• The Old New Thing

    Developing a Chinese/English dictionary: Introduction


    The other day, one of my colleagues mentioned that his English name "Ben" means "stupid" in Chinese: 笨/bèn/ㄅㄣˋ. (His wife is Chinese; that's why he knows this in the first place.) Knowing that the Chinese language is rich in homophones, I fired up my Chinese/English dictionary program to see if we could find anything better. (Unfortunately, the best I could come up with was 賁/贲/bēn/ㄅㄣ, which means "energetic".)

    Ben seemed to take his appellative fate in stride; he seemed much more interested in the little dictionary program I had written. So, as an experiment, instead of developing tiny samples that illustrate a very focused topic, I'll develop a somewhat larger-scale program (though still small by modern standards) so you can see how multiple techniques come together. The task will take many stages, some of which may take only a day or two, others of which can take much longer. If a particular stage is more than two or three days long, I'll break it up with other articles, and I'll try to leave some breathing room between stages.

    Along the way, we'll learn about owner-data (also known as "virtual") listviews, listview custom-draw, designing for accessibility, window subclassing, laying out child windows, code pages, hotkeys, and optimization.

    If you're going to play along at home, beware that you're going to have to install Chinese fonts to see the program as it evolves, and when you're done, you'll have a Chinese/English dictionary program, which probably won't be very useful unless you're actually studying Chinese...

    If you're not into Win32 programming at all, then, well, my first comment to you is, "So what are you doing here?" And my second comment is, "I guess you're going to be bored for a while." You may want to go read another blog during those boring stretches, or just turn off the computer and go outside for some fresh air and exercise.

    Those who have decided to play along at home will need the following: a copy of the CEDICT Chinese-English dictionary in Big5 format (note: Big5 format) and the Chinese Encoding Converter source code (all we need is the file hcutf8.txt). We'll start digging in next time.

  • The Old New Thing

    How to query properties of the taskbar


    Occasionally, people want to query properties of the taskbar. I don't quite understand why; you should just get on with your life and let the taskbar get on with its life. After all, there might not even be a taskbar, as we discussed last time.

    But if you really want to know (perhaps you're collecting usability data), here's how:

    #include <stdio.h>
    #include <windows.h>
    #include <shellapi.h>
    int __cdecl main(int argc, const char* argv[])
     APPBARDATA abd = { sizeof(abd) };
     UINT uState = (UINT)SHAppBarMessage(ABM_GETSTATE, &abd);
     printf("Taskbar on top? %s\n",
            (uState & ABS_ALWAYSONTOP) ? "yes" : "no");
     printf("Taskbar autohide? %s\n",
            (uState & ABS_AUTOHIDE) ? "yes" : "no");
     return 0;

    This little program uses the ABM_GETSTATE message of the SHAppBarMessage function to get the "Always on top" and "Auto-hide" properties of the taskbar.

    Since you're using the SHAppBarMessage function, if a future version of Windows changes the way it maintains the taskbar state (or perhaps even changes the name of the taskbar to something else), your program will still work because the SHAppBarMessage function will be kept in sync with whatever changes happen to the taskbar.

    You can also use the ABM_SETSTATE message to change these states. Note that doing so from a program is discouraged; these state bits belong to the user's preferences. A program shouldn't be messing with the user's preferences. (Well, unless the whole point of the program is to change the user's preferences, of course. But the frequency with which I see this question makes me wonder whether there really are that many settings-tweaking programs out there. I suspect people are using this power for evil, not for good.)

    And to stave off follow-up questions: These are the only two properties of the taskbar that are programmable. Exposing a programmable interface for something as highly visible as the taskbar is a very sensitive issue, because once you grant programmatic access to something, there is a very strong temptation for programs to start abusing it.

  • The Old New Thing

    How do I cover the taskbar with a fullscreen window?


    For some reason, people think too hard. If you want to create a fullscreen window that covers the taskbar, just create a fullscreen window and the taskbar will automatically get out of the way. Don't go around hunting for the taskbar and poking it; let it do its thing.

