InterviewQuestions

Interview

VB------------1 What is the difference between activeX Exe and ActiveX DLL2 Late Binding Vs Early Binding3 Inheritense - Type of inheritense4 Version Compatibility5 Error handling6 How to compile code in VB7 Can we use events in VB how to declare it With Events key words8 What is marshelling9 what is DLL Hell10 Can we validate a control by default11 What is a collection How to use it12 What are class instancing properties(Private PublicNotCreatable MultiUse GlobalMultiUse for dll)(SingleUse and Global Single use for activeX exe)13 What are access modifier14 When an access modifier friend is used15 What kind of threading model is used in VB16 What is unattened Execution17 Can we provide any command line agruements to vb program18 Can we do conditional compilation in VB

COM---------------1 What is com3 What is IUNKnown Interface (Addref release queryinterface) 2 What is QueryInterface4 What is polymorphism Can we implement polymorphism in VB5 COM components implements which interface for automation IDispatch What are IDispatch methods6 What is dual interface how it is different to Idispatch interface

DCOM----------------1 What is DCOM2 What is the difference between DCOM and Webservices3 What is stub and proxy4

ASP-------------1 What are different objects in ASP2 What are the different modes to pass data from one page to another3 How to know which user has logged into the system Logon_User4 How to abandon the session5 How to include a file in ASP6 How to make variable declaration mandatory in ASP7 What is dictionary object in aSP8 What is responsebuffer property9 What is responseflush property10 How to lock the application before making any update through application object

11 Error handling in ASP12 How to open a text file using ASP13 What are different authentication types in IIS

ADO----------------1 What are different object in ADO2 what are different locks type3 What are different cursor types What is cursor location property4 How can we execute the stored procedure5 How to get a recordset from stored procedure oraclesql server6 Error handling in ADO

XML----------------------------------1 What is XML2 When to use XML and when to use Database3 Can we query an XML How4 How to validate an XML5 what is object navigator 7 Fatest way to read XML in net 8 Storing foreign language characters in XMl like jap russsian chinese 9

SourceSafe------------------1 What is source safe2 Can multiple users can simultaniouly checkout the same file3 How a ascii file and binary files are stored in the VSS

Javascript---------------------

NET----------------1 What is differene between VBNETCnet2 What is Web service3 What are the building blocks of Webservice4 What is difference between ASPCOM based architecture and NET architecture5 What is an Assembly what is GAC6 what is CLR7 What is type safety8 What is namespace9 What are NET enterprise servers10What are muticast delegates when are they used 11 What are reflections what is Type object 12 Boxing and Unboxing and when are they done 13 Event handlings and custom events in Dotnet 14 How do you ActiveXExe equivalent in Dotnet 15 how does inner keyword affect classvisibility

16 Public and private keys concept When and how do you use it17 How is that the assembly is preserved using key pairs 18 What is binding policy How do u dynamically load dlls 17 what is codebase property in the app config file How do use it dynamically download an assembly 18 what is native image generator 19 Difference btwn GAC and Native image storing 20 Explain app config file 21 Relation between namespace and assemblies 22 what are sealed classes 23 Architecture of Net remoting 24 Remoting types 25 Explain singleton singlecall client activated objects Their merits and demerits 26 configuration of remoting using app config file 27 Ways to Hosting of Remote objects 28 How do convert remote object to resceptive webservice 29 How do you handle concurrency in Remote objects30 What is attribute programming Example 31 WHat is Distributed transtaction coordinator How is it in net 32 Different kinds of formatter available How is serialize and deserialize33 What is a context in a application ow do explain it with Marshalbyref 34 what is marshalbyVal 35 How do you bind webservices dynamically 36 Async reading of websewrvice 37 Explain multithreaded app and sync concept 38 what are windows services how is configure them in Net 39 how is object poooling achieved in net 40 Explain store and forward pattern and how do u implement the same in net

ADONet 1WHy datasets what is commandbuilder 2Dynamic generations of update insert commands for dataadapters3How do u build relations in dataset 4Explain xml support for dataset 5 How do generate typed datasets

webservies

GDI programming

COM+ Interop

soapsuds tools installuitl snk install regsrvr32 wsdlproxygenerator console admintools gtnet config wizard

ASPNET1 What is server control2 What is validation control3 What are different type of caching(Page Fragment data)4 what is XMLHTTP5 Different kinds of session management 6 Types of caching dependency7 Dynamic caching 8 Role based authetication using Principals and Identity objects

VBNET1 What is alising

COMDCOM

1 What is COM

COM provides a group of conventions and supporting libraries that allow interaction between different pieces of software in a consistent object-oriented way

