SAMPLE: Vcspnp.exe Demonstrates Passing SQL NULL Parameters and Reading NULL Values with ADO (229088)

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:

Vcspnp.exe

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:

119591 How to Obtain Microsoft Support Files from Online Services

Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file. 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:

182389 FILE: Adovcbm.exe ADO 1.5 with #import and Getrows/Bookmarks

184968 FILE: Adovcsp.exe Demonstrates Using Stored Procedures with ADO

181733 FILE: Adovcbtd.exe #import Using UpdateBatch and CancelBatch

220152 FILE: Sample: ADOVC1 Simple ADO/VC++ Application

200122 SAMPLE: ATL2ADO returns disconnected recordset from COM to VB