I have hooked the cocreateinstance() function.
When it's called with a specific CLSID, I want to use my dll instead the dll system.
So here is my code :
HOOK_CoCreateInstance(rclsid,pUnkOuter,dwClsContext,riid,*ppv){
...
if(myCLSID){
module = LoadLibrary(mydll);
dllGetClassObject = (FUNC)GetProcAddress(module,"DllGetClassObject");
hr = dllGetClassObject(rclsid, IID_IClassFactory, &pClassFactory);
hr = pClassFactory->CreateInstance(NULL,IID_IUnknown, (void**)&data_source);
return hr;
}
else{
hr = CoCreateInstanceReal(rclsid,pUnkOuter,dwClsContext,riid,ppv);
return hr;
}
}
But it's not working.
I think the problem is in pClassFactory::CreateInstance(), with the second parameter :
I don't know how to retrieve automatically the REFIID of my dll.
And if I use riid it's not working either.
So if anyone has an idea,
Thanks !
If you want to follow proper COM conventions, you'll need to handle the CoCreateInstance parameters correct (as documented here).
The __in REFIID riid parameter is the GUID of the interface you want to use, not the DLL itself. The CLSID parameter is the class of the object, which you should know ahead of time. Because you want to return the expected interface, you really only need to know the CLSID of your new implementation (coclass) and call using that.
A simpler, but not quite COM-spec, method would be to export a factory from your DLL:
__declspec(dllexport) MyObject * CreateObject()
{
return new MyObject();
}
and call that from your wrapper:
HOOK_CoCreateInstance(rclsid,pUnkOuter,dwClsContext,riid,*ppv)
{
if(myCLSID)
{
module = LoadLibrary(mydll);
dllCreate = (FUNC)GetProcAddress(module,"CreateObject");
*ppv = dllCreate();
return S_OK;
} else {
hr = CoCreateInstanceReal(rclsid,pUnkOuter,dwClsContext,riid,ppv);
return hr;
}
}
Related
RANT-BEGIN
Before jumping right into already answered band wagon, please read this paper about SE outdated answers https://ieeexplore.ieee.org/document/8669958
Things changes after a time, and I am afraid Computer science is one of the most if not the most field out there where APIs and Interfaces change radically very very fast. Needless to say that a solution that might worked last month might not after latest feature added to a platform/framework. I humbly request you to not mark this question as answered with decade old post when many mainstream things did not even existed. If you dont know latest solution dont bother about it and leave question for someone else who might.
For a community representative of Computer Science where innovations is everyday thing, it is very toxic, new comer unfriendly and conservative.
END-RANT
This question has already been answered by me and will be accepted tomorrow (SE policy). Thank you for your interest.
Many times you have function pointers in unmanaged context which are called by some kind of events, We will see how it can be achieved with Top-Level Functions and also with member functions of a managed class.
Again, Please dont mark it as answered by linking to a decade old posts.
PS:
So many edits due to unstable internet in third world country, yeah bite me!
unmanaged.cpp
#pragma unmanaged
// Declare an unmanaged function type that takes one int arguments and callbacks
// our function after incrementing it by 1
// Note the use of __stdcall for compatibility with managed code
// if your unmanaged callback uses any other calling convention you can
// UnmanagedFunctionPointerAttribute (check msdn for more info) on your delegate
typedef int(__stdcall* ANSWERCB)(int);//Signature of native callback
int TakesCallback(ANSWERCB fp, int a) {
if (fp) {
return fp(a+1);//Native Callback
}
// This code will be executed when passed without fp
return 0;
}
#pragma managed
managed.cpp
using namespace System;
using namespace System::Runtime::InteropServices;
namespace Callbacks {
// Following delegate is for unmanaged code and must match its signature
public delegate void MyNativeDelegate(int i);
// This delegate is for managed/derived code and ideally should have only managed parameters
public delegate void MyManagedDelegate(int i);
public ref class TestCallback {// Our demo Managed class
private:
GCHandle gch;// kept reference so that it can be freed once we are done with it
void NativeCallbackListener(int i);//unmanaged code will call this function
public:
void TriggerCallback(int i); // Its here for demo purposes, usually unmanaged code will call automatically
event MyManagedDelegate^ SomethingHappened;//plain old event
~TestCallback();//free gch in destructor as its managed.
};
};
void Callbacks::TestCallback::NativeCallbackListener(int i) {
// Callback from Native code,
// If you need to transform your arguments do it here, like transforming void* to somekind of native structure.
// and then pass SomethingHappened::raise with Managed Class/Struct
return SomethingHappened::raise(i); // similar to SomethingHappened.Invoke() in c#
}
void Callbacks::TestCallback::TriggerCallback(int i)
{
MyNativeDelegate^ fp = gcnew MyNativeDelegate(this, &TestCallback::NativeCallbackListener);
// use this if your nativecallback function is not a member function MyNativeDelegate^ fp = gcnew MyNativeDelegate(&NativeCallbackListener);
gch = GCHandle::Alloc(fp);
IntPtr ip = Marshal::GetFunctionPointerForDelegate(fp);
ANSWERCB cb = static_cast<ANSWERCB>(ip.ToPointer());// (ANSWERCB)ip.ToPointer(); works aswell
// Simulating native call, it should callback to our function ptr NativeCallbackListener with 2+1;
// Ideally Native code keeps function pointer and calls back without pointer being provided every time.
