Why does EnumWindows return more windows than I expected?

The windows that you are talking about, with an X button and a title bar, etc. are not the only kind of windows. Buttons, dropdown menus, labels, icons, text boxes, the task bar, and just about everything else is a window too¹. So EnumWindows is doing exactly what it's supposed to do: enumerate all the top level windows.

¹ Even though this is true, EnumWindows only enumerates the top level windows. That means it won't enumerate any child windows:

The EnumWindows function does not enumerate child windows, with the exception of a few top-level windows owned by the system that have the WS_CHILD style.

However, many things on your desktop are windows as well, not just the "windows" you're thinking about.

The answer provided by @jondinham does work perfectly for me. So I work out my own solution.

1.Problems I met with previous solution

Running on Windows 10 home edition 1909., I get two extra unexpected Windows "Calculator" and "Setting".

In addition, windows of Tencent QQ can not be detected, because the following fails:

// the following removes some task tray programs and "Program Manager"
ti.cbSize = sizeof(ti);
GetTitleBarInfo(hwnd, &ti);
if(ti.rgstate[0] & STATE_SYSTEM_INVISIBLE)
    return FALSE;

However, I think the bug may be resulted by the particularity of Tencent QQ, I can not even make its' window TOPMOST with DeferWindowPos.

Perhaps someone can help me figure out why this happened and help improving the previous solution by @jondinham.

2.My Solution

I tried to examing the icons of the windows, and filter out windows that does not have its own icon or uses the icon same as the system default. I use code snippets from answer and answer and do some modification. This solution works very well for me.

HICON get_windows_HICON_critical(HWND hwnd)
{
    // Get the window icon
    HICON icon = reinterpret_cast<HICON>(::SendMessageW(hwnd, WM_GETICON, ICON_SMALL, 0));
    if (icon == 0) {
      // Alternative method. Get from the window class
      icon = reinterpret_cast<HICON>(::GetClassLongPtrW(hwnd, GCLP_HICONSM));
    }
    // Alternative method: get the first icon from the main module (executable image of the process)
    if (icon == 0) {
      icon = ::LoadIcon(GetModuleHandleW(0), MAKEINTRESOURCE(0));
    }
//    // Alternative method. Use OS default icon
//    if (icon == 0) {
//      icon = ::LoadIcon(0, IDI_APPLICATION);
//    }
    if(icon == ::LoadIcon(0, IDI_APPLICATION)){
        // Filter out those with default icons
        icon = 0;
    }
    return icon;
}


static BOOL CALLBACK enumWindowCallback(HWND hWnd, LPARAM lparam) {
    int length = GetWindowTextLength(hWnd);
    char* buffer = new char[length + 1];
    GetWindowText(hWnd, buffer, length + 1);
    std::string windowTitle(buffer);

    // List visible windows with a non-empty title
    if (IsWindowVisible(hWnd) && length != 0) {
        HICON icon = get_windows_HICON_critical(hWnd);
        if(icon!=0){
            std::cout << hWnd << ":  " << windowTitle << std::endl;
        }
    }
    return TRUE;
}

3.Problems with my solution

My solution can not deal with Windows Store APP, according to this question.

The way to list out only windows in taskbar (or similarly in Alt-Tab box) is described by Raymond in this article on MSDN blog:

Which windows appear in the Alt+Tab list?

And this is the super function to check whether a window is shown in alt-tab:

BOOL IsAltTabWindow(HWND hwnd)
{
    TITLEBARINFO ti;
    HWND hwndTry, hwndWalk = NULL;

    if(!IsWindowVisible(hwnd))
        return FALSE;

    hwndTry = GetAncestor(hwnd, GA_ROOTOWNER);
    while(hwndTry != hwndWalk) 
    {
        hwndWalk = hwndTry;
        hwndTry = GetLastActivePopup(hwndWalk);
        if(IsWindowVisible(hwndTry)) 
            break;
    }
    if(hwndWalk != hwnd)
        return FALSE;

    // the following removes some task tray programs and "Program Manager"
    ti.cbSize = sizeof(ti);
    GetTitleBarInfo(hwnd, &ti);
    if(ti.rgstate[0] & STATE_SYSTEM_INVISIBLE)
        return FALSE;

    // Tool windows should not be displayed either, these do not appear in the
    // task bar.
    if(GetWindowLong(hwnd, GWL_EXSTYLE) & WS_EX_TOOLWINDOW)
        return FALSE;

    return TRUE;
}

Credited to the source code here:
http://www.dfcd.net/projects/switcher/switcher.c