How To Write to the Windows NT Event Log from Visual Basic

Event logging in Windows provides a standard, centralized way for Windows and any other applications to record important software and hardware events. It also supplies a standard user interface for viewing the logs and a programming interface for examining the logs.

This article illustrates how to write to the NT or Windows 2000 Event Log with Visual Basic versions 4.0 and later. With Visual Basic version 4.0, you must use the Win32 API. Visual Basic versions 5.0 and later have built-in functionality for event-logging so the API functions are unnecessary.

Visual Basic versions 5.0 and Later

Visual Basic versions 5.0 and later expose three methods and properties of the App object by which event-logging can be enabled: The LogMode property returns a value that determines how logging (through the LogEvent method) will be carried out. (Read-only at run time).

The LogPath property returns the path and filename of the file used to capture output from the LogEvent method. (Read-only at run time).

The LogEvent method writes an event into the application's log target. On Windows NT or Windows 2000 platforms, the method writes to the NT or Windows 2000 Event log. On Windows 95, Windows 98, and Windows Me platforms, the method writes to the file specified in the LogPath property; by default, if no file is specified, events will be written to a file named vbevents.

The Event Log only updates when your application is running as a compiled .EXE. It will not write events to the Event log when run from the IDE. This is to prevent excessive data from being written to the Event Log during debugging.

Visual Basic 4.0 (32-bit)

The following example shows how to send three different types of events. These steps are for applications written with Visual Basic 4.0 only.

Information, Warnings, and Errors:

1. Start a new project in Visual Basic. Form1 is created by default.
2. From the File menu, choose Remove file to remove the default form.
3. From the Insert menu, choose Module to add a new module, Module1, to the project.
4. Insert the following code into Module1:

         Option Explicit
   
         Declare Function RegisterEventSource Lib "advapi32.dll" Alias _
           "RegisterEventSourceA" ( ByVal lpUNCServerName As String, _
           ByVal lpSourceName As String) As Long
         Declare Function DeregisterEventSource Lib "advapi32.dll" ( _
           ByVal hEventLog As Long) As Long
         Declare Function ReportEvent Lib "advapi32.dll" Alias  _
         "ReportEventA" ( _
           ByVal hEventLog As Long, ByVal wType As Integer, _
           ByVal wCategory As Integer, ByVal dwEventID As Long, _
           ByVal lpUserSid As Any, ByVal wNumStrings As Integer, _
           ByVal dwDataSize As Long, plpStrings As Long, _
           lpRawData As Any) As Boolean
         Declare Function GetLastError Lib "kernel32" () As Long
         Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" ( _
           hpvDest As Any,hpvSource As Any, _
           ByVal cbCopy As Long)
         Declare Function GlobalAlloc Lib "kernel32" ( _
            ByVal wFlags As Long, _
            ByVal dwBytes As Long) As Long
         Declare Function GlobalFree Lib "kernel32" ( _
            ByVal hMem As Long) As Long
   
         Public Const EVENTLOG_SUCCESS = 0
         Public Const EVENTLOG_ERROR_TYPE = 1
         Public Const EVENTLOG_WARNING_TYPE = 2
         Public Const EVENTLOG_INFORMATION_TYPE = 4
         Public Const EVENTLOG_AUDIT_SUCCESS = 8
         Public Const EVENTLOG_AUDIT_FAILURE = 10
   
         Public Sub LogNTEvent(sString As String, iLogType As Integer, _
           iEventID As Long)
           Dim bRC As Boolean
           Dim iNumStrings As Integer
           Dim hEventLog As Long
           Dim hMsgs As Long
           Dim cbStringSize As Long
           hEventLog = RegisterEventSource("", App.Title)
           cbStringSize = Len(sString) + 1
           hMsgs = GlobalAlloc(&H40, cbStringSize)
           CopyMemory ByVal hMsgs, ByVal sString, cbStringSize
           iNumStrings = 1
           If ReportEvent(hEventLog, _
              iLogType, 0, _
              iEventID, 0&, _
              iNumStrings, cbStringSize, _
              hMsgs,hMsgs) = 0 Then
              MsgBox GetLastError()
           End If
           Call GlobalFree(hMsgs)
           DeregisterEventSource (hEventLog)
         End Sub
   
         Sub Main()
           Call LogNTEvent("Information from " & App.EXEName, _
             EVENTLOG_INFORMATION_TYPE, 1001)
           Call LogNTEvent("Warning from " & App.EXEName, _
             EVENTLOG_WARNING_TYPE, 1002)
           Call LogNTEvent("Error from " & App.EXEName, _
             EVENTLOG_ERROR_TYPE, 1003)
           Msgbox "Done"
         End Sub
   
   					

5. Press the F5 key to start the project.

You need to start the NT Applet, EVENTVWR.EXE, to view the events entered with the code. Because your events are coming from an Application, you need to select the "Application" option from the Log Menu and then press the F5 key to refresh the view. Your events should be there under the name of Project1.

For additional information, please click the article numbers below to view the articles in the Microsoft Knowledge Base: Microsoft Developer Support Network (MSDN)

Platform SDK; Reference; Functions -- Win32 Functions

Microsoft Visual Basic 5.0 Online Help