关于win32使用com编程的问题

Question

如以下代码，查询不同的字段，经常会在 HRESULT hr = pEnumerator->Next( WBEM_INFINITE, 1,  &pclsObj, &uReturn ); 这句报出异常，读取0x....错误，该如何处理呢？

#include "stdafx.h"
#define _WIN32_DCOM
#include <atlcomcli.h>
//#include <iostream>
using namespace std;
#include <comdef.h>
#include <Wbemidl.h>
#include "wing_string.h"

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

class WingWmic{
private:
IWbemServices *pSvc; 
int has_error; 
IEnumWbemClassObject* pEnumerator; 
IWbemLocator *pLoc; 
char *query_table;
public:
WingWmic();
~WingWmic();
void query( const char *sql );
BOOL next();
char* get( const char *key);
};

WingWmic::WingWmic(){

this->pSvc = NULL;
this->pEnumerator = NULL;
this->has_error = 0;
this->pLoc = NULL;
this->query_table   = NULL;

HRESULT hres;
    hres =  CoInitializeEx(0, COINIT_MULTITHREADED); 
    if (FAILED(hres))
    {
this->has_error = 1;
        return;             
    }

    hres =  CoInitializeSecurity( NULL, -1,  NULL, NULL, RPC_C_AUTHN_LEVEL_DEFAULT, RPC_C_IMP_LEVEL_IMPERSONATE, NULL, EOAC_NONE, NULL );

if (FAILED(hres))
    {
this->has_error = 1;
        return ;
    }


    hres = CoCreateInstance( CLSID_WbemLocator, 0, CLSCTX_INPROC_SERVER,  IID_IWbemLocator, (LPVOID *) &pLoc );

    if (FAILED(hres))
    {
this->has_error = 1;
        return ;            
    }

    hres = pLoc->ConnectServer( _bstr_t(L"ROOT\\CIMV2"), NULL, NULL,  0,  NULL,  0,  0,   &this->pSvc  );

    if (FAILED(hres))
    {   
this->has_error = 1;
        return ;             
    }

    hres = CoSetProxyBlanket( pSvc,  RPC_C_AUTHN_WINNT, RPC_C_AUTHZ_NONE,  NULL, RPC_C_AUTHN_LEVEL_CALL, RPC_C_IMP_LEVEL_IMPERSONATE,  NULL,  EOAC_NONE );

    if (FAILED(hres))
    {    
this->has_error = 1;
        return;        
    }

}

WingWmic::~WingWmic(){
if( pSvc != NULL ) 
pSvc->Release();
    if( pLoc != NULL ) 
pLoc->Release();
    if( pEnumerator != NULL )
pEnumerator->Release();
if( this->query_table != NULL ) 
delete[] this->query_table;
    CoUninitialize();
}


void WingWmic::query( const char* _sql ){

if( this->has_error ) return;
char *sql = _strdup( _sql );

int i = 0;
while( sql[i] != '\0' ){
sql[i] = tolower(sql[i]);
i++;
}

char *from = strstr( sql , "from" )+4;
while( 1 ) {
char c = *from;
if( !isspace(c) ) break;
from++;
}

this->query_table = new char[32];
memset( this->query_table , 0 , 32);
int index = 0;
while(1) {
char c = *from;
if( isspace(c) || c == '\0' ) break;
this->query_table[index] = c;
index++;
from++;
}

//printf("table=%s\r\n",this->query_table);

HRESULT hres = pSvc->ExecQuery( bstr_t("WQL"), bstr_t(sql),WBEM_FLAG_FORWARD_ONLY | WBEM_FLAG_RETURN_IMMEDIATELY, NULL,&this->pEnumerator);

if (FAILED(hres))
{
this->has_error = 1;
}

delete[] sql;
}

BOOL WingWmic::next(){
return !!pEnumerator;
}

char* WingWmic::get( const char *key){

SetLastError(0);

if( this->has_error ) 
{
//printf("has error %ld\r\n",GetLastError());
pEnumerator->Release();
pEnumerator = NULL;
return NULL;
}

IWbemClassObject *pclsObj = NULL;
    ULONG uReturn = 0;

HRESULT hr = pEnumerator->Next( WBEM_INFINITE, 1,  &pclsObj, &uReturn );

if( 0 == uReturn )
{
//printf("\r\nfail %ld\r\n",GetLastError());
if( pclsObj != NULL ) {
pclsObj->Release();
pclsObj=NULL;
}
pEnumerator->Release();
pEnumerator = NULL;
        return NULL;
}

VARIANT vtProp;



wchar_t *wkey = wing_str_char_to_wchar( key );


hr = pclsObj->Get( wkey , 0, &vtProp, 0, 0);

//wcout<<"key=>"<<wkey<<"<=="<<endl;

char *res = NULL;
if( SUCCEEDED( hr ) && vtProp.bstrVal )
{
res = wing_str_wchar_to_char( (const wchar_t*)vtProp.bstrVal );

}else{
//wcout<<"fail key=>"<<wkey<<endl;
}

VariantClear(&vtProp);

if( pclsObj != NULL ) {
pclsObj->Release();
pclsObj=NULL;
}

return res;
}

int _tmain(int argc, _TCHAR* argv[])
{
char sql[] = "SELECT * FROM Win32_Process\0";

//char *sql = "SELECT * FROM Win32_Processor";

WingWmic mic;

mic.query(sql);
int count = 1;
char *c = NULL;

while( mic.next() ) {

c = mic.get("CommandLine");
printf("CommandLine:%ld=>%s\r\n",count,c);

count++;
}

return 0;
}

                       

Answer 1

读取0x...

那个被省略的是多少？是不是 0x00000000？

会不会是 IWbemClassObject *pclsObj = NULL; 因为没有分配内存而出错？

开调试器看一下吧。

另：报错的对话框内容都是可以用 Ctrl+C 完整复制的。

Answer 2

以上是官方demo修改而来的，如果是未分配内存的话，按道理来说所有的都会报错，以上demo是在查询部分字段的时候会出错，比如CommandLine字段，也不是所有的都会出错！在运行一段时间之后，比如查询了40多个进城之后，然后出错了！

Answer 3

Answer 4

Answer 5

像这样调用

int _tmain(int argc, _TCHAR* argv[])
{
char sql[] = "SELECT * FROM Win32_Process\0";
 
//char *sql = "SELECT * FROM Win32_Processor";

WingWmic mic;

mic.query(sql);
int count = 1;
char *c = NULL;

while( mic.next() ) {

c = mic.get("CommandLine");
printf("CommandLine:%ld=>%s\r\n",count,c);
c = mic.get("Caption");
printf("Caption:%ld=>%s\r\n",count,c);
c = mic.get("CSCreationClassName");
printf("CSCreationClassName:%ld=>%s\r\n",count,c);

count++;
}
   
return 0;
}

Answer 6

Hi 吉利儿，

感谢在MSDN论坛发帖。

WingWmic 是你自己的类吗？ 请提供一些具体的实现。

你的问题出在你没有对pEnumerator进行赋值。导致空指针调用。请使用一下代码对其进行赋值或将代码添加到你的mic.query实现中。

IEnumWbemClassObject* pEnumerator = NULL;
hres = pSvc->ExecQuery(
        bstr_t("WQL"), 
        bstr_t("SELECT * FROM Win32_OperatingSystem"),
        WBEM_FLAG_FORWARD_ONLY | WBEM_FLAG_RETURN_IMMEDIATELY, 
        NULL,
        &pEnumerator);

希望对你有所帮助。

Best Regards,

Sera Yu

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