Win32 Api Access violation - c++

Question

I´m learning Win32 api and trying to make it somewhat object oriented while also learning C++. I have created a BaseWindow class and a MainWindow class that derive from it. I have a menu that creates MessageBoxes and a menu option that creates a DialogBox.
It is when I click on this option when the program crashes.
Exception thrown at 0x00000001 in LearningWin32.exe: 0xC0000005: Access violation executing location 0x00000001.
This exception is thrown in BaseWindow.cpp
if (pBaseWindow)
{
OutputDebugString(L"BASE WINDOW pBASEWINDOW\n");
pBaseWindow->m_hwnd = hwnd;
lResult = pBaseWindow->HandleMessage(uMsg, wParam, lParam); // --> ExceptionThrown
}
I´m not sure if it is because I don´t understand the way message flow works, because of not dominating C++ enough or both. Heres is what I have done so far.
Main.cpp
#ifndef UNICODE
#define UNICODE
#endif
#include "MainWindow.h"
int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PWSTR pCmdLine, int nCmdShow)
{
MainWindow win(hInstance, L"MainWindow", nCmdShow);
if (!win.Create(L"Notepad --", WS_OVERLAPPEDWINDOW, 0, 1024, 720))
{
return 0;
}
// Run the message loop.
MSG msg = { };
while (GetMessage(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return 0;
}
BaseWindow.h
#pragma once
#include <Windows.h>
class BaseWindow
{
public:
BaseWindow();
~BaseWindow();
HWND Window() const;
static LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
protected:
virtual PCWSTR GetClassName() const = 0;
virtual LRESULT HandleMessage(UINT uMsg, WPARAM wParam, LPARAM lParam) = 0;
HWND m_hwnd;
};
BaseWindow.cpp
#include "BaseWindow.h"
BaseWindow::BaseWindow() : m_hwnd(NULL) { }
BaseWindow::~BaseWindow() { DestroyWindow(m_hwnd); }
HWND BaseWindow::Window() const { return m_hwnd; }
LRESULT CALLBACK BaseWindow::WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
OutputDebugString(L"BASE WINDOW WindowProc\n");
if (uMsg == WM_NCCREATE)
{
OutputDebugString(L"BASE WINDOW WindowProc -> WM_NCCREATE\n");
CREATESTRUCT* pCreate = (CREATESTRUCT*)lParam;
BaseWindow* pBaseWindow = (BaseWindow*)pCreate->lpCreateParams;
SetWindowLongPtr(hwnd, GWLP_USERDATA, (LONG_PTR)pBaseWindow);
}
BaseWindow* pBaseWindow = reinterpret_cast<BaseWindow*>(GetWindowLongW(hwnd, GWL_USERDATA));
LRESULT lResult;
if (pBaseWindow)
{
OutputDebugString(L"BASE WINDOW pBASEWINDOW\n");
pBaseWindow->m_hwnd = hwnd;
lResult = pBaseWindow->HandleMessage(uMsg, wParam, lParam);
}
else
{
OutputDebugString(L"BASE WINDOW DefWindowProc\n");
lResult = DefWindowProc(hwnd, uMsg, wParam, lParam);
}
return lResult;
}
MainWindow.h
#pragma once
#include "BaseWindow.h"
class MainWindow : public BaseWindow
{
private:
HINSTANCE m_hInstance;
LPCWSTR m_className;
int m_nCmdShow;
public:
MainWindow(HINSTANCE hInstance, LPCWSTR ClassName, int nCmdShow);
//~MainWindow();
BOOL Create(
PCWSTR lpWindowName,
DWORD dwStyle,
DWORD dwExStyle = 0,
int nWidth = CW_USEDEFAULT,
int nHeight = CW_USEDEFAULT,
int x = CW_USEDEFAULT,
int y = CW_USEDEFAULT,
HWND hWndParent = 0,
HMENU hMenu = 0);
virtual PCWSTR GetClassName() const;
virtual LRESULT HandleMessage(UINT uMsg, WPARAM wParam, LPARAM lParam);
BOOL CALLBACK AboutDlgProc(HWND hwnd, UINT Message, WPARAM wParam, LPARAM lParam);
};
MainWindow.cpp
#include "MainWindow.h"
#include "resource/resource.h"
#include <string>
MainWindow::MainWindow(HINSTANCE hInstance, LPCWSTR ClassName, int nCmdShow)
: m_hInstance(hInstance), m_className(ClassName), m_nCmdShow(nCmdShow)
{
OutputDebugString(L"MAIN WINDOW CONSTRUCTOR\n");
}
PCWSTR MainWindow::GetClassName() const { return m_className; }
BOOL MainWindow::Create(
PCWSTR lpWindowName,
DWORD dwStyle,
DWORD dwExStyle,
int nWidth,
int nHeight,
int x,
int y,
HWND hWndParent,
HMENU hMenu)
{
OutputDebugString(L"MAIN WINDOW CREATE\n");
WNDCLASS wc = { 0 };
wc.lpfnWndProc = BaseWindow::WindowProc;
wc.hInstance = m_hInstance;
wc.lpszClassName = GetClassName();
