C++ Interview QuestionsIntroduction

You maybe a great programmer who uses C/C++ everyday but if you really want that new job, it maybe a good idea to review the core principles of C/C++ before the interview. I have compiled a list of 10 questions that I feel you should know the answers to if you are applying for any C++ position. At the end of the article, I have also added some links to sites to help you prepare for your interview.What is the difference between C and C++ ? Would you prefer to use one over the other ?

C is based on structured programming whereas C++ supports the object-oriented programming paradigm.Due to the advantages inherent in object-oriented programs such as modularity and reuse, C++ is preferred. However almost anything that can be built using C++ can also be built using C.What are the access privileges in C++ ? What is the default access level ?

The access privileges in C++ are private, public and protected. The default access level assigned to members of a class is private. Private members of a class are accessible only within the class and by friends of the class. Protected members are accessible by the class itself and it's sub-classes. Public members of a class can be accessed by anyone.What is data encapsulation ?Data Encapsulation is also known as data hiding. The most important advantage of encapsulation is that it lets the programmer create an object and then provide an interface to the object that other objects can use to call the methods provided by the object. The programmer can change the internal workings of an object but this transparent to other interfacing programs as long as the interface remains unchanged.What is inheritance ?Inheritance is the process of deriving classes from other classes. In such a case, the sub-class has an 'is-a' relationship with the super class. For e.g. vehicle can be a super-class and car can be a sub-class derived from vehicle. In this case a car is a vehicle. The super class 'is not a' sub-class as the sub-class is more specialized and may contain additional members as compared to the super class. The greatest advantage of inheritance is that it promotes generic design and code reuse.What is multiple inheritance ? What are it's advantages and disadvantages ?Multiple Inheritance is the process whereby a sub-class can be derived from more than one super class. The advantage of multiple inheritance is that it allows a class to inherit the functionality of more than one base class thus allowing for modeling of complex relationships. The disadvantage of multiple inheritance is that it can lead to a lot of confusion when two base classes implement a method with the same name.What is polymorphism?Polymorphism refers to the ability to have more than one method with the same signature in an inheritance hierarchy. The correct method is invoked at run-time based on the context (object) on which the method is invoked. Polymorphism allows for a generic use of method names while providing specialized implementations for them. What do the keyword static and const signify ?

When a class member is declared to be of a static type, it means that the member is not an instance variable but a class variable. Such a member is accessed using Classname.Membername (as opposed to Object.Membername). Const is a keyword used in C++ to specify that an object's value cannot be changed.How is memory allocated/deallocated in C ? How about C++ ?

Memory is allocated in C using malloc() and freed using free(). In C++ the new() operator is used to allocate memory to an object and the delete() operator is used to free the memory taken up by an object.What is UML ?

UML refers to Unified Modeling Language. It is a language used to model OO problem spaces and solutions.What is the difference between a shallow copy and a deep copy ?A shallow copy simply creates a new object and inserts in it references to the members of the original object. A deep copy constructs a new object and then creates in it copies of each of the members of the original object.Here are some more interesting references on C++ interview preparation: be sure to check them out before your next interview. Good Luck!

