HOWTO: Trap an Invalid ODBC Logon Using the ODBC API

• Microsoft Visual Basic Professional and Enterprise Editions for Windows, version 4.0, 5.0
• Professional and Enterprise Editions of Microsoft Visual Basic for Windows, 16-bit and 32-bit, version 4.0

SUMMARY

This article demonstrates how to use Open Database Connectivity (ODBC) API calls to test the validity of a Data Source Name, User ID, and Password.

MORE INFORMATION

When a user tries opening an ODBC Data Source with an incorrect Data Source Name, User ID, or Password, ODBC prompts the user for the correct information. It is not possible to trap for this error using Visual Basic Error Handling methods.

The following steps demonstrate how to test the logon parameters:

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

2. Add a command button (Command1) to Form1.

3. Add three text boxes (Text1, Text2, and Text3) to Form1.

4. Add a check box (Check1) to Form1.

5. Add the following code to the General Declarations section of Form1:

         Option Explicit
   

         #If Win32 Then
           Private Declare Function SQLAllocEnv Lib "odbc32.dll" _
              (phenv As Long) As Integer
           Private Declare Function SQLAllocConnect Lib "odbc32.dll" _
              (ByVal henv As Long, phdbc As Long) As Integer
           Private Declare Function SQLConnect Lib "odbc32.dll" ( _
              ByVal hdbc As Long, ByVal szDSN As String, _
              ByVal cbDSN As Integer, ByVal szUID As String, _
              ByVal cbUID As Integer, ByVal szAuthStr As String, _
              ByVal cbAuthStr As Integer) As Integer
           Private Declare Function SQLFreeEnv Lib "odbc32.dll" _
              (ByVal henv As Long) As Integer
           Private Declare Function SQLFreeConnect Lib "odbc32.dll" _
              (ByVal hdbc As Long) As Integer
           Private Declare Function SQLError Lib "odbc32.dll" ( _
              ByVal henv As Long, ByVal hdbc As Long, ByVal hstmt As Long, _
              ByVal szSqlState As String, pfNativeError As Long, _
              ByVal szErrorMsg As String, ByVal cbErrorMsgMax As Integer, _
              pcbErrorMsg As Integer) As Integer
         #ElseIf Win16 Then
           Private Declare Function SQLAllocEnv Lib "odbc.dll" _
              (phenv As Long) As Integer
           Private Declare Function SQLAllocConnect Lib "odbc.dll" _
              (ByVal henv As Long, phdbc As Long) As Integer
           Private Declare Function SQLConnect Lib "odbc.dll" ( _
              ByVal hdbc As Long, ByVal szDSN As String, _
              ByVal cbDSN As Integer, ByVal szUID As String, _
              ByVal cbUID As Integer, ByVal szAuthStr As String, _
              ByVal cbAuthStr As Integer) As Integer
           Private Declare Function SQLFreeEnv Lib "odbc.dll" _
              (ByVal henv As Long) As Integer
           Private Declare Function SQLFreeConnect Lib "odbc.dll" _
              (ByVal hdbc As Long) As Integer
           Private Declare Function SQLError Lib "odbc.dll" ( _
              ByVal henv As Long, ByVal hdbc As Long, _
              ByVal hstmt As Long, ByVal szSqlState As String, _
              pfNativeError As Long, ByVal szErrorMsg As String, _
              ByVal cbErrorMsgMax As Integer, pcbErrorMsg As Integer) _
              As Integer
         #End If
   
         Private Const SQL_SUCCESS As Long = 0
         Private Const SQL_SUCCESS_WITH_INFO As Long = 1
   
         Private Function IsValidODBCLogin(ByVal sDSN As String, _
            ByVal sUID As String, ByVal sPWD As String) As Boolean
         Dim henv As Long    'Environment Handle
         Dim hdbc As Long    'Connection Handle
         Dim iResult As Integer
   
           'Obtain Environment Handle
           iResult = SQLAllocEnv(henv)
           If iResult <> SQL_SUCCESS Then
             IsValidODBCLogin = False
             Exit Function
           End If
   
           'Obtain Connection Handle
           iResult = SQLAllocConnect(henv, hdbc)
           If iResult <> SQL_SUCCESS Then
             IsValidODBCLogin = False
             iResult = SQLFreeEnv(henv)
             Exit Function
           End If
   
           'Test Connect Parameters
           iResult = SQLConnect(hdbc, sDSN, Len(sDSN), sUID, Len(sUID), _
                     sPWD, Len(sPWD))
           If iResult <> SQL_SUCCESS Then
             If iResult = SQL_SUCCESS_WITH_INFO Then
               'The Connection has been successful, but SQLState Information
               'has been returned
               'Obtain all the SQLState Information
               If Check1.Value Then ShowSQLErrorInfo hdbc, vbInformation
               IsValidODBCLogin = True
             Else
               'Obtain all the Error Information
               If Check1.Value Then ShowSQLErrorInfo hdbc, vbExclamation
               IsValidODBCLogin = False
             End If
           Else
             IsValidODBCLogin = True
           End If
   
           'Free Connection Handle and Environment Handle
           iResult = SQLFreeConnect(hdbc)
           iResult = SQLFreeEnv(henv)
   
         End Function
   
         Private Sub Form_Load()
   
           Text1.Text = "DSN"
           Text2.Text = "User ID"
           Text3.Text = ""
           Text3.PasswordChar = "*"
           Command1.Caption = "Test Connect"
           Check1.Caption = "Return Errors and Warnings"
   
         End Sub
   
         Private Sub Command1_Click()
         Dim sServer As String, sLogin As String, sPassword As String
   
           sServer = Text1.Text
           sLogin = Text2.Text
           sPassword = Text3.Text
   
           If IsValidODBCLogin(sServer, sLogin, sPassword) = True Then
             MsgBox "Connection Successful", vbInformation, "ODBC Logon"
           Else
             MsgBox "Connection Failed", vbExclamation, "ODBC Logon"
           End If
   
         End Sub
   
         Private Sub ShowSQLErrorInfo(hdbc As Long, iMSGIcon As Integer)
         Dim iResult As Integer
         Dim hstmt As Long
         Dim sBuffer1 As String * 16, sBuffer2 As String * 255
         Dim lNative As Long, iOutlen As Integer
   
           sBuffer1 = String$(16, 0)
           sBuffer2 = String$(256, 0)
   
           Do 'Cycle though all the Errors
             iResult = SQLError(0, hdbc, hstmt, sBuffer1, lNative, sBuffer2, _
                       256, iOutlen)
             If iResult = SQL_SUCCESS Then
               If iOutlen = 0 Then
                 MsgBox "Error -- No error information available", _
                 iMSGIcon, "ODBC Logon"
               Else
                 MsgBox Left$(sBuffer2, iOutlen), iMSGIcon, "ODBC Logon"
               End If
             End If
           Loop Until iResult <> SQL_SUCCESS
   
         End Sub
   
   

6. Press F5 to run the project. Enter a valid Data Source Name, User ID, and Password in the appropriate text boxes and click on the Test Connect button. A dialog box appears showing whether the connection is Successful or has Failed. Select the check box "Return Errors and Warnings," and click on the Test Connection button. Any errors and warnings are returned.

REFERENCES

Open Database Connectivity (ODBC) SDK, version 2.10, "Programmer's Reference," on the Microsoft Developer Network (MSDN) CD.

For additional information, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q150786
   TITLE     : How to Use SQLBindParameter with 32-bit Visual Basic 4.0