how can i get get the MACaddress of all the NICs on my PC using WMI

Question

HI all,

I am trying to modify the code provided by MS try to access the the Network Adapter Configuration

I am getting null pointer exception in it when i try to access the Mac Address or IPAddress property im using VC++ 2005. check for the // exception here: vtProp is returned as NULL line where am getting the exception.

#define _WIN32_DCOM
#include "stdafx.h"

#include <iostream>
using namespace std;
#include <comdef.h>
#include <Wbemidl.h>

# pragma comment(lib, "wbemuuid.lib")
#pragma comment(lib, "comsuppw.lib")

int _tmain(int argc, _TCHAR* argv[])
{
      HRESULT hres;

    // Step 1: --------------------------------------------------
    // Initialize COM. ------------------------------------------

    hres =  CoInitializeEx(0, COINIT_MULTITHREADED); 
    if (FAILED(hres))
    {
        cout << "Failed to initialize COM library. Error code = 0x" 
            << hex << hres << endl;
        return 1;                  // Program has failed.
    }

    // Step 2: --------------------------------------------------
    // Set general COM security levels --------------------------
    // Note: If you are using Windows 2000, you need to specify -
    // the default authentication credentials for a user by using
    // a SOLE_AUTHENTICATION_LIST structure in the pAuthList ----
    // parameter of CoInitializeSecurity ------------------------

    hres =  CoInitializeSecurity(
        NULL, 
        -1,                          // COM authentication
        NULL,                        // Authentication services
        NULL,                        // Reserved
        RPC_C_AUTHN_LEVEL_DEFAULT,   // Default authentication 
        RPC_C_IMP_LEVEL_IMPERSONATE, // Default Impersonation  
        NULL,                        // Authentication info
        EOAC_NONE,                   // Additional capabilities 
        NULL                         // Reserved
        );


    if (FAILED(hres))
    {
        cout << "Failed to initialize security. Error code = 0x" 
            << hex << hres << endl;
        CoUninitialize();
        return 1;                    // Program has failed.
    }

    // Step 3: ---------------------------------------------------
    // Obtain the initial locator to WMI -------------------------

    IWbemLocator *pLoc = NULL;

    hres = CoCreateInstance(
        CLSID_WbemLocator,             
        0, 
        CLSCTX_INPROC_SERVER, 
        IID_IWbemLocator, (LPVOID *) &pLoc);

    if (FAILED(hres))
    {
        cout << "Failed to create IWbemLocator object."
            << " Err code = 0x"
            << hex << hres << endl;
        CoUninitialize();
        return 1;                 // Program has failed.
    }

    // Step 4: -----------------------------------------------------
    // Connect to WMI through the IWbemLocator::ConnectServer method

    IWbemServices *pSvc = NULL;

    // Connect to the root\cimv2 namespace with
    // the current user and obtain pointer pSvc
    // to make IWbemServices calls.
    hres = pLoc->ConnectServer(
         _bstr_t(L"ROOT\\CIMV2"), // Object path of WMI namespace
         NULL,                    // User name. NULL = current user
         NULL,                    // User password. NULL = current
         0,                       // Locale. NULL indicates current
         NULL,                    // Security flags.
         0,                       // Authority (e.g. Kerberos)
         0,                       // Context object 
         &pSvc                    // pointer to IWbemServices proxy
         );

    if (FAILED(hres))
    {
        cout << "Could not connect. Error code = 0x" 
             << hex << hres << endl;
        pLoc->Release();     
        CoUninitialize();
        return 1;                // Program has failed.
    }

    cout << "Connected to ROOT\\CIMV2 WMI namespace" << endl;


    // Step 5: --------------------------------------------------
    // Set security levels on the proxy -------------------------

    hres = CoSetProxyBlanket(
       pSvc,                        // Indicates the proxy to set
       RPC_C_AUTHN_WINNT,           // RPC_C_AUTHN_xxx
       RPC_C_AUTHZ_NONE,            // RPC_C_AUTHZ_xxx
       NULL,                        // Server principal name 
       RPC_C_AUTHN_LEVEL_CALL,      // RPC_C_AUTHN_LEVEL_xxx 
       RPC_C_IMP_LEVEL_IMPERSONATE, // RPC_C_IMP_LEVEL_xxx
       NULL,                        // client identity
       EOAC_NONE                    // proxy capabilities 
    );

    if (FAILED(hres))
    {
        cout << "Could not set proxy blanket. Error code = 0x" 
            << hex << hres << endl;
        pSvc->Release();
        pLoc->Release();     
        CoUninitialize();
        return 1;               // Program has failed.
    }

    // Step 6: --------------------------------------------------
    // Use the IWbemServices pointer to make requests of WMI ----

    // For example, get the name of the operating system
    IEnumWbemClassObject* pEnumerator = NULL;
    hres = pSvc->ExecQuery(
        bstr_t("WQL"), 
        bstr_t("SELECT * FROM Win32_NetworkAdapterConfiguration"),
        WBEM_FLAG_FORWARD_ONLY | WBEM_FLAG_RETURN_IMMEDIATELY, 
        NULL,
        &pEnumerator);

    if (FAILED(hres))
    {
        cout << "Query for NIC(s) name failed."
            << " Error code = 0x" 
            << hex << hres << endl;
        pSvc->Release();
        pLoc->Release();
        CoUninitialize();
        return 1;               // Program has failed.
    }

    // Step 7: -------------------------------------------------
    // Get the data from the query in step 6 -------------------

    IWbemClassObject *pclsObj;
    ULONG uReturn = 0;

    while (pEnumerator)
    {
        HRESULT hr = pEnumerator->Next(WBEM_INFINITE, 1, 
            &pclsObj, &uReturn);

        if(0 == uReturn)
        {
            break;
        }

        VARIANT vtProp;

        // Get the value of the Name property

        //hr = pclsObj->Get(L"Caption", 0, &vtProp, 0, 0);
  //      wcout << " Caption : " << vtProp.bstrVal << endl;
  //      VariantClear(&vtProp);
     //   pclsObj->Release();

        hr = pclsObj->Get(L"MACAddress", 0, &vtProp, 0, 0);
        // exception here:  vtProp is returned as NULL
        wcout << " MACAddress : " << vtProp.bstrVal << endl;
        VariantClear(&vtProp);
        pclsObj->Release();


    }

    // Cleanup
    // ========

    pSvc->Release();
    pLoc->Release();
    pEnumerator->Release();
   // pclsObj->Release();
    CoUninitialize();

    return 0;   // Program successfully completed.
}

what is wrong in the code??

Abdul khaliq

Answer 1

This is old but I had the same problem and I didn't see a solution anywhere. I solved it by putting a check for VT_NULL.

if( vtProp.vt != VT_NULL )
    wcout << " MACAddress : " << vtProp.bstrVal << endl;

I don't understand why some of the results are VT_NULL but I suspect it could be avoided by adding a "where" clause to the "select" statement.

Thanks to finnw for the tip!

Answer 2

The list of network adapters usually contains a few "virtual" adapters, and they don't all have MAC addresses. Some (e.g. "Packet Scheduler Miniport') duplicate the MAC addresses of physical adapters. You just need to check the vt field (it may be VT_EMPTY) and remove duplicates from the resulting list.

Answer 3

I'd start by initializing the vtProp variable -- it shouldn't matter, but sometimes COM servers make assumptions about out params;

  VariantInit(&vtProp);

Then you can inspect vtProp after it's been returned and see what the actual type is (.vt member) -- maybe it's not a string, for some reason?

Could you post back with the type (you can cross-reference with the VARTYPE definition from oaidl.h to see what the friendly name(s) are)?