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Posted 8 Mar 2006


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Using managed delegate types in the unmanaged world

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8 Mar 2006
An article on how to use managed delegate types in the unmanaged world.


Creating a delegate in .NET is extremely simple. However, in a rare case, you might have to create an object of the .NET delegate type with an unmanaged function pointer (in unmanaged world). This article explains a simple way to do the same.


The problem I faced was:

In an ATL COM environment, I had to create an object of the .NET delegate type, AsyncCallback. In .NET, to create an object of this kind and assign a method to it is simple, by using a parameterized constructor. But in unmanaged COM world, parameterized constructors are not available, and it would be very difficult to do the same.

I solved this problem by creating a helper class in .NET which wraps an unmanaged function pointer (sent from the unmanaged world) as an AsyncCallback delegate. This delegate is then returned to the unmanaged world.

Using the code

Step 1. In .NET, create an interface IDelegateHelper. This interface provides a method AsyncCallbackDelegateWrapper that takes in a function pointer to an unmanaged function whose delegate is to be created. DelegateHelperCLass implements this interface. The method definition involves using Marshal.GeDelegateForFunctionPointer available in .NET to create a delegate out of the function pointer. The interface is provided for ease of use in the COM unmanaged world.

//Interface exposed to COM world 
public interface IDelegateHelper
      AsynCallbackDelegateWrapper(IntPtr funcPtr_in);

//Class exposed to COM world
public class DelegateHelperCLass : IDelegateHelper
    public AsyncCallback 
      AsynCallbackDelegateWrapper(IntPtr funcPtr_in)
        Delegate aAsyncCallbackDelegate = 

        return aAsyncCallbackDelegate as AsyncCallback;

Step 2. Export this .NET DLL into a TLB for use in COM. Use the tlbexp.exe utility to do the same. Register the .NET DLL using regasm.

tlbexp.exe DelegateHelper.dll 

regasm.exe DelegateHelper.dll

Step 3. To use this in the unmanaged world (COM C++, here), create an instance of IDelegateHelper using CoCreateInstance. Then call the method AsynCallbackDelegateWrapper, passing the function pointer of the method whose delegate is to be created. The result obtained is a .NET delegate type.

//Import the TLBs
#import "C:\WINDOWS\Microsoft.NET\Framework" 
        raw_native_types, no_namespace, 
        named_guids, rename("_Module", "ReflectionModule"), 
        rename("ReportEvent", "ReportEventModule")
#import "F:\DelegateHelper.tlb" 
        raw_interfaces_only named_guids, no_namespace

//Add this to the library block in IDL 
//file for recognizing IAsyncResult* 

//Create a function pointer FuncPtr that has 
//a signature same as that of the delgate methods
typedef void(*FuncPtr)(IAsyncResult*);

//CClient code that calls the helper methods
STDMETHODIMP CClient::CreateAsyncCallbackDelegate(void)
    //First create an instance of DelegateHelper class
    CComPtr<IDelegateHelper> aHelper;
    HRESULT hr = 
        return E_FAIL;
    //AsyncCallback delegate instnace 
    //that is to be populated with 
    _AsyncCallback* aCallBack = NULL;
    FuncPtr aPtr = TestMethod;
    hr = aHelper->AsynCallbackDelegateWrapper((long)aPtr, 
        return E_FAIL;

    //Now aCallBack can be used like 
    //a regular AsyncCallback instance!!
    return S_OK;

//Some static method whose delegate is to be created
void CClient::TestMethod(IAsyncResult* asyncResult_in)
    //Your Callback code


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Comments and Discussions

QuestionAPi Problem Pin
t4ure4n13-Aug-06 3:36
Membert4ure4n13-Aug-06 3:36 
I am doing a project to develop ”Software Defined Radio”. I have purchased a hardware radio receiver called WiNRADiO G303e. It connects to the computer via USB interface. It feeds the computer with down converted + demodulated RF signal (12kHz) to the computer. Which I have to process in some way.

The winradio company has provided an API to communicate with the radio receiver According to them
“The G303 receivers API is implemented as a single 32-bit library WRG303API.DLL. It provides functions for all communication with all types of G303 receivers. It can be used by any 32-bit application under Windows 98, ME as well as 2000 and XP.”
I am making my project in C#. I have written an API wrapper class. I used P/Invoke and defined all the method signatures in that class. I have used help from various different tools and web forums to write this class.

Now I particular problem is in the methods which use pointer to memory location, arrays or passing the reference of these arrays


The method uses a callback mechanism which can be provided by Delegates in c # but I can’t figure out the syntax to it.

C/C++ declaration given in the API
BOOL __stdcall CodecStart (int hRadio, void __stdcall (*CallbackFunc) (void *), void *CallbackTarget);
I have been suggested to use the following code for this function but I have absolutely no clue how to do coding for this method.

