Prerequisites

The code in this article uses Sessions in ASP, so you'll need to have them enabled on your server. See the References section at the end of this article for more information. You'll also need to have access to a file called global.asa in the root of your site. If you run your own Web server, this is not a problem; you can simply create the file yourself. If you are using an ISP, you'll need to check with them if they support the use of the global.asa file as, unfortunately, not all ISPs allow this. You'll also need to be able to write to a text file from within the global.asa file. This means that the account your Web site is running under (usually, IUSR_MachineName where MachineName is the name of your computer) needs sufficient permissions to write to the file. Finally, most Anti-virus software come with a "Script blocking" feature, that disables writing to text files from within ASP pages. If you find that your files are not written at all, you may need to disable this feature. Alternatively, read this article that explains how to store your counters in a database.

Counting Users

Just as in the article where the counters were stored in just the Application object, you can make use of the Session_OnStart event, defined in the global.asa file to keep track of your users. This event is fired whenever a user requests the first page in your Web site. This way, you have the ability to count each unique visitor only once during their visit. As long as the Session remains active on the server, the user won't be counted again. After the Session has timed out (it will automatically time out after a certain interval when no new pages have been requested) or has been explicitly ended, a request to a page will create a new Session, Session_OnStart will fire and the user will be counted again.

To keep track of the total number of users that have visited your site since you started the Web server, you can increase a counter for each request a user makes. Let's call this counter TotalNumberOfUsers. You can store that counter in a variable in Application state, so you can retrieve and display it on other pages in your site. You can also create a second counter, called CurrentNumberOfUsers for example, that counts the number of active Sessions on your server. Just as with TotalNumberOfUsers, you increase the value of this counter whenever a new Session is started. However, you should decrease its value again when the Session ends. so you can keep track of the number of users that are currently visiting your site.

Besides storing these values in the Application object, you can also write them to a text file. When your server is restarted, code in the global.asa file will read in the old values from the text file, so your counters will continue with the values they had before the restart.

Let's take a look at how you can accomplish all this:

Start by creating a file called global.asa (note that the extension is different from ordinary ASP pages) and save it in the root of your Web site. Open the file in Notepad or in your favorite editor, and make sure it's completely empty (it shouldn't contain any ASP or HTML tags). Add the following ASP code to the file:

This code defines the skeleton for the two methods that fire when a new Session is started and when a Session ends. You can add the code for the counters to these two Subs. To keep track of the total number of users and the current number of users, you'll need to add the following shaded lines of code that create two Application variables. Once the variables have been increased and stored in the Application object, the value for the total number of users is saved to a text file called Counter.txt in the root of your site:

When a user starts a new Session by requesting a page in your site, the code in the Session_OnStart event will fire. This code will lock the Application object temporarily, to prevent two users from writing to it at the same time. Then the Application variables TotalNumberOfUsers and CurrentNumberOfUsers are increased by one. Once they are increased, the Application is unlocked again, so it's available to other users.

The second block of code in the Session_OnStart event writes this value to a text file. The FileSystemObject is used to create the file, using its CreateTextFile method. This method expects two parameters: the name of the text file (created by using Server.MapPath and appending Counter.txt to it) and a boolean indicating whether the file can be overwritten if it already exists. In this example True is passed, so you'll end up with a new file each time the Session_OnStart event fires. This way, you can be sure you always have just a single line of text in this file, because the old one is overwriiten.
Once the file is created and opened, the Write method of the TextStream object is used to write the value of the counter to the text file. When that is done, the file is closed and all objects are set to Nothing to clean up resources.

Notice that just the value of the TotalNumberOfUsers counter is written to the text fiile. There is no need to store the current number of users; after all, when the Web server is restarted, there are no current users yet.

To decrease the counter for the CurrentNumberOfUsers, you'll need to add some code to the Session_OnEnd event, that will fire when a Session times out, or when it is explicitly ended. You should just decrease the value for CurrentNumberOfUsers, and leave TotalNumberOfUsers untouched. Add the following shaded lines of code to the Session_OnEnd event in your global.asa file:

Whenever a Session is ended, the value of CurrentNumberOfUsers is decreased by one. This way, its value will always reflect the number of users that are browsing your site right now.

