ShellWait() Function

[NeoPa]

Introduction :

The following code (module) provides the facility to execute a program, but synchronously. The Shell() function executes a command asynchronously, so returns control immediately after the command has been invoked, whether the command has completed execution or not. This is often not appropriate or convenient, so here is a version which causes the invoking code to wait until the command has terminated before resuming execution.

Solution :

Option Compare Database
Option Explicit

'Windows API Variable Prefixes
'cb = Count of Bytes (32-bit)
'w  = Word (16-bit)
'dw = Double Word (32-bit)
'lp = Long Pointer (32-bit)
'b  = Boolean (32-bit)
'h  = Handle (32-bit)
'ul = Unsigned Long (32-bit)

Private Const conUseShowWindow = &H1&
Private Const conNormalPriority = &H20&
Private Const conInfinite = -1&

Private Type typStartupInfo
    cbLen As Long
    lpReserved As String
    lpDesktop As String
    lpTitle As String
    dwX As Long
    dwY As Long
    dwXSize As Long
    dwYSize As Long
    dwXCount As Long
    dwYCount As Long
    dwFillAtt As Long
    dwFlags As Long
    wShowWindow As Integer
    cbReserved2 As Integer
    lpReserved2 As Long
    hStdIn As Long
    hStdOut As Long
    hStdErr As Long
End Type

Private Type typProcInfo
    hProc As Long
    hThread As Long
    dwProcID As Long
    dwThreadID As Long
End Type

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 typStartupInfo, _
    lpProcessInformation As typProcInfo) As Long
Private Declare Function WaitForSingleObject Lib "kernel32" ( _
    ByVal hHandle As Long, _
    ByVal dwMilliseconds As Long) As Long
Private Declare Function CloseHandle Lib "kernel32" ( _
    ByVal hObject As Long) As Long

'ShellWait() executes a command synchronously (Shell() works asynchronously).
Public Sub ShellWait(strCommand As String, _
                     Optional intWinStyle As Integer = vbNormalFocus)
    Dim objProcInfo As typProcInfo
    Dim objStart As typStartupInfo

    'Initialize the typStartupInfo structure:
    With objStart
        .cbLen = Len(objStart)
        .dwFlags = conUseShowWindow
        .wShowWindow = intWinStyle
    End With
    'Start the shelled application:
    Call CreateProcessA(lpApplicationName:=0&, _
                        lpCommandLine:=strCommand, _
                        lpProcessAttributes:=0&, _
                        lpThreadAttributes:=0&, _
                        bInheritHandles:=1&, _
                        dwCreationFlags:=conNormalPriority, _
                        lpEnvironment:=0&, _
                        lpCurrentDirectory:=0&, _
                        lpStartupInfo:=objStart, _
                        lpProcessInformation:=objProcInfo)
    'Wait for the shelled application to finish
    Call WaitForSingleObject(hHandle:=objProcInfo.hProc, _
                             dwMilliseconds:=conInfinite)
    Call CloseHandle(hObject:=objProcInfo.hProc)
End Sub