COM is a binary standard for component interoperability It helps to build language neutral components

2 What is dual interface

An interface that supports both IDispatch and VTBL binding COM Dlls developed in VB automatically inherits IdispatchImpl interface and

thus dual interface

3 Have you ever worked on DCOM If yes explain the architecture of any one of the application

ltlt Need to explain typical application architecture here gtgt

4 What are the various services provided by the MTSCOM+ system

Manage server process pools and thread pools Ultimately rather than dedicating a thread to work on behalf of a single client servers need to manage thread pools for servicing multiple client requests

Synchronize access to shared data and resources across concurrent requests from clients This requires sophisticated locking protocols that must account for deadlocks race conditions starvation and other performance issues

Manage client context including database connections and per-user data structures (or objects)

Cache state on the client for improved latency across slow networks Implement security to ensure that business functions and objects are only

available to those authorized to use them Implement management and configuration tools to allow remote installation

and administration of the servers

5 What are AdvantagesDisadvantages of ActiveX controls over DLL

Look for an answer similar to points mentioned in the table below

ActiveX DLLEncapsulates the whole aspects of the object

Encapsulates only functional aspect of the object

Pretty complicated for implementation and usage

Much easier to implement and use

Binary compatibility specification (may be used in different platforms)

Implemented only for Win32 platform

6 What is IUnknown What methods provided by IUnknown

It is generally good idea to have an answer for this question if you claim you know COM in your resume Otherwise you may consider your interview failed at this point

IUnknown is the base interface of COM All other interfaces must derive directly or indirectly from IUnknown There are three methods in that interface AddRef Release and QueryInterface

7 What are the purposes of AddRef Release and QueryInterface functions

AddRef increments reference count of the object Release decrements reference counter of the object and QueryInterface obtains a pointer to the requested interface

8 What is aggregation How can we get an interface of the aggregated object

Aggregation is the reuse mechanism in which the outer object exposes interfaces from the inner object as if they were implemented on the outer object itself This is useful when the outer object would always delegate every call to one of its interfaces to the same interface in the inner object Aggregation is actually a specialized case of containmentdelegation and is available as a convenience to avoid extra implementation overhead in the outer object in these cases We can get a pointer to the inner interface calling QueryInterface of the outer object with IID of the inner interface

9 C is aggregated by B which in turn aggregated by A Our client requested C What will happen

QueryInterface to A will delegate request to B which in turn will delegate request for the interface to C This pointer will be returned to the client

10 Whats the difference if any between OLE and COM

OLE is build on top of COM The question is not strict because OLE was built over COM for years while COM as a technology was presented by Microsoft a few years ago You may mention also that COM is a specification while OLE is a particular implementation of this specification which in todays world is not exactly true as well because what people call COM today is likely implementation of COM spec by Microsoft

11 Whats the difference between COM and DCOM

Again the question does not require strict answer Any DCOM object is yet a COM object (DCOM extends COM) and any COM object may participate in DCOM transactions

DCOM introduced several improvementsoptimizations for distributed environment such as MULTI_QI (multiple QueryInterface()) security contexts etc DCOM demonstrated importance of surrogate process (you cannot run in-proc server on a remote machine You need a surrogate process to do that) DCOM introduced a load balancing

12 What is a dual interface

Dual interface is one that supports both - IDispatch interface and vtbl-based interface Therefore it might be used in scripting environment like VBScript and yet to use power and speed of vtbl-based interface for non-scripting environment Discussion then may easily transform into analyzing of dual interface problems - be prepared to this twist

13 What is a multi-threaded apartment (MTA) and what is a Single-threaded apartment (STA)

This is pretty difficult question to describe shortly

Anyway apartments were introduced by Microsoft in NT 351 and late Windows 95 to isolate the problem of running legacy non-thread safe code into multithreaded environment Each thread was encapsulated into so called single-threaded apartment The reason to create an object in apartment is thread-safety

COM is the responsible synchronized way to access an object even if the object inside the apartment is not thread-safe Multithreaded apartments (MTA or free threading apartment) were introduced in NT 40 Idea behind MTA is that COM is

not responsible to synchronize object calls between threads In MTA the developer is responsible for that

ltlt See Professional DCOM Programming of Dr Grimes et al or Essential COM of Don Box for the further discussion on this topic gtgt

14 Lets assume we have object B and aggregated object C (in-proc server) created by B Can you access any interface of B from C Whats the difference between aggregated and contained objects

