Question

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?

Answer 1

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