Example: Creating a WMI Application

You can use the procedure and code examples in this topic to create a complete WMI client application that performs COM initialization, connects to WMI on the local computer, reads some data, and cleans up. Connecting to WMI on a Remote Computer describes how to obtain data from remote computers.

This following procedure includes all of the steps that are required by all C++ WMI applications.

1. Initialize COM parameters with a call to CoInitializeEx.

   For more information, see Initializing COM for a WMI Application.

2. Initialize COM process security by calling CoInitializeSecurity.

   For more information, see Setting the Default Process Security Level Using C++.

3. Obtain a pointer to IWbemServices for a namespace on a specified host computer—the local computer in the simple case—by calling IWbemLocator::ConnectServer.

   To connect to a remote computer, for example Computer_A, use the following object path parameter:

   _bstr_t(L"\\COMPUTER_A\ROOT\\CIMV2")
   

   For more information, see Creating a Connection to a WMI Namespace.

4. Set the IWbemServices proxy security so WMI service can impersonate the client by calling CoSetProxyBlanket.

   For more information, see Setting the Security Levels on a WMI Connection.

5. Use the IWbemServices pointer to make requests of WMI. For example, querying for all the Win32_Service instances to determine which services are stopped.

   For more information, see Manipulating Class and Instance Information, Querying WMI, and Receiving a WMI Event.

6. Clean up objects and COM.

   For more information, see Cleaning up and Shutting Down a WMI Application.

The following example code is a complete WMI client application.

#define _WIN32_DCOM
#include <iostream>
using namespace std;
#include <comdef.h>
#include <Wbemidl.h>

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

int main(int argc, char **argv)
{
    HRESULT hres;

    // 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.
    }

    // Initialize 
    hres =  CoInitializeSecurity(
        NULL,     
        -1,      // COM negotiates service                  
        NULL,    // Authentication services
        NULL,    // Reserved
        RPC_C_AUTHN_LEVEL_DEFAULT,    // authentication
        RPC_C_IMP_LEVEL_IMPERSONATE,  // 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.
    }

    // Obtain the initial locator to Windows Management
    // on a particular host computer.
    IWbemLocator *pLoc = 0;

    hres = CoCreateInstance(
        CLSID_WbemLocator,             
        0, 
        CLSCTX_INPROC_SERVER, 
        IID_IWbemLocator, (LPVOID *) &pLoc);
 
    if (FAILED(hres))
    {
        cout << "Failed to create IWbemLocator object. "
            << "Error code = 0x"
            << hex << hres << endl;
        CoUninitialize();
        return 1;       // Program has failed.
    }

    IWbemServices *pSvc = 0;

    // 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"), // WMI namespace
        NULL,                    // User name
        NULL,                    // User password
        0,                       // Locale
        NULL,                    // Security flags                 
        0,                       // Authority       
        0,                       // Context object
        &pSvc                    // 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;

    // Set the IWbemServices proxy so that impersonation
    // of the user (client) occurs.
    hres = CoSetProxyBlanket(
       
       pSvc,                         // the proxy to set
       RPC_C_AUTHN_WINNT,            // authentication service
       RPC_C_AUTHZ_NONE,             // authorization service
       NULL,                         // Server principal name
       RPC_C_AUTHN_LEVEL_CALL,       // authentication level
       RPC_C_IMP_LEVEL_IMPERSONATE,  // impersonation level
       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.
    }


    // Use the IWbemServices pointer to make requests of WMI. 
    // Make requests here:

    // For example, query for all the running processes
    IEnumWbemClassObject* pEnumerator = NULL;
    hres = pSvc->ExecQuery(
        bstr_t("WQL"), 
        bstr_t("SELECT * FROM Win32_Process"),
        WBEM_FLAG_FORWARD_ONLY | WBEM_FLAG_RETURN_IMMEDIATELY, 
        NULL,
        &pEnumerator);
    
    if (FAILED(hres))
    {
        cout << "Query for processes failed. "
             << "Error code = 0x" 
             << hex << hres << endl;
        pSvc->Release();
        pLoc->Release();     
        CoUninitialize();
        return 1;               // Program has failed.
    }
    else
    { 
        IWbemClassObject *pclsObj;
        ULONG uReturn = 0;
   
        while (pEnumerator)
        {
            hres = pEnumerator->Next(WBEM_INFINITE, 1, 
                &pclsObj, &uReturn);

            if(0 == uReturn)
            {
                break;
            }

            VARIANT vtProp;

            // Get the value of the Name property
            hres = pclsObj->Get(L"Name", 0, &vtProp, 0, 0);
            wcout << "Process Name : " << vtProp.bstrVal << endl;
            VariantClear(&vtProp);
            
            pclsObj->Release();
            pclsObj = NULL;
        }
         
    }
 
    // Cleanup
    // ========
    
    pSvc->Release();
    pLoc->Release();
    pEnumerator->Release();  
    
    CoUninitialize();

    return 0;   // Program successfully completed.
}