C++, WIN32, WndProc to Member Function Crash (Access violation at 0x88) - c++

Question

I've been writing a win32 wrapper class, and I've come across a problem: Because each instance of the class has a window, I've enclosed the this pointer in the user info space using SetWindowLongPtrW(), allowing me to call a message handler from the static WndProc function. This works fine: I can call the function. However, when I try to call another member function from the message handler, I get an access violation at 0x00000088
It does compile.
I posted quite a lot, because to be honest I'm not too sure where the problem originates from...
Please feel free to comment/criticize my code in general. Thanks for the help!
Here is the header:
#pragma once
#include <Windows.h>
#include "GlobalDefines.h"
#include "GraphicsWrapper.h"
#include "Keyboard.h"
namespace Startup
{
class GraphicsWrapper;
class WindowsWrapper
{
public:
WindowsWrapper(HINSTANCE hInstance,
HINSTANCE hPrevInstance,
LPSTR lpCmdLine,
INT nCmdShow);
~WindowsWrapper();
void EnterMsgLoop(GraphicsWrapper* Gfx);
static LRESULT _stdcall WindowProc(HWND hWnd,
UINT message,
WPARAM wParam,
LPARAM lParam);
LRESULT _stdcall MessageHandler(HWND hWnd,
UINT message,
WPARAM wParam,
LPARAM lParam);
WNDCLASSEX WndClass;
MSG Message;
RECT Desktop;
RECT Taskbar;
RECT WindowCoordinates;
LPSTR CommandLineArgs;
INT CmdShow;
HINSTANCE TheInstance;
HWND WindowHandle;
void InitializeWndClassEx();
void InitializeWindowHandleHWND();
void ShowWindowOnScreen();
bool GetScreenRect(RECT & Desktop);
bool GetTaskbarRect(RECT& rectTaskbar);
bool GetWindowCoords(RECT& WindowCoordinates);
int GetTaskbarSide();
enum TaskbarSides
{
Top,
Right,
Bottom,
Left
};
void SetFullScreen(bool Enable);
};
static IO::Keyboard * kbd;
}
And this is the relevant part of the implementation. I'll mark where the crash occurs.
void Startup::WindowsWrapper::InitializeWndClassEx()
{
WndClass.hIcon = LoadIcon(TheInstance,(MAKEINTRESOURCE(IDI_MAIN_ICON) ) );
WndClass.hIconSm = LoadIcon(TheInstance,(MAKEINTRESOURCE(IDI_MAIN_ICON) ) );
WndClass.cbSize = sizeof(WNDCLASSEX);
WndClass.style = CS_HREDRAW | CS_VREDRAW;
WndClass.lpfnWndProc = WindowProc;
WndClass.hInstance = TheInstance;
WndClass.hCursor = LoadCursor(NULL, IDC_ARROW);
WndClass.lpszClassName = L"WindowClassName";
RegisterClassEx(&WndClass);
SetWindowLongPtrW(WindowHandle, GWLP_USERDATA, (long)this);
}
void Startup::WindowsWrapper::SetFullScreen(bool Enable)
{
long style = Enable ? WS_POPUP : WS_OVERLAPPED | WS_SYSMENU;
static RECT windowRect = {};
static bool needRect = true;
if (needRect)
{
GetWindowRect(WindowHandle, &windowRect);
needRect = false;
}
SetWindowLong(WindowHandle, GWL_STYLE, style);
if (Enable)
{
SetWindowPos(WindowHandle, HWND_TOPMOST,
0,0,
GetSystemMetrics(SM_CXSCREEN),
GetSystemMetrics(SM_CYSCREEN),
SWP_SHOWWINDOW);
}
else
{
SetWindowPos(WindowHandle, 0,
windowRect.left,windowRect.top,
windowRect.right - windowRect.left,
windowRect.bottom - windowRect.top,
SWP_SHOWWINDOW);
}
}
and
LRESULT CALLBACK Startup::WindowsWrapper::WindowProc
(
HWND hWnd,
UINT message,
WPARAM wParam,
LPARAM lParam
)
{
WindowsWrapper* ourObjectPtr = NULL;
long thisObject = GetWindowLongW(hWnd, GWLP_USERDATA);
ourObjectPtr = (WindowsWrapper *)( (void*)thisObject);
long Result = ourObjectPtr->MessageHandler(hWnd, message, wParam, lParam);
RET(Result);
}
LRESULT _stdcall Startup::WindowsWrapper::MessageHandler
(
HWND hWnd,
UINT message,
WPARAM wParam,
LPARAM lParam
)
{
switch(message)
{
case WM_DESTROY:
PostQuitMessage(0);
break;
case WM_KEYDOWN:
switch(wParam)
{
case VK_ESCAPE:
PostQuitMessage(0); //Works fine here, but...
break;
case VK_SPACE:
this->SetFullScreen(false); //Crashes here w/ access violation
break;
case VK_SHIFT:
this->SetFullScreen(true); //Or here, w/ the same error.
break;
}
}
return DefWindowProc(hWnd, message, wParam, lParam);
}
This is the createWindowEx call. Thanks for your help, again.
void Startup::WindowsWrapper::InitializeWindowHandleHWND()
{
WindowHandle = CreateWindowEx(NULL,
L"WindowClassName",
L"WindowTitle"
WS_OVERLAPPED | WS_SYSMENU,
WindowCoordinates.left, WindowCoordinates.top,
WindowCoordinates.right, WindowCoordinates.bottom,
NULL, NULL, TheInstance,
CommandLineArgs);
}

Answer 1

I have some code from a custom dialog handler I wrote quite a while back, which might be of use to you.
Same principle applies for a window but switch the WM_INITDIALOG for WM_CREATE and also replace DWLP_USER with GWLP_USERDATA. The format of the callback is subtley different too. You should be able to salvage almost all of this function though.
LRESULT CALLBACK CDialog::DlgProc( HWND hWndDlg, UINT msg, WPARAM wParam, LPARAM lParam )
{
CDialog* pWindow;
if( msg == WM_INITDIALOG ) {
SetWindowLongPtr( hWndDlg, DWLP_USER, (LONG_PTR)lParam );
pWindow = reinterpret_cast<CDialog*>( lParam );
pWindow->m_hWnd = hWndDlg;
} else {
pWindow = reinterpret_cast<CDialog*>( (LPARAM)GetWindowLongPtr( hWndDlg, DWLP_USER ) );
}
if( pWindow != NULL ) {
LRESULT ret = pWindow->OnMessage( msg, wParam, lParam );
if( msg == WM_NCDESTROY ) pWindow->m_hWnd = NULL;
}
return FALSE;
}