Put Statement Allows Writing Beyond End of File (108385)

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Microsoft provides programming examples for illustration only, without warranty either expressed or implied. This includes, but is not limited to, the implied warranties of merchantability or fitness for a particular purpose. This article assumes that you are familiar with the programming language that is being demonstrated and with the tools that are used to create and to debug procedures. Microsoft support engineers can help explain the functionality of a particular procedure, but they will not modify these examples to provide added functionality or construct procedures to meet your specific requirements. You can use the Put statement to place data in a file at a specified location. However, when you write data beyond the end of a file, the gap between the end of file and the starting point of new data is filled with random data.

In order to see this behavior, you must first create a sample file. Follow these steps to create a sample file:

1. On the Start Menu, point to Programs, point to Accessories, and then click Notepad.
2. Type ABC into the blank Notepad document.
3. Click Save on the File Menu. In the Save As dialog box, open the My Documents folder. Then, type Test in the File name box, and click Save.
4. On the File menu, click Exit.
   
   This creates a file called Test.txt in the My Documents folder.

Next, create a Visual Basic for Applications procedure to illustrate the behavior discussed in this article.

1. Close and save any open workbooks, and then open a new workbook.
2. Start the Visual Basic Editor (press ALT+F11).
3. On the Insert menu, click Module.
4. In the module type the following code:

   Type Test_Record
        Test As String * 7
      End Type
   
      Sub PutTest()
        Dim P As Test_Record
        Dim filenum As Integer
   
        filenum = FreeFile()
   
        'Open the file you created.
        Open "c:\My Documents\Test.txt" For Random As filenum Len = Len(P)
   
          P.Test = "Testing"
   
          'Write a record to the file.
          Put #filenum, 2, P
   
        'Close the file.
        Close #filenum
      End Sub
   
   						

5. Run the PutTest macro.
6. Open the file Text.txt in Notepad.

Note that random data is written between the entry that you made in the file and Testing, which is the record that the PutTest macro wrote to the file. For additional information about Working with Random Access Files, please see the following article in the Microsoft Knowledge Base: