DLL call function in owning EXE

[Nathan Evans]

Can I send Strings using SendMessage? I've seen some variants in VB before, like SendMessageByString.

I tried declaring this in PB, but it reported a duplicate declaration - so I guess that idea is out unless I change my SendMessage declaration
in the win32api.inc entirely..

[Lance Edmonds]

Well, how about creating the "string buffer" in VB (say, using a BYTE array), and pass the first element BYREF to the PB code (ie, a pointer to the array) and let the PB code manipulate the storage buffer directly (DIM..AT or with a pointer, etc).

VB's VARPTR() function should help with this.

Also, it looks like you are really trying to read/write a UDT, so the same techquie could be applied. Allocate the storage in VB, pass a pointer to the UDT to the PB code.


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Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

[Semen Matusovski]

The easiest way to transfer string to VB is to make hidden textbox on VB form and to use SendWindowtext in PB.
VB controls have hWnd property, which you can pass to PB.


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E-MAIL: [email protected]

[Nathan Evans]

I think the real problem i'm having here is that this is a DLL performing a hook, so it has
multiple instances. I just tested this.. I made a 'GLOBAL lPtr AS LONG' in the General Decs section.

Then i added a parameter of 'lP AS LONG' to the first function my VB EXE calls, called "StartHook".
And in the Hook's callback I added 'MSGBOX FORMAT$(lPtr)', so when the hook is triggered it displays the number
that was in the second parameter in my 'StartHook' function.

In my VB EXE, I added the extra parameter to the declare, and called it like: 'Call StartHook(Me.hWnd, 123123)'

When i triggered the Hook's event - it displayed 0 in the MSGBOX.



Semen, I have experimented with this method, but there is no way to set the WindowProc's return if I rely
on VB to control WM_SETTEXT for the TextBox. I have to control the WindowProc return number so my DLL may respond
to what the EXE has told it.

- Nathan.

[Nathan Evans]

i feel the type of hook i'm using is of some relevance now: http://www.powerbasic.com/support/pb...ad.php?t=21331
it is some great code put together by semen matusovski.

i'm trying to perform all this in the function that's referenced in place of the original function.
this is the 'mytextout' function in the first example on the url above.

thanks!!

[updated]
in my vb exe i tested the strptr returned to me by the pb dll using isbadstringptr.
i called it like: msgbox isbadstringptr(lparam, 1), this would test if the app has read access to the pointer at a length of 1 byte.
it returned 1, according to msdn - nonzero means the app does not have read access to that location.


- nathan


[this message has been edited by nathan evans (edited august 08, 2001).]

[Semen Matusovski]

Nathan --
Try following (NT/2000) (POFFS, PB IDE ...)

Vb Exe

Form1:

Private Const UniqueName = "My Hook"
Private Sub Form_Load()
   Me.Caption = UniqueName
   Hook Me.hWnd
   SetHook Me.hWnd, Form2.hWnd
End Sub

Private Sub Form_Unload(Cancel As Integer)
   End
End Sub

Form2 - empty (no code)
Module1:

Option Explicit

Declare Function SetHook Lib "hookd" (hWndM As Long, hWndT As Long) As Long
Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" (ByVal lpPrevWndFunc As Long, _
   ByVal hWnd As Long, ByVal Msg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long

Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hWnd As Long, _
   ByVal nIndex As Long, ByVal dwNewLong As Long) As Long

Public Const GWL_WNDPROC = -4
Public Const WM_DESTROY = &H2
Public Const WM_USER = &H400
Global lpPrevWndProc As Long

Public Sub Hook(hWnd As Long)
   lpPrevWndProc = SetWindowLong(hWnd, GWL_WNDPROC, AddressOf WindowProc)
End Sub

Function WindowProc(ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
   Select Case wMsg
      Case WM_USER + 401:
         Form2.Caption = "[Hook]" + Form2.Caption
      Case WM_DESTROY: SetWindowLong hWnd, GWL_WNDPROC, lpPrevWndProc
   End Select
   WindowProc = CallWindowProc(lpPrevWndProc, hWnd, wMsg, wParam, lParam)
End Function