// Most likely with a dedicated function for that.
TakesCallback(cb, i);
}
void Callbacks::TestCallback::~TestCallBack() {
gch.Free();//Free GCHandle so GC can collect
}
implementation.cpp
using namespace System;
void OnSomethingHappened(int i);
int main(array<System::String^>^ args)
{
auto cb = gcnew Callbacks::TestCallback();
cb->SomethingHappened += gcnew Callbacks::MyManagedDelegate(&OnSomethingHappened);
cb->TriggerCallback(1);
return 0;
}
void OnSomethingHappened(int i)
{
Console::WriteLine("Got call back with " + i);
}
Application loads the regular dll. Each function in this dll contains AFX_MANAGE_STATE(AfxGetStaticModuleState()). In the preprocessor definitions included macro _USRDLL and _AFXDLL. For example, export function from regular dll (mydll.dll):
BOOL RM_GetModule(IRMPage** ppInterface)
{
AFX_MANAGE_STATE(AfxGetStaticModuleState());
HINSTANCE hInst = AfxGetInstanceHandle(); //**return NULL**
........
}
application:
BOOL CReMain2Dlg::OnInitDialog()
{
CDialog::OnInitDialog();
..........
HINSTANCE hmCurrentModule;
if((hmCurrentModule = AfxLoadLibrary("mydll.dll"))){
(FARPROC&)pPageItem->pfGetModule = GetProcAddress(
hmCurrentModule, "RM_GetModule");
pPageItem->pfGetModule(&(pPageItem->pPage)); //call
..........
}
}
The project was transferred out of 6 studios at 2010. At 6 AfxGetInstanceHandle() return correct value. GetLastError() return 0. Why AfxGetInstanceHandle() return NULL? How to fix it?
vs2010_sp1, win7_x64
The best way is to store the handle you receive as parameter in DllMain in a global variable, or, in case it's an MFC dll, it should already be stored in CWinApp::m_hInstance.
Is it possible to increase the RCW reference count on an unknown interface?
(i.e. not the reference count on the underlying COM object)
I have some old COM server code
int Method1(object comobject) {
try {
// do something with comobject
return 0;
}
finally {
Marshal.ReleaseComObject(comobject);
}
}
This code works fine but now I need to call it from another method.
int Method2(object comobject) {
int result = Method1(comobject);
// Do something with combject
}
The type of comobject will vary (that is why it is object)
There is a way, the RCW count counts how many times the object has been marshaled you can increase this number by performing an additional marshal.
public static T AddRcwRef<T>(T t)
{
IntPtr ptr = Marshal.GetIUnknownForObject(t);
try {
return (T)Marshal.GetObjectForIUnknown(ptr);
}
finally {
Marshal.Release(ptr); // done with the IntPtr
}
}
I'm not sure I would recommend using this method, it's probably better to try and get rid of your ReleaseComObject calls.
For further reading, see this blog post on the subject I wrote.
There's the Marshal.AddRef() method, wrong reference count change though. I'm pretty sure incrementing the RCW count directly is not possible. Dig yourself out of the deep hole you're in and fix the old code.
i have got a ScreenCameraSDK and it comes with a 11kb dll file, it has a documentation too which lists the functions which can be used. It says
ScreenCamera SDK ActiveX Reference Documentation
ActiveX Reference
The ActiveX ID on the system is: ScreenCameraSDK.RemoteControl
Every method on the interface returns FAIL or SUCCESS. (0 or 1).
Create an instance of the ActiveX on your application, and then call InitializeScreenCameraRemoteControl. If the return value is SUCCESS then ScreenCamera is properly installed and you can then call any other method on the ActiveX's interface. If not ScreenCamera could not be found and you should contact support.**
Now my question is, i have the dll and no other files. How can i use the functions inside it in a VC++ Project with Visual Studio 2008.
Thanks
I TRIED THE FOLLOWING CODE BUT GOT COMPILATION ERROR OF UNDEFINED IDENTIFIER
#include <stdio.h>
// This is the path for your DLL.
// Make sure that you specify the exact path.
#import "e:\ScreenCameraSDK.dll" no_namespace
void main()
{
BSTR bstrDesc;
try
{
CoInitialize(NULL);
short st = 2;
short st1;
// Declare the Interface Pointer for your Visual Basic object. Here,
// _Class1Ptr is the Smart pointer wrapper class representing the
// default interface of the Visual Basic object.
_Class1Ptr ptr;
// Create an instance of your Visual Basic object, here
// __uuidof(Class1) gets the CLSID of your Visual Basic object.
ptr.CreateInstance(__uuidof(Class1));
st1 = ptr->MyVBFunction(&st);
}
catch(_com_error &e)
{
bstrDesc = e.Description();
}
CoUninitialize();
}
it says _Class1Ptr is unknown!
