How to call WMI function correctly

The following code fails when ExecMethod is called. Can anyone pinpoint what I am doing wrong?

#define _WIN32_DCOM

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

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

int main(int iArgCnt, char ** 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 must 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 negotiates service
        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 local root\cimv2 namespace
开发者_Python百科    // and obtain pointer pSvc to make IWbemServices calls.
    hres = pLoc->ConnectServer(
        _bstr_t(L"ROOT\\wmi"), 
        NULL,
        NULL, 
        0, 
        NULL, 
        0, 
        0, 
        &pSvc
    );

    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 for 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.
    }


    ///////////////////////////////////////////////////////////////////////////////////////////////////////////////
    // set up to call the WmiSetBrightness Method
    BSTR MethodName = SysAllocString(L"WmiSetBrightness");
    BSTR ClassName = SysAllocString(L"WmiMonitorBrightnessMethods");

    IWbemClassObject* pClass = NULL;
    hres = pSvc->GetObject(ClassName, 0, NULL, &pClass, NULL);

    IWbemClassObject* pInParamsDefinition = NULL;
    hres = pClass->GetMethod(MethodName, 0, 
        &pInParamsDefinition, NULL);

    IWbemClassObject* pClassInstance = NULL;
    hres = pInParamsDefinition->SpawnInstance(0, &pClassInstance);

     VARIANT var1;
     VariantInit(&var1);

     V_VT(&var1) = VT_BSTR;
     V_BSTR(&var1) = SysAllocString(L"1000"); 
     hres = pClassInstance->Put(L"Timeout", 0, &var1, CIM_UINT32); //CIM_UINT64

     VARIANT var2;
     VariantInit(&var2);

     V_VT(&var2) = VT_BSTR;
     V_BSTR(&var2) = SysAllocString(L"30"); 
     hres = pClassInstance->Put(L"Brightness", 0, &var2, CIM_UINT8); 



    // Execute Method
    IWbemClassObject* pOutParams = NULL;
    hres = pSvc->ExecMethod(ClassName, MethodName, 0,
    NULL, pClassInstance, &pOutParams, NULL);



    if (FAILED(hres))
    {
        cout << "Could not execute method. Error code = 0x" 
             << hex << hres << endl;
        //VariantClear(&varCommand);
        SysFreeString(ClassName);
        SysFreeString(MethodName);
        pClass->Release();
        pInParamsDefinition->Release();
        pOutParams->Release();
        pSvc->Release();
        pLoc->Release();     
        CoUninitialize();
        return 1;               // Program has failed.
    }

    // To see what the method returned,
    // use the following code.  The return value will
    // be in &varReturnValue
    VARIANT varReturnValue;
    hres = pOutParams->Get(_bstr_t(L"ReturnValue"), 0, 
        &varReturnValue, NULL, 0);


    // Clean up
    //--------------------------
   // VariantClear(&varCommand);
    VariantClear(&varReturnValue);
    SysFreeString(ClassName);
    SysFreeString(MethodName);
    pClass->Release();
    pInParamsDefinition->Release();
    pOutParams->Release();
    pLoc->Release();
    pSvc->Release();
    CoUninitialize();
    return 0;
}

Since the question was tagged "C++" I tidied up your code by using C++ techniques for failure checking and cleanup. It turned out that you've forgotten to check for failure in several places. The code below reports first failure at GetObject(className, ...).

#define _WIN32_DCOM
#pragma comment(lib, "wbemuuid.lib")

#include <iostream>
#include <string>
#include <stdexcept>
#include <stdlib.h>     // EXIT_FAILURE, EXIT_SUCCESS
using namespace std;

#include <comdef.h>
#include <Wbemidl.h>
#define DEF_SMARTPTR_TYPE( Interface ) \
    _COM_SMARTPTR_TYPEDEF( Interface, __uuidof( Interface ) )