    As always, start with the scratch program and add the following:

    HWND CreateFullscreenWindow(HWND hwnd)
     HMONITOR hmon = MonitorFromWindow(hwnd,
     MONITORINFO mi = { sizeof(mi) };
     if (!GetMonitorInfo(hmon, &mi)) return NULL;
     return CreateWindow(TEXT("static"),
           TEXT("something interesting might go here"),
           WS_POPUP | WS_VISIBLE,
           mi.rcMonitor.right - mi.rcMonitor.left,
           mi.rcMonitor.bottom - mi.rcMonitor.top,
           hwnd, NULL, g_hinst, 0);
    void OnChar(HWND hwnd, TCHAR ch, int cRepeat)
     if (ch == TEXT(' ')) {
        HANDLE_MSG(hwnd, WM_CHAR, OnChar);

    Note that this sample program doesn't worry about destroying that fullscreen window or preventing the user from creating more than one. It's just a sample. The point is seeing how the CreateFullScreenWindow function is written.

    We use the MonitorFromWindow function to figure out which monitor we should go fullscreen to. Note that in a multiple monitor system, this might not be the same monitor that the taskbar is on. Fortunately, we don't have to worry about that; the taskbar figures it out.

    I've seen people hunt for the taskbar window and then do a ShowWindow(hwndTaskbar, SW_HIDE) on it. This is nuts for many reasons.

    First is a mental exercise you should always use when evaluating tricks like this: "What if two programs tried this trick?" Now you have two programs both of which think they are in charge of hiding and showing the taskbar, neither of which is coordinating with the other. The result is a mess. One program hides the taskbar, then the other does, then the first decides it's finished so it unhides the taskbar, but the second program wasn't finished yet and gets a visible taskbar when it thought it should be hidden. Things only go downhill from there.

    Second, what if your program crashes before it gets a chance to unhide the taskbar? The taskbar is now permanently hidden and the user has to log off and back on to get their taskbar back. That's not very nice.

    Third, what if there is no taskbar at all? It is common in Terminal Server scenarios to run programs by themselves without Explorer [archived]. In this configuration, there is no Explorer, no taskbar. Or maybe you're running on a future version of Windows that doesn't have a taskbar, it having been replaced by some other mechanism. What will your program do now?

    Don't do any of this messing with the taskbar. Just create your fullscreen window and let the taskbar do its thing automatically.

  • The Old New Thing

    When people ask for security holes as features: Stealing passwords


    Sometimes people ask for features that are such blatant security holes I don't know what they were thinking.

    Is there a way to get the current user's password? I have a program that does some stuff, then reboots the system, and I want to have the current user's password so I can log that user back in when I'm done, then my program can resume its operation.

    (Sometimes they don't bother explaining why they need the user's password; they just ask for it.)

    Imagine the fantastic security hole if this were possible. Anybody could write a program that steals your password without even having to trick you into typing it. They would just call the imaginary GetPasswordOfCurrentUser function and bingo! they have your password.

    For another angle on credential-stealing, read Larry Osterman's discussion of why delegation doesn't work over the network.

    Even if you didn't want the password itself but merely some sort of "cookie" that could be used to log the user on later, you still have a security hole. Let's call this imaginary function GetPasswordCookieOfCurrentUser; it returns a "cookie" that can be used to log the user on instead of using their password.

    This is just a thinly-disguised GetPasswordOfCurrentUser because that "cookie" is equivalent to a password. Log on with the cookie and you are now that person.

  • The Old New Thing

    Managing the UI state of accelerators and focus rectangles


    Starting with Windows 2000, keyboard indicators such as underlined accelerators and focus rectangles (collectively known as "keyboard cues") are hidden by default, and are revealed only when you start using the keyboard. You can control this behavior from the Desktop Control Panel, under Appearance, Effects, "Hide underlined letters for keyboard navigation until I press the Alt key".

