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Date:   Thu, 29 Jun 2000 12:46:28 GMT
Reply-To:   abushmakin@ARGOSE.COM
Sender:   "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:   abushmakin@ARGOSE.COM
Organization: - Before you buy.
Subject:   Re: API function equivalent to 'start' DOS command?

This is the example for VB, may be it will help.

Andrew Bushmakin ****************************** HOWTO: Launch a Win32 Application from Visual Basic Last reviewed: November 24, 1997 Article ID: Q129797 The information in this article applies to: Standard, Professional, and Enterprise Editions of Microsoft Visual Basic, 32-bit only, for Windows, version 4.0

SUMMARY A Windows application can consist of more than one process, and a process can consist of more than one thread. The Microsoft Win32 application program interface (API) supports multitasking, which creates the effect of simultaneous execution of multiple processes and threads. This article describes processes and threads, and explains how to create and use them from Microsoft Visual Basic version 4.0, with a step-by-step example.

MORE INFORMATION A process is a program that is loaded into memory and prepared for execution. Each process has a private virtual address space. A process consists of the code, data, and other system resources such as files, pipes, and synchronization objects that are accessible to the threads of the process. Each process is started with a single thread, but additional independently executing threads can be created.

A thread can execute any part of the program's code, including a part executed by another thread. Threads are the basic entity to which the operating system allocates CPU time. Each thread maintains a set of structures for saving its context while waiting to be scheduled for processing time. The context includes the thread's set of machine registers, the kernel stack, a thread environment block, and a user stack in the address space of the thread's process. All threads of a process share the virtual address space and can access the global variables and system resources of the process.

A multitasking operating system divides the available CPU time among the threads that need it. In Windows, the Win32 API is designed for preemptive multitasking; this means that the system allocates small slices of CPU time among the competing threads. The currently executing thread is suspended when its time slice elapses, allowing another thread to run. When the system switches from one thread to another, it saves the context of the suspended thread and restores the saved context of the next thread in the queue.

Because each time slice is small (approximately 20 milliseconds), it appears that multiple threads are executing at the same time. This is actually the case on multiprocessor systems where the executable threads are distributed among the available processors. On a single processor system, however, using multiple threads does not result in more instructions being executed. In fact, the system can slow down if it is forced to keep track of too many threads.

How to Launch Win32 Applications from Visual Basic There are two ways to launch another Win32 application from a Microsoft Visual Basic version 4.0 application:

Use the Visual Basic shell command. This spawns a new process and returns its process ID. However, to be able to do anything useful, a process handle is required, which can be obtained by a subsequent call to the OpenProcess Win32 API function. Use the CreateProcess Win32 API function that creates both a process object and a main thread object. Both the process and the initial thread are assigned a 32-bit identifier that remains valid until the respective object (process or thread) terminates. The 32-bit identifier can be used to uniquely identify the object within the system. The new process and new thread handles are also created with full access rights. All these four values are returned in the PROCESS_INFORMATION structure that is passed by reference to CreateProcess.

The process handle returned by either of the two methods can then be used with other Win32 APIs such as TerminateProcess to manipulate the newly launched application. It is important to understand that at creation time, the system gives each object an initial usage count of one. Then, just before CreateProcess returns, the function opens both the process and the thread object and places the process-relative handles for each in the hProcess and hThread members of the PROCESS_INFORMATION structure.

When CreateProcess opens these objects, the usage count for each increments to two. This means that before the Windows NT Executive can free the process object, the process must terminate (decrementing the usage count to one) and the parent process must call CloseHandle (decrementing the usage count to zero). To free the thread object, the thread must terminate and the parent process must close the handle to the thread object.

CAUTION: It is very important to close these handles. Failure to do so can result in a system memory leak because some Windows NT Executive objects are never destroyed.

Similar considerations are required when obtaining a process handle with OpenProcess. In this case too, the usage count is incremented by one, and unless the handle is closed, the process object will remain in memory even when the process itself has terminated.

Step-by-Step Example

Start a new project in Visual Basic. Form1 is created by default.

Add the following code to the General Declarations section of Form1: Private Type PROCESS_INFORMATION

hProcess As Long hThread As Long dwProcessId As Long dwThreadId As Long

End Type Private 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

Private Declare Function CreateProcess Lib "kernel32" Alias _ "CreateProcessA" (ByVal lpApplicationName As String, ByVal _ lpCommandLine As String, lpProcessAttributes As Any, _ lpThreadAttributes As Any, ByVal bInheritHandles As Long, _ ByVal dwCreationFlags As Long, lpEnvironment As Any, ByVal _ lpCurrentDriectory As String, lpStartupInfo As STARTUPINFO, _ lpProcessInformation As PROCESS_INFORMATION) As Long

Private Declare Function OpenProcess Lib "kernel32.dll" (ByVal _ dwAccess As Long, ByVal fInherit As Integer, ByVal hObject _ As Long) As Long

Private Declare Function TerminateProcess Lib "kernel32" (ByVal _ hProcess As Long, ByVal uExitCode As Long) As Long

Private Declare Function CloseHandle Lib "kernel32" (ByVal _ hObject As Long) As Long


Add the following code to the Form1_Click event: Dim pInfo As PROCESS_INFORMATION Dim sInfo As STARTUPINFO Dim sNull As String

sInfo.cb = Len(sInfo) success& = CreateProcess(sNull, "Calc.exe", ByVal 0&, ByVal 0&, 1&, NORMAL_PRIORITY_CLASS, ByVal 0&, sNull, sInfo, pInfo)

MsgBox "Calculator has been launched!"

ret& = TerminateProcess(pInfo.hProcess, 0&) ret& = CloseHandle(pInfo.hThread) ret& = CloseHandle(pInfo.hProcess)

MsgBox "Calculator has terminated!"

Press the F5 key to run the program. Click Form1. The Windows Calculator program launches, and a message tells you so. When you click the OK button on the MsgBox, the Calculator program terminates, and another message tells you so.

To see how this method works using the Shell and OpenProcess method, change the commented code into executed code, change the rest of the code into comments except for the two MsgBox statements. Keywords : APrgOther vb432 VB4WIN Version : WINDOWS:4.0 Platform : WINDOWS Issue type : kbhowto


In article <8jeve4$qe4$>, wrote: > I'm looking for an API function equivalent to the 'start' MS-DOS > command: > > start c:\image.bmp > > WinExec is not appropriate, > CreateProcess is hard but appropiate??? > > Sent via > Before you buy. >

Sent via Before you buy.

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