编程怎么实现win窗口置顶且不覆盖其他窗口？说明原理即可。

其实你试试不就知道了，又不是什么难事！
show时把垫底的窗口对象作为参数。
比如在form1中：
form2 frm =new form2();
frm.show(this);
这样打开的form2窗口就保持在本窗口之上了。

SetWindowPos
其中设置e799bee5baa6e59b9ee7ad94365HWND_TOPMOST

以下来MSDN
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SetWindowPos
The SetWindowPos function changes the size, position, and Z order of a child, pop-up, or top-level window. Child, pop-up, and top-level windows are ordered according to their appearance on the screen. The topmost window receives the highest rank and is the first window in the Z order.

BOOL SetWindowPos(
HWND hWnd, // handle to window
HWND hWndInsertAfter, // placement-order handle
int X, // horizontal position
int Y, // vertical position
int cx, // width
int cy, // height
UINT uFlags // window-positioning flags
);

Parameters
hWnd
Handle to the window.
hWndInsertAfter
Handle to the window to precede the positioned window in the Z order. This parameter must be a window handle or one of the following values: Value Meaning
HWND_BOTTOM Places the window at the bottom of the Z order. If the hWnd parameter identifies a topmost window, the window loses its topmost status and is placed at the bottom of all other windows.
HWND_NOTOPMOST Places the window above all non-topmost windows (that is, behind all topmost windows). This flag has no effect if the window is already a non-topmost window.
HWND_TOP Places the window at the top of the Z order.
HWND_TOPMOST Places the window above all non-topmost windows. The window maintains its topmost position even when it is deactivated.

For more information about how this parameter is used, see the following Remarks section.

X
Specifies the new position of the left side of the window, in client coordinates.
Y
Specifies the new position of the top of the window, in client coordinates.
cx
Specifies the new width of the window, in pixels.
cy
Specifies the new height of the window, in pixels.
uFlags
Specifies the window sizing and positioning flags. This parameter can be a combination of the following values: Value Meaning
SWP_ASYNCWINDOWPOS If the calling thread does not own the window, the system posts the request to the thread that owns the window. This prevents the calling thread from blocking its execution while other threads process the request.
SWP_DEFERERASE Prevents generation of the WM_SYNCPAINT message.
SWP_DRAWFRAME Draws a frame (defined in the window's class description) around the window.
SWP_FRAMECHANGED Sends a WM_NCCALCSIZE message to the window, even if the window's size is not being changed. If this flag is not specified, WM_NCCALCSIZE is sent only when the window's size is being changed.
SWP_HIDEWINDOW Hides the window.
SWP_NOACTIVATE Does not activate the window. If this flag is not set, the window is activated and moved to the top of either the topmost or non-topmost group (depending on the setting of the hWndInsertAfter parameter).
SWP_NOCOPYBITS Discards the entire contents of the client area. If this flag is not specified, the valid contents of the client area are saved and copied back into the client area after the window is sized or repositioned.
SWP_NOMOVE Retains the current position (ignores the X and Y parameters).
SWP_NOOWNERZORDER Does not change the owner window's position in the Z order.
SWP_NOREDRAW Does not redraw changes. If this flag is set, no repainting of any kind occurs. This applies to the client area, the nonclient area (including the title bar and scroll bars), and any part of the parent window uncovered as a result of the window being moved. When this flag is set, the application must explicitly invalidate or redraw any parts of the window and parent window that need redrawing.
SWP_NOREPOSITION Same as the SWP_NOOWNERZORDER flag.
SWP_NOSENDCHANGING Prevents the window from receiving the WM_WINDOWPOSCHANGING message.
SWP_NOSIZE Retains the current size (ignores the cx and cy parameters).
SWP_NOZORDER Retains the current Z order (ignores the hWndInsertAfter parameter).
SWP_SHOWWINDOW Displays the window.

Return Values
If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. To get extended error information, callGetLastError.