Question

I am trying to call wmisetbrightness, but it takes two inputs. How do I pass more than one input to ExecMethod? Code snippet below is obviously wrong.

// 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);

// Create the values for the in parameters
VARIANT varCommand;
varCommand.vt = VT_UI8;
varCommand.ullVal = 30;
//// Store the value for the in parameters
hres = pClassInstance->Put(L"CommandLine", 0, &varCommand, 0);

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

edit:
WmiSetBrightness takes two variables:

uint32 WmiSetBrightness(
uint64 Timeout,
uint8 Brightness
);

the above code only passes the first input parameter, and I dont know how to modify it to pass both parameters.

Full code here:

#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
// 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"0"); 
 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;
}

Answer 1

Try this, which supposedly works per info here. Apparently the docs are misleading on this API.

 VARIANT var1;
 VariantInit(&var1);

 V_VT(&var1) = VT_BSTR;
 V_BSTR(&var1) = SysAllocString(L"0"); 
 hr = 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"); 
 hr = pClassInstance->Put(L"Brightness", 0, &var2, CIM_UINT8);