Sometimes you may need to store and retrieve information but do no need the power of a spreadsheet or database. (not to mention the extra coding, configuration and support files that go along with it.) In these cases a text file may be just the thing you need. The process of storing and retrieving information is simple, and the file can be edited by anyone - even if that person doesn't have a spreadsheet/database tool.

Let's have a look first at reading from a sequential text file.
Let's say we have a text file containing a list of standard layers that we would like to import into AutoCAD.
Here's what we would need to do :

1.    Open the file for input.
2.    Read a line from the file and store it in a variable.
3.    Add the contents of the variable to a list box.
4.    Repeat steps 2 and 3 for each line in the file.
5.    Close the file.

O.K. first let's create our text file. Open Notepad and enter these layer names :

Annotations
Architectural
Beers
Border
Civil
Dimensions
Electrical
Existing
Instrumentation
Mechanical
Piping
Steel
Text

Now save this file as Layer.txt, ensuring that it is within your support path.

Now open a new Project and Userform. Place a Listbox on the form keeping the default name.
In the Userform Initialize event procedure, place the following code :

'CODING STARTS HERE

Private Sub UserForm_Initialize()

Dim sTemp As String

'clear listbox
ListBox1.Clear

'open the text file
Open "Layer.txt" For Input As #1

    'until the end of file
    While Not EOF(1)

        'read the line and store it in a variable
        Line Input #1, sTemp

        'display in the list box
        ListBox1.AddItem sTemp

    'loop
    Wend

'close the file
Close #1

End Sub

'CODING ENDS HERE

Run the Project. You Listbox should look like this :

In the preceding example, 1 is the file number. However, if you open and close multiple files throughout your program, using this number might not be a good idea. In that case, you should use the "FreeFile" function. I've re-written the coding below to include this function as well as some basic error trapping :

'CODING STARTS HERE

Private Sub UserForm_Initialize()

Dim sTemp As String
Dim nFile As Integer

On Error GoTo err_handler

'get the next free file number
nFile = FreeFile

'clear listbox
ListBox1.Clear

'open the text file
Open "Layer.txt" For Input As #nFile

    'until the end of file
    While Not EOF(nFile)

        'read the line and store it in a variable
        Line Input #nFile, sTemp

        'display in the list box
        ListBox1.AddItem sTemp

'loop
Wend

'close the file
Close #nFile

Exit Sub

err_handler:

MsgBox Err.Number & " " & Err.Description
Err.Clear
Exit Sub

End Sub

'CODING ENDS HERE

To write data, you open the file for sequential output or append. Have a look at the following two lines of code, each of which opens a file for output :

'output mode - always creates a new file, erases any existing information
Open "DwgLog.txt" for Output as #nFile

'append mode - adds to an existing file or creates one
Open "DwgLog.txt" for Append as #nFile

Append mode means data written to a file is added to the end of existing data. Opening a file for Output means that any existing data will be erased. In either case the Open statement automatically creates the file if it does not exist.

Have a look at the following coding that when you run it, will write a Log file containing the date, time and Drawing Number :

'CODING ENDS HERE

Sub DrgLog ()

Dim nFile1 As Integer
Dim Dname As String

On Error GoTo err_handler

'retrieve the drawing name
Dname = ThisDrawing.GetVariable("DWGNAME")

'get the next free file number
nFile1 = FreeFile

'open the file to append to
Open "DrgLog.txt" For Append As #nFile1

'write to the file
Print #nFile1, Format$(Now, "mm-dd-yy hh:mm:ss") & " - " & Dname

'close the file
Close #nFile1

Exit Sub

err_handler:

MsgBox Err.Number & " " & Err.Description
Err.Clear
Exit Sub

End Sub

'CODING ENDS HERE

DrgLog.txt should have been created in your working directory. Open it and have a look. It should look something like this :

11-02-01 09:57:20 - X3481.dwg
11-02-01 19:57:21 - X3482.dwg
11-02-01 14:40:20 - K2341.dwg
11-02-01 15:21:40 - K3418.dwg

Every time the routine is run, the date, time and Drawing Number is added to the file. (Hey, we could make a good drawing log file out of this?)

On the next page we'll have a look at opening and searching a text file for multiple instances of information required for a program to run.