Sparse File Logging

Public globalFileHandle As Long
Public globalFilePointer As Long
Public Const LogFilePath = "\somewhere\"
Public Const LogFileLimit = 65536

Sub StartUpCode()
Dim myHandle As Long, myPID As Long
Dim FileName As String
Dim myProgramName As String

  myHandle = GetMyHandle()                   ' function dependant on OS & API
  myPID = GetMyPID(myHandle)                 ' function dependant on OS & API
  myProgramName = GetMyProgramName(myHandle) ' function dependant on OS & API
  globalFileHandle = FreeFile
  globalFilePointer = 1                      ' dependent on filesystem, either 1 or 0
  ' Note on filename
  ' This format is setup for generating a unique filename per instance
  ' Might not be desirable, will create a lot of log files
  FileName = LogFilePath _
    & Format$(Date, "yy-mm-dd") & "_" & Format$(Time, "hhmmss") _
    & myProgramName _
    & "_" & Format$(myPID) & "_" & Format$(myHandle) _
    & ".txt"
  Open FileName For Binary As globalFileHandle
  ' main code
  Close globalFileHandle

End Sub

Sub LogFileMessage(strMessage As String)
Dim Work As String, msgLength As Long

  Work = Format$(Date, "yymmdd") & "_" & Format$(Time, "hhmmss") _
    & strMessage & vbCr
  msgLength = Len(Work & "--- ^ most recent ^ ---" & String$(5, vbCr))
  If ((msgLength + globalFilePointer) > LogFileLimit) Then
    globalFilePointer = 1                      ' dependent on filesystem, either 1 or 0
  End If
  Seek globalFileHandle, globalFilePointer
  Put #fileout, , Work
  globalFilePointer = Seek(globalFileHandle)
  Put #fileout, , "--- ^ most recent ^ ---" & String$(5, vbCr)

End Sub