    Note that this setting actually controls both underlined letters and focus rectangles, even though the text describes only one of the effects. Underlines are hidden until you press the Alt key, and focus rectangles are hidden until you either press the Alt key or press the Tab key.

    Here's how it works.

    There are three UI state mesages: WM_CHANGEUISTATE, WM_QUERYUISTATE and WM_UPDATEUISTATE. The third one is, in my opinion, a misnomer. It really should be called something like WM_UISTATECHANGED since it is a notification that something has happened, not a message that you send to cause something to happen.

    When a dialog box or menu is displayed via a mouse click, keyboard cues are hidden; if the dialog box or menu was displayed via a keypress, then keyboard cues are visible. This decision is made by sending a WM_CHANGEUISTATE message to the root window with the UIS_INITIALIZE flag. This is done automatically by the dialog manager, but if you're doing your own custom windows, you'll have to send it yourself.

    The WM_CHANGEUISTATE message bubbles up to the top-level window, which changes the window UI state accordingly, then broadcasts a WM_UPDATEUISTATE message to all its child windows to notify them that the state has changed. (Of course, if the WM_CHANGEUISTATE message has no effect—for example, hiding something that is already hidden—then the WM_UPDATEUISTATE message is optimized out since the entire operation is a no-op.)

    When a window that draws keyboard cues receives a WM_UPDATEUISTATE message, it typically invalidates itself so that the cues can be redrawn/erased, depending on the new state.

    At drawing time, a window that draws keyboard cues can use the WM_QUERYUISTATE message to determine which keyboard cues are visible and which are hidden, and draw its content accordingly. If focus rectangles are hidden, then the window should skip the call to the DrawFocusRect function. If keyboard underlines are hidden, then the window suppresses underlines in its text drawing. If the window uses the DrawText function, it can pass the DT_HIDEPREFIX flag to suppress the underlines. If you are responding to the WM_DRAWITEM message, then you should check for the ODS_NOACCEL and ODS_NOFOCUSRECT flags to determine you should draw an underline accelerator or a focus rectangle.

    Finally, during execution you may discover that the user has used the keyboard to perform navigation within your control. For example, the listview control may have noticed that the user has used the arrow keys to change the selected item. When this happens, the control sends itself a WM_CHANGEUISTATE specifying which keyboard cues should be revealed. As noted above, the WM_CHANGEUISTATE message eventually causes all the windows in the window tree to receive a WM_UPDATEUISTATE message if their states need to change.

    The IsDialogMessage function sends WM_CHANGEUISTATE messages as appropriate, so dialog boxes and anybody else who uses IsDialogMessage gets keyboard-cues tracking for free.

  • The Old New Thing

    Another dead computer: My personal laptop


    I'm kind of surprised at how much people reacted to my previous dead computer story. I guess there's an audience for stories about dead computers.

    Today's dead computer is my Sony Vaio PCG-Z505LE laptop, with a 600MHz processor and 192MB of RAM. Certainly a big step up from that 486/50 with 12MB of RAM.

    Laptop computers have a comparatively short lifetime. (Hardware vendors must love them.) I've learned that the best value comes from buying used laptops. You have to accept being a bit behind the curve, but the way I use my laptop, it needs to do only a small number of things:

    • surf the web,
    • read e-mail,
    • use Remote Desktop Connection to access my desktop machine,
    • download pictures from my digital camera, and
    • compile the occasional program.

    Only that last operation requires a hefty processor, and I do it so rarely that it doesn't bother me that it's kind of slow. (I just run the command line version of the compiler, so that at least takes the IDE overhead out of the picture.)

    I bought this laptop two years ago, used, and it ran just fine until a couple months ago when the internal power supply burnt out. I was ready to abandon the model line and give away the accessories I had bought, including a $200+ double-capacity battery.

    Allow me to digress on laptop batteries. Observe that batteries for old-model laptops cost almost as much as the laptops themselves. That's because the battery is the only real consumable in a laptop computer. The other components will run practically indefinitely if you don't drop them or douse them in soda, but batteries just plain wear out. That's where the money is.