Yes you can This is fundamental postulate of COM If you can get there from here you can get there from anywhere ie QIing for IUnknown you may proceed and to get a pointer to any other interface supported by the object Aggregated object exposes its interface directly without visible intervention of the object container Contained object is created within the object container and its interfaces might be altered or filtered by the object container

15 Is there a way to register in-proc server without regsvr32exe

Yes Call DllRegisterServer() from the client Do not forget to call DLLUnregisterServer() from the same client You may also use Registrar object for the same purpose or use direct manipulation of the windows registry

16 What is VARIANT Why and where would you use it

VARIANT is a huge union containing automation type This allows easy conversion of one automation type to another The biggest disadvantage of VARIANT is size of the union

17 What is __declspec(novtable) Why would you need this

__declspec(novtable) is a Microsofts compiler optimization The main idea of this optimization is to strip the vtable initialization code from abstract class (for abstract class the vtable is empty while it is initialized in contructor) MSDN has an excellent article on this topic (search for ATL Virtual Functions and vtables)

18 What is an IDL

IDL stands for Interface Definition Language IDL is the language to describe COM interfaces

19 What is In-proc

In-proc is in-process COM object ie COM object that implemented as DLL and supposed to be hosted by a container When you have to instantiate the in-proc object remotely you may use DLLHostexe application that was design specially for this purpose

20 What is OLE

OLE is an object and embedding first implementation of COM spec available from MS before COM was officially named COM

21 Give examples of OLE usage

The most famous examples are probably drag and drop and structured storage implementations

22 What are 2 storage types for composite document

The two storage types are Storage and Stream

23 Is doc document a compound document Is it a structured storage

Compound document is a document that contains information about other documents hosted in this document All office documents may or may not be compound documents Word documents from version 60 and up are stored as structured storage

Non-VB COMDCOM

1 What should QueryInterface functions do if requested object was not found

Return E_NOINTERFACE and nullify its out parameter

2 How would you create an instance of the object in COM

ltlt Well it all depends on your project Start your answer from CoCreateInstance or CoCreateInstanceEx explain the difference between them If interviewer is still not satisfied youll have to explain the whole kitchen behind the scenes including a difference between local server and inproc server meaning and mechanism of class factory etc You may also mention other methods of object creation like CoGetInstanceFromFile but discussion will likely turn to discussion of monikers then gtgt

3 What happens when client calls CoCreateInstance

ltlt Again all depends on the level of detail and expertise of interviewer Start with simple explanation of class object and class factory mechanism Further details would depend on a specific situation gtgt

4 What are the limitations of CoCreateInstance

Well a major problem with CoCreateInstance is that it is only able to create one object and only on local system To create a remote object or to get several objects based on single CLSID at the same time one should use CoCreateInstanceEx

5 What is a moniker

It is an object that implements the IMoniker interface A moniker acts as a name that uniquely identifies a COM object In the same way that a path identifies a file in the file system a moniker identifies a COM object in the directory namespace

6 Can you have two dual interfaces in one class

Yes You may have two dual interfaces in one class but only one of them may be default The bottom line is that you cannot work with two dual interfaces at the same time due to nature of dual interfaceTo support two dual interfaces in VB you would write something like

dim d1 as IDualInterface1 dim d2 as IDualInterface2

set d1 = new MyClassWithTwoDualsset d2 = d1

In ATLs class you would have to use macro COM_INTERFACE_ENTRY2(IDispatch IDualInterface1) to distinguish between different dual interfaces

7 What is a marshalling by value

Some objects can essentially be considered static regardless of which methods are called the state of the object does not change Instead of accessing such an object remotely it is possible to copy the static state of the object and create a new object with the same state information on the caller side The caller wont be able to notice the difference but calls will be more efficient because they do not involve network round trips This is called marshaling by value

8 What is ROT What is GIT Give pros and cons of both

By definition running object table (ROT) is a globally accessible table on each computer that keeps track of all COM objects in the running state that can be identified by a moniker Moniker providers register an object in the table which increments the objects reference count Before the object can be destroyed its moniker must be released from the tableGlobal Interface Table (GIT) allows any apartment (either single- or multi-threaded) in a process to get access to an interface implemented on an object in any other apartment in the process

9 If you have an object with two interfaces can you custom marshal one of them

No The decision to use custom marshaling is an all-or-nothing decision an object has to custom marshal all its interfaces or none of them

