C / C++ / MFC

2-Jan-12 13:14

I'm working on a class array, but I thought it would structure my data different.

I'm working with this code below. I was hoping it would create a single object, with 2 internal members of [0] and [1] creating a single object uaListBoxPtrArray with 2 members [0] Tim and [1] John, Tim and John being inside uaListBoxPtrArray.

But it looks like it creates separate objects
uaListBoxPtrArray[0] which is Tim
uaListBoxPtrArray[1] which is John
and I would have to pass uaListBoxPtrArray[0], uaListBoxPtrArray[1] to a function.

I want to be able to pass the single object to a function in the future, and not separate objects. pass uaListBoxPtrArray by itself, with Time and John inside it.

Q: Is my result or implementation correct?, and that this is the correct result format for the method below?. Or do I now need to work on the constructor, to form a single object of records.

CSS

DWORD dwCount;
DB_UserAccount dbUA;
dwCount = dbUA._get_UserAccount_Listbox_Count();

// Create an Class Array Structure to hold the values
UA_Listbox **uaListBoxPtrArray;
uaListBoxPtrArray = new UA_Listbox*[dwCount];

uaListBoxPtrArray[0] = new UA_Listbox;
uaListBoxPtrArray[0]->iUserID = 47;
uaListBoxPtrArray[0]->szFirstName = L"Tim";
uaListBoxPtrArray[0]->szLastName = L"Parker";
uaListBoxPtrArray[0]->szAccountName = L"tparker";

uaListBoxPtrArray[1] = new UA_Listbox;
uaListBoxPtrArray[1]->iUserID = 48;
uaListBoxPtrArray[1]->szFirstName = L"Joe";
uaListBoxPtrArray[1]->szLastName = L"Smoe";
uaListBoxPtrArray[1]->szAccountName = L"jsmoe";

Richard MacCutchan2-Jan-12 22:02

2-Jan-12 22:02

jkirkerx wrote:
I was hoping it would create a single object

But the lines:

C++

uaListBoxPtrArray = new UA_Listbox*[dwCount];
uaListBoxPtrArray[0] = new UA_Listbox;
...
uaListBoxPtrArray[1] = new UA_Listbox;

specifically say: create an array of object pointers and create two new objects which can be referenced by the pointers in the array. If you want a single object to hold both names then you need a different class definition.

Unrequited desire is character building. OriginalGriff
I'm sitting here giving you a standing ovation - Len Goodman

jkirkerx3-Jan-12 7:22

3-Jan-12 7:22

Thanks Richard

I just want to make sure that I understood your thoughts correctly first.

Richard MacCutchan wrote:
create an array of object pointers

uaListBoxPtrArray = new UA_Listbox*[dwCount];

Richard MacCutchan wrote:
create two new objects which can be referenced by the pointers in the array

uaListBoxPtrArray[0] = new UA_Listbox;
uaListBoxPtrArray[1] = new UA_Listbox;

Richard MacCutchan3-Jan-12 22:28

3-Jan-12 22:28

That's correct, if you break things down to their constituent parts you get:

C++

UA_Listbox             // declares a UA_Listbox
UA_Listbox*            // declares a pointer to a UA_Listbox
UA_Listbox*[dwCount]   // declares an array of pointers, of length dwCount
uaListBoxPtrArray      // declares an array a variable

So the statement

C++

uaListBoxPtrArray = new UA_Listbox*[dwCount];

initialises an array variable by creating the array of pointers (via the new operator). Each array element can then be initialised with a pointer to an object of the type previously defined.

Unrequited desire is character building. OriginalGriff
I'm sitting here giving you a standing ovation - Len Goodman

jkirkerx4-Jan-12 6:54

4-Jan-12 6:54

Thanks again Richard.

Well my class array worked. I was able to pass the array to the function and get the values back. But after implementing it, changing the design and format several times, I determined that it will never work in the way I wanted it to.

After studying how they work in principle, the source which is a ODBC function creates pointers to buffers in the heap, in which the SQL Handle maintains, and once the handle is freed, the pointers are lost.

So I brought the GUI (hWnd) to the ODBC, populated the listbox, and exited.

No one wonder I was confused, but overall in the end, I learned alot about pointers. Oh Well.

Stefan_Lang3-Jan-12 5:26

Stefan_Lang

3-Jan-12 5:26

Why not this way?

C++

// Create an Class Array Structure to hold the values
UA_Listbox *uaListBoxArray;
uaListBoxArray = new UA_Listbox[dwCount];
 
uaListBoxArray[0].iUserID = 47;
uaListBoxArray[0].szFirstName = L"Tim";
uaListBoxArray[0].szLastName = L"Parker";
uaListBoxArray[0].szAccountName = L"tparker";
 
uaListBoxArray[1].iUserID = 48;
uaListBoxArray[1].szFirstName = L"Joe";
uaListBoxArray[1].szLastName = L"Smoe";
uaListBoxArray[1].szAccountName = L"jsmoe";

// ... do something

delete [] uaListBoxArray; // clean up

jkirkerx3-Jan-12 7:24

3-Jan-12 7:24

That's a question to a question, in which I cannot answer at the moment.

