Inside Technique : Creating Counters with ASP : Advanced Browser-Based Counters

Now, let's revisit our original goal and create a browser counter. To determine what browser the visitor is using, we analyze the user-agent string provided as part of the http header. This string contains information identifying the browser, platform, and version. Below we process the user-agent string to determine what browser is being used:

sub application_onstart
  ' Initialize
  Dim objFSO, sPath,sToken,sValue
  Set objFSO = CreateObject("Scripting.FileSystemObject")
  sPath = Server.mapPath("counters.inc")
  if objFSO.fileExists(sPath) then
    Set objFile = objFSO.OpenTextFile(sPath)
    while not (objFile.AtEndOfStream) 
      sToken = objFile.readLine
      sValue = objFile.readLine
      Application(sToken) = sValue 
    wend
  end if
  objFile.close()
end sub

function SaveCounters()
  Dim objFSO, sPath, c
  Set objFSO = CreateObject("Scripting.FileSystemObject")
  sPath = Server.mapPath("counters.inc")
  Set objFile = objFSO.CreateTextFile(sPath)
  for each c in application.contents
    if left(c,3)="NUM" then
      objFile.write c & chr(13) & chr(10)
      objFile.write application(c) & chr(13) & chr(10)
    end if
  next
  objFile.close()
end function

sub session_onstart
  ' Session Starts
  sAgent = Request.ServerVariables("HTTP_USER_AGENT")
  application.lock
  if (inStr(sAgent,"MSIE")>0) then
    application("num_ie") = application("num_ie") + 1
  elseif inStr(sAgent,"Mozilla")>0 then
    application("num_nav") = application("num_nav") + 1
  else
    application("num_other") = application("num_ie") + 1
  end if
  application("num_visitors") = application("num_visitors") + 1
  if application("num_visitors") mod 50=0 then
    SaveCounters()
  end if
  application.unlock 
End Sub

Sub Application_OnEnd
  SaveCounters
End Sub

The above script is a complete framework for tracking and persisting counters. Additional counters are defined simply by prefixing the application property with "num". All application properties with this prefix are automatically persisted into the counters.inc file.

Outputting any of these counters onto your web-page is extremely simple. You merely response.write the corresponding application property. For example, to output all counters:

<%
  Dim c
  for each c in application.contents
    if left(c,3)="NUM" then
      response.write(c &  ":" & "<BR>")
      response.write(application.contents(c) & "<BR>")
    end if
  next
%>

Or in a more likely scenario, you will output individual counters specifically:

Total Visitors: <%=Application("num_visitors")%>

You can easily create more counters by further analyzing the user-agent string. For example. you can test for Mac or Windows with the following statements:

if (instr(sAgent,"Win")) > 0
  application("num_win") = application("num_win") + 1
elseif (instr(sAgent,"Mac")) > 0
  application("num_mac") = application("num_mac") + 1
end if

This concludes our introduction on creating counters usign ASP. ASP's session and application objects greatly simplify adding real-time counters to your site. By combining this with the user-agent string, you can maintain and track interesting statistics on your users.

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