从WMI看VC++到.Net的变迁

WMI(Windows Management Instrumentation)是Windows下可以与系统信息(包括软硬件等)的一个管理框架，通过WMI可以很方便地对机器进行管理。现在以通过WMI来打开(或创建)一个记事本(notepad.exe)进程为例，看看VC++到.Net的变迁，一览.Net是如何让程序员从繁琐晦涩的程序中解放出来。

1、预工作：
VC++中需要在源代码中加入：
#include <Wbemidl.h>
#pragma comment(lib, "wbemuuid.lib")

VC#中需要：
在工程中添加引用：System.Management
在代码中加入using System.Management;

2、流程：
VC++的代码，需要6步和查询返回值、最后释放资源：

// Step 1: --------------------------------------------------

// Initialize COM. ------------------------------------------

hres = CoInitializeEx(0, COINIT_MULTITHREADED);

// Step 2: --------------------------------------------------

// Set general COM security levels --------------------------

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

);

// Step 3: ---------------------------------------------------

// Obtain the initial locator to WMI -------------------------

IWbemLocator *pLoc = NULL;

hres = CoCreateInstance(

CLSID_WbemLocator,

CLSCTX_INPROC_SERVER,

IID_IWbemLocator, (LPVOID *) &pLoc);

// 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\\CIMV2"),

NULL,

&pSvc

);

// 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

);

// Step 6: --------------------------------------------------

// Use the IWbemServices pointer to make requests of WMI ----

// set up to call the Win32_Process::Create method

BSTR MethodName = SysAllocString(L"Create");

BSTR ClassName = SysAllocString(L"Win32_Process");

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_BSTR;

varCommand.bstrVal = L"notepad.exe";

// Store the value for the in parameters

hres = pClassInstance->Put(L"CommandLine", 0,

&varCommand, 0);

wprintf(L"The command is: %s\n", V_BSTR(&varCommand));

// Execute Method

IWbemClassObject* pOutParams = NULL;

hres = pSvc->ExecMethod(ClassName, MethodName, 0, NULL, pClassInstance, &pOutParams, NULL);

// Get return value

VARIANT varReturnValue;

hres = pOutParams->Get(_bstr_t(L"ReturnValue"), 0, &varReturnValue, NULL, 0);

// Last: clean up

VariantClear(&varCommand);

VariantClear(&varReturnValue);

SysFreeString(ClassName);

SysFreeString(MethodName);

pClass->Release();

pInParamsDefinition->Release();

pOutParams->Release();

pLoc->Release();

pSvc->Release();

CoUninitialize();

VC#只需寥寥数行就可以实现（暂不考虑错误处理）：
跳过VC++中的Step1~5，直接从Step6开始。而且非常直观：

ManagementClass mc = new ManagementClass("Win32_Process");

ManagementBaseObject obj = mc.GetMethodParameters("Create");

obj["CommandLine"]="notepad.exe";

mc.InvokeMethod("Create", obj, null);

mc.Dispose();

.Net对WMI良好的封装，还有对字符串的更强支持、方便的垃圾回收机制，使程序既一目了然，又易于维护。其实类似的区别在VC vs VB年代已经出现了（特别是在COM组件编写和调用方面可以看出），从这点也可以看出.Net完全继承了VB易学易用的特性，又不失强大的功能。