What's wrong with my Win32 Wrapper code?

Please help me check my Win32 Wrapper code, it compiled right, and run with no error, but it exit immediately after running, I have look at my code many times but still don't know what's wrong with it. Here's my code:

main.cpp

Code:

---

#include <windows.h>

#include "Window.h"

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
                    PSTR szCmdLine, int iCmdShow)
{
    CWindow test(hInstance);
    test.RegisterWindow();
    test.Create();

    MSG msg;

    while(GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return msg.wParam;
}

---

Window.cpp

Code:

---

#include "Window.h"

LRESULT CALLBACK CWindow::staticWinMsgHandler(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    CWindow* pWnd;

    if(uMsg == WM_NCCREATE)
    {
        SetWindowLong(hwnd, GWL_USERDATA, (long)((LPCREATESTRUCT(lParam))->lpCreateParams));
    }

    pWnd = (CWindow *)GetWindowLong(hwnd, GWL_USERDATA);

    if(pWnd)
        return pWnd->WinMsgHandler(hwnd, uMsg, wParam, lParam);
    else
        return DefWindowProc(hwnd, uMsg, wParam, lParam);
}

LRESULT CALLBACK CWindow::WinMsgHandler(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    switch(uMsg)
    {
        case WM_CREATE:
            MessageBox(NULL, "Create", "test", MB_OK);
            break;
        case WM_CLOSE:
            PostQuitMessage(0);
            break;
        default:
            return CWindow::WinMsgHandler(hwnd, uMsg, wParam, lParam);
    }
    return 0;
}

BOOL CWindow::RegisterWindow()
{
    WNDCLASS wcx;

    wcx.style        = CS_HREDRAW | CS_VREDRAW;
    wcx.lpfnWndProc  = CWindow::staticWinMsgHandler;
    wcx.cbClsExtra    = 0;
    wcx.cbWndExtra    = 0;
    wcx.hInstance    = m_hInstance;
    wcx.hIcon        = LoadIcon(NULL, IDI_APPLICATION);
    wcx.hCursor      = LoadCursor(NULL, IDC_ARROW);
    wcx.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
    wcx.lpszMenuName  = NULL;
    wcx.lpszClassName = "Window";

    return (RegisterClass(&wcx) != 0);
}

BOOL CWindow::Create()
{
    m_hwnd = CreateWindow("Window", "Hello",
        WS_OVERLAPPEDWINDOW | WS_VISIBLE,
        CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
        NULL, NULL, m_hInstance, (void *)this);

    return (m_hwnd != NULL);
}

---

Window.h

Code:

---

#ifndef Window_H_
#define Window_H_

#include <windows.h>

// The class is based on the example taken from Code Project article:
// "A Simple Win32 Window Wrapper Class" By Jason Henderson

class CWindow
{
protected:
    HINSTANCE m_hInstance;
    HWND m_hwnd;
    char szClassName[256];
    char szWindowTitle[256];

    virtual LRESULT CALLBACK WinMsgHandler(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);

public:
    CWindow(HINSTANCE hInst)
        : m_hInstance(hInst){};
    virtual BOOL RegisterWindow();
    virtual BOOL Create();
    static LRESULT CALLBACK staticWinMsgHandler(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
};

#endif

---

I think that the

Code:

---

    CWindow test(hInstance);
    test.RegisterWindow();
    test.Create();

---

runs ok, the problem is in CWindow::staticWinMsgHandler, I think.

Recursively calling your class member function window procedure (WinMsgHandler) by default is not a good idea; replace the default of the switch statment with a call to DefWindowProc instead:

Code:

---

LRESULT CALLBACK CWindow::WinMsgHandler(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    switch(uMsg)
    {
        case WM_CREATE:
            MessageBox(NULL, "Create", "test", MB_OK);
            break;
        case WM_CLOSE:
            /*default system processing of WM_CLOSE involves a call to DestroyWindow
              so if you intercept this message, do the same*/
            DestroyWindow(hwnd);
            PostQuitMessage(0);
            break;
        default:
            //return CWindow::WinMsgHandler(hwnd, uMsg, wParam, lParam);
            DefWindowProc(hwnd,uMsg,wParam,lParam);
    }
    return 0;
}

---

You might want to read up on GetMessage, too; there's a possibility of that function returning -1, a result which will break your code.

Ken Fitlike, thanks for the tips.

I haven't change the GetMessage() while loop, I find that CreateWindow() is the one that fails, m_hwnd returns 0! I replace "(void *)this" with "NULL", CreateWindow() works! why!? what's wrong?

I checked my CWindow::RegisterWindow(), no problems there.

Does the WM_CREATE message box ever come up?

