What is MFC?
MFC is the C++ class library Microsoft provides to place an object-oriented wrapper around the Windows API.The Microsoft Foundation Class (MFC) Library is a collection of classes written in the C++ that can be used in building application programs. It allows developers to more easily work with Windows operating systems and in developing Windows applications.
What is the difference between the ASSERT and VERIFY macros?
Both ASSERT and VERIFY macros behave in the same Manner in debug Version.But in Release version the Expression in the ASSERT is ignored. And in Release version the Expression in the VERIFY is evaluated. But not verified. Means the expression is evaluated. And like dubug it is NOT stop the execution if the expression evaluated to FALSECan you explain the relashionship between document,frame and view ?
The frame window is the application's top-level window. It's normally a WS_OVERLAPPEDWINDOW-style window with a resizing border, a title bar, a system menu, and minimize, maximize, and close buttons.The view is a child window sized to fit the frame window so that it becomes the frame window's client area.
The application's data is stored in the document object, a visible representation of which appears in the view.
For an SDI application, the frame window class is derived from CFrameWnd, the document class is derived from CDocument, and the view class is derived from CView or a related class such as CScrollView.
What is the difference between hinsrtance and hprevinstance in WinMain function?
hInstance : will be having the handle of the current instancehPrevInctance : will be having the handle of last instance. hPrevInstance is NULL if only one instance is running
if you are using 32-bit os then the entry to the hPrevInstance is always NULL.
It was used in the 16 bit os where the instance of previosly running application was saved . so that it can be refered again ! due the memory restriction.
What is the difference between hinsrtance and hprevinstance in WinMain function?
hInstance : will be having the handle of the current instancehPrevInctance : will be having the handle of last instance. hPrevInstance is NULL if only one instance is running
if you are using 32-bit os then the entry to the hPrevInstance is always NULL.
It was used in the 16 bit os where the instance of previosly running application was saved . so that it can be refered again ! due the memory restriction.
Explain about MDI and CMultiDocTemplate ?
To Established the relationship between CView and CDocument with CDoctemplate and Multidoctemplate.Cdoctemplate for SDI and CMultidoctemplate for MDIWhat function is used to disable a control at runtime?
// Get a pointer to the control's window.CWnd *p = GetDlgItem(IDC_NEWCONTROL);
// Disable the control.
p->EnableWindow(FALSE);
Which CPrintInfo member variable must be set for multiple page printouts?
RTTI (Run Time Type Identification) in MFC can be handled by using the class CRunTimeClass.
But CRunTimeClass can be use to identify the type of the class which are derived from CObject.
For eg -
void MyFunction()
{
CObject *mObject = new MyClass;
if(mObject->IsKindOf(RUNTIME_CLASS( MyClass) ) )
{
printf("Class is of type MyClass\n");
}
else
{
printf("Class is of type someotherclass\n");
}
}
We can use "type_info" for other type of classes which are
not derived from CObject.What is the use of CObject::Dump function ?
Dumps the contents of your object.When you write your own class, you should override the Dump function to provide diagnostic services for yourself and other users of your class. The overridden Dump usually calls the Dump function of its base class before printing data members unique to the derived class.Dump function should not print a newline character at the end of its output.Dump is a const function, you are not permitted to change the object state during the dump.
// example for CObject::Dump
void CAge::Dump( CDumpContext &dc ) const
{
CObject::Dump( dc );
dc << "Age = " << m_years;
}
What is the use of UpdateData funciton ?
UpdateData function is used to get or set the values in your appropriate control variables. UpdateData ( FALSE ) would update the data from control variables to control, while UpdateData ( TRUE ) would assing the data from controls to control variable.This function need not be called if you are using DDX ( Dynamic Data Exchange ).
BOOL UpdateData( BOOL bSaveAndValidate = TRUE );
UpdateData(TRUE) indicate dialog box is being initialized
UpdateData(FALSE) indicates data is being retrieved from the
dialog box.
Call this member function to initialize data in a dialog box, or to retrieve and validate dialog data.
What is the difference between GetMessage and PeekMessage ?
