SAMPLE: Vcspnp.exe Demonstrates Passing SQL NULL Parameters and Reading NULL Values with ADO

ID: Q229088

The information in this article applies to:

ActiveX Data Objects (ADO), version 2.0
Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0

SUMMARY

The Vcspnp.exe sample demonstrates correct handling of SQL NULL with Microsoft ADO using #import and Visual C++.

The sample demonstrates sending SQL NULL parameters to a SQL Server stored procedure with ADO. It also shows how to read SQL NULL values.

In SQL, NULL means having no value entered or unknown, completely different than a null C string. This sample shows how to package and send SQL NULL parameters to SQL Server stored procedure using ADO. It also shows how to read SQL NULL values.

MORE INFORMATION

The following file is available for download from the Microsoft Download Center. Click the file name below to download the file:

Vcspnp.exe

For more information about how to download files from the Microsoft Download Center, please visit the Download Center at the following Web address

http://www.microsoft.com/downloads/search.asp

and then click How to use the Microsoft Download Center.

ReadMe.txt	3579
resource.h	1098
StdAfx.cpp	208
StdAfx.h	1171
VCSPNP.cpp	2063
VCSPNP.dsp	4163
VCSPNP.dsw	535
VCSPNP.h	1324
VCSPNP.rc	5921
VCSPNPDlg.cpp	13988
VCSPNPDlg.h	2072

To send a SQL NULL parameter, create a _variant_t and then change the type to VT_NULL. The following code snippet shows this:


_variant_t  vtNull; 
    vtNull.ChangeType(VT_NULL);

To read a field value that could be SQL NULL, you must test it for VT_NULL. The following code snippet demonstrates this:


_variant_t v(rs->Fields->Item[_variant_t("StudName")]->Value);
   if( v.vt == VT_NULL){
       ....// Field is SQL NULL

REFERENCES

For additional information, please see the following articles in the Microsoft Knowledge Base:

Q182389 FILE: Adovcbm.exe ADO 1.5 with #import and Getrows/Bookmarks

Q184968 FILE: Adovcsp.exe Demonstrates Using Stored Procedures with ADO

Q181733 FILE: Adovcbtd.exe #import Using UpdateBatch and CancelBatch

Q220152 FILE: Sample: ADOVC1 Simple ADO/VC++ Application

Q200122 SAMPLE: ATL2ADO returns disconnected recordset from COM to VB

Additional query words:

Keywords : kbfile kbsample kbADO kbADO200 kbDatabase kbVC kbVC600 kbGrpVCDB kbGrpMDAC
Version : WINDOWS:2.0,6.0
Platform : WINDOWS
Issue type : kbhowto