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

ID: Q229088

The information in this article applies to:

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 Software Library:

Vcspnp.exe
Release Date: May 14-1999

For more information about downloading files from the Microsoft Software Library, please see the following article in the Microsoft Knowledge Base:
Q119591 How to Obtain Microsoft Support Files from Online Services
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
(c) Microsoft Corporation 1999, All Rights Reserved. Contributions by Rick Anderson, Microsoft Corporation.

Additional query words: 


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

Last Reviewed: May 20, 1999