Access Denied in VC++ COM

RevathiRamakumar

Hi all...I have a server Component which is a inprocess exe and a dialog based client... Server has 3 methods ..One method returning CPU usuage , other method returning the memory usuage and the third method just returns a BSTR String... In client code ,when I try to call the third method(returns the BSTR srting) I get Access Denied error.. How can I overcome this issue...:confused: Thank u.. Here's my sample code..(Client). CoInitialize(NULL); HRESULT hr = NULL,hr1=NULL; IGetStatus* pGetStatus; hr=CoCreateInstance(CLSID_GetStatus,NULL,CLSCTX_LOCAL_SERVER,IID_IGetStatus,(void **)&pGetStatus); if(SUCCEEDED(hr)) { try { _bstr_t str1 ; str1 = pGetStatus->GetBeat(); char* Text = _com_util::ConvertBSTRToString(str1); AfxMessageBox(Text); ::SysFreeString(str1); UINT CPU_Info = pGetStatus->Get_CPU(); int Memory_Info = pGetStatus->Get_Memory(); } catch(_com_error e) { AfxMessageBox(e.ErrorMessage(),MB_ICONSTOP); } }

Roger Stoltz

RevathiRamakumar wrote:

I have a server Component which is a inprocess exe

Ummm, I think not... If it's an EXE it is out-of-process. Try and change CLSCTX_LOCAL_SERVER in the call to ::CoCreateInstance() into CLSCTX_INPROC_SERVER and the call will most likely fail.

RevathiRamakumar wrote:

IGetStatus* pGetStatus;
....
str1 = pGetStatus->GetBeat();

It looks like you're using the raw COM interface and not a wrapper for dispatch interfaces. If this is the case you're violating the COM rule that says every function must return a HRESULT. Thus you cannot return a string, it has to be an output parameter. How is your IGetStatus::GetBeat() interface function declared in the IDL-file? What attributes have you added to your IGetStatus interface? "oleautomation"? Is your IGetStatus interface declared as a "dispinterface" or just "interface" in the IDL-file? I would suggest that you declare your IGetStatus interface as an ordinary interface using the "interface" keyword in the IDL-file, but add the "oleautomation" attribute in order to use typelib-marshalling. The benefit is that you don't have to worry about how the interface is marshalled, but the downside is that you're restricted to use automation compatible data types such as BSTR (any type that can be contained in a VARIANT). Then your interface function declaration should look something like this:

HRESULT GetBeat( [out] BSTR* pTheBeat );

and you should call it some way similar to this:

BSTR* pbstrTheBeat = NULL;
hr = pGetStatus->GetStatus( pbstrTheBeat ); // pGetStatus is the interface pointer
if( SUCCEEDED( hr ) )
{
// The call was successful, do whatever you like with the string
::SysFreeString( pbstrTheBeat ); // Since it was allocated by the server or stub
}

"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown

RevathiRamakumar

Hi.. Thanks for the help extended...I have added oleautomation...its an ordinary Interface.. I tried ur suggestion.. But,in the following code I get error ... BSTR* pbstrTheBeat = NULL; hr = pGetStatus->GetBeat(pbstrTheBeat); C2660: 'Get_Beat' : function does not take 1 parameters The prototype and the definition are similar and they just return a single value only..And also the intelligence shows me two methods ie 1.HRESULT raw_Get_Beat(BSTR*) and 2._bstr_t GetBeat(). When I use hr = pGetStatus->raw_Get_Beat(pbstrTheBeat) I dont get any error..But, HRESULT fails.. Why is that so?I dont understand...Can u please help me.. Thank u..

modified on Tuesday, March 31, 2009 2:33 AM

Roger Stoltz · modified on Tuesday, March 31, 2009 2:33 AM

You probably have the "dual" attribute added to the interface. If this is the case you should remove it. The dual attribute mean that a client can use the interface as an ordinary COM virtual table based interface and as a dispatch (automation) interface. Read more here[^]. When the typelib is imported and the interface is a "dual" interface, two functions will be declared for each interface function; one for the dispinterface and one for the "raw" virtual table based interface. If you add the "raw_interfaces_only" attribute to the #import you tell the preprocessor to declare functions only for the vtable based part of the interface. Read more here[^].

