Re: pointer/handle - C / C++ / MFC Discussion Boards

Re: Popup menu

Anonymous12-Sep-02 5:10

Anonymous

12-Sep-02 5:10

Ok I don't use ON_COMMAND_RANGE because I don't know in advance how many items I will add...

Re: Popup menu

Tomasz Sowinski12-Sep-02 5:19

Tomasz Sowinski

12-Sep-02 5:19

But there's upper limit. You won't be adding 10000 items for sure.

Tomasz Sowinski -- http://www.shooltz.com

To some its a six-pack, to me it's a support group

Re: Popup menu

Anonymous12-Sep-02 5:31

Anonymous

12-Sep-02 5:31

Ok you're right ;o)

But this isn't the problem : I try to access to the dynamically created menu :

CMenu menu;
menu.LoadMenu(ID_MENU); // load the menu

CMenu* submenu = menu.GetSubMenu(1);
CMenu* namesmenu = submenu.GetSubMenu(...);

int nItem = namesmenu.GetMenuItemCount();

but it doesn't work...

Re: Popup menu

Tomasz Sowinski12-Sep-02 5:39

Tomasz Sowinski

12-Sep-02 5:39

Have no idea how your menu looks like. Check if 'submenu' points is non-NULL. If it points to some CMenu object, then check if it's actually the submenu you're looking for - use GetMenuItemCount/GetMenuString. If you get this right, proceed to namesmenu.

Tomasz Sowinski -- http://www.shooltz.com

To some its a six-pack, to me it's a support group

pointer/handle

brianwelsch12-Sep-02 3:55

brianwelsch

12-Sep-02 3:55

Is there actually a difference between a pointer and a handle, or is it just the context of what you happen to be talking about?

BW
{insert witty/thought-provoking saying here}

Re: pointer/handle

Tomasz Sowinski12-Sep-02 4:04

Tomasz Sowinski

12-Sep-02 4:04

Pointer is an address of object. Handle is an opaque value. The implementor may use a pointer as handle, but it's also free to use index in array or any other value identifying the object. You can't dereference the handle as you do with pointer - you just obtain the handle from CreateFoo-style function and pass it to other functions. These functions know how to interpret the value of handle, while you don't.

Tomasz Sowinski -- http://www.shooltz.com

To some its a six-pack, to me it's a support group

Re: pointer/handle

brianwelsch12-Sep-02 4:15

brianwelsch

12-Sep-02 4:15

Would it be fair to say that handles are references to objects defined by the Win32API? Kind of a pointer to a pointer. Whereas pointers are references to objects created and defined within the application itself.

BW
{insert witty/thought-provoking saying here}

Re: pointer/handle

Tomasz Sowinski12-Sep-02 4:26

Tomasz Sowinski

12-Sep-02 4:26

Not exactly. While Win32 API uses handles, it's by no means the only place where handles are used. And surely you can't call them pointer to pointer, because they can be indices in array as well.

You can think of handles as magic cookies passed from/to library code. You don't need to know what do they mean. This knowledge is encapsulated in library itself.

Tomasz Sowinski -- http://www.shooltz.com

To some its a six-pack, to me it's a support group

Re: pointer/handle

brianwelsch12-Sep-02 4:32

brianwelsch

12-Sep-02 4:32

I think I get the difference, thanks!

we need an lightbulb icon, or something else denoting understanding

BW
{insert witty/thought-provoking saying here}

Re: pointer/handle

jhwurmbach12-Sep-02 4:13

jhwurmbach

12-Sep-02 4:13

Handle is the more general concept, an arbitrary identifier for something.
A pointer is a memory address at which may (or may not) be an object.
All pointers are handles to their object(s memory), but most handles are not pointers.

Windows HWNDs are not pointers but (I think) indices into an array of windows.
STL iterators are handle-objects, with operators overloaded to mimic pointers.

I hope I have added my share to the confusion Big Grin | :-D

afxDump

Jawache12-Sep-02 3:26

Jawache

12-Sep-02 3:26

I'm having problems with installing my app on other machines. I keep on gettting
"Failed to create empty document", after going through the source code It looks to me like this message is ouput when creation of the MainFrame fails.