wc.lpszMenuName = MAKEINTRESOURCE(IDR_MENU1);
wc.hIcon = LoadIcon(m_hInstance, MAKEINTRESOURCE(IDI_ICON1));
if (RegisterClass(&wc))
{
OutputDebugString(L"MAIN WINDOW CREATE CLASS REGISTERED\n");
}
else
{
OutputDebugString(L"MAIN WINDOW CREATE CLASS UNABLE TO REGISTER\n");
}
m_hwnd = CreateWindowEx(
dwExStyle,
GetClassName(),
lpWindowName,
dwStyle,
x, y,
nWidth, nHeight,
hWndParent,
hMenu,
m_hInstance,
this);
if (!m_hwnd)
{
OutputDebugString(L"--------- Window Creation Failed ---------\n");
ExitProcess(0);
}
// Centering the window in the screen
RECT rc;
GetWindowRect(m_hwnd, &rc);
int xPos = (GetSystemMetrics(SM_CXSCREEN) - rc.right) / 2;
int yPos = (GetSystemMetrics(SM_CYSCREEN) - rc.bottom) / 2;
SetWindowPos(m_hwnd, HWND_TOP, xPos, yPos, 0, 0, SWP_NOZORDER | SWP_NOSIZE);
ShowWindow(m_hwnd, m_nCmdShow);
UpdateWindow(m_hwnd);
return (m_hwnd ? TRUE : FALSE);
}
LRESULT MainWindow::HandleMessage(UINT uMsg, WPARAM wParam, LPARAM lParam)
{
OutputDebugString(L"MAIN WINDOW HANDLEMESSAGE\n");
switch (uMsg)
{
case WM_COMMAND: // Menu options
{
switch (LOWORD(wParam))
{
case ID_FILE_NEW:
MessageBox(m_hwnd, L"New file", L"Menu option New", MB_OK | MB_ICONASTERISK);
break;
case ID_FILE_OPEN:
MessageBox(m_hwnd, L"Menu option Open", L"Open", MB_OK | MB_ICONASTERISK);
break;
case ID_FILE_EXIT:
{
int msgBoxID = MessageBox(m_hwnd, L"Are you sure you want to exit?", L"Exit", MB_OKCANCEL | MB_ICONHAND);
if (msgBoxID == IDOK) PostMessage(m_hwnd, WM_CLOSE, 0, 0);
}
break;
case ID_HELP_SHOWDIALOGBOX:
{
OutputDebugString(L"MAIN WINDOW SHOWDIALOGBOX\n");
int ret = DialogBox(
m_hInstance,
MAKEINTRESOURCE(IDD_DIALOG1),
m_hwnd,
(DLGPROC)AboutDlgProc(m_hwnd, uMsg, wParam, lParam));
if (ret == IDOK) {
MessageBox(m_hwnd, L"Dialog exited with IDOK.", L"Notice",
MB_OK | MB_ICONINFORMATION);
}
else if (ret == IDCANCEL) {
MessageBox(m_hwnd, L"Dialog exited with IDCANCEL.", L"Notice",
MB_OK | MB_ICONINFORMATION);
}
else if (ret == -1) {
MessageBox(m_hwnd, L"Dialog failed!", L"Error",
MB_OK | MB_ICONINFORMATION);
}
}
break;
}
break;
}
case WM_CLOSE:
OutputDebugString(L"MAIN WINDOW HANDLEMESSAGE -> WM_CLOSE\n");
DestroyWindow(m_hwnd);
return 0;
case WM_DESTROY:
OutputDebugString(L"MAIN WINDOW HANDLEMESSAGE -> WM_DESTROY\n");
PostQuitMessage(0);
return 0;
case WM_PAINT:
{
PAINTSTRUCT ps;
HDC hdc = BeginPaint(m_hwnd, &ps);
FillRect(hdc, &ps.rcPaint, (HBRUSH)(COLOR_WINDOW + 1));
EndPaint(m_hwnd, &ps);
}
return 0;
default:
OutputDebugString(L"MAIN WINDOW HANDLEMESSAGE -> DefWindowProc\n");
return DefWindowProc(m_hwnd, uMsg, wParam, lParam);
}
return TRUE;
}
BOOL CALLBACK MainWindow::AboutDlgProc(HWND hwnd, UINT Message, WPARAM wParam, LPARAM lParam)
{
OutputDebugString(L"MAIN WINDOW AboutDlgProc\n");
switch (Message)
{
case WM_INITDIALOG:
// Do any process before dialog is shown
return TRUE;
case WM_COMMAND:
switch (LOWORD(wParam))
{
case IDOK:
EndDialog(hwnd, IDOK);
break;
case IDCANCEL:
EndDialog(hwnd, IDCANCEL);
break;
}
break;
default:
return FALSE;
}
return TRUE;
}
Edit
Solution:
Credit goes to Errorist.
Changed MainWindow.h from
BOOL CALLBACK AboutDlgProc(HWND hwnd, UINT Message, WPARAM wParam, LPARAM lParam);
to
static BOOL CALLBACK AboutDlgProc(HWND hwnd, UINT Message, WPARAM wParam, LPARAM lParam);
and in MainWindow.cpp changed it from
int ret = DialogBox(
m_hInstance,
MAKEINTRESOURCE(IDD_DIALOG1),
m_hwnd,
(DLGPROC)AboutDlgProc(m_hwnd, uMsg, wParam, lParam));
to simply
int ret = DialogBox(
m_hInstance,
MAKEINTRESOURCE(IDD_DIALOG1),
m_hwnd,
(DLGPROC)AboutDlgProc);

Answer 1

don't call AboutDlgProc
rather pass the address of a valid DLGPROC to be called
.....
case ID_HELP_SHOWDIALOGBOX:
{
OutputDebugString(L"MAIN WINDOW SHOWDIALOGBOX\n");
int ret = DialogBox(
m_hInstance,
MAKEINTRESOURCE(IDD_DIALOG1),
m_hwnd,
(DLGPROC)AboutDlgProc(m_hwnd, uMsg, wParam, lParam)); // <---- BOOL value returned
// where a valid DLGPROC address should be passed
....