The major difference between the two is that GetMessage() doesn't return until it finds a message to retrieve from the Application Queue, this allows us to free up precious CPUusage for other programs to use. PeekMessage() returns immediately weather there are any messages or not, this allows us to utilize the time between messages, for example
to render a 3D scene.
How to update all the views whenver document got updated ?
Calling UpdateAllViews() functionWhat are the types of button controls?
Command Button
What is the base class for most MFC classes?
CObject
How to handle command line arguements from simple MFC application?
m_lpCmdLine Corresponds to the lpCmdLine parameter passed by Windows to WinMain. Points to a null-terminated string that specifies the command line for the application. Use m_lpCmdLine to access any command-line arguments the user entered when the application was started. m_lpCmdLine is a public variable of type LPTSTR.If I derive a new class from CObject what are the basic features my derived will get?
Searialization, Debugging support, Runtime time class information, compatibility with collection classes.What is the use of CCmdTarget ?
It is the base class for the MFC library message map architecture.Which maps commands/messages to the member functions to handle them. Classes derived from this are CWnd,CWinApp,CFrameWnd,CView, CDocumentHow to access document object from view ?
Using GetDocument() function within a CView class.What is the entry point for window based applications ?
WinMain() is the entry point for window based applications.What is the use of message map ?
Message map is a macro used to handle messgaes by calling appropriate functions. i.e
BEGIN_MESSAGE_MAP(CMywnd,CFrameWnd)
ON_WM_PAINT()
END_MESSAGE_MAP
Here OnPaint method will be called whn WM_PAINT message comes. MessageMap is a logical table that maps the windows messages to the member functions of the class. MFC handles Windows message in a different way. Because MFC applications are built upon classes, it is more convenient to handle messages within class member functions instead of one big callbackfunction.In MFC, this is achieved through message mapping: we can implement the functions that will be used to execute commands, and use macros defined in MFC to direct the messages into these member functions.
How to convert a CString variable to char* or LPTSTR?
Use CString::GetBuffer(). It can be used in a manner similar to this:// prototype of a function that takes a LPTSTR parameter
// presented for argument's sake.
void test_func ( LPTSTR lpszString, int length );
CString string;
test_func ( string.GetBuffer ( 50 ), 50 );
string.ReleaseBuffer ( );
Forgetting to call CString::ReleaseBuffer() can cause problems very difficult to debug as it releases the lock on CString's inner buffer. One thing to keep in mind about CString::GetBuffer() is that it returns a TCHAR* value (or LPTSTR, it's the same), so it is subject to the same ANSI/MBCS Vs. UNICODE convertions as most other Win32 APIs. It also means that if you're compiling a unicode version of your application, and
specifically need a char* from your CString instance, you'll have to use a separate buffer of the appropriate type, and then make the convertion to unicode using one of the vailable API's before asigning it's value to the CString instance. The same goes if you're doing the exact opposite: getting a WCHAR* out of a CString, while compiling in MBCS mode.
ii) Use a temporary variable. For example:
char temp[256];
CString string;
test_func ( temp, 256 );
string = temp;
How to handle dynamic menus in MFC?
Dynamic menus can be handled using Cmenu's Createmenu,Insrtmenu and Appendmenu functions.What is serialization ?which function is responsible for serializing data ?
Serialization is the process of writing or reading an object to or from a persistent storage medium, such as a disk file. Serializing an object requires 3 ingredients:• A CFile object representing the datafile
• A CArchive object that provides the serialization context
• The object being serialized
Serialization represents a relationship between objects derived from the CObject class, the CArchive class representing an archive, and the CFile class that represents physical storage.
What function is used to retrieve the currently selected index in a list box?
GetCurSel() will be used to retrieve the index number and GetText() is used to retrieve the text.
//Example
int index;
CString strText;
index = m_ctlListBox.GetCurSel();
m_ListBox.GetText(index,strText);
CString strText;
index = m_ctlListBox.GetCurSel();
m_ListBox.GetText(index,strText);
What is CArchive class dowes?