10 How can you guarantee that only a remote server is ever created by a client

Create an object (call CoCreateObjectEx()) with CLSCTX_REMOTE_SERVER flag

Visual Basic

1 What are the properties and methods of ObjectControl interface

Activate Deactivate CanBePooled

2 How will you implement transaction in a visual basic ActiveX dll

Set the MTSTransactionMode property of the class modules Use the ObjectContextSetcomplete SetAbort methods to commitrollback

the transactions

3 How to execute a stored proc from VB using ADO

A stored proc can be executed using the command object

4 What are the objects in ADO

These are Connection Command Recordset Record Parameter and stream

Visual Basic UI

1 How to access a member variable in one form from another

Set the access modifier of the member variable as Public Create a property procedure

2 What is the listindex property of a list box control

Listindex is the index of the currently selected item in the control

3 Have you worked on grid controls

ltlt Answer should be Yes or No gtgt

ASP

1 How will you describe a session

Session object in ASP provides dynamic associative array that a script can use to store information

ASP Sessions Are Cookie-based

2 What are the different methods to pass an argument from one page to another

Using Query string Using Hidden controls

NET

1 How NET My Services work

From the developers perspective NET My Services is a set of XML Web services accessed by sending and receiving SOAP messages sent though the HTTP or DIME protocols and using the NET Passport system for authentication NET My Services consists of three things Authentication which will be provided by NET Passport when NET My Services goes live SOAP the communication protocol XML following the rules and schemas set out in the XMI Reference which provides the data formatting and organization

2 What are Web Services

Web Services are applications delivered as a service on the Web Web services allow for programmatic access of business logic over the Web Web services typically rely on XML-based protocols messages and interface descriptions for communication and access Web services are designed to be used by other programs or applications rather than directly by end user Programs invoking a Web service are called clients SOAP over HTTP is the most commonly used protocol for invoking Web services

3 How do I use a proxy server when invoking a Web service

If you are using the SOAP Toolkit you need to set some connector properties to use a proxy server Dim soap As SoapClient Set soap=New SoapClient soapConnectorProperty(ProxyServer) = ldquoproxyservernamerdquo soapConnectorProperty(ProxyPort) = ldquo8080rdquo soapConnectorProperty(UseProxy) = True While with NET you just need to create a SystemNetWebProxy object and use it to set the Proxy property Dim webs As localhostMyService() websProxy=New SystemNetWebProxy(ldquohttpproxyserver8080rdquo)

4 What is Simple Object Access Protocol (SOAP)

SOAP is an XML-based messaging framework specifically designed for exchanging formatted data across the Internet for example using request and reply messages or sending entire documents SOAP is simple easy to use and completely neutral with respect to operating system programming language or

distributed computing platform

5 What is Web Services Description Language (WSDL)

After SOAP became available as a mechanism for exchanging XML messages among enterprises (or among disparate applications within the same enterprise) a better way was needed to describe the messages and how they are exchanged The Web Services Description Language (WSDL) is a particular form of an XML Schema developed by Microsoft and IBM for the purpose of defining the XML message operation and protocol mapping of a web service accessed using SOAP or other XML protocol WSDL defines web services in terms of endpoints that operate on XML messages The WSDL syntax allows both the messages and the operations on the messages to be defined abstractly so they can be mapped to multiple physical implementations The current WSDL spec describes how to map messages and operations to SOAP 11 HTTP GETPOST and MIME WSDL creates web service definitions by mapping a group of endpoints into a logical sequence of operations on XML messages The same XML message can be mapped to multiple operations (or services) and bound to one or more communications protocols (using ports)

6 What is Universal Description Discovery and Integration (UDDI)

The Universal Description Discovery and Integration (UDDI) framework defines a data model (in XML) and SOAP APIs for registration and searches on business information including the web services a business exposes to the Internet UDDI is an independent consortium of vendors founded by Microsoft IBM and Ariba for the purpose of developing an Internet standard for web service description registration and discovery Microsoft IBM and Ariba also are hosting the initial deployment of a UDDI service which is conceptually patterned after DNS (the Internet service that translates URLs into TCP addresses) UDDI uses a private agreement profile of SOAP (ie UDDI doesnt use the SOAP serialization format because its not well suited to passing complete XML documents (its aimed at RPC style interactions) The main idea is that businesses use the SOAP APIs to register themselves with UDDI and other businesses search UDDI when they want to discover a trading partner for example someone from whom they wish to procure sheet metal bolts or transistors The information in UDDI is categorized according to industry type and geographical location allowing UDDI consumers to search through lists of potentially matching businesses to find the specific one they want to contact Once a specific business is chosen another call to UDDI is made to obtain the specific contact information for that business The contact information includes a pointer to the target businesss WSDL or other XML schema file describing the web service that the target business publishes

The interviewer should be well versed in NET to ask these questions The interview should know the answers