    This means that many ads for used laptops will mention "needs new battery" at the end. And those are the ones I sought out. Because I have a working battery! Most prospective buyers would be turned off by a dead battery, but that didn't bother me one bit.

    The replacement laptop arrived a few days ago, and it runs great. I wiped the drive and reinstalled Windows XP from scratch. (Challenging because the laptop doesn't come with a bootable CD-ROM drive. I had to use floppies!) I may install a handful of programs but that's all. I don't like installing software on my computer. The more programs you install, the more likely there's going to be a conflict somewhere.

    The old laptop has already started being scavenged for parts. A friend of mine needed a replacement laptop hard drive, so I gave him my old one. The battery and power brick can of course be used by the new laptop. The memory from the old Vaio is no use, since the Vaio has only one memory expansion slot. The other parts of the old laptop aren't much use for anything aside from spares. Perhaps I should put the old laptop on concrete blocks on my front lawn.

    Next time (if there is a next time), the story of the dead AlphaServer.

  • The Old New Thing

    Building a dialog template at run-time


    We've spent quite a bit of time over the past year learning about dialog templates and the dialog manager. Now we're going to put the pieces together to do something interesting: Building a dialog template on the fly.

    What we're going to write is an extremely lame version of the MessageBox function. Why bother writing a bad version of something that Windows already does? Because you can use it as a starting point for further enhancements. For example, once you learn how to generate a template dynamically, you can dynamically add buttons beyond the boring "OK" button, or you can add additional controls like a "Repeat this answer for all future occurrences of this dialog" checkbox or maybe insert an animation control.

    I'm going to start with a highly inefficient dialog template class. This is not production-quality, but it's good enough for didactic purposes.

    #include <vector>
    class DialogTemplate {
     LPCDLGTEMPLATE Template() { return (LPCDLGTEMPLATE)&v[0]; }
     void AlignToDword()
      { if (v.size() % 4) Write(NULL, 4 - (v.size() % 4)); }
     void Write(LPCVOID pvWrite, DWORD cbWrite) {
      v.insert(v.end(), cbWrite, 0);
      if (pvWrite) CopyMemory(&v[v.size() - cbWrite], pvWrite, cbWrite);
     template<typename T> void Write(T t) { Write(&t, sizeof(T)); }
     void WriteString(LPCWSTR psz)
      { Write(psz, (lstrlenW(psz) + 1) * sizeof(WCHAR)); }
     vector<BYTE> v;

    I didn't spend much time making this class look pretty because it's not the focus of this article. The DialogTemplate class babysits a vector of bytes to which you can Write data. There is also a little AlignToDword method that pads the buffer to the next DWORD boundary. This'll come in handy, too.

    Our message box will need a dialog procedure which ends the dialog when the IDCANCEL button is pressed. If we had made any enhancements to the dialog template, we would handle them here as well.

    INT_PTR CALLBACK DlgProc(HWND hwnd, UINT wm, WPARAM wParam, LPARAM lParam)
     switch (wm) {
     case WM_INITDIALOG: return TRUE;
     case WM_COMMAND:
      if (GET_WM_COMMAND_ID(wParam, lParam) == IDCANCEL) EndDialog(hwnd, 0);
     return FALSE;

    Finally, we build the template. This is not hard, just tedious. Out of sheer laziness, we make the message box a fixed size. If this were for a real program, we would have measured the text (using ncm.lfCaptionFont and ncm.lfMessageFont) to determine the best size for the message box.

