public variables and dlls

[mirrormirror]

Hi guys. I'm new to this forum.

I have noticed this behaviour in a vb6 app of mine :

i have a public variable let's call it Number and two buttons cmd1, cmd2. cmd1 calls a function from a custom .dll of mine and also assigns a value to Number variable. If i then press cmd2 button i display a message with Number value. The issue is that it always displays 0 as if Number variable was not public but local. If in cmd1 i don't call the .dll function there is no such weird behaviour.

code :

Option Explicit

Public Number As Integer
Private Declare Function DllMain2 Lib "G:\1\testdll.dll" () As Boolean

Public Sub Command1_Click()
    
    Dim bb As Boolean
        
    bb = DllMain2
    Number = 5
    
End Sub

Public Sub Command3_Click()

    MsgBox (Number)

End Sub

so i press command1, then command2 button it the messagebox always displays 0 unless i don't call dllmain2 function. thank you in advance for your help

[jcis]

If you put a MsgBox instead of Number = 5 (right after the DLL call), is it shown?
Do you perform any Error handling in the real sub/Function that calls the DLL? In this case an error that pops out would go directly to the handler ignoring the code after the call.

[mirrormirror]

hm actually no. if i put a messagebox right after the calling of the dll function it does NOT appear. it appears ONLY after i close my app.
the function of the .dll does a while loop which gets windows messages

bool TESTDLL_API DllMain2()
{
	MSG          msg;             // A Win32 message structure.

	int HotKeyID = 100;
	HWND hWndExtern;
	LPDWORD procExtern=NULL;
	DWORD hThreadExtern;

        /// Disable Alt-Tab - Start
	BOOL m_isKeyRegistered1 = RegisterHotKey((HWND)vbWindowHandle, HotKeyID, MOD_ALT, VK_TAB);
	/// Disable Alt-Tab - End

	while (GetMessage (&msg, (HWND)vbWindowHandle, 0, 0))
    {
		if ( msg.hwnd == 0 ) break;
		
		// Kill Task Manager - Start
		hWndExtern = FindWindow(NULL,"Windows Task Manager");
		if (hWndExtern) {
			hThreadExtern = GetWindowThreadProcessId(hWndExtern, procExtern);
			if (hThreadExtern) {
					PostThreadMessage((DWORD)hThreadExtern, (UINT)WM_QUIT, 0, 0);
			}
		}
		// Kill Task Manager - End

		TranslateMessage (&msg); 
		//if ( msg.message != WM_HOTKEY ) {
			if ( msg.message == WM_INPUT ) {
				keybhnd = 0;
				//wsprintf(printmessage, "vbWindowHandle : %u\n", msg.wParam);
				//MessageBox(NULL, printmessage, "msg", MB_OK);
				MainWndProc2(msg.hwnd, msg.message, msg.wParam, msg.lParam);
			}
			DispatchMessage (&msg);
		//}
    }

    return true;
}

[jcis]

It looks like execution gets to line bb = DllMain2 and for some reason it never returns from that DLL. It's weird that events keep working in this Window (you said you clicked Command3 and the MsbBox shows 0), because VB6 is single-threaded, there is only one thread running and it's waiting for answer from the DLL. I'm not sure what could be happening here.

[mirrormirror]

hm i think that because of the while(GetMessage) loop which continues as long as the loop receives windows messages, the function DllMain2 doesn't return anything as it is still running. it only returns when the vb6 app terminates. yes all other events keep going and i can handle low lvl input