RevathiRamakumar wrote:

When I use hr = pGetStatus->raw_Get_Beat(pbstrTheBeat) I dont get any error..But, HRESULT fails..

If you add the "raw_interfaces_only" attribute, the "raw" prefix will be removed from the name of this function. So, the call fails.... What is the error code and what do you suspect may be wrong?

"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown

RevathiRamakumar

Thank u..Ho it seems I need to know alot...I tried the following... BSTR* pbstrTheBeat = NULL; hr1 = pGetStatus->raw_Get_Beat(pbstrTheBeat); if( SUCCEEDED( hr1 ) ) //-2147023116 { AfxMessageBox("Text"); } else { _com_error e(hr1); AfxMessageBox(e.ErrorMessage()); } And I got the error message ...A null pointer reference was passed to stub... hr1=-2147023116 :doh:

Roger Stoltz

RevathiRamakumar wrote:

And I got the error message ...A null pointer reference was passed to stub...

Oops... Sorry about that, must have been a temporary brain hiccup. :-\ The error makes perfectly sense if you think about it, how is the caller suppose to get the result.... Of course it should be:

BSTR bstrTheBeat = NULL;
hr = pGetStatus->GetBeat( &bstrTheBeat ); // pGetStatus is the interface pointer
if( SUCCEEDED( hr ) )
{
// The call was successful, do whatever you like with the string
::SysFreeString( bstrTheBeat ); // Since it was allocated by the server or stub
bstrTheBeat = NULL;
}

"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown

RevathiRamakumar

Thank u... NO It doesn't work... error C2664: 'raw_GetBeat' : cannot convert parameter 1 from 'unsigned short *** ' to 'unsigned short ** ' Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast. So, I tried this one.. hr1 = pGetStatus->raw_GetBeat((BSTR*)&pbstrTheBeat); But, still I get ACCESS DENIED... :doh:

Roger Stoltz

RevathiRamakumar wrote:

cannot convert parameter 1 from 'unsigned short *** ' to 'unsigned short **

Read my code snippet again. The type has changed from BSTR* to a simple BSTR compared to the code snippet in my previous post.

"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown

RevathiRamakumar

Ho extremely sorry...Now no errors..But y is the access denied...sorry to bug u alot..Thank u..

RevathiRamakumar

Is there something to do with the firewall settings...I'm not sure if firewall settings has to something with COM..Thank u in advance..

Roger Stoltz

RevathiRamakumar wrote:

Is there something to do with the firewall settings...I'm not sure if firewall settings has to something with COM.

If you would be using DCOM, Distributed COM, where the server and client resides on different machines, a network firewall may present some troubles. Some firewalls, such as Comodo, could prevent the client process from accessing the server process or ask the user for action. However, I very much doubt any firewall would cause any troubles in your case since you're able to successfully call other functions of the same interface of the same server.

"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown

Roger Stoltz

RevathiRamakumar wrote:

Ho extremely sorry...

No worries, you were not the only one who made a mistake.

RevathiRamakumar wrote:

Now no errors..

Good.

RevathiRamakumar wrote:

But y is the access denied

What are you trying to do when do you experience this? Have you tried to debug it and step though the code? Does the BSTR variable point to a valid string? What does the source code look like where you get this error?

