Microsoft KB Archive/150786

= How To Use SQLBindParameter with 32-bit Visual Basic =

Article ID: 150786

Article Last Modified on 7/13/2004

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APPLIES TO


 * Microsoft Visual Basic 4.0 Standard Edition
 * Microsoft Visual Basic 4.0 Professional Edition
 * Microsoft Visual Basic 4.0 Enterprise Edition

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This article was previously published under Q150786



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.



Sample Program
The following example uses the ODBC API SQLBindParameter function with the 32-bit edition of Visual Basic 4.0 and higher and changes the au_lname column of the authors table to a different value. You need to change the table and column name to match your ODBC datasource.

 Start a new project in Visual Basic. Form1 is created by default. 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. Add a Command button to Form1. Command1 is created by default.  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



NOTE: You need to change your DSN, UID, and PWD parameters in the Form_Load event before continuing.


 * 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.

When working with the ODBC API, you cannot use the String data type because the 32-bit edition of Visual Basic 4.0 stores all strings as UNICODE strings. ODBC32.DLL is an ANSI DLL file, so all communication involves one-byte character strings. Visual Basic can only accomplish this behavior with the new byte data type. If you bind a UNICODE string variable, Visual Basic allocates a temporary buffer to hold an ANSI version of the string, and passes that address to the SQLBindParameter function. The address is then on the stack and is invalid as soon as the stack frame is adjusted.