Execution cycle of an assembly How does CLR comes into picture- Platform independence

Managed unmanaged code Information about GAC How does GAC help in maintaining different versions of an assembly if

changes are made to an assembly and the new version does not support some of functionality that previous version supported how will the runtime handle ito What is the sequence of steps followed by the runtime to look for the

references like first to bin then GAC etco How to add assemblies in GAC

How do we use MTS capabilities in NET assemblies Different type of data persistence in NET

o Caching Data caching Output caching

o Serialization Xml Bin

Usercontrols vc Custom Controls ndash Composite controls Datareader vs Dataset Sorting in Datagrid adding custom controls in datagrid columns Use of view state in ASPX pages How to improve performance of the pages in web environment Is it possible to have both client side and server side functionality on aspx

server controls In the page execution life cycle when is the page_init called What is AutoEventWireUp attribute used for What are delegates used for Webservices

o How do you deploy web services Reflections Remoting

o What is client activated objects and what are server activated objectso What are channels used for

Interopo How does a NET component call a primitive one What are the steps taken

General Scripting Questions

1 How do you add a quotation mark to VB script string

The first method uses two quotation marks in a row to create a single quotation mark The second method uses the ASCII value of the quotation mark character

2 How do you break a single VBScript Statement into multiple lines

A single VBScript Statement can be broken into multiple lines by using the _underscore character

3 What is the proper method of comparing strings in VBScript

The first method uses VBScript function with the vbTextCompare constant The second method forces both strings into uppercase

4 How do you re-enable errors after using ON ERROR RESUME NEXT

ltlt Need an answer gtgt

5 How do you prevent My Script from timing out

You can extend the amount of time a script is allowed to run by using the ScriptTimeout property of the Server object

6 When do you need to explicitly convert a variable to a particular data type

If you are comparing numbers or dates and there is a danger that VBScript might interpret the values as strings one of the VBScript conversion functions should be used

7 When should one pass a variable by value and when by reference

When you pass a variable by value to a subordinate or function a new instance of the variable is created Any changes made to the value of the variable do not affect the value of the original variable On the other hand whne you pass a variable by reference changes made to the variable do affect the value of the original variable

8 How can you add a space between the output of two variables

ltlt Need an answer gtgt

9 Does ASP support dynamic includes

It does not support

10 How do you use the option Explicit statement in an ASP

It must be used before nay other VBScript statement or HTML content in a script else it will generate and error

Session and Application Variable Questions

1 Why do session variables sometimes fail to work

Session variables depend on browser cookies If a browser does not support cookies or a user has turned off cookies or the userrsquos cookie file is corrupted Session variables will not work

2 How do you remove an application variable

ltlt Need an answer gtgt

3 How do you detect whether a File exists

I can detect by using the FileExists method of the FileSystemObject

4 How do you automatically display a list of the Files in a directory

By using a list of files in a folder by using the FileSystemObject and the Folder object

Image Questions

1 How do you store an image in a database table

Although you can store an image in a SQL Server BLOB column it is almost always better to store the URL of an image in a database table rather than the image itself

2 How do you dynamically generate a graph or image in an ASP

Several third-party ASP components enable you to dynamically create custom images

Browser Questions

1 How do you detect the type of browser a person is using to visit your web site

The User-Agent header indicates the type of browser

2 How do you detect a page from which a person originated

The Referer header contains the URL of the last page the person visited This header can be retrieved from the ServerVariables collection

ActiveX Data Objects Questions

1 Why do you sometimes receive an error when using the Connection Object to execute a SQL string

ltlt Need an answer gtgt

2 How do you retrieve a Text filed in an ASP

If you do not take special precautions when retrieving a Text field from a database table the value of the Text field might be truncated If you are using a forward-only cursor type you should use the Text field as the very last field in your select list Alternatively consider using a richer cursor type when opening a Recordset that contains a Text field

3 Why does the RecordCount always return the Value-1

The RecordCount property returns the number of rows in a Recordset after it has been opened you cannot use this property with a forward-only cursor when using SQL Server (it will always return ndash1)

4 Why do you receive an error whenever you try to update the value of a filed in a recordset

By default when you open a Recordset it is opened with a forward-only cursor and read-only lock type To update a Recordset you must open a Recordset that is not read-only

5 How do you limit the number of rows returned by a Database Query

If using SQL 70 or Access you can use the SQL Top keyword to limit the number of records returned Otherwise if you are using SQL 65 use the MaxRecords property of the Recordset object

ltlt What about SQL 2000 gtgt

6 How do you retrieve the value from a SQL Statement that uses Count() Max Min or Identity

There are two methods that you can use to retrieve the value from a SQL function or a SQL global variable You can either use an alias for the value or refer to the value by its ordinal position in the Recordset