"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown

RevathiRamakumar

Thanks for ur reply..Actually I couldn't call any of the methods in the interface..Whenever I try to call any of these methods I get Access denied exception... HRESULT hr1; hr1 = pGetStatus->raw_Get_Beat(&pbstrTheBeat);//This raises Access Denied /*BSTR does not point to a valid String..It shows 0xc000000 */ if( SUCCEEDED( hr1 ) ) { AfxMessageBox("Text"); } else { _com_error e(hr1); AfxMessageBox(e.ErrorMessage()); } } catch(_com_error e) { AfxMessageBox(e.ErrorMessage(),MB_ICONSTOP);//This tells me ACCESS IS DENIED } I tried to debug..Actually the purpose is that I need to get the CPU and Memory usuage of a Server machine which is remote..I wanted to try it on a local machine first and then to implement on a remote machine..But, in the local machine itself I get Access Denied..Can u please tell me how to solve this...Thank u in advance...

Roger Stoltz

RevathiRamakumar wrote:

Actually I couldn't call any of the methods in the interface..Whenever I try to call any of these methods I get Access denied exception...

:confused: I assumed you were able to call the two other functions successfully since you wrote

RevathiRamakumar wrote:

when I try to call the third method(returns the BSTR srting) I get Access Denied error.

in your original post. I suggest you unregister the server, rebuild the complete server and register it. Clean up the client project, and especially the files generated when #importing the typelib of the server. Rebuild the client, debug it and verify that the server can be successfully created, i.e. make sure that the HRESULT returned from ::CoCreateInstance() equals zero and your interface pointer points to a valid address. Also make sure you have the named_guids attribute when #importing since this will declare the CLSID and IIDs correctly for you.

"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown

RevathiRamakumar

Thanks for the reply Roger..I tried the way u suggested.. I unregistered the server ,built it again and then registered it..I also cleaned up the client and tried to built it again..HRESULT Of ::CoCreateInstance() returned 0 and the interface pointer points a valid address..But, again Access Denied while calling the server method... :(

Vi2

try
{
_bstr_t str1 ;
str1 = pGetStatus->GetBeat();

char* Text = str1;
AfxMessageBox(Text);

UINT CPU_Info = pGetStatus->Get_CPU();
int Memory_Info = pGetStatus->Get_Memory();
}

With best wishes, Vita

Roger Stoltz

RevathiRamakumar wrote:

HRESULT Of ::CoCreateInstance() returned 0 and the interface pointer points a valid address..But, again Access Denied while calling the server method...

That's odd... If you're able to successfully create the server and get a valid pointer to the interface, I cannot see how you could get an access violation making the call. It feels like there's some kind of mismatch between the server, typelib and client. If you have changed from an IDispatch-derived interface to an IUnknown-derived, the virtual table the client tries to use may be out of sync. That's why I suggested that you should unregister all and rebuild from scratch. How is your interface declared in the IDL-file? It should be something like this:

[
object,
uuid( xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx ),
oleautomation,
helpstring( "IGetStatus interface" ),
]
interface IGetStatus : IUnknown
{
HRESULT GetBeat( [out] BSTR* pbstrTheBeat );
HRESULT GetCPU( [out] unsigned long* pulCpuLoad );
HRESULT GetMemory( [out] unsigned long* pulMemory );
};

Also make sure in the client that the IGetStatus interface, declared in the complier generated header file, only contains QueryInterface(), AddRef(), Release(), GetBeat(), GetCPU() and GetMemory(). Try using one of the other interface functions since it's more straight forward with integer values and you don't have to worry about string obscurities. When you get that working you can continue with IGetStatus::GetBeat().

"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown

RevathiRamakumar

Thanks for ur reply...When I tried calling AddRef() It worked fine... ULONG i = pGetStatus->AddRef();//i=2 But, when the other methods are being called, it gives me access denied error..K I'll keep trying ..Thank u...

RevathiRamakumar

Thank u....Ya I tried them but ,getting Access Denied Error..

RevathiRamakumar

Hi.. Now I could call the methods... I changed the Authentication level as NONE in the DCOM configuration... Its working fine.. Thank u ... :)

modified on Wednesday, April 15, 2009 6:28 AM