The MFC Library uses CArchive objects for serialization. A CArchive object represents persistent storage of some kind. When an object is about to be serialized, CArchive calls the object's Serialize member function, one of the overridable functions in CObject. Thus, the underlying philosophy is that it is the object that knows best how to prepare itself for persistent storage, while it is the CArchive object that knows how to transfer the resulting data stream to persistent media.The CArchive class allows you to save a complex network of objects in a permanent binary form (usually disk storage) that persists after those objects are deleted. Later you can load the objects from persistent storage, reconstituting them in memory. This process of making data persistent is called “serialization.”
What is the use of OninitDialog ?
All your initialization for your dialog can be inside "OnInitDialog". Basically to set default / preset values to your dialog controls.What is the use of Mutex and critical section?
An object of class CMutex represents a “mutex” — a synchronization object that allows one thread mutually exclusive access to a resource. Mutexes are useful when only one thread at a time can be allowed to modify data or some other controlled resource. For example, adding nodes to a linked list is a process that should only be allowed by one thread at a time. By using a CMutex object to control the linked list, only one thread at a time can gain access to the list.To use a CMutex object, construct the CMutex object when it is needed. Specify the name of the mutex you wish to wait on, and that your application should initially own it. You can then access the mutex when the constructor returns. Call CSyncObject::Unlock when you are done accessing the controlled resource.
What is model and modeless dialog box ? Give some examples?
When we create Modal Dialog Box we can't move to other windows until this dialog is closed. For eg: MessageBox, where we can't move to the other window until we press ok or cancel. When we create Modeless Dilaog Box we can swap to the other windows. For eg: like a conventional window.How to create open & save dialogs ?
In CommonDialogs class we have to use CFileDialog class where the first parameter TRUE for open dialog and FALSE for Save dialog.For file open:
CFileDialog SampleDlg(TRUE,NULL,NULL,OFN_OVERWRITEPROMPT,"Text Files (*.txt)|*.txt|Comma Separated Values(*.csv)|*.csv||");
int iRet = SampleDlg.DoModal();
What is CSingleDocTemplate?
It’s a document template class used to create single document interface SDI applications. Only one document can be opened at a time. It identifies the document class used to manage the application's data, the frame window class that encloses views of that data, and the view class used to draw visual representations of the data. The document template also stores a resource ID that the framework uses to load menus, accelerators, and other resources that shape the application's user interface.Explain about MDI and CMultiDocTemplate ?
MDI applications are designed using the doc-view architectures in which there could be many views associated with a single document object and an application can open multiple docuements at the same time for eg:WORD.In MDI terms, your main window is called the Frame, this is probably the only window you would have in a SDI (Single Document Interface) program. In MDI there is an additional window, called the MDI Client Window which is a child of your Frame window. CMultiDocTemplate is the document template class used to create MDI applications..The document template also stores a resource ID that the framework uses to load menus, accelerators, and other resources that shape the application's user interface.
Tell me the different controls in MFC ?
CAnimateCtrl,CButton,CEdit,CListBox,CComboBox,CRic hEditCtrl,CStatic, CTreeCtrl,CToolTipCtrl,CIPAddressCtrl,CTabCtrl,CDa teTimeCtrl,CHeaderCtrl,CListCtrl,CMonthCalCtrl,COl eCtrl,CProgressCtrl,CScrollBar,CSliderCtrl,CStatus BarCtrl,CTollBarCtrl etc.,What is the use of OnInitDialog ?
This message is sent to the dialog box during the Create, CreateIndirect, or DoModal calls, which occur immediately before the dialog box is displayed. This can be used to intialize the dialog controls or show/hide the controls etc.,What is the functioning of UpdateData() funciton ?
This is to initialize data in a dialog box, or to retrieve and validate dialog data.The framework automatically calls UpdateData with bSaveAndValidate set to FALSE when a modal dialog box is created in the default implementation of CDialog::OnInitDialog. The call occurs before the dialog box is visible. The default implementation of CDialog::OnOK calls this member function with bSaveAndValidate set to TRUE to retrieve the data, and if successful, will close the dialog box. If the Cancel button is clicked in the dialog box, the dialog box is closed without the data being retrieved.
How to handle RTTI in MFC ?
Run-Time Type Information is a mechanism that allows the type of an object to be determined during the program execution.Three main elements to RTTI in MFC are:
1.Dynamic_cast operator - Used for conversion of polymorphic types.