7 How do you retrieve an output parameter from a SQL stored procedure within an ASPScript

You must use the ADO Command nad parameter objects

Form and Query String Questions

1 How do you accept file uploads in an HTML form

ltlt Need an answer gtgt

2 What causes the value of a form field to become truncated

HTML uses quotation marks to mark the beginning and end of a value So If a variable contains question marks in its values the value of the variablewill be truncated when displayed

3 How do you include spaces or other special characters in a query string

URL encode the query string

C++ Questions

1 What is an object in C++

An object is a package that contains related data and instructions The data relates to what the object represents while the instructions define how this object relates to other objects and itself

2 What is a message

A message is a signal from one object to another requesting that a computation take place It is roughly equivalent to a function call in other languages

3 What is a class

A class defines the characteristics of a certain type of object It defines what its members will remember the messages to which they will respond and what form the response will take

4 What is an instance

It is an individual object that is a member of some class

5 What is a super-class

Given a class a super-class is the basis of the class under consideration The given class is defined as a subset (in some respects) of the super-class All objects of the given class potentially posses all the characteristics belonging to objects of the super-class

6 What is inheritance

Inheritance is property such that a parent (or super) class passes the characteristics of itself to children (or sub) classes that are derived from it The sub-class has the option of modifying these characteristics in order to make a different but fundamentally related class from the super-class

7 To what does message protocol refer

An objects message protocol is the exact form of the set of messages to which the object can respond

8 What is polymorphism

Polymorphism refers to the ability of an object to respond in a logically identical fashion to messages of the same protocol containing differing types of objects Consider 1 + 5 and 1 + 51 In the former the message + 5 is sent to an object of class integer (1) In the later the message + 51 is sent to the same integer object The form of the message (its protocol) is identical in both cases What differs is the type of object on the right-hand side of these messages The former is an integer object (5) while the later is a floating point object (51) The receiver (1) appears (to other objects) to respond in the same way to both messages Internally however it knows that it must treat the two types of objects differently in order to obtain the same overall response

9 What are instance variables

These represent an objects private memory They are defined in an objects class

18 What is a virtual member function

A virtual function allows derived classes to replace the implementation provided by the base class The compiler makes sure the replacement is always called whenever the object in question is actually of the derived class even if the object is accessed by a base pointer rather than a derived pointer This allows algorithms in the base class to be replaced in the derived class even if users dont know about the derived class

The derived class can either fully replace (override) the base class member function or the derived class can partially replace (augment) the base class member function The latter is accomplished by having the derived class member function call the base class member function if desired

19 How can C++ achieve dynamic binding yet also static typing

When you have a pointer to an object the object may actually be of a class that is derived from the class of the pointer (eg a Vehicle that is actually pointing to a Car object) Thus there are two types the (static) type of the pointer (Vehicle in this case) and the (dynamic) type of the pointed-to object (Car in this case)

Static typing means that the legality of a member function invocation is checked at the earliest possible moment by the compiler at compile time The compiler uses the static type of the pointer to determine whether the member function invocation is legal If the type of the pointer can handle the member function certainly the pointed-to object can handle it as well Eg if Vehicle has a certain member function certainly Car also has that member function since Car is a kind-of Vehicle

Dynamic binding means that the address of the code in a member function invocation is determined at the last possible moment based on the dynamic type of the object at run time It is called dynamic binding because the binding to the code that actually gets called is accomplished dynamically (at run time) Dynamic binding is a result of virtual functions

20 Whats the difference between how virtual and non-virtual member functions are called

Non-virtual member functions are resolved statically That is the member function is selected statically (at compile-time) based on the type of the pointer (or reference) to the object

In contrast virtual member functions are resolved dynamically (at run-time) That is the member function is selected dynamically (at run-time) based on the type of the object not the type of the pointerreference to that object This is called dynamic binding Most compilers use some variant of the following technique

if the object has one or more virtual functions the compiler puts a hidden pointer in the object called a virtual-pointer or v-pointer This v-pointer points to a global table called the virtual-table or v-table

The compiler creates a v-table for each class that has at least one virtual function For example if class Circle has virtual functions for draw() and move() and resize() there would be exactly one v-table associated with class Circle even if there were a gazillion Circle objects and the v-pointer of each of those Circle objects would point to the Circle v-table The v-table itself has pointers to each of the virtual functions in the class For example the Circle v-table would have three pointers a pointer to Circledraw() a pointer to Circlemove() and a pointer to Circleresize()

