* VB-CODE (1)
Tip 173: Launching Applications in Visual Basic

December 5, 1995

Abstract
This article explains how to control the way in which a launched
Microsoft? Visual Basic? application is run.

Using the CreateProcess Function to Launch Applications
Under the Microsoft? Windows? 95 operating system, you can use the Windows
application programming interface (API) CreateProcess function to load and
run any application (or process) you want. Using this function, you have
complete control over how the launched application is run.

To use the CreateProcess function, add the following Declare statement to
the General Declarations section of your Microsoft Visual Basic? project
or to a BAS module:

Declare Function CreateProcessA Lib "kernel32" (ByVal lpApplicationName As Long,
   ByVal lpCommandLine As String, ByVal lpProcessAttributes As Long, ByVal
   lpThreadAttributes As Long, ByVal bInheritHandles As Long, ByVal
   dwCreationFlags As Long, ByVal lpEnvironment As Long, ByVal
   lpCurrentDirectory As Long, lpStartupInfo As STARTUPINFO,
   lpProcessInformation As PROCESS_INFORMATION) As Long

As you can see, the CreateProcess function requires ten arguments, as
follows:

lpApplicationName     The name of the process you want to launch.
LpCommandLine         The command line to be passed to the launched
                      process.
LpProcessAttributes   Points to a SECURITY_ATTRIBUTES structure for the
                      created process.
LpThreadAttributes    Points to a SECURITY_ATTRIBUTES structure for the
                      primary thread of the created process.
BInheritHandle        If True, the created process inherits handles from
                      the calling application.
DwCreationFlags       A combination of one or more creation flags for
                      controlling the priority class and the creation
                      of the process.
LpEnvironment         Points to an environment block for the new process.
                      If set to NULL, the new process uses the calling
                      process's environment block.
LpCurrentDirectory    A string containing the drive and directory for the
                      new process. If NULL, the calling process's drive
                      and directory are used.
LpStartupInfo         A STARTUPINFO structure that specifies the
                      appearance of the main window for the new process.
LpProcessInformation  A PROCESS_INFORMATION structure that receives
                      identification information about the new process.

The example program below launches the Windows 95 Notepad application.
Note that you specify the complete path to Notepad and launch the
application as a normal process (NORMAL_PRIORITY_CLASS).

After you call the CreateProcess function to launch the Notepad
application, notice that Notepad retains the focus. You cannot switch
to another running application. This is accomplished by executing the
Windows API WaitForSingleObject function.

The WaitForSingleObject function forces the system to wait until a
specific process has finished its work. You pass the handle of the
process you want to wait for and the length of time, in milliseconds,
to pause. In the example program below, the time-out value is set to
INFINITE, which means that the system will not resume running until
the user has quit Notepad.

The final step you must perform, after the user has quit Notepad, is to
close the open handle for the just-launched process. This removes all
references to Notepad having been launched.

Example Program
This program shows how to launch a Windows or MS-DOS? application from
within Microsoft Visual Basic. Control remains with the launched
application until you quit that application.

 1. Create a new project in Visual Basic. Form1 is created by default.
 2. Add a Command Button control to Form1. Command1 is created by default.
 3. Add the following code to the Click event for Command1:

Private Sub Command1_Click()
    Dim AppToLaunch As String
    AppToLaunch = "c:\windows\notepad.exe"
    Call ExecuteAndWait(AppToLaunch)
End Sub

 4. Create a new subroutine called ExecuteAndWait. Add the following code
    to this subroutine:

Public Sub ExecuteAndWait(cmdline$)
    Dim NameOfProc As PROCESS_INFORMATION
    Dim NameStart As STARTUPINFO
    Dim X As Long

    NameStart.cb = Len(NameStart)
    X = CreateProcessA(0&, cmdline$, 0&, 0&, 1&, NORMAL_PRIORITY_CLASS,
       0&, 0&, NameStart, NameOfProc)
    X = WaitForSingleObject(NameOfProc.hProcess, INFINITE)
    X = CloseHandle(NameOfProc.hProcess)
End Sub

 5. From the Visual Basic Insert menu, select Module to add a new module
    to your project. Module1.Bas is created by default.
 6. Add the following code to Module1.Bas (note that each Declare
    statement must be typed as a single line of code):

Type STARTUPINFO
    cb As Long
    lpReserved As String
    lpDesktop As String
    lpTitle As String
    dwX As Long
    dwY As Long
    dwXSize As Long
    dwYSize As Long
    dwXCountChars As Long
    dwYCountChars As Long
    dwFillAttribute As Long
    dwFlags As Long
    wShowWindow As Integer
    cbReserved2 As Integer
    lpReserved2 As Long
    hStdInput As Long
    hStdOutput As Long
    hStdError As Long
End Type
Type PROCESS_INFORMATION
    hProcess As Long
    hThread As Long
    dwProcessID As Long
    dwThreadID As Long
End Type
Global Const NORMAL_PRIORITY_CLASS = &H20&
Global Const INFINITE = -1&

Declare Function CloseHandle Lib "kernel32" (hObject As Long) As Boolean
Declare Function WaitForSingleObject Lib "kernel32" (ByVal hHandle As Long,
   ByVal dwMilliseconds As Long) As Long
Declare Function CreateProcessA Lib "kernel32" (ByVal lpApplicationName As Long,
   ByVal lpCommandLine As String, ByVal lpProcessAttributes As Long, ByVal
   lpThreadAttributes As Long, ByVal bInheritHandles As Long, ByVal
   dwCreationFlags As Long, ByVal lpEnvironment As Long, ByVal
   lpCurrentDirectory As Long, lpStartupInfo As STARTUPINFO,
   lpProcessInformation As PROCESS_INFORMATION) As Long

Run the example program by pressing F5. Click the Command Button control.
This immediately starts the Windows Notepad application. Notice that you
are unable to switch to another running application until you quit Notepad.