    BOOL FakeMessageBox(HWND hwnd, LPCWSTR pszMessage, LPCWSTR pszTitle)
     BOOL fSuccess = FALSE;
     HDC hdc = GetDC(NULL);
     if (hdc) {
      NONCLIENTMETRICSW ncm = { sizeof(ncm) };
      if (SystemParametersInfoW(SPI_GETNONCLIENTMETRICS, 0, &ncm, 0)) {
       DialogTemplate tmp;
       // Write out the extended dialog template header
       tmp.Write<WORD>(1); // dialog version
       tmp.Write<WORD>(0xFFFF); // extended dialog template
       tmp.Write<DWORD>(0); // help ID
       tmp.Write<DWORD>(0); // extended style
       tmp.Write<WORD>(2); // number of controls
       tmp.Write<WORD>(32); // X
       tmp.Write<WORD>(32); // Y
       tmp.Write<WORD>(200); // width
       tmp.Write<WORD>(80); // height
       tmp.WriteString(L""); // no menu
       tmp.WriteString(L""); // default dialog class
       tmp.WriteString(pszTitle); // title
       // Next comes the font description.
       // See text for discussion of fancy formula.
       if (ncm.lfMessageFont.lfHeight < 0) {
         ncm.lfMessageFont.lfHeight = -MulDiv(ncm.lfMessageFont.lfHeight,
                  72, GetDeviceCaps(hdc, LOGPIXELSY));
       tmp.Write<WORD>((WORD)ncm.lfMessageFont.lfHeight); // point
       tmp.Write<WORD>((WORD)ncm.lfMessageFont.lfWeight); // weight
       tmp.Write<BYTE>(ncm.lfMessageFont.lfItalic); // Italic
       tmp.Write<BYTE>(ncm.lfMessageFont.lfCharSet); // CharSet
       // Then come the two controls.  First is the static text.
       tmp.Write<DWORD>(0); // help id
       tmp.Write<DWORD>(0); // window extended style
       tmp.Write<DWORD>(WS_CHILD | WS_VISIBLE); // style
       tmp.Write<WORD>(7); // x
       tmp.Write<WORD>(7); // y
       tmp.Write<WORD>(200-14); // width
       tmp.Write<WORD>(80-7-14-7); // height
       tmp.Write<DWORD>(-1); // control ID
       tmp.Write<DWORD>(0x0082FFFF); // static
       tmp.WriteString(pszMessage); // text
       tmp.Write<WORD>(0); // no extra data
       // Second control is the OK button.
       tmp.Write<DWORD>(0); // help id
       tmp.Write<DWORD>(0); // window extended style
       tmp.Write<DWORD>(WS_CHILD | WS_VISIBLE |
                        WS_GROUP | WS_TABSTOP | BS_DEFPUSHBUTTON); // style
       tmp.Write<WORD>(75); // x
       tmp.Write<WORD>(80-7-14); // y
       tmp.Write<WORD>(50); // width
       tmp.Write<WORD>(14); // height
       tmp.Write<DWORD>(IDCANCEL); // control ID
       tmp.Write<DWORD>(0x0080FFFF); // static
       tmp.WriteString(L"OK"); // text
       tmp.Write<WORD>(0); // no extra data
       // Template is ready - go display it.
       fSuccess = DialogBoxIndirect(g_hinst, tmp.Template(),
                                    hwnd, DlgProc) >= 0;
      ReleaseDC(NULL, hdc); // fixed 11 May
     return fSuccess;

    The fancy formula for determining the font point size is not that fancy after all. The dialog manager converts the font height from point to pixels via the standard formula:

    fontHeight = -MulDiv(pointSize, GetDeviceCaps(hdc, LOGPIXELSY), 72);
    Therefore, to get the original pixel value back, we need to solve this formula for pointSize so that when it is sent through the formula again, we get the original value back.

    The template itself follows the format we discussed earlier, no surprises.

    One subtlety is that the control identifier for our OK button is IDCANCEL instead of the IDOK you might have expected. That's because this message box has only one button, so we want to let the user hit the ESC key to dismiss it.

    Now all that's left to do is take this function for a little spin.

    void OnChar(HWND hwnd, TCHAR ch, int cRepeat)
     if (ch == TEXT(' ')) {
       L"This is the text of a dynamically-generated dialog template. "
       L"If Raymond had more time, this dialog would have looked prettier.",
       L"Title of message box");
        // add to window procedure
        HANDLE_MSG(hwnd, WM_CHAR, OnChar);

    Fire it up, hit the space bar, and observe the faux message box.