Quote:

---

I find that CreateWindow() is the one that fails, m_hwnd returns 0! I replace "(void *)this" with "NULL", CreateWindow() works! why!? what's wrong?

---

miica, did you do as Ken said?

Did you replace the default of the switch statement with a call to DefWindowProc instead?

Wouldn't that produce a stack overflow if he hadn't?

I couldn't think of anything else.

After modifying his code using Ken's suggestions, my version of his program runs properly.

sorry, I spent a whole day cleaning up my disk so I can install a new big MSVC .Net, I thought the code does not compile because I am using MSVC 6.0, so I tried to compile it with .Net, unfortunately, the problems still isn't solved, CreateWindow() still fails and returns 0. I then tried in a yet another different compiler, Dev-C++ 4.9.8.0, the result still is the same.

"Does the WM_CREATE message box ever come up?"
no. I changed my code as Ken Fitlike suggested, this time the program run but it does no show, I can only see it in Windows Task Manager, the Processes tab, it is not in the Applications tab.

"Did you replace the default of the switch statement with a call to DefWindowProc instead?"
Is this just what I need to do? I did it, but the test.Create() still returns 0.

"After modifying his code using Ken's suggestions, my version of his program runs properly."
Dante Shamest, what compiler are you using? I wonder why mine doesn't works properly.

This is my revised code:

main.cpp

Code:

---

#include <windows.h>

#include "Window.h"

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
                    PSTR szCmdLine, int iCmdShow)
{
    int returnvalue;
    CWindow test(hInstance);
    returnvalue = test.RegisterWindow();
    returnvalue = test.Create();

    // I checked the return value in debugging, found that
    // test.RegisterWindow() returns 1 while
    // test.Create() returns 0.

    MSG msg;

    while((returnvalue = GetMessage(&msg, NULL, 0, 0)) > 0)
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return 0;
}

---

[edit]
sorry, forget this:

Window.cpp

Code:

---

#include "Window.h"

LRESULT CALLBACK CWindow::staticWinMsgHandler(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    CWindow* pWnd;

    if(uMsg == WM_NCCREATE)
    {
        SetWindowLong(hwnd, GWL_USERDATA, (long)((LPCREATESTRUCT(lParam))->lpCreateParams));
    }

    pWnd = (CWindow *)GetWindowLong(hwnd, GWL_USERDATA);

    if(pWnd)
        return pWnd->WinMsgHandler(hwnd, uMsg, wParam, lParam);
    else
        return DefWindowProc(hwnd, uMsg, wParam, lParam);
}

LRESULT CALLBACK CWindow::WinMsgHandler(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    switch(uMsg)
    {
        case WM_CREATE:
            MessageBox(NULL, "Create", "test", MB_OK);
            break;
        case WM_CLOSE:
            DestroyWindow(hwnd);
            PostQuitMessage(0);
            break;
        default:
            DefWindowProc(hwnd,uMsg,wParam,lParam);
    }
    return 0;
}

BOOL CWindow::RegisterWindow()
{
    WNDCLASS wcx;

    wcx.style        = CS_HREDRAW | CS_VREDRAW;
    wcx.lpfnWndProc  = CWindow::staticWinMsgHandler;
    wcx.cbClsExtra    = 0;
    wcx.cbWndExtra    = 0;
    wcx.hInstance    = m_hInstance;
    wcx.hIcon        = LoadIcon(NULL, IDI_APPLICATION);
    wcx.hCursor      = LoadCursor(NULL, IDC_ARROW);
    wcx.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
    wcx.lpszMenuName  = NULL;
    wcx.lpszClassName = "Window";

    return (RegisterClass(&wcx) != 0);
}

BOOL CWindow::Create()
{
    m_hwnd = CreateWindow("Window", "Hello",
        WS_OVERLAPPEDWINDOW | WS_VISIBLE,
        CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
        NULL, NULL, m_hInstance, (void *)this);

    return (m_hwnd != NULL);
}

---

Window.h hasn't changed.

Code:

---

LRESULT CALLBACK CWindow::WinMsgHandler(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    switch(uMsg)
    {
        case WM_CREATE:
            MessageBox(NULL, "Create", "test", MB_OK);
            break;
        case WM_CLOSE:
            DestroyWindow(hwnd);
            PostQuitMessage(0);
            break;
        default:
            return DefWindowProc(hwnd,uMsg,wParam,lParam);
    }
    return 0;

---

[edit to my last post]
"I thought the code does not compile"
actually it did compiled under MSVC but the program doesn't work.

Ah, that return, sorry, if only I could understand more about the code myself, then I would be able to solve it. It works now, I am very happy :) thank you Ken Fitlike and others who has helped.