How To Use SQLBindParameter with 32-bit Visual Basic (150786)

MORE INFORMATION

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.

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
   
   						

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.