Solved

Pointer to NETRESOURCE

Posted on 2004-10-08
4
232 Views
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

Featured Post

Courses: Start Training Online With Pros, Today

Brush up on the basics or master the advanced techniques required to earn essential industry certifications, with Courses. Enroll in a course and start learning today. Training topics range from Android App Dev to the Xen Virtualization Platform.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

IntroductionThis article is the second in a three part article series on the Visual Studio 2008 Debugger.  It provides tips in setting and using breakpoints. If not familiar with this debugger, you can find a basic introduction in the EE article loc…
Introduction This article is a continuation of the C/C++ Visual Studio Express debugger series. Part 1 provided a quick start guide in using the debugger. Part 2 focused on additional topics in breakpoints. As your assignments become a little more …
The viewer will learn how to pass data into a function in C++. This is one step further in using functions. Instead of only printing text onto the console, the function will be able to perform calculations with argumentents given by the user.
The viewer will be introduced to the technique of using vectors in C++. The video will cover how to define a vector, store values in the vector and retrieve data from the values stored in the vector.

774 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question