Stefan_Lang3-Jan-12 22:41

Stefan_Lang

3-Jan-12 22:41

You asked how to define a single object containing two UA_ListBox objects and I gave you a definition: Rather than define an array of two pointers, I defined an array of two UA_ListBox objects. If that is not what you want, then sorry, I don't understand the question. (Besides, even your own definition of an array of two pointers to objects in a way satisfies your request: it is a single object representing two objects. Why is this not sufficient for your purposes?)

jkirkerx4-Jan-12 7:08

4-Jan-12 7:08

I can comment on it now, it was a fine post.

I implemented your revised edition, and liked it better, because I wasn't using the new statement for each record.

It worked great, thank you very much.

I ended up deleting the whole thing, and took the gui (hwnd)to the ODBC function. The ODBC function created pointers to buffers, that were held by the SQLHandle. The first array record was fine, but records after that were corrupted.

So I have to rethink how this would work in ODBC, Which is another subject. I'm thinking that I need to implement your version of the array inside the ODBC Function itself.

The code below was a bad idea. I tried using the array directly in the GetData, but I wasn't able to use the size in the array elements. Anyways, that's a different subject.

if (retcode == SQL_SUCCESS || retcode == SQL_SUCCESS) {			
												
INT			i = 0;
INT			pzUserID; <- This should of been an array element
WCHAR			pzFirstName[cbFirstName]; <- This should of been an array element
WCHAR			pzLastName[cbLastName]; <- This should of been an array element
WCHAR			pzUserName[cbUserName]; <- This should of been an array element
						
while (SQLFetch(hstmt) == SQL_SUCCESS) {
	// Get Data from the Table
	SQLGetData(hstmt, 1, SQL_C_ULONG, &pzUserID, 0, NULL );
	SQLGetData(hstmt, 2, SQL_C_WCHAR, &pzFirstName, cbFirstName, NULL );
	SQLGetData(hstmt, 3, SQL_C_WCHAR, &pzLastName, cbLastName, NULL );
	SQLGetData(hstmt, 4, SQL_C_WCHAR, &pzUserName, cbUserName, NULL );

        // Original -I used the pointers above to populate the array at this point, but I should of just went direct into the array, instead of using the temporary pointers in between. But in theory once I free the SQL handle, the pointers are gone. So Perhaps in the future, I need to create multi part functions, one that Initializes, one that gets the data and packages it, and one that closes the handle, passing the handle to each function until complete.

}

CreateThread

columbos149272-Jan-12 5:14

columbos14927

2-Jan-12 5:14

Hello,
Im writing an MFC App,
I want to create some threads using the CreateThread function.

The function that i send as a parameter to the createThread function must be declared as static and then i cant reference none static members of my object,how can i by pass it?

Thanks

Richard MacCutchan2-Jan-12 6:18

2-Jan-12 6:18

You can still pass an object reference to a static function.

Unrequited desire is character building. OriginalGriff
I'm sitting here giving you a standing ovation - Len Goodman

image processing toolkits | batch image processing

C^hris L^osinger2-Jan-12 6:56

C^hris L^osinger

2-Jan-12 6:56

something like this:

C++

int CMyClass::staticFunc(void *p)
{
  CMyClass *pObj = (CMyClass *)p;

  ...

  return 0;
}


void CMyClass::someFunc()
{
   CreateThread(NULL, 0, staticFunc, (void *)this, ... );
}

Richard MacCutchan2-Jan-12 7:31

2-Jan-12 7:31

Why cast the object to a void * and the back to a CMyClass *?

Unrequited desire is character building. OriginalGriff
I'm sitting here giving you a standing ovation - Len Goodman

image processing toolkits | batch image processing

C^hris L^osinger2-Jan-12 7:34

C^hris L^osinger

2-Jan-12 7:34

not sure i understand the question.
threadprocs take a void* param...

Richard MacCutchan2-Jan-12 21:52

2-Jan-12 21:52

Sorry, I mis-read what you had posted; I was thinking of something else I suspect.

Unrequited desire is character building. OriginalGriff
I'm sitting here giving you a standing ovation - Len Goodman

Rajesh R Subramanian2-Jan-12 7:42

Rajesh R Subramanian

2-Jan-12 7:42

If you're using MFC, you should rather use the AfxBeginThread()[^] call that MFC provides to create thread. There are many good reasons to this, mainly that MFC has its own storekeeping mechanism that you'll bypass if you call a windows API instead of the MFC call to create thread. Likewise, use _beginthreadex()[^] otherwise. There should be basically no good reason for you to call CreateThread() directly.

"Real men drive manual transmission" - Rajesh.