETYPE? members.

With best wishes,
Vita

Re: Problems passing a DISPPARAMS structure to IDispatch::Invoke

Dark Magus26-Dec-03 10:03

Dark Magus

26-Dec-03 10:03

Okay, thank you again. In fact I simply wanted to be able to pass an arbitrary number of parameters to my VB function (I set its last parameter to be ParamArray). I just found an article on Microsoft's website explaining how to do this: http://support.microsoft.com/default.aspx?scid=http://support.microsoft.com:80/support/kb/articles/Q158/4/51.asp&NoWebContent=1 (I'm giving the link incase someone needs it some day).

Thank you for your answers.

about LocalServer COM Register

yingkou22-Dec-03 15:05

yingkou

22-Dec-03 15:05

I want to find a LocalServer COM example not using ATL here. I have finished one but I don't know how to Register. I have tried it as below: mycom.exe -/RegServer
but my client can't create instance.so I think I have made mistaken on Registry.who can tell me something about registry?

Re: about LocalServer COM Register

User 78226222-Dec-03 23:16

User 782262

22-Dec-03 23:16

i my project i search the /RegServer and /UnregServer in order to reg or unreg my server.

i do it like this in my CWinApp::InitInstance:
// ( _AtlModule is derived from CAtlMfcModule )

<br />
TCHAR szToken[] = _T("-/");<br />
long operation = 0;<br />
LPCTSTR lpsztoken = _AtlModule.FindOneOf( lpCmdline, szToken );<br />
<br />
while ( lpszToken != NULL )<br />
{<br />
  if ( lstrcmpi( lpszToken, _T("RegServer") ) == 0 )<br />
  {<br />
     operation = 1;<br />
     break;<br />
  }<br />
  if ( lstrcmpi( lpszToken, _T("UnregServer") ) == 0 )<br />
  {<br />
     operation = 2;<br />
     break;<br />
  }<br />
  lpsztoken = _AtlModule.FindOneOf( lpCmdline, szToken );<br />
}<br />
<br />
switch ( operation )<br />
{<br />
  case 0: // launch my app ...<br />
    break:<br />
  case 1: // regserver<br />
    _AtlModule.UpdateRegistryFromResource( MYUINT, TRUE );<br />
    _AtlModule.RegisterServer( TRUE );<br />
    break;<br />
  case 2: // unreg server<br />
    _AtlModule.UpdateRegistryFromResource( MYUINT, TRUE );<br />
    _AtlModule.UnregisterServer( TRUE );<br />
    break;<br />
}<br />

try like this ...

modified 14-Jun-22 21:01pm.

Re: about LocalServer COM Register

Vi223-Dec-03 23:29

Vi2

23-Dec-03 23:29

You have to use either

mycom.exe -RegServer

mycom.exe /RegServer

With best wishes,
Vita

COM Apartments and Marshalling

Jörgen Sigvardsson22-Dec-03 14:03

Jörgen Sigvardsson

22-Dec-03 14:03

Would this be safe? (the following code is implemented in a DLL, used by a single EXE D'Oh! | :doh:

and a bunch of COM DLLs)

CComAutoCriticalSection cs;
DWORD                   dwOwnerThreadId;
ISomeInterface*         pObject = 0;
IStream*                pObjMarshalled = 0;
 
HRESULT RegisterGlobalObject(ISomeInterface* pObj)
{
    if(!cs.Lock()) 
        return E_FAIL;
     
    if(pObject != 0) {
        cs.Unlock();
        return E_UNEXPECTED;
    }
 
    HRESULT hr = CoMarshalInterThreadInterfaceInStream(
        __uuidof(ISomeInterface),
        pObj,
        &pObjMarshalled
    );
 
    if(FAILED(hr)) {
        cs.Unlock();
        return hr;
    }
 
    pObject = pObj;
    dwOwnerThreadId = GetCurrentThreadId();
    cs.Unlock();
 
    return S_OK;
}
  
HRESULT GetGlobalObject(ISomeInterface** ppObj)
{
    if(!ppObj)
        return E_POINTER;

    if(!pObject)
        return E_FAIL;
    
    if(!cs.Lock())
        return E_FAIL;
    
    if(GetCurrentThreadId() == dwOwnerThreadId) {
        *ppObj = pObject;
        (*ppObject)->AddRef();
        cs.Unlock();
        return S_OK;
    }
 
