Allocating Heap Memory

So far, you all have been a greate resource so I am asking one last question (hopefully).

I am threading some database functions and am passing a struct via the CreateThread(...) function. No problem there. (See definition of the struct)

Code:

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        typedef struct _dbThreadData{
                CString dbData1;
                CString dbData2;
                char dbTime[6];
                CString dbCommand;
                CString dbStatus;
                long dbProcess;
        }DBTHREAD, *PDBTHREAD;

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I am initializing in the main() like so:

Code:

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        PDBTHREAD dbth;
        dbth-> dbData1 = Data1;
        dbth->dbData2 =Data2;
        dbth->dbStatus = stat;
        sprintf(dbth->dbTime , "%d", stopTime);
        dbth->dbProcess = 1;
        // create thread here for mdtMetrics
        dbThreadHandle[1] = CreateThread(
                NULL,                // default security attributes
                0,                // use default stack size
                dbThreadProc,
                dbth,                // argument to thread function
                0,                // use defailt creation flags
                &dwThreadID        // returns thead identifier
        );

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The compiler barked that the dbth struct was not initialized

Quote:

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C:\Visual Studio Projects\Poller\PollerDlg.cpp(1096) : warning C4700: local variable 'dbth' used without having been initialized

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, so investigation shows that the HeapAlloc(...) might be needed.

I added:

Code:

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        PDBTHREAD dbth;
        dbth = HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, sizeof(DBTHREAD));

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but am now getting teh error:

Quote:

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C:\Visual Studio Projects\Poller\PollerDlg.cpp(1095) : error C2440: '=' : cannot convert from 'void *' to 'struct _dbThreadData *'
Conversion from 'void*' to pointer to non-'void' requires an explicit cast

---

.

Am I doing this part right??? Since i am declaring the struct as a pointer (_dbThreadData *dbth), is HeapAlloc(...) necessary to initialize the struct? I am missing something but cannot figure out what? Suggestions?

try:

Quote:

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dbth =(DBTHREAD*) HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, sizeof(DBTHREAD));

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to explicitly cast as the compiler req.

HTH,

ahoodin

PS If this post helped dont forget to rate. Just click the scale icon and click the approve radio button.

Quote:

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Originally Posted by rick7423

I am initializing in the main() like so:

Code:

---

        PDBTHREAD dbth;
          dbth-> dbData1 = Data1;
          dbth->dbData2 =Data2;
          dbth->dbStatus = stat;
          sprintf(dbth->dbTime , "%d", stopTime);
          dbth->dbProcess = 1;
          // create thread here for mdtMetrics
          dbThreadHandle[1] = CreateThread(
                  NULL,
                  0,       
                  dbThreadProc,
                  dbth,
                  0,       
                  &dwThreadID  );

---

---

One problem here is that you declared a pointer to the structure rather than the structure itself.
Try the following (which should work as long as dbth doesn't go out of scope).

Code:

---

DBTHREAD dbth;
          dbth.dbData1 = Data1;
          dbth.dbData2 =Data2;
          dbth.dbStatus = stat;
          sprintf(dbth.dbTime , "%d", stopTime);
          dbth.dbProcess = 1;
          // create thread here for mdtMetrics
          dbThreadHandle[1] = CreateThread(
                  NULL,               
                  0,               
                  dbThreadProc,
                  static_cast<LPVOID>(&dbth),
                  0,         
                  &dwThreadID  );

---

Quote:

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Originally Posted by rick7423

The compiler barked that the dbth struct was not initialized , so investigation shows that the HeapAlloc(...) might be needed.

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You may need to allocate the DBTHREAD structure memory on the heap if there is a chance that a stack allocated struct will go out of scope. If you do need to allocate it, prefer to use new/delete over HeapAlloc et. al. Maybe this is just personal preference, but you already are using CString which internally uses new to allocate. My feeling is you should be consistent with your memory allocation throughout the program ( well as much as possible anyway ).

Code:

---

 
  PDBTHREAD pdbth = new DBTHREAD;
            dbth->dbData1 = Data1;
            dbth->dbData2 =Data2;
            dbth->dbStatus = stat;
            sprintf(dbth->dbTime , "%d", stopTime);
            dbth->dbProcess = 1;
            // create thread here for mdtMetrics
            dbThreadHandle[1] = CreateThread(
                    NULL,               
                    0,               
                    dbThreadProc,
                    static_cast<LPVOID>(pdbth),
                    0,               
                    &dwThreadID  );
 
    // Wait on thread
 
    // cleanup
    if(pdbth)
    {
          delete pdbth;
          pdbth = NULL;
    }
 
    CloseHandle( dbThreadHandle[1] );

---

Arjay

Thanks for your help. That works for this problem (it compiles at least, testing will tell for sure).

A question :

Is "HeapAlloc()" fater than "malloc" or "new" ?

There has been a time I used "HeapAlloc()" in a project, with flag "HEAP_NO_SERIALIZE" which causes an unpredicted nightmare, my project is down from time to time(only happen in some PC, and release version !), and can't found the reason. It really costs me two weeks to found the reason! Should be very careful to use flag "HEAP_NO_SERIALIZE" !

wuxf