BSTR bstrDesc;
try
{
HRESULT hr= CoInitialize(NULL);
CLSID clsid;
hr = CLSIDFromProgID(OLESTR("<complete class name as see in registry>"),&clsid);
short st = 2;
short st1;
//nameOfClassInOCX is placeholder for explanation. If you OCX com class name is blabla
//use _blabla and so on.
_nameOfClassInOCX * ptr;
hr = CoCreateInstance(clsid,NULL,CLSCTX_INPROC_SERVER,__uuidof(_nameOfClassInOCX ),(LPVOID*)&ptr);
cout << ptr->GetFees("hi") <<endl;
ptr->Release();
}
catch(_com_error &e)
{
bstrDesc = e.Description();
}
CoUninitialize();
First of all you have to do this is #import the dll, and the compiler will automatically generate all required definitions from it. Then create objects from the library by using either smart pointers, or CreateInstance().
#import "C:\files\test.dll" no_namespace rename("EOF", "EOFile")
...
int main() {
if (FAILED(::CoInitialize(NULL)))
return 0;
........
::CoUninitialize();
return 0;
}
I'm trying to use WTL within an in-process COM server DLL (an IE BHO), but am struggling with _Module.
My DLL needs CMyModule derived from CAtlDllModuleT<>:
class CMyModule : public CAtlDllModuleT< CMyModule >
{
public:
DECLARE_LIBID(LIBID_MyLib)
DECLARE_REGISTRY_APPID_RESOURCEID(IDR_MYPROJ, "{...}")
};
CMyModule _Module;
extern "C" BOOL WINAPI DllMain(...)
{
hInstance;
return _Module.DllMain(dwReason, lpReserved);
}
...
STDAPI DllUnregisterServer(void)
{
return _Module.DllUnregisterServer();
}
But this conflicts with most WTL examples, which require something like this within stdafx.h:
extern CAppModule _Module; // WTL version of CComModule
No matter which way I do it, I (unsurprisingly) get compile errors. CMyModule derived from CAppModule borks on _Module.DllUnregisterServer(), etc. CMyModule derived from CAtlDllModuleT<> borks on code like _Module.GetMessageLoop().
Any good references on how WTL is supposed to work within a DLL? Google finds lots of questions, with few answers.
I have a project that uses WTL in a DLL. I looked at how my headers are set up and it looks like I hacked around this same problem...
I have my module set up like your sample code inheriting from CAtlDllModuleT<> except the name of the global module variable is _AtlModule rather than _Module. For example:
class CMyModule : public CAtlDllModuleT< CMyModule >
{
public:
DECLARE_LIBID(LIBID_MyLib)
DECLARE_REGISTRY_APPID_RESOURCEID(IDR_MYPROJ, "{...}")
};
CMyModule _AtlModule;
So, all of the DllMain.cpp entry points use _AtlModule. Then in the stdafx.h file it looks like this:
// WTL includes
#define _Module (*_pModule)
#include <atlapp.h>
#include <atlctrls.h>
#include <atldlgs.h>
#undef _Module
That _pModule thing is defined in atlbase.h like:
__declspec(selectany) CComModule* _pModule = NULL;
There must be a better way, but this does work.
Have you considered the option of multiple inheritance? Try inheriting from both CAtlDllModule and CAppModule since you need both.
I use WTL in an Office add-in; the following works for me. (At the bottom of stdafx.h)
class DECLSPEC_UUID("XXXX-...") MyLib;
using namespace ATL;
/*
* Application module
*/
class CAddInModule : public CAtlDllModuleT< CAddInModule >
{
public:
CAddInModule() : m_hInstance(NULL)
{
}
DECLARE_LIBID(__uuidof(MyLib))
HINSTANCE GetResourceInstance()
{
return m_hInstance;
}
void SetResourceInstance(HINSTANCE hInstance)
{
m_hInstance = hInstance;
}
private:
HINSTANCE m_hInstance;
};
extern CAddInModule _AtlModule;
And then the DLL main use _AtlModule:
// DLL Entry Point
extern "C" BOOL WINAPI DllMain(HINSTANCE hInstance, DWORD dwReason, LPVOID lpReserved)
{
_AtlModule.SetResourceInstance(hInstance);
return _AtlModule.DllMain(dwReason, lpReserved);
}
// Used to determine whether the DLL can be unloaded by OLE
STDAPI DllCanUnloadNow(void)
{
return _AtlModule.DllCanUnloadNow();
}
// Returns a class factory to create an object of the requested type
STDAPI DllGetClassObject(REFCLSID rclsid, REFIID riid, LPVOID* ppv)
{
return _AtlModule.DllGetClassObject(rclsid, riid, ppv);
}
// DllRegisterServer - Adds entries to the system registry
STDAPI DllRegisterServer(void)
{
// registers object, typelib and all interfaces in typelib
HRESULT hr = _AtlModule.DllRegisterServer();
return hr;
}
// DllUnregisterServer - Removes entries from the system registry
STDAPI DllUnregisterServer(void)
{
HRESULT hr = _AtlModule.DllUnregisterServer();
return hr;
}