DEF_SMARTPTR_TYPE( IWbemLocator );
DEF_SMARTPTR_TYPE( IWbemServices );
DEF_SMARTPTR_TYPE( IWbemClassObject );

bool throwX( string const& s ) { throw std::runtime_error( s ); }

string hexFrom( unsigned long v )
{
    char    buf[40];
    sprintf( buf, "%08lx", v );
    return buf;
}

struct Fail
{
    string  message;
    explicit Fail( string const& aMessage ): message( aMessage ) {}
};

void operator ||( HRESULT hr, Fail const& failure )
{
    SUCCEEDED( hr )
        || throwX( failure.message + " (Error code 0x" + hexFrom( hr ) + ")" );
}

struct ComLibUsage
{
    struct Threading
    {
        enum Enum {
            singleThreaded  = COINIT_APARTMENTTHREADED,
            multiThreaded   = COINIT_MULTITHREADED
        };
    };

    ComLibUsage( Threading::Enum threading = Threading::multiThreaded )
    {
        ::CoInitializeEx( 0, threading )
            || Fail( "Failed to initialize COM library." );
    }

    ~ComLibUsage() { ::CoUninitialize(); }
};

void cppMain()
{
    // Step 1: --------------------------------------------------
    // Initialize COM. ------------------------------------------
    ComLibUsage     comLibUsage( ComLibUsage::Threading::multiThreaded );

    // Step 2: --------------------------------------------------
    // Set general COM security levels --------------------------
    // Note: If you are using Windows 2000, you must specify -
    // the default authentication credentials for a user by using
    // a SOLE_AUTHENTICATION_LIST structure in the pAuthList ----
    // parameter of CoInitializeSecurity ------------------------
    CoInitializeSecurity(
        NULL, 
        -1,                          // COM negotiates service
        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
        ) || Fail( "Failed to initialize security" );

    // Step 3: ---------------------------------------------------
    // Obtain the initial locator to WMI -------------------------
    IWbemLocatorPtr     pLoc;
    CoCreateInstance(
        CLSID_WbemLocator,             
        0, 
        CLSCTX_INPROC_SERVER, 
        IID_IWbemLocator, (LPVOID *) &pLoc
        ) || Fail( "Failed to create IWbemLocator object." );

    // Step 4: ---------------------------------------------------
    // Connect to WMI through the IWbemLocator::ConnectServer method
    // Connect to the local root\cimv2 namespace
    // and obtain pointer pSvc to make IWbemServices calls.
    IWbemServicesPtr    pSvc;
    pLoc->ConnectServer(
        _bstr_t(L"ROOT\\wmi"), 
        NULL,
        NULL, 
        0, 
        NULL, 
        0, 
        0, 
        &pSvc
        ) || Fail( "Could not connect." );
    cout << "Connected to ROOT\\CIMV2 WMI namespace" << endl;


    // Step 5: --------------------------------------------------
    // Set security levels for the proxy ------------------------
    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 
        ) || Fail( "Could not set proxy blanket" );

    ////////////////////////////////////////////////////////////////
    // set up to call the WmiSetBrightness Method
    _bstr_t     methodName  = L"WmiSetBrightness";
    _bstr_t     className   = L"WmiMonitorBrightnessMethods";

    IWbemClassObjectPtr pClass;
    pSvc->GetObject(className, 0, NULL, &pClass, NULL)
        || Fail( "GetObject(className, ...) failed" );

    IWbemClassObjectPtr pInParamsDefinition;
    pClass->GetMethod(methodName, 0, &pInParamsDefinition, NULL)
        || Fail( "GetMethod(methodName, ...) failed" );

    IWbemClassObjectPtr pClassInstance;
    pInParamsDefinition->SpawnInstance(0, &pClassInstance)
        || Fail( "SpawnInstance failed" );

    _variant_t  var1( L"1000" );
    pClassInstance->Put(L"Timeout", 0, &var1, CIM_UINT32)   //CIM_UINT64
        || Fail( "Put failed for 'Timeout'" );

    _variant_t  var2( L"30" );
    pClassInstance->Put(L"Brightness", 0, &var2, CIM_UINT8)
        || Fail( "Put failed for 'Brightness'" );

    // Execute Method
    IWbemClassObject* pOutParams = NULL;
    //hres = pSvc->ExecMethod(className, methodName, 0,
    //NULL, pClassInstance, &pOutParams, NULL)
        //|| Fail( "Could not execute method" );

    // To see what the method returned,
    // use the following code.  The return value will
    // be in &varReturnValue
    _variant_t varReturnValue;
    pOutParams->Get(_bstr_t(L"ReturnValue"), 0, &varReturnValue, NULL, 0)
        || Fail( "Get failed" );
}

int main()
{
    try
    {
        cppMain();
        return EXIT_SUCCESS;
    }
    catch( exception const& x )
    {
        cerr << "!" << x.what() << endl;
    }
    return EXIT_FAILURE;
}

Cheers & hth. (even if it's a bit on the side of your question!),

Instead of the Step 4 & 6 from Example: Calling a Provider Method, it can set the brightness ABSOLUTELY.

