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Pointer to NETRESOURCE

Posted on 2004-10-08
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Last Modified: 2010-04-01
Hi, this is a little complicated...
I'm passing a pointer to NETRESOURCE to my class to be used later, like so:

NETRESOURCE *nr; //valid at this point
HTREEITEM  ht;
CDomains * e = new CDomains( FALSE, &ht, nr );

Then in the class constructor I'm making a copy of the pointer:

CDomains( BOOL bWMI, HTREEITEM *hProvider, NETRESOURCE * nr = NULL, LPVOID r = NULL )
{
      m_hProvider = new HTREEITEM;
      memcpy(m_hProvider, hProvider, sizeof(HTREEITEM));
      if ( nr ) {
            m_pnr = new NETRESOURCE;
            memcpy(m_pnr, nr, sizeof(NETRESOURCE));
      } else {
            m_pnr = NULL;
      }
}

Now comes the tricky part. This class inherits from another class that has Start() function. I call it next:
e->Start();

The Start() function of the class CDomains inherits from:
void CSuper::Start()
{
      HANDLE      hThread = NULL;
      InterlockedIncrement( &g->ThreadCount );

      DWORD      id;
      hThread = CreateThread( NULL, THREAD_STACK_SIZE, Enumerate, this, CREATE_SUSPENDED, &id );

      DWORD dwWaitResult = WaitForSingleObject( g->hSemaphore, INFINITE);  //wait

      switch( dwWaitResult )
      {
          
      case WAIT_OBJECT_0:
            {
                  if ( hThread )  {
                        // thread created
                        SetThreadPriority( hThread, THREAD_PRIORITY_LOWEST );
                        ResumeThread( hThread );
                  }
            }
            break;

      case WAIT_TIMEOUT:
      case WAIT_ABANDONED:
            {
                  //report error
                  TRACE(_T("startThreadProcessLog SEMAPHORE Timed Out"));
            }
            break;
      }
      CloseHandle( hThread );
      
}

This goes well, the parameter passed to Enumerate function (this) contains the inheriting class CDomain
with all variables still valid.

The Enumerate function:
DWORD WINAPI  CSuper::Enumerate( LPVOID This )
{
       CSuper * o = ( CSuper *)This;
      o->Enumerate();
      return 0;
}

This where the things go sour. All the variables in o->CDomains are still valid,
numeric values in o->CDomains->m_pnr are still valid, but all the string
members of that struct are now invalid pointers.

Please help, I'm willing to give more points if necessary.
0
Comment
Question by:jd9288
  • 2
  • 2
4 Comments
 
LVL 86

Accepted Solution

by:
jkr earned 500 total points
ID: 12260446
>>but all the string members of that struct are now invalid pointers.

That's not really surprising, since the strings/arrays might go out of scope.

>> memcpy(m_pnr, nr, sizeof(NETRESOURCE));

Is prone to 'loose' the strings. How are you filling the NETRESOURCE structures? You should always take care of that memory on your own instead of using 'memcpy()', e.g. by using

void CopyNetReource ( NETRESOURCE* dst, NETRESOURCE* src) {

   dst->dwScope = src->dwScope;
   dst->dwType = src->dwType;
   dst->dwDisplayType = src->dwDisplayType;
   dst->dwUsage = src->dwUsage;
   dst->lpLocalName = _tcsdup(src->lpLocalName);
   dst->lpRemoteName = _tcsdup(src->lpRemoteName);
   dst->lpComment = _tcsdup(src->lpComment);
   dst->lpProvider = _tcsdup(src->lpProvider);
}

void FreeNetResource ( NETRESOURCE* p) {

   free(p->lpLocalName);
   free(p->lpRemoteName);
   free(p->lpComment);
   free(p->lpProvider );
}
0
 

Author Comment

by:jd9288
ID: 12260575
Brilliant! I suspected this might be the case, but since I'm so unsure of myself,
I thought I'm missing something.

Could you please tell me why it would still work sometimes
the way I had it?
0
 
LVL 86

Expert Comment

by:jkr
ID: 12260614
>>Could you please tell me why it would still work sometimes
>>the way I had it?

Because the strings are 'there' for a while, at least during an enumeration. You never know when the system will free the momry it used to store the strings in.

BTW, you could extend the above to

class CNetResource : public NETRESOURCE {

public:

    CNetResource () { /* ...  */ }
    CNetResource ( const NETRESOURCE& nr)  { /* ...  */ }
    CNetResource& operator=(const NETRESOURCE& nr)  { /* ...  */ }
};

to 'automate' that copying process.
0
 

Author Comment

by:jd9288
ID: 12260703
Thank you very much, I think I'm getting there.
0

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