注意GetMessage()的返回值

这个函数虽然返回值类型是BOOL，但是还有可能返回-1 ！

Return Value

BOOL

If the function retrieves a message other than WM_QUIT , the return value is nonzero.

If the function retrieves the WM_QUIT message, the return value is zero.

If there is an error, the return value is -1. For example, the function fails if hWnd is an invalid window handle or lpMsg is an invalid pointer. To get extended error information, call GetLastError .

 

Because the return value can be nonzero, zero, or -1, avoid code like this:

while (GetMessage( lpMsg, hWnd, 0, 0)) ...

The possibility of a -1 return value means that such code can lead to fatal application errors. Instead, use code like this:

BOOL bRet;



while( (bRet = GetMessage( &msg, hWnd, 0, 0 )) != 0)

{ 

    if (bRet == -1)

    {

        // handle the error and possibly exit

    }

    else

    {

        TranslateMessage(&msg); 

        DispatchMessage(&msg); 

    }

}