VB3 Launch an App Based on File Extension Using ShellExecute

Article ID: Q126220
Creation Date: 16-FEB-1995
Revision Date: 09-JAN-1997

The information in this article applies to:

- Standard and Professional Editions of Microsoft Visual Basic for

  Windows, versions 2.0 and 3.0

SUMMARY

You can use the Windows API ShellExecute() function to start the application associated with a given document extension without knowing the name of the associated application. For example, you could start the Paintbrush program by passing the filename ARCADE.BMP to the ShellExecute() function.

MORE INFORMATION

The ShellExecute function opens or prints the specified file. Here is the declaration to use when calling this function from Visual Basic:

   ' Enter the following three lines as one, single line:
   Declare Function ShellExecute Lib "SHELL" (ByVal hwnd%, ByVal lpszOp$,
      ByVal lpszFile$, ByVal lpszParams$, ByVal lpszDir$,
      ByVal fsShowCmd%) As Integer

Here is a table providing descriptions for each parameter:

Parameter   Description

hwnd%       Identifies the parent window. This window receives any message
            boxes an application produces (for example, for error
            reporting).

lpszOp$     Points to a null-terminated string specifying the operation to
            perform. This string can be "open" or "print." If this
            parameter is NULL, "open" is the default value.

lpszFile$   Points to a null-terminated string specifying the file to open.

lpszParams$ Points to a null-terminated string specifying parameters

            passed to the application when the lpszFile parameter
            specifies an executable file. If lpszFile points to a
            string specifying a document file, this parameter is NULL.

lpszDir$    Points to a null-terminated string specifying the default
            directory.

fsShowCmd% Specifies whether the application window is to be shown when

            the application is opened. This parameter can be one of the
            values described in the API ShowWindow().

Step-by-Step Example

The following example demonstrates how to start an application or load a document into its associated application. The Windows API ShellExecute() function is different from the Visual Basic Shell() function in that you can pass the ShellExecute() function the name of a document and it will launch the associated application, and then pass the filename to the application.

Start a New Project in Visual Basic (ALT, F, N), Form1 is created by default.

Add the following code to the general declarations section of Form1:
Option Explicit Const SW_SHOWNORMAL = 1 ' Enter the following declaration on one single line Declare Function ShellExecute Lib "SHELL" (ByVal hwnd%, ByVal lpszOp$,
```
      ByVal lpszFile$, ByVal lpszParams$, ByVal lpszDir$,
      ByVal fsShowCmd%) As Integer
```
Declare Function GetDesktopWindow Lib "USER" () As Integer

Add the following procedure to the general declarations section of Form1:

Function StartDoc (DocName As String) As Integer

      Dim Scr_hDC As Integer
      Scr_hDC = GetDesktopWindow()
      StartDoc=ShellExecute(Scr_hDC,"Open",DocName,"","C:\",SW_SHOWNORMAL)

End Function

Place the following code in the Form_Click event of Form1:
Sub Form_Click ()
```
      Dim r As Integer
      r = StartDoc("C:\WINDOWS\ARCADE.BMP")
```
End Sub

General Information About the Process

The return value for the StartDoc() function is the same as for the Shell() function. It is the Windows instance handle of the application that was started.

The ShellExecute() function returns the value 31 if there is no association for the specified file type or if there is no association for the specified action within the file type. Other error values are:

Error     Meaning

 0        System was out of memory or executable file was corrupt.

 2        The file was not found.

 3        The path was not found.

 5        Attempt was made to link to a task dynamically, or there
          was a sharing or network-protection error.

 6        Library required separate data segments for each task.

 8        There was insufficient memory to start the application.

10        The Windows version was incorrect.

11        The executable file was invalid. Either it was not a Windows-
          based application or there was an error in the .EXE image.

12        Application was designed for a different operating system.

13        Application was designed for MS-DOS version 4.0.

14        Type of executable file was unknown.

15        Attempt was made to load a real-mode application that was
          developed for an earlier version of Windows.

16        Attempt was made to load a second instance of an executable
          file containing multiple data segments not marked read-only.

19        Attempt was made to load a compressed executable file. The
          file must be decompressed before it can be loaded.

20        Dynamic-link library (DLL) file was invalid. One of
          the DLLs required to run this application was corrupt.

21        Application requires Microsoft Windows 32-bit extensions.

REFERENCES

"Programmer's Reference, Volume 2: Functions" of the Microsoft Windows Software Development Kit (SDK), pages 901-904.

ShellExecute topic of the Windows 3.1 SDK Help file.

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