Microsoft Win32 Interview Questions
- What types of threads are supported by MFC framework? A: Working thread and windows thread. Working thread usually does not have a user interface and easier to use. Windows thread has an user interface and usually used to improve responsiveness of the user input. Message Map
- When ON_UPDATE_COMMAND_UI is called? (message may vary) A: When a user of your application pulls down a menu, each menu item needs to know whether it should be displayed as enabled or disabled. The target of a menu command provides this information by implementing an ON_UPDATE_COMMAND_UI handler.
- What is a “hook”? A: A point in the Windows message-handling mechanism where an application can install a subroutine to monitor messages. You need hooks to implement your own Windows message filter.
- What are the difference between MFC Exception macros and C++ exception keywords? A:Actually, MFC macros may accept exception of only CException class or class, derived from CException, where as C++ exception mechanism accepts exception of ANY type Reusable Control Class
- How would you set the background of an edit control to a customized color? A: You have several choices, but the simplest one is subclassing. Kruglinski in his “Inside Visual C++” describes pretty well this process. Generally, you derive the class from none control class, override the messages you want (like WM_CTLCOLOR) and then in init function like OnInitialUpdate of CDialog, subclass the control with SubclassDlgItem().
- What is Message Reflection? How could you accomplish the above task using message reflection? A: See Technical Note 62 of MSDN. Usually, message is handled in the parent class that means you have to override message handler for each parent. Sometimes it is nice to handle a message in the control itself, without parent invocation. Such handling mechanism is called message reflection. Control “reflects” message to itself and then processes it. Use ON_<MESSAGE_NAME>_REFLECT macro to create a reflected message.
- What is the command routing in MFC framework? A: CView => CDocument => CFrameWnd => CWinApp
- What’s the purpose of CView class? CDocument class? What are relationships between them? A: The CView class provides the basic functionality for user-defined view classes. A view is attached to a document and acts as an intermediary between the document and the user: the view renders an image of the document on the screen or printer and interprets user input as operations upon the document. The CDocument class provides the basic functionality for user-defined document classes. A document represents the unit of data that the user typically opens with the File Open command and saves with the File Save command. Users interact with a document through the CView object(s) associated with it. A view is a child of a frame window. The relationship between a view class, a frame window class, and a document class is established by a CDocTemplate object. A view can be attached to only one document, but a document can have multiple views attached to it at once.
- What class is responsible for document template in MDI application? A: CMultiDocTemplate.
- What function must be used to add document template? A: AddDocTemplate.
- What the main objects are created for SDI and MDI applications? A: CWinApp - application object. For MDI application with New document implementation CDocTemplate, CDocument, CView, CMainFrame. If your application is SDI, your CMainFrame class is derived from class CFrameWnd. If your application is MDI, CMainFrame is derived from class CMDIFrameWnd. For MDI application CMDIChildWindow is also created.
- We have a loop for 800,000. It fails on 756,322. How can we get the information before it fails? A: You could think of several way to debug this: Set the condition in debugger to stop when loop is passed around 756321 times. Throw an exception within a loop (may be not the best idea since exception does not show you the exact location of the fail. Create a log file and to put detailed information within a loop.
- Our Debug version works fine, but Release fails. What should be done? A: There are four differences between debug and release builds:
- heap layout (you may have heap overwrite in release mode - this will cause 90% of all problems),
- compilation (check conditional compilation statements, assertion functions etc.),
- pointer support (no padding in release mode which may increase chances of a pointer to point into sky)
- optimization.
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