Before You Start

You should also read Section I before you embark on this section.

Detecting The End of a File

Visual Basic provides us with the EOF function. It takes the unique ID of an open file (from here on, we will call this a file handle, like in the real world) as a parameter, and returns either True or False. We use it like this:

   EOF(file handle)

With this info, we could write a little program that reads all the lines in a file, on at a time, testing if we've reached the end-of-file for each line. It would look like this:

   Dim Data As String

   Open "C:\Windows\My File.txt" For Input As #1
      If Not EOF(1) Then Line Input #1, Data: Debug.Print "Line 1: " & Data
      If Not EOF(1) Then Line Input #1, Data: Debug.Print "Line 2: " & Data
      If Not EOF(1) Then Line Input #1, Data: Debug.Print "Line 3: " & Data
      If Not EOF(1) Then Line Input #1, Data: Debug.Print "Line 4: " & Data
   Close #1

... and so on. Try this on a 1 or 2 line file, and you will notice that it doesn't do any reading after the last line in the file.

Reading Entire Files

   Dim Data As String

   Open "C:\Windows\My File.txt" For Input As #1
      Do While Not EOF(1)
         Line Input #1, Data: Debug.Print "Line X: " & Data
      Loop
   Close #1

If you chose to read a large file, you will see the Debug Window being flooded with lines of text, all of them saying Line X:.

Let's do something else for a change. How about counting the lines in the file? If we want to do that, we need a new variable; the counter.

   Dim Counter As Long

In this code, we won't print the Data to the Debug Window, we'll only print the line count.

   Dim Data As String
   Dim Counter As Long

   Open "C:\Windows\My File.txt" For Input As #1
      Do While Not EOF(1)
         Line Input #1, Data: Counter = Counter + 1
      Loop
   Close #1

   Debug.Print "Line count: " & Counter

The line Counter = Counter + 1 increases the line count with 1 each time we read a line. When the code is run, you will only see one line in the Debug Window; the line saying Line count: n.

Reading Record-Style Files

The answer is simple. We use the Do...Loop structure from earlier, but instead of reading 1 line inside the loop, we read as many lines as the record contains fields. In our example, we have a record consisting of three fields: Firstname, Lastname, and Age.

We also use a counter to keep count of the records.

   Dim Firstname As String
   Dim Lastname As String
   Dim Age As String

   Dim Counter As Long

   Open "C:\Windows\My File.txt" For Input As #1
      Do While Not EOF(1)
         Counter = Counter + 1
         Debug.Print "Record#: " & Counter

         Line Input #1, Firstname: Debug.Print "Firstname: " & Firstname
         Line Input #1, Lastname: Debug.Print "Lastname: " & Lastname
         Line Input #1, Age: Debug.Print "Age: " & Age
      Loop
   Close #1

To try this example, you need a file where the data is arranged in groups of three lines. If you wish, you can download one here (hold down Shift. If not, you will see it on screen). Remember to modify the filename to Records.txt instead of My File.txt -- you choose the folder.

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