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SQL Server Tips by Gama and Naughter Consulting


Adding COM / Win32 DLL Support

We next need to implement the COM support. To do this, we create a COM object in the project, using the menu item “Insert -> New ATL Object”. We select the “Simple Object” type and specify a short name of “ServerReachable”. We accept all the other defaults values and click the “OK” button. In the “ClassView”, we select the “IServerReachable” COM interface in the class “CServerReachable” and using the context menu, select “Add Method”. We specify a method name of “ServerReachable” and specify parameters as “[in] BSTR Server, [out, retval] VARIANT_BOOL* pbReachable”. This completes the framework code for COM support.

We next need to add support for “IP Helper” to our project. We do this by adding the following to the bottom of our precompiled header “stdafx.h”:

#include <IPHlpApi.h>
#include <Icmpapi.h>

In addition we need to add “IPHlpApi.lib” and “wsock32.lib” to the “Object / Library Modules” setting in the Project settings linker tab. Make sure you update the settings for both your Release as well as Debug build configurations. In addition you might want to take this opportunity to remove unreferenced import libraries.

Now we implement the Win32 DLL support by creating a new “PingMachine.cpp / h” pair of source code modules. “PingMachine.h” contains the following:

#ifndef __PINGMACHINE_H__
#define __PINGMACHINE_H__

#define XP_SERVERREACHABLE_API __declspec(dllexport)
#define XP_SERVERREACHABLE_API __declspec(dllimport)

//This function forms the Win32 DLL implementation
extern "C" BOOL XP_SERVERREACHABLE_API IcmpServerReachable(LPCTSTR pszServer);

#endif //__PINGMACHINE_H__

and “PingMachine.cpp” contains the following code:

#include "stdafx.h"
#include "PingMachine.h"

//This function forms the Win32 DLL implementation
BOOL IcmpServerReachable(LPCTSTR pszServer)
//Create the ICMP handle
HANDLE hICMP = IcmpCreateFile();
return FALSE;

//Do a DNS lookup of the server name if not already in dotted notation
LPSTR lpszAsciiServer = T2A((LPTSTR) pszServer);
unsigned long ipAddress = inet_addr(lpszAsciiServer);
if (ipAddress == INADDR_NONE)
//Not a dotted address, then do a lookup of the name
hostent* hp = gethostbyname(lpszAsciiServer);
if (hp)
memcpy(&ipAddress, hp->h_addr, hp->h_length);
return FALSE;

//assume the worst
BOOL bSuccess = FALSE;

//do the actual ping, note we hard code a number of values to reasonable default values

BYTE byDataToSend[32];
int nDataSize = sizeof(byDataToSend);
memset(byDataToSend, nDataSize, 'E'); //Use 32 "E"'s which is what the command line ping utility uses by default

//Set the options to use for the ping
memset(&ipOptions, 0, sizeof(ipOptions));
ipOptions.Ttl = 10;

//Setup a stack buffer to receive the reply
BYTE byReplyBuffer[3];
int nReplySize = sizeof(byReplyBuffer);
DWORD nReplies = IcmpSendEcho(hICMP, ipAddress, byDataToSend, nDataSize, &ipOptions, byReplyBuffer, nReplySize, 5000); //Use a default timeout of 5 seconds

//Check the reply if one was received
if (nReplies == 1)
//Check what we got back is what we sent
bSuccess = TRUE;
ICMP_ECHO_REPLY* pEchoReply = (ICMP_ECHO_REPLY*) byReplyBuffer;
char* pReplyData = (char*) pEchoReply->Data;
for (int i=0; i<pEchoReply->DataSize && bSuccess; i++)
bSuccess = pReplyData[i] == 'E';

//Free the ICMP handle we have been using

//Return the success indicator
return bSuccess;

At this point we also need to add a new pre-processor define “BUILD_XP_SERVERREACHABLE” to the C++ tab of the project’s settings. This ensures that the function is exported from the DLL when the project is built and the function is imported otherwise. Again make sure you add this define for all your project definitions. This completes the Win32 DLL implementation for the project.

We can now complete the COM support by simply calling the “IcmpServerReachable” function in the “ServerReachable” COM method as follows:

STDMETHODIMP CServerReachable::ServerReachable(BSTR Server, VARIANT_BOOL *pbReachable)

//Validate our parameters
if (pbReachable == NULL)
return E_POINTER;

//Convert the BSTR string to a LPCTSTR
LPCTSTR pszServer = W2T(Server);

//Call the function we have developed
BOOL bReachable = IcmpServerReachable(pszServer);
if (bReachable)
*pbReachable = VARIANT_TRUE;
*pbReachable = VARIANT_FALSE;

return S_OK;

This completes the Win32 DLL and COM support.

The above book excerpt is from:

Super SQL Server Systems
Turbocharge Database Performance with C++ External Procedures

ISBN: 0-9761573-2-2
Joseph Gama, P. J. Naughter





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