During a dispatch of a virtual function the run-time system follows the objects v-pointer to the classs v-table then follows the appropriate slot in the v-table to the method code

The space-cost overhead of the above technique is nominal an extra pointer per object (but only for objects that will need to do dynamic binding) plus an extra pointer per method (but only for virtual methods) The time-cost overhead is also fairly nominal compared to a normal function call a virtual function call requires two extra fetches (one to get the value of the v-pointer a second to get the address of the method) None of this runtime activity happens with non-virtual functions since the compiler resolves non-virtual functions exclusively at compile-time based on the type of the pointer

21 When should my destructor be virtual

When you may delete a derived object via a base pointer

virtual functions bind to the code associated with the class of the object rather than with the class of the pointerreference When you say delete basePtr and the base class has a virtual destructor the destructor that gets invoked is the one associated with the type of the object basePtr rather than the one associated with the type of the pointer This is generally A Good Thing

TECHNO-GEEK WARNING PUT YOUR PROPELLER HAT ON Technically speaking you need a base classs destructor to be virtual if and only if you intend to allow someone to invoke an objects destructor via a base class pointer (this is normally done implicitly via delete) and the object being destructed is of a derived class that has a non-trivial destructor A class has a non-trivial destructor if it either has an explicit destructor or if it has a member object or a base class that has a non-trivial destructor (note that this is a recursive definition (eg a class has a non-trivial destructor if it has a member object (which has a base class (which has a member object (which has a base class (which has an explicit destructor)))))) END TECHNO-GEEK WARNING REMOVE YOUR PROPELLER HAT

If you had a hard grokking the previous rule try this (over)simplified one on for size A class should have a virtual destructor unless that class has no virtual functions Rationale if you have any virtual functions at all youre probably going to be doing stuff to derived objects via a base pointer and some of the stuff you may do may include invoking a destructor (normally done implicitly via delete) Plus once youve put the first virtual function into a class youve already paid all the per-object space cost that youll ever pay (one pointer per object note that this is theoretically compiler-specific in practice everyone does it pretty much the same way) so making the destructor virtual wont generally cost you anything extra

22 What is a virtual constructor

An idiom that allows you to do something that C++ doesnt directly support

You can get the effect of a virtual constructor by a virtual clone() member function (for copy constructing) or a virtual create() member function (for the default constructor)

class Shape public virtual ~Shape() A virtual destructor virtual void draw() = 0 A pure virtual function virtual void move() = 0 virtual Shape clone() const = 0 Uses the copy constructor virtual Shape create() const = 0 Uses the default constructor class Circle public Shape public Circle clone() const return new Circle(this) Circle create() const return new Circle()

In the clone() member function the new Circle(this) code calls Circles copy constructor to copy the state of this into the newly created Circle object In the create() member function the new Circle() code calls Circles default constructor

Users use these as if they were virtual constructors

void userCode(Shapeamp s) Shape s2 = sclone() Shape s3 = screate() delete s2 You probably need a virtual destructor here

delete s3

23 How do you link a C++ program to C functions

By using the extern C linkage specification around the C function declarations

24 Explain the scope resolution operator

The scope resolution operator permits a program to reference an identifier in the global scope that has been hidden by another identifier with the same name in the local scope

25 What are the differences between a C++ struct and C++ class

The default member and base class access specifiers are different

26 How many ways are there to initialize an int with a constant

Two

27 How does throwing and catching exceptions differ from using setjmp and longjmp

The throw operation calls the destructors for automatic objects instantiated since entry to the try block

28 How does throwing and catching exceptions differ from using setjmp and longjmp

The throw operation calls the destructors for automatic objects instantiated since entry to the try block

29 What is a default constructor

A constructor that has no arguments or one where all the arguments have default argument values

If you dont code a default constructor the compiler provides one if there are no other constructors If you are going to instantiate an array of objects of the class the class must have a default constructor

30 What is a conversion constructor

It is a constructor that accepts one argument of a different type

The compiler uses this idiom as one way to infer conversion rules for a class A constructor with more than one argument and with default argument values can be interpreted by the compiler as a conversion constructor when the compiler is looking for an object of the type and sees an object of the type of the constructors first argument

31 What is the difference between a copy constructor and an overloaded assignment operator

A copy constructor constructs a new object by using the content of the argument object An overloaded assignment operator assigns the contents of an existing object to another existing object of the same class