2.typeid - used for identifying the exact type of an object
3. type_info class used to hold the type information returned by typeid.
What is serialization ?which function is responsible for serializing data ?
Searialization is the process of streaming the object data to or from a persistent storage medium. It's useful in Doc-View Architecture. CObject :: Serialize() function is used to do serialization.Explain about different kinds of threads in MFC?
Two types of thread in MFc are UserInterface thread and worker thread. UserInterface threads maintain the message loops and used to handles user input,creates windows and process messges sent to those windows.Worker thread don't use message loops and mainly used to perform background operations such as printing etc.,Created using AfxBeginThread bypassing ThreadFunction to create worker thread and Runtime class object to create a user interface thread.what is the use of Mutex and critical section ?
Mutex as the name suggest allows a mutullay exclusive access to a shared resource among the threads. Critical section is a piece of code that can be executed safely to be accessed by two or more threads. Criticalsection provides synchronization means for one process only, while mutexes allow data synchronization across processes. Means two or more threads can share the common resources among more than one application or process boundaries in mutex.What is socket?
A "socket" is an endpoint of communication: an object through which your application communicates with other Windows Sockets applications across a network.The two MFC Windows Sockets programming models are supported by the following classes: CAsyncSocket and CSocket.What is the difference between Synchronous sockets and asynchronous sockets?
Consider a server application that is listening on a specific port to get data from clients. In synchronous receiving, while the server is waiting to receive data from a client, if the stream is empty the main thread will block until the request for data is satisfied. Hence, the server cannot do anything else until it receives data from the client. If another client attempts to connect to the server at that time, the server cannot process that request because it is blocked on the first client. This behavior is not acceptable for a real-world application where we need to support multiple clients at the same time.In asynchronous communication, while the server is listening or receiving data from a client, it can still process connection requests from other clients as well as receive data from those clients. When a server is receiving asynchronously, a separate thread (at the OS level) listens on the socket and will invoke a callback function when a socket event occurs. This callback function in turn will respond and process that socket event.
Have you ever used win32 APIs ?
MFC is a wrapper around win32 API, It provides classes which uses the win32 API, Some of the API's we usually work with are : GetDlgItemInt,GetDlgItemText,GetWindowTextA,Messag eBoxA,CreateFile,CreateMutex,CreateEvent,WaitForSi ngleObject,CreateWindow,ShowWindow etc.,What is the difference between ANSI Code and UNICODE ?
ANSI code represents 8bytes data where UNICODE represents 16bytes data for supporting universal languages. One major draw back to ASCII was you could only have 256 different characters. However, languages such as Japanese and Arabic have thousands of characters. Thus ASCII would not work in these situations. The result was Unicode which allowed for up to 65,536 different characters.What is a message map, and what is the advantage of a message map over virtual function?
MessageMap is a logical table that maps the windows messages to the member functions of the class. We use message maps over virtual function because of lots of overhead. If every windows message had a virtual function associated with it , there would be several hundred bytes per window class of vtable. Message maps means we only pay for the messages we use.Given two processes, how can they share memory?
Processes and thread are very similar but they differ in the way they share their resources. Processes are independent and have its own address space. If two independent processes want to communicate they do this by using the following techniques 1.Message Passing 2.Sockets 3. named pipesHow to Initialize contents of a dialog?
In MFC, the contents of a dialog are initialized if they are associated with their corresponding data members. This is done through "UpdateData(FALSE)" function. The control data is transferred to the data members through "UpdateData(TRUE)".In WIN32, the dialog data in controls can be initialized during WM_INITDIALOG call. The control data can be updated to the dialog members using apppropriate "SendMessage" functions.
About GDI object?
GDI object (is a graphical device object) used to write on a device context for graphical output. GDI objects are: Pen, Brush, Font,Line, Rectangle etc. These objects are created using their corresponding win32 function. For eg, CreatePen, CreatePenIndirect are used to create a pen object. After these objects are created they would need to be selected to the device context before processing using "SelectObject" function.GDI objects are not associated with any device context during its creation. SelectObject function does that assocaition. Once an object is selected into the device context it would be available until the object is destroyed through DeleteObject or the program exits.
