ATL Tutorial

If you are new to ATL ( Active Template Library ) please refer the below items.

1. Basics of ATL

In this tutorial we will be creating

1. MathComp which is a DLL or Inproc server and exposes the Add and Sub functions.

2. An MFC Dialog Based Application which acts like a Client for MathComp

Steps for creating MathComp

1. Open VS 2008
2. File->NewProject Click OK -> Click Next Select Server type: as DLL Select Addition options: as 'Allow merging of proxy/stub code' and click Finish
3. Add Component Class

Select ATL simple Object

Enter Short name: "CMath" to add the component class -> Click 'Finish'

Add a Method to ICMath Interface

The classes created are shown below in the class diagram.

CCMath

// CCMath
class ATL_NO_VTABLE CCMath :
       public CComObjectRootEx<CComSingleThreadModel>,
       public CComCoClass<CCMath, &CLSID_CMath>,
       public IDispatchImpl<ICMath, &IID_ICMath, &LIBID_MathCompLib, /*wMajor =*/ 1, /*wMinor =*/ 0>
{
public :
      CCMath()
      {
      }

DECLARE_REGISTRY_RESOURCEID(IDR_CMATH)

BEGIN_COM_MAP(CCMath)
      COM_INTERFACE_ENTRY(ICMath)
      COM_INTERFACE_ENTRY(IDispatch)
END_COM_MAP()

DECLARE_PROTECT_FINAL_CONSTRUCT()

      HRESULT FinalConstruct()
      {
             return S_OK;
      }

       void FinalRelease()
      {
      }

public :

      STDMETHOD(Add)(DOUBLE i, DOUBLE j, DOUBLE* result);
      STDMETHOD(Sub)(DOUBLE i, DOUBLE j, DOUBLE* result);
};

OBJECT_ENTRY_AUTO( __uuidof(CMath), CCMath)

CMath.h
// CCMath
STDMETHODIMP CCMath::Add(DOUBLE i, DOUBLE j, DOUBLE* result)
{
      *result = i + j;
       return S_OK;
}

STDMETHODIMP CCMath::Sub(DOUBLE i, DOUBLE j, DOUBLE* result)
{
      *result = i - j;
       return S_OK;
}

MathComp.idl

// MathComp.idl : IDL source for MathComp
// This file will be processed by the MIDL tool to
// produce the type library (MathComp.tlb) and marshalling code.

import "oaidl.idl" ;
import "ocidl.idl" ;

[
       object ,
       uuid (F3BDE3CF-884A-461A-A377-1F96A72239B0),
       dual ,
       nonextensible ,
       helpstring ("ICMath Interface" ),
       pointer_default (unique )
]
interface ICMath : IDispatch{
      [ id (1), helpstring ( "method Add")] HRESULT Add([ in ] DOUBLE i, [in ] DOUBLE j, [out ] DOUBLE* result);
      [ id (2), helpstring ( "method Sub")] HRESULT Sub([ in ] DOUBLE i, [in ] DOUBLE j, [out ] DOUBLE* result);
};
[
       uuid (44FF4D78-6AAD-4D2B-9150-DEBCCE79D8E0),
       version (1.0),
       helpstring ("MathComp 1.0 Type Library" )
]
library MathCompLib
{
       importlib ("stdole2.tlb" );
      [
             uuid (4A8C8314-6C03-4AF7-96A1-9D6052A89363),
             helpstring ("CMath Class" )
      ]
       coclass CMath
      {
            [ default ] interface ICMath;
      };
};

NOTE: Other classes are not shown here please Download the source for complete code.

Steps for creating MFC Client

1. Create an MFC Dialog based application

2. Design the Dialog as shown below

3. Add a Add button Handler (OnBnClickedButtonAdd) 4. Inside Add button handler add the below code

//Step1: import include .tlb file
#import "..MathCompMathComp.tlb" no_namespace

void CCMathClientDlg::OnBnClickedButtonAdd()
{
      //Step2/////////////// Initialize the COM libraries ///////////////////////////////
     CoInitialize(NULL);

      //Step3/////////////////////////Retriving CLSID from ProgID///////////////////////
      CLSID clsid;
      CLSIDFromProgID(OLESTR("MathComp.CMath.1"),&clsid); // will be in CMath.rgs file

      //Step4/////////////////////////////Creating instance of server///////////////////
      ICMath *pICMath;

      HRESULT hr = CoCreateInstance(
                     clsid,             //The CLSID associated with the data and code that will be used to create the object.
                     NULL,              //If NULL, indicates that the object is not being created as part of an aggregate
                     CLSCTX_LOCAL_SERVER|CLSCTX_INPROC_SERVER, //ontext in which the code that manages the newly created object will run
                     __uuidof(ICMath),  //riid: A reference to the identifier of the interface to be used to communicate with the object.
                     (LPVOID*)&pICMath); //*ppv: Address of pointer variable that receives the interface pointer requested in riid.
                                       //Upon successful return, *ppv contains the requested interface pointer. Upon failure, *ppv contains NULL.

      if (FAILED(hr))
      {
            AfxMessageBox(_T("ICMath Failed"));
      }

      //Step5/////////////////////////////Using COM Component//////////////////////////
      UpdateData(TRUE);

      double res =0;
      pICMath->Add(m_i, m_j, &res);
      m_Result = res;

      pICMath->Release(); // To avoid memory leak
      pICMath = NULL;

      //Step6////////////////////////////Uninit'ializing the COM libraries//////////////
      CoUninitialize();

      UpdateData(FALSE);
}