Why does my window child creation fails?

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I have an MDI created and it works until I press on menu new file and I get this error message I wrote on message box.. that the New MDI child creation failed this is the part where the compiler says Local mcs. szClass "Cannot acces memory at adress 0xcdbaabcd"

C++

HWND CreateNewMDIChild(HWND hMDIClient)
{
    MDICREATESTRUCT mcs;
    HWND hChild;

    mcs.szTitle     = "Act 1";
    mcs.szClass     = ChildClass;
    mcs.hOwner      = GetModuleHandle(NULL);
    mcs.x = mcs.cx  = CW_USEDEFAULT;
    mcs.y = mcs.cy  = CW_USEDEFAULT;
    mcs.style       = MDIS_ALLCHILDSTYLES;

    hChild = (HWND)SendMessage(hMDIClient, WM_MDICREATE, 0, (LONG)&mcs);
    if(!hChild)
    {
        MessageBox(hMDIClient, "Act 1 MDI child creation failed !", "Error", MB_ICONERROR | MB_OK);
    }
    return hChild;
}

What I have tried:

I didn't try anything because the compiler doesn't give me any errors ..
and if the entire code is needed I can uploaded right away...

Well I did ask someone and told me this would be the issue:

C++

hChild = (HWND)SendMessage(hMDIClient, WM_MDICREATE, 0, (LONG)&mcs);

It means I did a bad cast...?!
What will be look like?

C++

hChild = (HWND)SendMessage(hMDIClient, WM_MDICREATE, 0, reinterpret_cast<LPARAM>(&mcs));

Posted 15-May-20 3:59am

M@gelearn

Updated 15-May-20 5:29am

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Comments

Richard MacCutchan 15-May-20 11:02am

"the compiler says Local mcs. szClass "Cannot acces memory at adress 0xcdbaabcd""
That is not a compiler message, but a runtime exception. Where exactly does that occur and what is "ChildClass"?

2 solutions

Solution 1

This someone is right the LONG is truncating the value and so a simple cast to LPARAM is enough.

So this should work when your hMDIClient is a good citizen.

Posted 15-May-20 4:49am

KarstenK

Comments

M@gelearn 15-May-20 11:04am

Well i did change that and doesn't change anything.. the child window refuse to create.. :(

Richard MacCutchan 15-May-20 11:05am

LONG and LPARAM are both the same size. Oops - only in 32 bit.

M@gelearn 15-May-20 11:21am

yes my compiler is 32 bit... IF 64 I would use the LPARAM well that's what the function expectes.

hChild = (HWND)SendMessage(hMDIClient, WM_MDICREATE, 0, (LPARAM)&mcs);

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M@gelearn · Accepted Answer · 2020-05-15T05:30:00

but hey.. that someone I have mention has solved my problem.
I just give him the hole code.. well in poor words i didn't register the MDI child window at the WM_CREATE.. and ofc. the window can't show up.. but the problem was that the compiler didn't gave me any errors .. that was the real problem so.. i just forgot to put this ..

// registering MDI after client window is made here!
       SetUpMDIChildWindowClass(GetModuleHandleA(NULL)

here

C++

<pre>case WM_CREATE:
	{
		/// Create MDI client ///////////////////////////////////

		////////// Find window menu where children will be listed
		CLIENTCREATESTRUCT ccs;

		ccs.hWindowMenu = GetSubMenu(GetMenu(hwnd), 2);
		ccs.idFirstChild = ID_MDI_FIRSTCHILD;

		hMDIClientWindow = CreateWindowEx(WS_EX_CLIENTEDGE, "mdiclient", NULL,
			WS_VISIBLE | WS_CHILD | WS_CLIPCHILDREN | WS_VSCROLL | WS_HSCROLL,
			CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
			hwnd, (HMENU)IDC_MAIN_MDI, GetModuleHandle(NULL), (LPVOID)&ccs);

		if (hMDIClientWindow == NULL)
		{
			MessageBox(hwnd, "Could not create MDI client !", "Error", MB_ICONERROR | MB_OK);
		}

		// Create Status bar
		HWND hStatus;
		int statwidths[] = { 140, 300, -1 };

		hStatus = CreateWindowEx(0, STATUSCLASSNAME, NULL,
			WS_VISIBLE | WS_CHILD | SBARS_SIZEGRIP,
			0, 0, 0, 0, hwnd, (HMENU)IDC_MAIN_STATUS, GetModuleHandle(NULL), NULL);

		SendMessage(hStatus, SB_SETPARTS, sizeof(statwidths) / sizeof(int), (LPARAM)statwidths);

		SendMessage(hStatus, SB_SETTEXT, 0, (LPARAM)" Author:      Me");
		SendMessage(hStatus, SB_SETTEXT, 1, (LPARAM)"                 - MDI2 - ");
		SendMessage(hStatus, SB_SETTEXT, 2, (LPARAM)"                  May 2020");


                // registering MDI after client window is made here!
		SetUpMDIChildWindowClass(GetModuleHandleA(NULL));

	}

However thanks everyone ... cheers