    Okay, so it's not very exciting visually, but that wasn't the point. The point is that you now know how to build a dialog template at run-time.

  • The Old New Thing

    Rescuing thread messages from modal loops via message filters


    As we have seen recently, thread messages are eaten by modal loops because they have nowhere to go when dispatched. However, there is a way to see them before they vanish, provided the modal loop is cooperative.

    The WH_MSGFILTER message hook allows you to receive messages passed to the CallMsgFilter function. Fortunately, all the modal loops in the window manager use CallMsgFilter to allow the thread to capture thread messages before they are lost. Therefore, this gives you a way to snoop on messages as they travel through modal loops.

    Let's add a message filter to the program we wrote last time to see how messages pass through a message filter. Note that this is the wrong way to solve the problem. The correct solution was illustrated last time. I'm doing it the wrong way to illustrate message filters since they are not well-understood. (For example, a valid reason for a message filter would to prevent the menu loop from seeing certain input.)

    Start with the program from last the before we changed the PostThreadMessage to a PostMessage, then make the following changes:

    HHOOK g_hhkMSGF;
    LRESULT CALLBACK MsgFilterProc(int code, WPARAM wParam, LPARAM lParam)
     MSG* pmsg = (MSG*)lParam;
     if (code >= 0 && IsThreadMessage(pmsg)) return TRUE;
     return CallNextHookEx(g_hhkMSGF, code, wParam, lParam);
    OnCreate(HWND hwnd, LPCREATESTRUCT lpcs)
     g_hhkMSGF = SetWindowsHookEx(WH_MSGFILTER, MsgFilterProc,
        NULL, GetCurrentThreadId());
     if (!g_hhkMSGF) return FALSE;
     DWORD dwThread;
     HANDLE hThread = CreateThread(NULL, 0, ThreadProc,
           UintToPtr(GetCurrentThreadId()), 0, &dwThread);

    Here, we installed a message filter hook on our thread so that we can seem messages as they pass through modal loops. The code parameter tells us what type of modal loop retrieved the message; we ignore it here since we want to do our filtering for all modal loops.

    Run this program and observe that the beeps are no longer lost because our message filter is getting a chance to see them and react to them.

    The message filter trick relies on all modal loops sending the messages they retrieve through a message filter before dispatching them. If you are writing code that is going into a library, and you have a modal loop, then you too should call the message filter before dispatching messages you've retrieved, in case the program using your library wants to do something with the message.

    MSG msg;
    while (GetMessage(&msg, NULL, 0, 0)) {
     if (!CallMsgFilter(&msg, MSGF_MYLIBRARY)) {

    The value MSGF_MYLIBRARY is an arbitrary positive value you can choose and document in your library's header file. You can see examples of this in the commctrl.h header file:

    #define MSGF_COMMCTRL_BEGINDRAG     0x4200
    #define MSGF_COMMCTRL_SIZEHEADER    0x4201
    #define MSGF_COMMCTRL_DRAGSELECT    0x4202
    #define MSGF_COMMCTRL_TOOLBARCUST   0x4203

    These are the message filters called by the modal loops in the shell common controls library.

    One question you might ask is, "Why use a message filter hook instead of a GetMessage hook?"

    Message filter hooks are less expensive than GetMessage hooks because they are called only upon request, as opposed to a GetMessage hook which is called for every retrieved message. Message filter hooks also tell you which modal loop is doing the filtering, in case you want to adjust your behavior accordingly.

    The downside of message filter hooks is that all modal loops need to remember to call CallMsgFilter as part of their dispatch loop.

  • The Old New Thing

    Watching thread messages disappear


    We saw last time that thread messages are eaten by modal loops. Today we'll illustrate, and then we'll try to fix it next time.