First you must know that a copy constructor is one that has only one argument which is a reference to the same type as the constructor The compiler invokes a copy constructor wherever it needs to make a copy of the object for example to pass an argument by value If you do not provide a copy constructor the compiler creates a member-by-member copy constructor for you

You can write overloaded assignment operators that take arguments of other classes but that behavior is usually implemented with implicit conversion constructors If you do not provide an overloaded assignment operator for the class the compiler creates a default member-by-member assignment operator

This discussion is a good place to get into why classes need copy constructors and overloaded assignment operators By discussing the requirements with respect to data member pointers that point to dynamically allocated resources you demonstrate a good grasp of the problem

32 When should you use multiple inheritance

There are three acceptable answers Never Rarely and When the problem domain cannot be accurately modeled any other way

33 What is a virtual destructor

The simple answer is that a virtual destructor is one that is declared with the virtual attribute

The behavior of a virtual destructor is what is important If you destroy an object through a pointer or reference to a base class and the base-class destructor is not virtual the derived-class destructors are not executed and the destruction might not be complete

34 Explain the ISA and HASA class relationships How would you implement each in a class design

A specialized class is a specialization of another class and therefore has the ISA relationship with the other class An Employee ISA Person This relationship is best implemented with inheritance Employee is derived from Person A class may have an instance of another class For example an Employee has a Salary therefore the Employee class has the HASA relationship with the Salary class This relationship is best implemented by embedding an object of the Salary class in the Employee class

The answer to this question reveals whether you have an understanding of the fundamentals of object-oriented design which is important to reliable class design

There are other relationships The USESA relationship is when one class uses the services of another The Employee class uses an object (cout) of the ostream class to display the employees name onscreen for example But if you get ISA and HASA right you usually dont need to go any further

35 When is a template a better solution than a base class

When you are designing a generic class to contain or otherwise manage objects of other types when the format and behavior of those other types are unimportant to their containment or management and particularly when those other types are unknown (thus the genericity) to the designer of the container or manager class

Prior to templates you had to use inheritance your design might include a generic List container class and an application-specific Employee class To put employees in a list a ListedEmployee class is multiply derived (contrived) from the Employee and List classes These solutions were unwieldy and error-prone Templates solved that problem

Questions for ANSI-Knowledgeable Applicants

There are six questions for those who profess knowledge of the progress of the ANSI committee If you claim to have that much interest in the language you should know the answers to all these questions

1 What is a mutable member

A mutable member is one that can be modified by the class even when the object of the class or the member function doing the modification is const

Understanding this requirement implies an understanding of C++ const which many programmers do not have I have seen large class designs that do not employ the const qualifier anywhere Some of those designs are my own early C++ efforts One author suggests that some programmers find const to be such a bother that it is easier to ignore const than to try to use it meaningfully No

wonder many programmers dont understand the power and implications of const Someone who claims to have enough interest in the language and its evolution to keep pace with the ANSI deliberations should not be ignorant of const however

2 What is an explicit constructor

A conversion constructor declared with the explicit keyword The compiler does not use an explicit constructor to implement an implied conversion of types Its purpose is reserved explicitly for construction

3 What is the Standard Template Library

It is a library of container templates approved by the ANSI committee for inclusion in the standard C++ specification

4 Describe run-time type identification

It is the ability to determine at run time the type of an object by using the typeid operator or the dynamic_cast operator

5 What problem does the namespace feature solve

Multiple providers of libraries might use common global identifiers causing a name collision when an application tries to link with two or more such libraries The name-space feature surrounds a librarys external declarations with a unique namespace that eliminates the potential for those collisions

This solution assumes that two library vendors dont use the same namespace of course

6 Are there any new intrinsic (built-in) data types

Yes The ANSI committee added the bool intrinsic type and its true and false value keywords and the wchar_t data type to support character sets wider than eight bits

SQL Server

1 What is a foreign key

A foreign key is a column or combination of columns used to establish and enforce a link (referential integrity) between the data in two tables A link is created between two tables by adding the column or columns that hold one tablersquos primary key values to the other table This column becomes a foreign key in the second table

2 What is the difference between a primary key and unique key

There can be only one primary key constrain on a table but there can be many unique key constraints in a table

Primary key doesnrsquot allow null values but Unique allows 1 Null value

3 What is an index

Indexes are database objects which provides faster data access The index provides pointers to the data values stored in specified columns of

the table and then orders those pointers according to the sort order you specify

Different types of indexes are unique index clustered index and non-clustered index

4 How to return multiple result set from a stored proc and capture it in ADO

Use multiple Select statements to return multiple result sets Use ADOrsquos GetNextRecordset() method to get the second recordset during the

execution of the stored proc