Q267925: PRB: Opening Binary File for Input Returns Only One Character

Article: Q267925
Product(s): Microsoft Visual Basic for Windows
Version(s): 3.0
Operating System(s): 
Keyword(s): kbOSWinCEsearch kbGrpDSVB kbDSupport kbVBM300
Last Modified: 17-AUG-2001

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The information in this article applies to:

- Microsoft eMbedded Visual Basic, version 3.0 
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SYMPTOMS
========

In an eMbedded Visual Basic application, if you open a file in Binary mode and
use the Input function to read the file, only one character is returned,
regardless of how many characters you specified.

CAUSE
=====

When you use the Put method to write data to a file, the data is implicitly
written as Variant data. Because it is Variant data and must be able to be read
back in from the file, the Put method parses the Variant data to determine what
kind of data it is and how big it is. This information is written out to the
file along with the data; thus, according to the illustration in the "More
Information" section, the type of data is VT_BSTR (0800) and the length is 5
bytes (0005).

If you use the Input method to read the data back in, when you specify the number
of bytes to read, and you get whatever is there. According to the scenario in
the "More Information" section, you read 5 bytes, which consist of the 4 byte
header in the BSTR structure and the letter "T." The Input method does not allow
you to specify the number of bytes to read; instead, you provide a list of
Variant variables, and it decodes for you.

RESOLUTION
==========

To read what you just wrote out, use the Get method instead of the Input method.
To do this, replace the following line in the "More Information" section

  result = File1.Input(5)

with this line:

  File1.Get result

STATUS
======

This behavior is by design.

MORE INFORMATION
================

Steps to Reproduce Behavior
---------------------------

1. Start a new Windows CE project in eMbedded Visual Basic. Form1 is created by
  default.

2. From the Project menu, click Components, and then select the "Microsoft CE
  File System Control" check box.

3. Place a list box, a command button, a file system control, and a file control
  on Form1.

4. Paste the following code into Form1:

  Private Sub Command1_Click()
    Dim result
    File1.Open "Binary.txt", fsModeBinary
    File1.Put "Test1"
    File1.Put "Test2"
    File1.Close
    File1.Open "Binary.txt", fsModeBinary
    result = File1.Input(5)
    File1.Close
    List1.AddItem result
    FileSystem1.Kill "Binary.txt"
  End Sub

5. Click the command button. All that is returned to the ListBox is a small
  white box.

Additional query words: evb fso filesystemobject

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Keywords          : kbOSWinCEsearch kbGrpDSVB kbDSupport kbVBM300 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword2 kbVBeMbSearch kbVBeMb300
Version           : :3.0
Issue type        : kbprb

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