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Sequential File Input (Variables)

• To read variables from a sequential file, we essentially reverse the write procedure. First, open the file using:

Open SeqFileName For Input As #N

where N is an integer file number and SeqFileName is a complete file path. The file is closed using:

Close N

• The Input statement is used to read in variables from a sequential file. The format is:

Input #N, [variable list]

The variable names in the list are separated by commas. If no variables are listed, the current line in the file N is skipped.

• Note variables must be read in exactly the same manner as they were written. So, using our previous example with the variables A, B, C, and D, the appropriate statements are:

Input #1, A, B, C
Input #1, D

These two lines read the variables A, B, and C from the first line in the file and D from the second line. It doesn’t matter whether the data was originally written to the file using Write or Print (i.e. commas are ignored).

Quick Example: Reading Variables from Sequential Files

  1. Start a new project or simply modify the previous quick example.

  2. Attach the following code to the Form_Load procedure. This code reads in files created in the last quick example.

    Private Sub Form_Load()
    Dim A As Integer, B As String, C As Single, D As Integer
    Open "Test1.Txt" For Input As #1
    Input #1, A, B, C
    Debug.Print "A="; A
    Debug.Print "B="; B
    Debug.Print "C="; C
    Input #1, D
    Debug.Print "D="; D
    Close 1
    End Sub

    Note the Debug.Print statements and how you can add some identifiers (in quotes) for printed information.

  3. Run the program. Look in the debug window and note the variable values. Save the application, if you want to.

  4. Rerun the program using Test2.Txt as in the input file. What differences do you see? Do you see the problem with using Print and string variables? Because of this problem, I almost always use Write (instead of Print) for saving variable information to files. Edit the Test2.Txt file (in Notepad), putting quotes around the words Visual Basic. Rerun the program using this file as input - it should work fine now.


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