I NEED the trace statements to figure our what is going on!

Is there any way i can redirect the TRACE statements to a file, i've thought redirecting the afxDump variable to a file but the assignment = operator is protected Cry | :((

BOOL CExplorerApp::InitInstance()
{
	CFile dumpfile;
	dumpfile.Open(_T("C:\\Jexlog.txt"),CFile::modeCreate|CFile::modeWrite);
	CDumpContext dc(&dumpfile);
    afxDump = dc;

Asim Hussain
e: asim@jawache.net
w: www.jawache.net

Re: afxDump

Tomasz Sowinski12-Sep-02 3:50

Tomasz Sowinski

12-Sep-02 3:50

http://www.microsoft.com/msj/defaultframe.asp?page=/msj/0497/c++/c++0497.htm[^]

Tomasz Sowinski -- http://www.shooltz.com

To some its a six-pack, to me it's a support group

Re: afxDump

Jawache12-Sep-02 4:11

Jawache

12-Sep-02 4:11

WOW...

I have to admit in the time its taken me to respond i've fixed the problem using another method.

But still i'll definately bookmarking that site.

Asim Hussain
e: asim@jawache.net
w: www.jawache.net

Local machine ip address

Anonymous12-Sep-02 2:24

Anonymous

12-Sep-02 2:24

How can i retrieve the local machine ip address and hostname. I searched here at CP but didn't find proper article.

Re: Local machine ip address

JohnnyG12-Sep-02 2:30

JohnnyG

12-Sep-02 2:30

Close....but search this forum. Wink | ;)

Re: Local machine ip address

lucy12-Sep-02 5:43

lucy

12-Sep-02 5:43

// print out local host IP address
char name[256] = "";
int nRet = gethostname(name, sizeof(name));
if ( nRet == SOCKET_ERROR )
    MessageBox("gethostname() failed");
else
{
    struct hostent * host = gethostbyname(name);
    if ( host == NULL )
        MessageBox("gethostbyname() failed");
    else
    {
        struct in_addr addr;
        memcpy(&addr, host->h_addr_list[0], sizeof(addr));
        CString m_strHost;
        m_strHost.Format( "%s", inet_ntoa(addr));
        // do whatever you want to do with the obtained IP address
    }
}

Scripting for Applications

Ciufudean Sorin12-Sep-02 2:16

Ciufudean Sorin

12-Sep-02 2:16

thanks for the ideas, it works, but now i have another question. I's like to load two different script files and rund the scripts almoust the same time. What do i have to do when i'm using the ActiveX Scripting engine from Microsoft (IActiveScript)?

How to check if field value is NULL?

anju12-Sep-02 1:53

anju

12-Sep-02 1:53

Hi all,
How to check if field value is NULL?

In my application i am using the code as follows to get the Recordset field value
while (VARIANT_FALSE == pRecordset->EndOfFile)
{ strTemp.Format("Test Column:%s",
(LPSTR)(_bstr_t)pRecordset->Fields->GetItem("Test")->Value);
AfxMessageBox(strTemp);
pRecordset->MoveNext();
}
while running the application if the Field value is NULL. I am getting Runtime Error
as "abnormal Programme termination".
please help me

anju

Re: How to check if field value is NULL?

Imran Farooqui12-Sep-02 2:12

Imran Farooqui

12-Sep-02 2:12

Consider query:

select nick from from mytable.

