全部，
我正在尝试修改MS提供的代码，尝试访问网络适配器配置
当我尝试使用VC ++ 2005访问Mac地址或IPAddress属性时，我得到空指针异常。在这里检查 //异常：vtProp返回为NULL 行在哪里得到例外。
#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.
}
代码中出了什么问题？
Abdul khaliq
答案 0 :(得分：2)
这是旧的，但我有同样的问题，我没有看到任何解决方案。我通过检查VT_NULL来解决它。
if( vtProp.vt != VT_NULL )
wcout << " MACAddress : " << vtProp.bstrVal << endl;
我不明白为什么有些结果是VT_NULL但我怀疑可以通过在“select”语句中添加“where”子句来避免这种情况。
感谢finnw提示！
答案 1 :(得分：0)
我首先要初始化vtProp变量 - 它应该没关系，但有时候COM服务器会假设有关params;
VariantInit(&vtProp);
然后你可以在它被返回后检查vtProp并查看实际类型是什么（.vt成员） - 也许它不是字符串，出于某种原因？
您可以使用该类型回发（您可以使用oaidl.h中的VARTYPE定义进行交叉引用，以查看友好名称是什么）？
答案 2 :(得分：0)
网络适配器列表通常包含一些“虚拟”适配器，并且它们并非都具有MAC地址。一些（例如“数据包调度程序微型端口”）复制物理适配器的MAC地址。您只需要检查vt字段（可能是VT_EMPTY）并从结果列表中删除重复项。