There is an example usage of this function in C++

#include "stdafx.h"<br />
#include <windows.h><br />
#include <stdio.h><br />
<br />
// G3 API function type declarations<br />
typedef int (__stdcall *FNCOpenRadioDevice)(int iDeviceNum);<br />
typedef BOOL (__stdcall *FNCCloseRadioDevice)(int hRadio);<br />
typedef BOOL (__stdcall *FNCSetAtten)(int hRadio, BOOL fAtten);<br />
typedef BOOL (__stdcall *FNCSetPower)(int hRadio, BOOL fPower);<br />
typedef BOOL (__stdcall *FNCSetAGC)(int hRadio, int iAGC);<br />
typedef BOOL (__stdcall *FNCCodecStart)(int hRadio,void (__stdcall *CallbackFunc)(void *),<br />
void *CallbackTarget);<br />
typedef BOOL (__stdcall *FNCCodecStop)(int hRadio);<br />
typedef unsigned int (__stdcall *FNCCodecRead)(int hRadio,void *Buf,unsigned int Size);<br />
<br />
typedef struct {<br />
int hRadio;<br />
FILE *IFFile;<br />
FNCCodecRead CodecRead;<br />
} CallbackContext;<br />
<br />
void __stdcall CodecCallback(void *Target)<br />
{<br />
unsigned int i;<br />
char Buf[4096];<br />
CallbackContext *Ctx=(CallbackContext *)Target;<br />
<br />
while ((i=Ctx->CodecRead(Ctx->hRadio,Buf,sizeof(Buf)))!=0) <br />
fwrite(Buf,i,1,Ctx->IFFile);<br />
}<br />
//int _tmain(int argc, _TCHAR* argv[])<br />
int main(int argc, char* argv[])<br />
{<br />
// load the G3 API library<br />
HMODULE dll=LoadLibraryA("wrg303api.dll");<br />
if (!dll) {puts("WRG303API.DLL not found !"); return 0;}<br />
<br />
// link G3 API functions<br />
FNCOpenRadioDevice OpenRadioDevice=(FNCOpenRadioDevice)GetProcAddress(dll,"OpenRadioDevice");<br />
FNCCloseRadioDevice CloseRadioDevice=(FNCCloseRadioDevice)GetProcAddress(dll,"CloseRadioDevice");<br />
FNCSetAtten SetAtten=(FNCSetAtten)GetProcAddress(dll,"SetAtten");<br />
FNCSetPower SetPower=(FNCSetPower)GetProcAddress(dll,"SetPower");<br />
FNCSetAGC SetAGC=(FNCSetAGC)GetProcAddress(dll,"SetAGC");<br />
FNCCodecStart CodecStart=(FNCCodecStart)GetProcAddress(dll,"CodecStart");<br />
FNCCodecStop CodecStop=(FNCCodecStop)GetProcAddress(dll,"CodecStop");<br />
FNCCodecRead CodecRead=(FNCCodecRead)GetProcAddress(dll,"CodecRead");<br />
<br />
// open the first available radio<br />
int hRadio=OpenRadioDevice(0);<br />
if (!hRadio) {puts("No WR-G303 device could be opened !");FreeLibrary(dll); return 0;}<br />
<br />
// set Power, AGC and Attenuator<br />
if (SetPower(hRadio,TRUE)) puts("The device is turned ON"); else puts("The device failed to turn ON");<br />
if (SetAtten(hRadio,FALSE)) puts("The attenuator is OFF"); else puts("The attenuator failed to turn OFF");<br />
if (SetAGC(hRadio,3)) puts("The AGC is FAST"); else puts("The AGC failed to switch");<br />
<br />
// open the IF samples destination file<br />
FILE *f=fopen("IF2.pcm","wb");<br />
<br />
// start the IF stream from the codec<br />
CallbackContext Ctx;<br />
<br />
Ctx.hRadio=hRadio;<br />
Ctx.IFFile=f;<br />
Ctx.CodecRead=CodecRead;<br />
if (!CodecStart(hRadio,CodecCallback,&Ctx)) puts("Codec streaming couldn't be started!");<br />
else {<br />
puts("Codec streaming properly started!");<br />
while (!ftell(f) ) <br />
{<br />
}<br />
CodecStop(hRadio);<br />
fclose(f);<br />
}<br />
<br />
// close the device handle<br />
if (CloseRadioDevice(hRadio)) puts("The device is closed properly"); else puts("The device failed to close");<br />
<br />
// free the G3 API library<br />
FreeLibrary(dll);<br />
<br />
return 0;<br />
}<br />

o O º(`'•.,(`'•., ☆,.•''),.•'')º O o°
»•'"`»* *☆ t4ure4n ☆* *«•'"`«
°o O º(,.•''(,.•'' ☆`'•.,)`'•.,)º O o°

o O º(`'·.,(`'·., ☆,.·''),.·'')º O o°
»·'"`»* *☆ t4ure4n ☆* *«·'"`«
°o O º(,.·''(,.·'' ☆`'·.,)`'·.,)º O o°

GeneralAlternatively... Pin
Richard Deeming15-Mar-06 8:44
mveRichard Deeming15-Mar-06 8:44 
AnswerRe: Alternatively... Pin
NidhiGupta15-Mar-06 21:16
MemberNidhiGupta15-Mar-06 21:16 
GeneralRe: Alternatively... Pin
Richard Deeming16-Mar-06 0:53
mveRichard Deeming16-Mar-06 0:53 
GeneralComments Pin
manishjain768-Mar-06 19:32
Membermanishjain768-Mar-06 19:32 

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