Tip 125: Retrieving a Compressed File's Original Name

July 1, 1995

Abstract

When designing a Microsoft® Visual Basic® application, you may need to use an installation program to compress and decompress files needed by your program. This article explains how to retrieve the original file name of a compressed file.

Using the GetExpandedName API Function

The MS-DOS® COMPRESS.EXE program allows you to compress one or more files on disk. Compressed files take up less space on your disk, and they are typically used to create installation programs.

The Microsoft® Windows®-based LZEXPAND.DLL function library contains several routines to open, close, read, and write compressed files. However, you need to first determine the file's original, uncompressed name.

The Windows application programming interface (API) function GetExpandedName can retrieve the original name of a compressed file. Compressed files are stored on disk with the last character in the file name extension set to an underscore ("_") character. When you run the COMPRESS.EXE program, you have the option of using the "/r" command line parameter. This command line parameter tells COMPRESS.EXE to create the file with an underscore character as the last character in the file name.

To use the GetExpandedName function in a Microsoft Visual Basic® application, add the following Declare statement to the General Declarations section of your form (note that this Declare statement must be typed as a single line of code):

Private Declare Function GetExpandedName Lib "LZEXPAND.DLL" (ByVal lpszSource 
   As String, ByVal lpszBuffer As String) As Integer

The GetExpandedName function requires two arguments, as follows.

After this function is called, a value greater than zero will be returned if the operation was successful. If the function was not successful, a negative value will be returned.

Example Program

This program shows how to retrieve the full name of a file that was previously compressed by the COMPRESS.EXE program.

1. Create a new project in Visual Basic. Form1 is created by default.
   
   
2. Add the following Declare statement to the General Declarations section of Form1 (note that this Declare statement must be typed as a single line of code):

   Private Declare Function GetExpandedName Lib "LZEXPAND.DLL" (ByVal lpszSource 
      As String, ByVal lpszBuffer As String) As Integer
   

3. Add a Text Box control to Form1. Text1 is created by default.
   
   
4. Add a Command Button control to Form1. Command1 is created by default.
   
   
5. Add the following code to the Click event for Command1:

   Private Sub Command1_Click()
       Dim Temp As String
       Dim X As Integer
       
       Text1.Text = ""
       Temp = Space$(128)
       X = GetExpandedName("C:\TEMP\MYFILE.DL_", Temp)
       Text1.Text = "Filename: " & Temp
   End Sub
   

Note   This program assumes that you have a previously compressed file called MYFILE.DL_ stored in the C:\TEMP directory.

Run the example program by pressing F5. Click the command button. The full name of the compressed file will be displayed in the Text Box control.

Additional Reference

Knowledge Base Q93426. "Use COMPRESS-r to Avoid Error: Could not execute: SETUP1.EX2."