    Start with our scratch program and make the following changes:

    #include <shellapi.h>
    BOOL IsThreadMessage(MSG *pmsg)
     if (pmsg->hwnd == NULL) {
      switch (pmsg->message) {
       case WM_APP: MessageBeep(-1); return TRUE;
     return FALSE;
    // For illustration, we'll post a thread message every two seconds
    DWORD CALLBACK ThreadProc(void *lpParameter)
     DWORD dwThread = PtrToUint(lpParameter);
     for (;;) {
      PostThreadMessage(dwThread, WM_APP, 0, 0);
     return 0;
    OnCreate(HWND hwnd, LPCREATESTRUCT lpcs)
     // Start the timer that posts the thread message
     DWORD dwThread;
     HANDLE hThread = CreateThread(NULL, 0, ThreadProc,
           UintToPtr(GetCurrentThreadId()), 0, &dwThread);
     if (!hThread) return FALSE;
     // create some content - just to make things interesting
     g_hwndChild = CreateWindow(WC_LISTVIEW, NULL,
                                WS_CHILD | WS_VISIBLE | LVS_ICON, 0, 0, 0, 0,
                                hwnd, (HMENU)1, g_hinst, 0);
        if (!g_hwndChild) return FALSE;
        SHFILEINFO sfi;
        HIMAGELIST himl = (HIMAGELIST)SHGetFileInfo(TEXT("C:\\"), 0,
                &sfi, sizeof(sfi),
        if (!himl) return FALSE;
        ListView_SetImageList(g_hwndChild, himl, LVSIL_NORMAL);
        for (int i = 0; i < 50; i++) {
         LVITEM item;
         item.iItem = i;
         item.iSubItem = 0;
         item.mask = LVIF_TEXT | LVIF_IMAGE;
         item.pszText = sfi.szDisplayName;
         item.iImage = sfi.iIcon;
         if (ListView_InsertItem(g_hwndChild, &item) < 0) return FALSE;
        return TRUE;
    void OnClose(HWND hwnd)
     if (MessageBox(hwnd, TEXT("Really?"), TEXT("Title"),
         MB_YESNO) == IDYES) {
    // add to window procedure
        HANDLE_MSG(hwnd, WM_CLOSE, OnClose);
        while (GetMessage(&msg, NULL, 0, 0)) {
          if (!IsThreadMessage(&msg)) {

    Run this program and notice that it beeps every two seconds, or at least it does most of the time. If you right-click on the caption bar or grab the edge of the window to start resizing it or grab the scollbar or start a drag-selection or display a message box, the beeps stop. That's because all of those actions are modal operations, and the modal message loop is eating the thread messages.

    Save this program because we'll come back to it.

    The obvious solution is to post the message to the main window itself rather than to the thread. You have a window handle; use it!

    DWORD CALLBACK ThreadProc(void *lpParameter)
     HWND hwnd = reinterpret_cast<HWND>(lpParameter);
     for (;;) {
      PostMessage(hwnd, WM_APP, 0, 0);
     return 0;
     HANDLE hThread = CreateThread(NULL, 0, ThreadProc,
           reinterpret_cast<void*>(hwnd), 0, &dwThread);
    // add to window procedure
     case WM_APP: MessageBeep(-1); return 0;
        while (GetMessage(&msg, NULL, 0, 0)) {
          if (!IsThreadMessage(&msg)) {

    Now that that problem has been solved, I'm going to tempt fate and solve the problem the wrong way because I want to illustrate message filters. Next time.

  • The Old New Thing

    If you pull a 1920's fire extinguisher out of the ocean, for pete's sake don't drink it!


    Oceanographer Curtis Ebbesmeyer is a fascinating source of information. He appeared again on my local public radio station to discuss issues related to garbage floating in the ocean. For example, at the 5:05 mark, he reminds us that, if you pull a 1920's fire extinguisher out of the ocean, you shouldn't drink it.

    Other fascinating facts:

    • Ten-pound bowling balls float.
    • Sneakers float upside-down, and the tongue acts as a rudder, resulting in left-footed sneakers and right-footed sneakers washing up on different shores. (Beachcombers from different-footed shores occasionally meet up to try to assemble a pair.)
    • There are 1939 different species of plastic ducks.
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