Suppose the value represented by nick can be NULL. So change the query as:

select isnull(nick, 'something') as nick from mytable

Here 'something' can be anything you desire. This can be a single space character also. Now when you collect value of nick from Recordset object, it'll not be null but the value supplied by you as a parmeter above. You can check it and treat as NULL

Imran Farooqui

World first Urdu Instant Messenger[^]

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Java is a tool for creating applications that torture users with its awful speed and its ugly interfaces.
Daniel Turini commenting on this article

Re: How to check if field value is NULL?

anju12-Sep-02 18:39

anju

12-Sep-02 18:39

Hi Imran Farooqui,
Thanks for Your Reply.
Please need more help to me..............
Suppose i have to select entire table then how can i make all null fields in the table to 'Something'.

in my application i am opening the recordset as follows

pRecordset->Open("mytable",
_variant_t((IDispatch*)pConnection,true),
adOpenDynamic, adLockPessimistic,adCmdTable);
and i am getting all the fields
pRecordset->MoveFirst();
while (!pRecordset->EndOfFile)
{
strTemp.Format("Field1:%s",(LPSTR)(_bstr_t)pRecordset->Fields->GetItem("Field1")->Value);
AfxMessageBox(strTemp);
pRecordset->MoveNext();
}
Rose | [Rose]

anju

Re: How to check if field value is NULL?

Imran Farooqui12-Sep-02 19:06

Imran Farooqui

12-Sep-02 19:06

In your code, you'r opening a complete table using RecordSet object. I do not prefer this technique because you have no control over the selected records. Instead i prefer to explicitly open the table using SQL queries.

m_pRecordSet = m_pConnection->Execute("select * from mytable", &vRecsAffected, adOptionUnspecified);

Only if you are accessing the table in this way, you can use, isnull option.

Imran Farooqui

World first Urdu Instant Messenger[^]

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Java is a tool for creating applications that torture users with its awful speed and its ugly interfaces.
Daniel Turini commenting on this article

Re: How to check if field value is NULL?

Rama Krishna Vavilala12-Sep-02 2:09

Rama Krishna Vavilala

12-Sep-02 2:09

You need to do something like this.

_variant_t vt = pRecordset->Fields->GetItem("Test")->Value;

if (vt.vt == VT_NULL)
{
  AfxMessageBox("Field is NULL");
}
else
{
strTemp.Format("Test Column:%s",(LPSTR)(_bstr_t)vt); 
AfxMessageBox(strTemp);
}

C# is fundamentally broken. - Christian Graus

Re: How to check if field value is NULL?

[James Pullicino]12-Sep-02 2:36

[James Pullicino]

12-Sep-02 2:36

This line:

<br />
(LPSTR)(_bstr_t)pRecordset->Fields->GetItem("Test")->Value); <br />

is very dangerous because of the following reasons:

If Fields fails, an exception will be thrown.
If GetItem fails, an exception will be thrown.
If Value cannot be converted to a _bstr_t, an exception will be thrown.

Segment your code a little better. Add exception handling, or use the raw_ methods of your smart pointers. Here is an example on how to improve your code (this is from memory):

<br />
IFieldPtr field;<br />
try<br />
{<br />
  field = pRecordset->Fields->GetItem("Test");<br />
} <br />
catch(com_error e) <br />
{ <br />
  field = NULL;<br />
}<br />
<br />
if(field != NULL)<br />
{<br />
  _variant_t vtVal;<br />
  try<br />
  {<br />
    vtVal = field->Value;<br />
  } catch (_com_error e) {vtVal.vt = VT_ERROR; }<br />
  <br />
  _bstr_t bstrVal;<br />
  if(vtVal.vt != VT_ERROR)<br />
  {<br />
     try{ bstrVal = (_bstr_t)vtVal; }<br />
     catch(com_error e) {bstrVal = L"";}<br />
  }<br />
  <br />
  AfxMessageBox((LPCTSTR)bstrVal);<br />
}<br />
<br />

--James

Drinking In The Sun
Forgot Password?

Re: How to check if field value is NULL?

anju12-Sep-02 18:44

anju

12-Sep-02 18:44

Hi Rama Krishna,
ThankQ this technique is work to me well
Rose | [Rose]

anju

Re: How to check if field value is NULL?

anju12-Sep-02 18:51

anju

12-Sep-02 18:51

Hi James Pullicino,
Thanks a lot..
I never thing about what u pointed.
now my code is changed as per your instructions.
once again thank to you
Rose | [Rose]

anju

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