I faced an issue using WMI with C .
It is the first time I've used it so I took the basic documentation example. But running it doesn't work for me.
I tried to extract the OS Name from Win32_OperatingSystem but, when I display it, I got 0x9a2fec.
I tried then with MaxNumberOfProcesses, and I got "-1".
I am on Windows 10, and I have no idea what's going on.
My code:
#include <iostream>
#define _WIN32_DCOM
#include <windows.h>
#include <Wbemidl.h>
#include <comdef.h>
# pragma comment(lib, "wbemuuid.lib")
bool initializeCom(){
// Step 1: --------------------------------------------------
// Initialize COM. ------------------------------------------
HRESULT hres = CoInitializeEx(0, COINIT_MULTITHREADED);
if (FAILED(hres))
{
std::cout << "Failed to initialize COM library. Error code = 0x"
<< std::hex << hres << std::endl;
return false; // Program has failed.
}
// Step 2: --------------------------------------------------
// Set general COM security levels --------------------------
hres = CoInitializeSecurity(
nullptr,
-1, // COM authentication
nullptr, // Authentication services
nullptr, // Reserved
RPC_C_AUTHN_LEVEL_DEFAULT, // Default authentication
RPC_C_IMP_LEVEL_IMPERSONATE, // Default Impersonation
nullptr, // Authentication info
EOAC_NONE, // Additional capabilities
nullptr // Reserved
);
if (FAILED(hres))
{
std::cout << "Failed to initialize security. Error code = 0x"
<< std::hex << hres << std::endl;
CoUninitialize();
return false; // Program has failed.
}
return true;
}
bool setUpWBEM(IWbemLocator*& wbemLocator, IWbemServices*& wbemServices){
// Step 3: ---------------------------------------------------
// Obtain the initial locator to WMI -------------------------
HRESULT hres = CoCreateInstance(
CLSID_WbemLocator,
0,
CLSCTX_INPROC_SERVER,
IID_IWbemLocator, (LPVOID *) &wbemLocator);
if (FAILED(hres))
{
std::cout << "Failed to create IWbemLocator object."
<< " Err code = 0x"
<< std::hex << hres << std::endl;
CoUninitialize();
return false; // Program has failed.
}
// Step 4: -----------------------------------------------------
// Connect to WMI through the IWbemLocator::ConnectServer method
// Connect to the root\cimv2 namespace with
// the current user and obtain pointer wbemServices
// to make IWbemServices calls.
hres = wbemLocator->ConnectServer(
_bstr_t(L"ROOT\\CIMV2"), // Object path of WMI namespace
nullptr, // User name. NULL = current user
nullptr, // User password. NULL = current
0, // Locale. NULL indicates current
0, // Security flags.
0, // Authority (for example, Kerberos)
0, // Context object
&wbemServices // pointer to IWbemServices proxy
);
if (FAILED(hres))
{
std::cout << "Could not connect. Error code = 0x" << std::hex << hres << std::endl;
wbemLocator->Release();
CoUninitialize();
return false; // Program has failed.
}
std::cout << "Connected to ROOT\\CIMV2 WMI namespace" << std::endl;
// Step 5: --------------------------------------------------
// Set security levels on the proxy -------------------------
hres = CoSetProxyBlanket(
wbemServices, // Indicates the proxy to set
RPC_C_AUTHN_WINNT, // RPC_C_AUTHN_xxx
RPC_C_AUTHZ_NONE, // RPC_C_AUTHZ_xxx
nullptr, // Server principal name
RPC_C_AUTHN_LEVEL_CALL, // RPC_C_AUTHN_LEVEL_xxx
RPC_C_IMP_LEVEL_IMPERSONATE, // RPC_C_IMP_LEVEL_xxx
nullptr, // client identity
EOAC_NONE // proxy capabilities
);
if (FAILED(hres))
{
std::cout << "Could not set proxy blanket. Error code = 0x"
<< std::hex << hres << std::endl;
wbemServices->Release();
wbemLocator->Release();
CoUninitialize();
return false; // Program has failed.
}
return true;
}
int main() {
std::cout << "HelloWorld" << std::endl;
IWbemLocator* wbemLocator{nullptr};
IWbemServices* wbemServices{nullptr};
try{
if(!initializeCom())
throw "initializeCom failed";
if(!setUpWBEM(wbemLocator,wbemServices))
throw "setUpWBEM failed";
// Step 6: --------------------------------------------------
// Use the IWbemServices pointer to make requests of WMI ----
BSTR bstr_wql = SysAllocString(L"WQL" );
BSTR bstr_sql = SysAllocString(L"SELECT * FROM Win32_OperatingSystem" );
// For example, get the name of the operating system
IEnumWbemClassObject* pEnumerator{nullptr};
HRESULT hres = wbemServices->ExecQuery(
bstr_wql,
bstr_sql,
WBEM_FLAG_FORWARD_ONLY | WBEM_FLAG_RETURN_IMMEDIATELY,
nullptr,
&pEnumerator);
if (FAILED(hres))
{
std::cout << "Query for operating system name failed."
<< " Error code = 0x"
<< std::hex << hres << std::endl;
wbemServices->Release();
wbemLocator->Release();
CoUninitialize();
throw "ExecQuery failed";; // Program has failed.
}
// Step 7: -------------------------------------------------
// Get the data from the query in step 6 -------------------
IWbemClassObject *pclsObj{nullptr};
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"Name", 0, &vtProp, 0, 0);
if(FAILED(hr))
std::cout << "Failed to get name " << std::endl;
std::cout << " OS Name : " << vtProp.bstrVal << std::endl;
VariantClear(&vtProp);
pclsObj->Release();
}
// Cleanup
// ========
wbemServices->Release();
wbemLocator->Release();
pEnumerator->Release();
CoUninitialize();
} catch(const std::string& error){
std::cout << error << std::endl;
}
return 0;
}
If you have any idea, please tell me.
CodePudding user response：
The issue is in the (almost) last stage of your program: the code that displays the retrieved "OS Name":
std::cout << " OS Name : " << vtProp.bstrVal << std::endl; // Prints pointer address
The problem here is that the BSTR type uses a wchar_t* for its buffer1 and the std::cout stream (an object of the std::ostream class) doesn't have an << overload that takes a wchar_t* argument (it has one for char*) – so it uses the version that takes a const void* (as the best match), which prints the address itself, rather than the pointed-to string.
In your case, there is a simple fix: Use the std::wcout stream (a std::wostream object), instead2, which does have an << overload that takes a wchar_t* argument:
std::wcout << L" OS Name : " << vtProp.bstrVal << std::endl; // Prints the wchar_t* string
Simply replacing your output line with the above, on my platform, changed the displayed output from a pointer value (as you are seeing) to the following:
OS Name : Microsoft Windows 10 Pro|C:\WINDOWS|\Device\Harddisk0\Partition3
I'm not sure if that's exactly what you would like but it seems like a great improvement. I'm sure you can readily add code to edit that string into the exact format you want.
1 Note that, although the BSTR type is defined as a wchar_t*, it's not really quite the same thing, in some ways. See this answer for more information.
2 On re-reading the document you linked, I see that wcout is used there, for the display of the OS Name.