Reading the Counter When the Web Server Starts

As long as the Web server keeps running, this code will run fine. For each new Session that is created, the counters are increased by one and the value of TotalNumberOfUsers is written to the file. If, however, the Web server stops unexpectedly, or your restart or reboot the Web server yourself, the values for TotalNumberOfUsers and CurrentNumberOfUsers are lost. But because the value for TotalNumberOfUsers has also been stored in a text file, it's easy to retrieve the counter again from that file when the Web server starts. To read in the value from the Counter.txt file, you'll need to add some code to the Application_OnStart event that is also defined in the global.asa. Add the following code to the end of the global.asa file, right before the closing </script> tag:

The code looks a bit complicated, but it's actually rather simple. The FileSystemObject is used again to see if the counter file exists. If it doesn't, the code simply does nothing. If it does exist, a TextStream object reads the first line from the file into a string called Result. If the line contained some text (the Len of the string Result is greater than zero) this line of text is split into two elements. If you look at the code that writes to the file in the beginning of this article, you can see that the word TOTAL, then a Tab and then the value are written to the file. Since all you're interested in is the value for the counter, you'll need to split the line in two elements; both sides of the Tab character. If the UBound (or Upper Bound, the index of the greatest element in the array) of ArrResults equals 1 (this means two elements, item 0 and item 1) you can be sure you read in a valid line. The second element, ArrResults(1), is then used as the new value for the Application variable TotalNumberOfUsers.

It would have been easier to leave out the TOTAL in the text file, so there is no need to split the line of text you retrieved from the file. I did include it in this example though, because it can be useful if you want to store multiple counters in the same text file. This way, you can save individual counters as TOTALUSERS, TOTALDOWNLOADS and so on all in the same file, while you can still see which value means what.

At the end, the file is closed and the objects are cleaned up again, just as in the code for the Session_OnStart event.

Testing it Out

To test out your hit counter, create a new ASP file and call it Counter.asp. You can save it anywhere in your site. Add the following ASP code to that page:

These two lines of code write out the total number of visitors and the current number of visitors. Open the page in your browser and you'll see there is one current user. Also, the total number of users is 1. Open another browser (don't use Ctrl+N, but start a fresh instance or use an entirely different brand of browser) and open the counter page. You'll see there are two current users, and two users in total.
Next, restart your Web server. If you are using IIS, you can choose Restart IIS... from the All Tasks context menu for your Web server in the IIS Management Console.
Open Counter.asp again. You'll see that currently you're the only user browsing the site, but the total number of users has maintained its value.

Summary

This article demonstrated how to create a hit counter that keeps track of the current and total number of users to your site. It stores these variables in Application state so they are available in each page in your Web site. It also stores the value for the total number of users in a text file so its value won't be lost when the Web server restarts.

A disadvantage of using text files is that it's difficult to scale out your Web site to lots of users. Only one user has access to the file at any given moment, so if you have a real busy site, you'll soon run into problems.
Check out the following article to see how you can improve the counter page even further by using a database instead of a text file.

• Howto Create a Hit Counter Using a Database (http://Imar.Spaanjaars.Com/165/howto-create-a-hit-counter-using-a-database)

Related Articles

• When Sessions End - Once And For All! at www.asp101.com (http://www.asp101.com/articles/john/sessionsend/default.asp)

References

• ASP Session Object (http://msdn.microsoft.com/library/default.asp?url=/library/en-us/iissdk/html/050e0924-fd83-45e7-b105-50710538d6c1.asp)
• ASP Application Object (http://msdn.microsoft.com/library/default.asp?url=/library/en-us/iissdk/html/925aacf6-ea4f-423a-984c-414a68d91f1f.asp)
• FileSystemObject (http://msdn.microsoft.com/library/default.asp?url=/library/en-us/script56/html/sgprogrammingfilesystemobject.asp)
• How to Configure an ASP Web Application (and Enable Session State) (http://support.microsoft.com/?kbid=324278#4)

Download Files

• Source Code for this Article
  (http://Imar.Spaanjaars.Com/Downloads/Articles/HitCounterInTextFile.zip)