C / C++ / MFC

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

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

anju12-Sep-02 18:39

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

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

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

[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?

anju12-Sep-02 18:44

12-Sep-02 18:44

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

anju

anju12-Sep-02 18:51

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

MFC and old functions

Tolias12-Sep-02 1:38

Tolias

12-Sep-02 1:38

I need to ask a question that's been bothering me for some time now. I created an SDI application from the Visual C++ wizard. Everything was fine then. When I added a function (that someone else) created in old C, all of a sudden the menu and status bar dissapeared and I haven't seen them since then. I get no errors after building the project but I can't make the bars appear, neither through menu->view nor with right clicking. Could it be that some old function (like atoi) has a side-effect on the program? All functions in the old C file are global to the project.

Tomasz Sowinski12-Sep-02 1:42

12-Sep-02 1:42

Sounds strange. 'Old functions like atoi' shouldn't have any side-effects. What is the purpose of function you've added?

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

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

Anonymous12-Sep-02 1:52

Anonymous

12-Sep-02 1:52

It reads two files containing neurules definitions and variable definitions, asks the user to insert values to variables and then uses the neurules to make an inference. It also evaluates the rules if needed. My part was to convert all the 'printf' calls to something visual.

Tomasz Sowinski12-Sep-02 1:54

12-Sep-02 1:54

At what point exactly are you calling this function? Are you using dialogs for entering variables' values?

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

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

Tolias12-Sep-02 1:59

Tolias

12-Sep-02 1:59

Well, this function was originally writen in C with a console user interface. I erased all printf and scanf calls and used dialogs to prompt messages and get input. The function is called inside ON_OPTIONS_INFERENCE.

Tomasz Sowinski12-Sep-02 2:03

12-Sep-02 2:03

It shouldn't have side-effects you've described. I guess you'll have to look for the cause of problems by commenting out parts of the code or inserting temporary return statements.

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

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

Michael P Butler12-Sep-02 1:44

Michael P Butler

12-Sep-02 1:44

Put a breakpoint in the CMainFrame::OnCreate function. This is where the toolbar and status bar should be created. It should give you more of a clue to why they have gone.

Michael

Programming is great. First they pay you to introduce bugs into software. Then they pay you to remove them again.

Compiler directives

Ruca12-Sep-02 1:20

Ruca

12-Sep-02 1:20

Hi,
I have 2 projects ( project A and B)which use most of the same functions, but there are others which are unique to project A and others to B.
I would like to be able to use a #define to compile Project A with its own functions and then by changing the #define compile project B with its functions. In other words, I would like to avoid defining 2 different projects.
Is this possible?
And how does one do it, both in the header and source code files?

Thanking you in anticipation.

Rui

Re: Compiler directives

Tomasz Sowinski12-Sep-02 1:29