SQLGetData returns an empty buffer on Query (ODBC)

Question

I am executing the following simple query in SQL Server Management Studio:

SELECT name, definition FROM sys.default_constraints

This works fine and I can see that there are some rows in my data.  I try to execute the same query in my test application (implemented in C++), using ODBC in the following way, using SQLGetData:

SQLGetData( *pStatementHandle, i, SQL_C_WCHAR, pvData ,nLen, &nActualLen ) );

The result is successful, but my buffer,pvData, is empty.  I have tried some other applications that use ODBC as well to see if I am missing something but they also fail to retrieve any data.  Am I missing something?  Or is this only possible using SQL Native Client?

Any pointers, clues?

Thanks in advance,
Mohan

Answer 1

From this code snippet it's hard to tell exactly what's wrong.

First thing to check would be the return code from 'SQLFetch()', called just before SQLGetData(). If this returns "SQL_NO_DATA_FOUND", then you're probably in the wrong database. Try executing 'use <database>' prior to your call.

If 'SQLFetch()' returns SQL_SUCCESS, then you have something wrong with your SQLGetData() call.

1) You're binding as 'SQL_C_WCHAR'. Is 'pvData' an array of char's or wchar's?

2) What's your value for nLen? Is it non-zero?

3) Is your column number correct (i == 1 for 'name' column, etc. )

4) What's returned by nActualLength? Is it 'SQL_NULL_DATA', or is it a positive number. If it's positive, then go back and check point 1) above.

Hope this helps. If not, please attach a more lengthy code sample. I may be missing something.

~Warren