Step 4:

        IWbemServices *pSvc = NULL;

        // Connect to the local root\cimv2 namespace
        // and obtain pointer pSvc to make IWbemServices calls.
        hres = pLoc->ConnectServer(
            _bstr_t(L"ROOT\\WMI"),
            NULL,
            NULL,
            0,
            NULL,
            0,
            0,
            &pSvc
            );

        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\\WMI WMI namespace" << endl;

Step 6:

        BSTR ClassName = SysAllocString(L"WmiMonitorBrightnessMethods");
        BSTR MethodName = SysAllocString(L"WmiSetBrightness");
        BSTR bstrQuery = SysAllocString(L"Select * from WmiMonitorBrightnessMethods");
        IEnumWbemClassObject *pEnum = NULL;

        hres = pSvc->ExecQuery(_bstr_t(L"WQL"), //Query Language  
            bstrQuery, //Query to Execute  
            WBEM_FLAG_FORWARD_ONLY | WBEM_FLAG_RETURN_IMMEDIATELY, //Make a semi-synchronous call  
            NULL, //Context  
            &pEnum /*Enumeration Interface*/);

        hres = WBEM_S_NO_ERROR;

        ULONG ulReturned;
        IWbemClassObject *pObj;
        DWORD retVal = 0;

        //Get the Next Object from the collection  
        hres = pEnum->Next(WBEM_INFINITE, //Timeout  
            1, //No of objects requested  
            &pObj, //Returned Object  
            &ulReturned /*No of object returned*/);

        IWbemClassObject* pClass = NULL;
        hres = pSvc->GetObject(ClassName, 0, NULL, &pClass, NULL);

        IWbemClassObject* pInParamsDefinition = NULL;
        hres = pClass->GetMethod(MethodName, 0, &pInParamsDefinition, NULL);

        IWbemClassObject* pClassInstance = NULL;
        hres = pInParamsDefinition->SpawnInstance(0, &pClassInstance);

        VARIANT var1;
        VariantInit(&var1);
        BSTR ArgName0 = SysAllocString(L"Timeout");

        V_VT(&var1) = VT_BSTR;
        V_BSTR(&var1) = SysAllocString(L"0");
        hres = pClassInstance->Put(ArgName0,
            0,
            &var1,
            CIM_UINT32); //CIM_UINT64  
        printf("\nPut ArgName0 returned 0x%x:", hres);
        VariantClear(&var1);

        VARIANT var;
        VariantInit(&var);
        BSTR ArgName1 = SysAllocString(L"Brightness");

        V_VT(&var2) = VT_BSTR;
        V_BSTR(&var2) = SysAllocString(L"80"); //Brightness value
        hres = pClassInstance->Put(ArgName1,
            0,
            &var2,
            CIM_UINT8);
        VariantClear(&var2);
        printf("\nPut ArgName1 returned 0x%x:", hres);

        // Call the method  
        VARIANT pathVariable;
        VariantInit(&pathVariable);

        hres = pObj->Get(_bstr_t(L"__PATH"),
            0,
            &pathVariable,
            NULL,
            NULL);
        printf("\npObj Get returned 0x%x:", hres);

        hres = pSvc->ExecMethod(pathVariable.bstrVal,
            MethodName,
            0,
            NULL,
            pClassInstance,
            NULL,
            NULL);
        VariantClear(&pathVariable);
        printf("\nExecMethod returned 0x%x:", hres);

        printf("Terminating normally\n");


        // Clean up
        //--------------------------
        //VariantClear(&varCommand);
        //VariantClear(&varReturnValue);
        SysFreeString(ClassName);
        SysFreeString(MethodName);
        pClass->Release();
        pClassInstance->Release();
        pInParamsDefinition->Release();
        //pOutParams->Release();
        pLoc->Release();
        pSvc->Release();
        CoUninitialize();

        system("pause");
        return 0;

ref: 通过WMI的方式去设置LCD背光亮度 Author: Tody