HOWTO: Use SQLBindParameter with 32-bit Visual Basic

• Microsoft Visual Basic Standard, Professional, and Enterprise Editions for Windows, version 4.0

SUMMARY

This article demonstrates how to use the ODBC API SQLBindParameter function with the 32-bit edition of Visual Basic 4.0 and higher. It includes the use of a Visual Basic byte array, required with the UNICODE to ANSI string conversion implemented in Visual Basic, to pass string data back and forth.

Programming directly to the ODBC API is an alternative to using RDO and DAO code to access the ODBC database, both of which depend on an OLE interface and the associated overhead. This direct method allows the programmer to have low-level control over the ODBC datasource. This article also introduces the Visual Basic programmer to a complex programming model that requires in-depth knowledge of the ODBC 2.0 specification.

If you feel you can benefit from this direct approach, obtain a copy of the "ODBC 2.0 Programmer's Reference and SDK Guide" that fully documents the ODBC API before you proceed.

MORE INFORMATION

Sample Program

1. Start a new project in Visual Basic. Form1 is created by default.



2. Add the file ODBC32.TXT to your project. From the File menu, select Add File, or, from the Context menu, right-click Project, and select Add File. The file ODBC32.TXT is found in the \VB\SAMPLES\REMAUTO\DB_ODBC directory of your Visual Basic 4.0 Enterprise Edition CD-ROM, or it is included with the ODBC SDK.



3. Add a Command button to Form1. Command1 is created by default.



4. Paste the following code into the General Declarations section of Form1:

   
         Option Explicit
         Dim hen As Long     ' environment handle.
         Dim hdbc As Long     ' connect handle.
         Dim hstmt As Long    ' statement handle.
         Dim intRc As Integer ' return value.
         Const ROWSETSIZE As Long = 1
   
         Private Sub Form_Load()
           ' load driver manager.
           intRc = SQLAllocEnv(hen)            ' allocate environment handle.
           intRc = SQLAllocConnect(ByVal hen, hdbc) ' allocate connection
                                                    ' handle.
   
           ' load driver.
           Dim strDSN As String, strUID As String, strPWD As String
           strDSN = "pubs"
           strUID = "sa"
           strPWD = ""
           intRc = SQLConnect(hdbc, strDSN, Len(strDSN), strUID, _
                    Len(strUID), strPWD, Len(strPWD))
         End Sub
   
         Private Sub Command1_Click()
            intRc = SQLAllocStmt(hdbc, hstmt) ' allocate a statement handle.
   
           intRc = SQLSetStmtOption(hstmt, SQL_CONCURRENCY, SQL_CONCUR_ROWVER)
           intRc = SQLSetStmtOption(hstmt, SQL_CURSOR_TYPE, _
             SQL_CURSOR_KEYSET_DRIVEN)
           intRc = SQLSetStmtOption(hstmt, SQL_ROWSET_SIZE, ROWSETSIZE)
           intRc = SQLSetCursorName(hstmt, "C1", SQL_NTS)
   
           Dim strSQL As String
           strSQL = "Select au_lname from authors"
           intRc = SQLExecDirect(hstmt, strSQL, Len(strSQL))
           Debug.Print intRc
   
           Dim szField1_Value(256) As Byte
           Dim cbField1_Value As Long
           intRc = SQLBindCol(hstmt, 1, SQL_C_CHAR, szField1_Value(0), 256, _
             cbField1_Value)
   
           Dim irow As Long
           Dim pcrow As Long
           Dim rgfRowStatus(ROWSETSIZE) As Integer
   
           intRc = SQLExtendedFetch(ByVal hstmt, SQL_FETCH_NEXT, 0, pcrow, _
             rgfRowStatus(0))
           Debug.Print BytesToString(szField1_Value())
   
           irow = 1
           intRc = SQLSetPos(hstmt, irow, SQL_POSITION, SQL_LOCK_NO_CHANGE)
   
           Dim hstmtU As Long
           intRc = SQLAllocStmt(hdbc, hstmtU) ' alloc statement handle for
                                              ' update.
   
           strSQL = "UPDATE AUTHORS SET AU_LNAME=? WHERE CURRENT OF C1"
           intRc = SQLPrepare(hstmtU, strSQL, Len(strSQL))
   
           Call StringToBytes("John Doe", 256, szField1_Value())
           Debug.Print BytesToString(szField1_Value())
   
           intRc = SQLBindParameter(hstmtU, 1, SQL_PARAM_INPUT, SQL_C_CHAR, _
             SQL_CHAR, 256, 0, szField1_Value(0), 0, SQL_NTS)
   
           intRc = SQLExecute(hstmtU)
           intRc = SQLFreeStmt(hstmtU, SQL_DROP)
         End Sub
   
         Private Function BytesToString(byte_array() As Byte) As String
           ' convert byte array to string.
           Dim Data As String, StrLen As String
           Data = StrConv(byte_array(), vbUnicode)
           StrLen = InStr(Data, Chr(0)) - 1
           BytesToString = Left(Data, StrLen)
         End Function
   
         Private Sub StringToBytes(Data As String, ByteLen As Integer, _
           return_buffer() As Byte)
           ' convert string to byte array.
           Dim StrLen As Integer, Count As Integer
           For Count = 0 To Len(Data) - 1
             return_buffer(Count) = Asc(Mid(Data, Count + 1, 1))
           Next Count
           For Count = Len(Data) To ByteLen
             return_buffer(Count) = 0
           Next Count
         End Sub
   
         Private Sub Form_Unload(Cancel As Integer)
           intRc = SQLDisconnect(ByVal hdbc)
           intRc = SQLFreeEnv(ByVal hen)
           intRc = SQLFreeStmt(hstmt, SQL_DROP)
         End Sub
    

1. Press the F5 key to start the program.



2. Click the Command1 button to execute the ODBC API code. If the code executes successfully, the previous value and the current value of the au_lname column printed to the debug window appear.

REFERENCES

For more information, please see: "ODBC 2.0 Programmer's Reference and SDK Guide," published by Microsoft Press.

(Hitchhiker's Guide to Visual Basic and SQL Server, Microsoft Press.
ISBN: 1-55615-906-4.).

Additional query words: kbVBp kbdse kbDSupport kbVBp400 kbODBC

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