Pb/Dll

   #Compile Dll "HookD.Dll"
   #Register None
   #Dim All
   #Include "Win32Api.Inc"

   $UniqueName = "My Hook"
   Global hInstDLL As Long, MainDll As Long

   Function SetHookProc(Op As Long) As Long
      Static hProc As Long, tProc As String
      Local hLib As Long
      If hProc = 0 Then
         hLib = GetModuleHandle("gdi32.dll")
         hProc = GetProcAddress(hLib, "TextOutA")
         tProc = Peek$(hProc, 7)
         If IsFalse(VirtualProtect (ByVal hProc, 7, ByVal %PAGE_EXECUTE_READWRITE, ByRef hLib)) Then _
            MsgBox "Error in VirtualProtect": hProc = 0: Exit Function
         ' Under 9x VirtualProtect doesn't work in the shared virtual address space (from 0x80000000 through 0xBFFFFFFF).
         ' For example, for system dlls.
      End If
      If Op = 1 Then Poke$ hProc, Chr$(&HB8) + Mkl$(CodePtr(MyTextOut)) + Chr$(&HFF, &HE0)
      If Op = 2 Then Poke$ hProc, tProc
      FlushInstructionCache GetCurrentProcess, ByVal hProc, ByVal 7
   End Function

   Function MyTextOut (ByVal hdc As Long, ByVal x As Long, ByVal y As Long, ByVal lpString As Dword, ByVal nCount As Long) As Long
      Static hDlg As Long, hWndT As Long
      Local MyString As Asciiz * 1000
      If hWndT = 0 Then hDlg = FindWindow("", $UniqueName): _
         If hDlg Then hWndT = GetProp(hDlg, ByVal 2)
      If hWndT Then
         SetWindowText hWndT, ByVal lpString
         SendMessage hDlg, %WM_USER + 401, 0, 0
         GetWindowText hWndT, MyString, SizeOf(MyString)
         SetHookProc 2
         TextOut hdc, x, y, MyString, Len(MyString)
         SetHookProc 1
      End If
   End Function

   Function LibMain(ByVal hInstance As Long, ByVal fwdReason As Long, _
      ByVal lpvReserved As Long) Export As Long
      Select Case fwdReason
         Case %DLL_PROCESS_ATTACH: hInstDLL = hInstance: LibMain = 1: SetHookProc 1
         Case %DLL_PROCESS_DETACH: LibMain = 1: SetHookProc 2
      End Select
   End Function

   Function HookProc(ByVal nCode As Long, ByVal wParam As Long, ByVal lParam As Long) Export As Long
      Static hHook As Long, hDlg As Long
      hDlg = FindWindow("", $UniqueName)
      If hHook = 0 Then If hDlg Then hHook = GetProp(hDlg, ByVal 1)
      If hHook Then Function = CallNextHookEx(ByVal hHook, ByVal nCode, ByVal wParam, ByVal lParam)
      If IsFalse(MainDll) And (IsFalse(hDlg) Or IsFalse(hHook)) Then FreeLibrary hInstDll
   End Function

   Function SetHook Alias "SetHook" (hWndM As Long, hWndT As Long) Export As Long
      Local hHook As Long
      hHook = SetWindowsHookEx (%WH_CBT, CodePtr(HookProc), ByVal hInstDLL, ByVal 0)
      SetProp hWndM, ByVal 1, ByVal hHook
      SetProp hWndM, ByVal 2, ByVal hWndT
      MainDll = 1
   End Function

Because VB IDE doesn't like hooks, I'd recommend to compile and to run Vb.Exe from explorer

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E-MAIL: [email protected]

[Nathan Evans]

Thanks Semen. I overlooked the possibility of using SETTEXT and another SendMessage together!

Many thanks to you all!

- Nathan

[Edwin Knoppert]

Didn't read much about this topic yet but,
I saw the statement VB doesn't do exported functions.

Well www.desaware.com has a tool for that.
Click spyworks and scroll down.

Or: http://www.desaware.com/ExportedFunctionsL3.htm

Don't know how it works tough.


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