DLL variables scope

This is a discussion on DLL variables scope within the Windows Programming forums, part of the Platform Specific Boards category; I'm writing a DLL in C. This is the dllmain.c code: Code: #include "dll.h" char* szClassName = "hidden window class ...

  1. #1
    Registered User
    Join Date
    Jul 2004
    Posts
    35

    DLL variables scope

    I'm writing a DLL in C. This is the dllmain.c code:
    Code:
    #include "dll.h"
    
    char* szClassName = "hidden window class name";
    char* szWndName   = "hidden window window name";
    
    HINSTANCE g_hinstance  = NULL;
    HWND      g_hWnd       = NULL;
    DWORD     g_dwThreadId;
    
    DWORD WINAPI ThreadProc (LPVOID lpParameter);
    LRESULT CALLBACK WindowProcedure(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam);
    
    DLLIMPORT void HelloWorld()
    {
        CreateThread
        (
            NULL, 
            0,
            ThreadProc,
            NULL,
            0,
            &g_dwThreadId
        );
    
    }
    
    DWORD WINAPI ThreadProc(LPVOID lpParameter)
    {
        WNDCLASSEX wincl;
        MSG        messages;
        
        wincl.hInstance = g_hinstance;
        wincl.lpszClassName = szClassName;
        wincl.lpfnWndProc = WindowProcedure;
        wincl.style = CS_HREDRAW | CS_VREDRAW;
        wincl.cbSize = sizeof (WNDCLASSEX);
        
        wincl.hIcon = NULL;
        wincl.hIconSm = NULL;
        wincl.hCursor = NULL;
        wincl.lpszMenuName = NULL;
        wincl.cbClsExtra = 0;
        wincl.cbWndExtra = 0;
        wincl.hbrBackground = (HBRUSH) COLOR_BACKGROUND;
        
        if (!RegisterClassEx (&wincl)) return 0;
        
        g_hWnd = CreateWindowEx
        (
            0,
            szClassName,
            szWndName,
            WS_OVERLAPPEDWINDOW,
            0,
            0,
            100,
            100,
            NULL,
            NULL,
            g_hinstance,
            NULL 
        );
        
        ShowWindow(g_hWnd, SW_HIDE);
        
        while (GetMessage (&messages, NULL, 0, 0)) {
            TranslateMessage(&messages);
            DispatchMessage(&messages);
        }        
    
        UnregisterClass(szClassName, g_hinstance);
        
        return 0;    
    }
    
    LRESULT CALLBACK WindowProcedure(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
    {
        switch (message)
        {
            case WM_CREATE:
            {
                break;
            }
            /* other messages processing */
            case WM_DESTROY:
            {
                PostQuitMessage(0);
                break;
            }
            default:
                return DefWindowProc (hwnd, message, wParam, lParam);
        }
        return 0;
    }
    
    
    BOOL APIENTRY DllMain (HINSTANCE hInst, DWORD reason, LPVOID reserved)
    {
        switch (reason)
        {
            case DLL_PROCESS_ATTACH:
            {
                g_hinstance = (HINSTANCE)hInst;
                break;
            }    
            case DLL_PROCESS_DETACH:
                break;
            case DLL_THREAD_ATTACH:
                break;
            case DLL_THREAD_DETACH:
                break;
        }
        return TRUE;
    }
    This is the dll.h code:

    Code:
    #ifndef _DLL_H_
    #define _DLL_H_
    
    #if BUILDING_DLL
    # define DLLIMPORT __declspec (dllexport)
    #else /* Not BUILDING_DLL */
    # define DLLIMPORT __declspec (dllimport)
    #endif /* Not BUILDING_DLL */
    
    
    DLLIMPORT void DoSomething (void);
    
    #endif /* _DLL_H_ */
    If I check the value of the global variable called g_hWnd in the WindowProcedure, when the WM_CREATE occurs, I always get NULL. What is problem? Whar is the real scope of the global variables? Can't WindowsProcedure access to the global variables because it simply can't or just because the window has been created in a different thread?

  2. #2
    Registered User Codeplug's Avatar
    Join Date
    Mar 2003
    Posts
    4,671
    CreateWindow[Ex]() will dispatch several messages to the window procedure before returning from the call.......which is when g_hwnd is assigned.

    gg

  3. #3
    Registered User
    Join Date
    Sep 2004
    Location
    California
    Posts
    3,246
    you should initialize g_hwnd in the WM_CREATE message handler.

    Code:
            case WM_CREATE:
            {
                g_hwnd = hwnd;
                break;
            }

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