    *ppObj = 0;
 
    LARGE_INTEGER seek;
    seek.QuadPart = 0; 
    HRESULT hr = pObjMarshalled->Seek(seek, STREAM_SEEK_SET, NULL);
    if(FAILED(hr) {
        cs.Unlock();
        return hr;
    }
 
    hr = CoUnmarshalInterface(
        pObjMarshalled, 
        __uuidof(ISomeInterface), 
       (void**)ppObj
    );
 
    cs.Unlock();
    return hr;
}

I'm marshalling the interface pointer upon registration using the inter thread marshalling function, because I know that this function will not be called from any other process (it can't be). I also assume that CoUnmarshalInterface() will work for interfaces marshalled with CoMarshalInterThreadInterfaceInStream().

I have yet to try this out (it's way past bedtime Roll eyes | :rolleyes:

). But if you read this and spot any inherent danger with this code, please let me know. Smile | :)

--
Sancte Míchael Archángele, defénde nos in proélio contra nequítiam et
insídias diáboli esto præsídium. Imperet illi Deus, súpplices deprecámur:
tuque, princeps milítiæ cæléstis, Sátanam aliósque spíritus malígnos, qui
ad perditiónem animárum pervagántur in mundo, divína virtúte,
In inférnum detrude. Amen.

No, that sucked

Jörgen Sigvardsson23-Dec-03 7:07

Jörgen Sigvardsson

23-Dec-03 7:07

Once the marshalled interface has been "picked up" from the stream and used, it seems that it's been used up already. I receive RPC_E_DISCONNECTED on method access.

I decided to make a singleton COM object which stores the ISomeInterface pointer instead. Then COM will handle everything automatically. Cool | :cool:

Re: No, that sucked

geo_m30-Dec-03 0:32

geo_m

30-Dec-03 0:32

You might have look to the IGlobalInterfaceTable. This allows multiple unmarshalling of once marshalled interface - if it helps you somehow.

All COM that expose a specific interface

IreneVassileva22-Dec-03 0:00

IreneVassileva

22-Dec-03 0:00

Hello there,

Does anyone know how I can search for all registered COM objects that expose some specific (defined by me) interface?

Re: All COM that expose a specific interface

Abhishek Srivastava22-Dec-03 1:01

Abhishek Srivastava

22-Dec-03 1:01

hi frnd

One can search a component installed on a particular machine based on the CATID i.e category ID in which it falls.
there are two interfaces
ICatInformation using methods of which you can enumerate all the component of a CATID.

and ICatRegister interface which provides methods for registering and unregistering component category information in the Registry.

have look on these interfaces in your MSDN , u might find your solution.

Abhishek Srivastava
Software Engg (VC++)
India ,Noida
Mobile no 9891492921 Smile | :)

Yahoo messenger login interface. Urgent

SiddharthAtw21-Dec-03 18:35

SiddharthAtw

21-Dec-03 18:35

HI!
I need Yahoo messenger login interface urgently. I want to access yahoo messenger window from my application bypassing the login screen for a particular user. any links or suggestions is most welcome.

D'Oh! | :doh:

How to access COM objects during runtime?

dapipi21-Dec-03 17:13

dapipi

21-Dec-03 17:13

Hi, I need to access COM objects during runtime or dynamically using VC++6. Can somebody please help me in this? Is there a way I can call the COM objects during runtime by entering the GUID or something like that? I am a beginner in COM..

Thx!!

Re: How to access COM objects during runtime?

Anonymous21-Dec-03 18:47

Anonymous

21-Dec-03 18:47

Is this the function you're looking for?

<code>
CoCreateInstance(REFCLSID rclsid, 
                 LPUNKNOWN pUnkOuter, 
                 DWORD dwClsContext, 
                 REFIID riid,
                 LPVOID * ppv);
</code>

I hope this helps you.

-John

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