Q173085: HOWTO: Create a Process for Reading and Writing to a Pipe
Article: Q173085
Product(s): Microsoft Visual Basic for Windows
Version(s): WINDOWS:4.0,5.0,6.0
Operating System(s):
Keyword(s):
Last Modified: 11-JAN-2001
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The information in this article applies to:
- Microsoft Visual Basic Professional Edition for Windows, version 6.0
- Microsoft Visual Basic Enterprise Edition for Windows, version 6.0
- Microsoft Visual Basic Control Creation Edition for Windows, version 5.0
- Microsoft Visual Basic Enterprise Edition for Windows, version 5.0
- Microsoft Visual Basic Professional Edition, 32-bit, for Windows, version 4.0
- Microsoft Visual Basic Enterprise Edition, 32-bit, for Windows, version 4.0
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SUMMARY
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This example illustrates a Visual Basic application starting another process
with the purpose of redirecting that process's standard IO handles. The Visual
Basic application redirects the created process's standard output handle to an
anonymous pipe, then proceeds to read the output through the pipe. This sample
just redirects STDOUT of the new process. To redirect other handles (STDIN and
STDERR), create a pipe for each handle for which redirection is desired. The
Visual Basic application would read from the read ends of the pipes for the
redirected STDOUT and STDERR. If STDIN redirection was desired, the Visual Basic
application would write to the write end of the appropriate pipe. An example
follows:
'A pipe for redirection of STDOUT
CreatePipe(hReadPipe1, hWritePipe1, sa, 0)
'A pipe for redirection of STDERR
CreatePipe(hReadPipe2, hWritePipe2, sa, 0)
'A pipe for redirection of STDIN
CreatePipe(hReadPipe3, hWritePipe3, sa, 0)
'Preparing to start the process with redirected handles
start.hStdOutput = hWritePipe1
start.hStdError = hWritePipe2
start.hStdInput = hReadPipe3
'Reading output from the started process's STDOUT
ReadFile(hReadPipe1, mybuff1, 100, bytesread, ByVal 0&)
'Reading output from the started process's STDERR
ReadFile(hReadPipe2, mybuff2, 100, bytesread, ByVal 0&)
'Writing to the started process's STDIN
WriteFile(hWritePipe3, mybuff3, 100, byteswritten, ByVal 0&)
MORE INFORMATION
================
1. Start a new project in Visual Basic. Form1 is created by default.
2. Add the following code to the General Declarations section of Form1:
Option Explicit
Private Declare Function CreatePipe Lib "kernel32" ( _
phReadPipe As Long, _
phWritePipe As Long, _
lpPipeAttributes As Any, _
ByVal nSize As Long) As Long
Private Declare Function ReadFile Lib "kernel32" ( _
ByVal hFile As Long, _
ByVal lpBuffer As String, _
ByVal nNumberOfBytesToRead As Long, _
lpNumberOfBytesRead As Long, _
byval lpOverlapped As Any) As Long
Private Type SECURITY_ATTRIBUTES
nLength As Long
lpSecurityDescriptor As Long
bInheritHandle As Long
End Type
Private Type STARTUPINFO
cb As Long
lpReserved As Long
lpDesktop As Long
lpTitle As Long
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 Type PROCESS_INFORMATION
hProcess As Long
hThread As Long
dwProcessID As Long
dwThreadID As Long
End Type
Private Declare Function CreateProcessA Lib "kernel32" (ByVal _
lpApplicationName As Long, ByVal lpCommandLine As String, _
lpProcessAttributes As Any, lpThreadAttributes As Any, _
ByVal bInheritHandles As Long, ByVal dwCreationFlags As Long, _
ByVal lpEnvironment As Long, ByVal lpCurrentDirectory As Long, _
lpStartupInfo As Any, lpProcessInformation As Any) As Long
Private Declare Function CloseHandle Lib "kernel32" (ByVal _
hObject As Long) As Long
Private Const NORMAL_PRIORITY_CLASS = &H20&
Private Const STARTF_USESTDHANDLES = &H100&
Private Sub ExecCmd(cmdline$)
Dim proc As PROCESS_INFORMATION, ret As Long, bSuccess As Long
Dim start As STARTUPINFO
Dim sa As SECURITY_ATTRIBUTES, hReadPipe As Long, hWritePipe _
As Long
Dim bytesread As Long, mybuff As String
Dim i As Integer
mybuff = String(256, Chr$(65))
sa.nLength = Len(sa)
sa.bInheritHandle = 1&
sa.lpSecurityDescriptor = 0&
ret = CreatePipe(hReadPipe, hWritePipe, sa, 0)
If ret = 0 Then
MsgBox "CreatePipe failed. Error: " & Err.LastDllError
Exit Sub
End If
start.cb = Len(start)
start.dwFlags = STARTF_USESTDHANDLES
start.hStdOutput = hWritePipe
' Start the shelled application:
ret& = CreateProcessA(0&, cmdline$, sa, sa, 1&, _
NORMAL_PRIORITY_CLASS, 0&, 0&, start, proc)
If ret <> 1 Then
MsgBox "CreateProcess failed. Error: " & Err.LastDllError
End If
bSuccess = ReadFile(hReadPipe, mybuff, 100, bytesread, 0&)
If bSuccess = 1 Then
List1.AddItem Left(mybuff, bytesread)
Else
MsgBox "ReadFile failed. Error: " & Err.LastDllError
End If
ret& = CloseHandle(proc.hProcess)
ret& = CloseHandle(proc.hThread)
ret& = CloseHandle(hReadPipe)
ret& = CloseHandle(hWritePipe)
End Sub
3. Add a CommandButton (Command1) to Form1.
4. Add the following code to the Command1_Click event:
Private Sub Command1_Click()
ExecCmd ("C:\Console\Debug\console.exe")
End Sub
Additional query words: kbInetdev kbInternet kbVBp400 kbVBp500 kbVBp600 kbdsi kbDSupport kbVBp
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Keywords :
Technology : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVBA500Search kbVBA500 kbVBA600 kbVB500 kbVB600 kbVB400Search kbVB400 kbZNotKeyword3
Version : WINDOWS:4.0,5.0,6.0
Issue type : kbhowto
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