Is it possible to spawn a synchronous process in VB6 (i.e. calling an external .exe), wait for it to terminate, and grab the return value?
We have legacy code (in VB6 obviously) that we need to call a .NET application to perform some complicated tasks, and based on the .NET app's return value, either proceed or fail. Is there a better way of doing such a thing?
Your first option should probably be to expose an interface to expose the .NET interfaces to COM and use that (it is much cleaner), but if for some reason you have to do it through a spawned process use this VB6 code.
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 Type PROCESS_INFORMATION
hProcess As Long
hThread As Long
dwProcessID As Long
dwThreadID As Long
End Type
Private Declare Function WaitForSingleObject Lib "kernel32" (ByVal hHandle As Long, ByVal dwMilliseconds As Long) As Long
Private 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
Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long
Private Declare Function GetExitCodeProcess Lib "kernel32" (ByVal hProcess As Long, lpExitCode As Long) As Long
Private Const NORMAL_PRIORITY_CLASS = &H20&
Private Const INFINITE = -1&
Private Const SW_HIDE = 0
Private Const SW_SHOWMINNOACTIVE = 7
Public Function ExecCmd(cmdline As String, workdir As String) As Integer
Dim proc As PROCESS_INFORMATION
Dim start As STARTUPINFO
Dim ret as Long
ChDrive Left(workdir, 1) & ":"
ChDir workdir
start.cb = Len(start)
start.wShowWindow = SW_SHOWMINNOACTIVE
Call CreateProcessA(0&, cmdline, 0&, 0&, 1&, NORMAL_PRIORITY_CLASS, 0&, 0&, start, proc)
Call WaitForSingleObject(proc.hProcess, INFINITE)
Call GetExitCodeProcess(proc.hProcess, ret)
Call CloseHandle(proc.hThread)
Call CloseHandle(proc.hProcess)
ExecCmd=ret
End Function
' References: "Windows Script Host Shell Object Model" '
Function ExecuteCommand(cmd As String, ExpectedResult as Long) As Boolean
Dim shell As New IWshRuntimeLibrary.WshShell
Dim Result As Long
Result = shell.Run(Command:=cmd, WindowStyle:=WshHide, WaitOnReturn:=True)
ExecuteCommand = (Result = ExpectedResult)
End Function
You could use:
Option Explicit
Private Const INFINITE = &HFFFF&
Private Const SYNCHRONIZE = &H100000
Private Const PROCESS_QUERY_INFORMATION = &H400&
Private Declare Function CloseHandle Lib "kernel32" ( _
ByVal hObject As Long) As Long
Private Declare Function GetExitCodeProcess Lib "kernel32" ( _
ByVal hProcess As Long, _
lpExitCode As Long) As Long
Private Declare Function OpenProcess Lib "kernel32" ( _
ByVal dwDesiredAccess As Long, _
ByVal bInheritHandle As Long, _
ByVal dwProcessId As Long) As Long
Private Declare Function WaitForSingleObject Lib "kernel32" ( _
ByVal hHandle As Long, _
ByVal dwMilliseconds As Long) As Long
Private Function SyncShell( _
ByVal PathName As String, _
ByVal WindowStyle As VbAppWinStyle) As Long
'Shell and wait. Return exit code result, raise an
'exception on any error.
Dim lngPid As Long
Dim lngHandle As Long
Dim lngExitCode As Long
lngPid = Shell(PathName, WindowStyle)
If lngPid <> 0 Then
lngHandle = OpenProcess(SYNCHRONIZE _
Or PROCESS_QUERY_INFORMATION, 0, lngPid)
If lngHandle <> 0 Then
WaitForSingleObject lngHandle, INFINITE
If GetExitCodeProcess(lngHandle, lngExitCode) <> 0 Then
SyncShell = lngExitCode
CloseHandle lngHandle
Else
CloseHandle lngHandle
Err.Raise &H8004AA00, "SyncShell", _
"Failed to retrieve exit code, error " _
& CStr(Err.LastDllError)
End If
Else
Err.Raise &H8004AA01, "SyncShell", _
"Failed to open child process"
End If
Else
Err.Raise &H8004AA02, "SyncShell", _
"Failed to Shell child process"
End If
End Function
