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how to handle null

Posted on 2001-09-17
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Last Modified: 2013-12-03
sir using ado i retrieve alues from a field like this

_ConnectionPtr con;
_RecordsetPtr rec;

con.CreateInstance(__uuidof(Conection));
con->Open() // to connect to the data source

rec.CreateInstance(__uuidof(Recordset));
rec->PutRefActiveConection(con);

rec->Open() // to open recordset using sql statement
               select emp_phone from employees

 Now this emp_phone field can contain NULL values also
 Then i use the following code to extract values from emp_phone

_variant_t v_phone;
v_phone=rec->GetCollect(L"emp_phone");

now this GetCollect() retrns value of type _variant_t which then gets stored in v_phone

then i use something like this

lstrcpy(str,(_bstr_t)v_phone)

and then i use str to show emp_phone's value

the point is that if emp_phone contains value
then lstrcpy() works fine

but if emp_phone's value is NULL
then if i use lstrcpy(str,(_bstr_t)v_phone)
the program gives error at run time
saying abnormal termination

so how should i find whether value in v_phone is null so that i dont use lstrcpy() in that case
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Question by:chikersal
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Accepted Solution

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jhance earned 50 total points
ID: 6487575
if(v_phone != NULL){
  lstrcpy(str,(_bstr_t)v_phone);
}
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Author Comment

by:chikersal
ID: 6490572
if(v_phone != NULL){
 lstrcpy(str,(_bstr_t)v_phone);
}

instead of this what i tried was

if(v_phone==NULL) MessageBox(hwnd,"Null Values","Message",MB_OK);

but it never displayed the dialog box.

but anyway thanks for it
i will try again
if it does not work i will get back to you
thanks
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LVL 2

Expert Comment

by:mirec
ID: 6494908
Hi chikersal,
have you tried:
if(v_phone.vt == VT_NULL) MessageBox(hwnd,"Null Values","Message",MB_OK);
?
I think that variant wrapper for NULL database values should have this type.

m.
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Expert Comment

by:Netminder
ID: 6771973
chikersal,

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Thanks,

Netminder
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by:Netminder
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