The C++ Interview

These 40 questions and answers will help you land the assignmentby Alex BykovHow do you rank your C++ skills on a scale of 1 to 10? This is often the first question you will hear on an interview for a C++ contract. You will be tempted to rate yourself high, and you should. This is your chance to convince the client that you are just what he is looking for--an assertive and knowledgeable professional who will be productive either working on a team or on your own. Naturally, though, you should be able to support the ranking you gave yourself by doing well on the interview. This article will help you prepare for your C++ interview. I put together a list of 40 questions that I have had to answer during numerous technical interviews in the past few years. You, too, will have to answer at least some of them during an interview. Even if you use C++ on a daily basis, it pays to go through the questions. Most of us, no matter how experienced, use only a segment of the language that we are most comfortable with. Brief answers are included, but you can find more information in the references listed. Q1. Is there anything you can do in C++ that you cannot do in C? A1. No. There is nothing you can do in C++ that you cannot do in C. After all you can write a C++ compiler in C. Q2. What is the difference between C++ structure and C++ class? A2. The default access level assigned to members of struct is public while the default access level assigned to a class is private. Q3. What is encapsulation? A3. Encapsulation is welding of code and data together into objects.Q4. What is inheritance? A4. Inheritance is a mechanism through which a subclass inherits the properties and behavior of its superclass. Q5. What is polymorphism? A5. In Greek this means "many shapes." As a consequence of inheritance and virtual functions, a single task (for example, drawing a geometrical shape) can be implemented using the same name (like draw()) and implemented differently (via virtual functions) as each type in object hierarchy requires(circle.draw() or rectangle.draw()). Later, when a polymorphic object (whose type is not known at compile time) executes the draw() virtual function, the correct implementation is chosen and executed at run time. Q6. What would you say if you saw "delete this" while reviewing your peer's code? A6. You should never do this. Since compiler does not know whether the object was allocated on the stack or on the heap, "delete this" could cause a disaster. Q7. What is the difference between public, protected, and private members of a class? A7. Private members are accessible only by members and friends of the class. Protected members are accessible by members and friends of the class and by members and friends of derived classes. Public members are accessible by everyone. Q8. What is the difference between non-virtual and virtual functions? A8. The behavior of a non-virtual function is known at compile time while the behavior of a virtual function is not known until the run time. Q9. What is a pure virtual function? A9. "A pure virtual function is a function declared in a base class that has no definition relative to the base."Q10. What is an abstract base class? A10. It is a class that has one or more pure virtual functions. Q11. What is the difference between MyClass p; and MyClass p();? A11. MyClass p; creates an instance of class MyClass by calling a constructor for MyClass. MyClass p(); declares function p which takes no parameters and returns an object of class MyClass by value. Q12. How do you know that your class needs a virtual destructor? A12. If your class has at least one virtual function, you should make a destructor for this class virtual. This will allow you to delete a dynamic object through a pointer to a base class object. If the destructor is non-virtual, then wrong destructor will be invoked during deletion of the dynamic object. Q13. Why were the templates introduced?

A13. Many data structures and algorithms can be defined independently of the type of data they work with. You can increase the amount of shared code by separating data-dependent portions from data-independent portions, and templates were introduced to help you do that. Q14. What is a static member of a class? A14. Static data members exist once for the entire class, as opposed to non-static data members, which exist individually in each instance of a class. Q15. What feature of C++ would you use if you wanted to design a member function that guarantees to leave "thisÓ object unchanged? A15. It is "const" as in: "int MyFunc (int test) const;" Q16. Can you overload a function based only on whether a parameter is a value or a reference? A16. No. Passing by value and by reference looks identical to the caller. Q17. What is the difference between function overloading and function overriding? A17. Overloading is a method that allows defining multiple member functions with the same name but different signatures. The compiler will pick the correct function based on the signature. Overriding is a method that allows the derived class to redefine the behavior of member functions which the derived class inherits from a base class. The signatures of both base class member function and derived class member function are the same; however, the implementation and, therefore, the behavior will differ. Q18. Can derived class override some but not all of a set of overloaded virtual member functions inherited from the base class? A18. Compiler will allow this, but it is a bad practice since overridden member functions will hide all of the inherited overloads from the base class. You should really override all of them. Q19. What is the difference between assignment and initialization in C++? A19. Assignment changes the value of the object that has already been constructed. Initialization constructs a new object and gives it a value at the same time. Q20. When are copy constructors called? A20. Copy constructors are called in three cases: when a function returns an object of that class by value, when the object of that class is passed by value as an argument to a function, and, finally, when you construct an object based on another object of the same class (Circle c1=c2;). Q21. Why do you have to provide your own copy constructor and assignment operator for classes with dynamically allocated memory? A21. If you don't, the compiler will supply and execute the default constructor and the assignment operator, but they will not do the job correctly. The default assignment operator does memberwise assignment and the default copy constructor does memberwise copy. In both cases you will only assign and manipulate pointers to dynamic memory, which will lead to memory leaks and other abnormalities. You should write your own assignment operator and copy constructor, which would copy the pointer to memory so that each object has its own copy. Q22. Does compiler guarantee that initializers will be executed in the same order as they appear on the initialization list? A22. No. C++ guarantees that base class subobjects and member objects will be destroyed in the opposite order from which they were constructed. This means that initializers are executed in the order, which supports the above-mentioned guarantee. Q23. What is function's signature? A23. Function's signature is its name plus the number and types of the parameters it accepts.Q24. What does extern "C" int func(int *, Foo) accomplish? A24. It will turn off "name mangling" for this function so that one can link to code compiled by C compiler. Q25. Why do C++ compilers need name mangling? A25. Name mangling is the rule according to which C++ changes function's name into function signature before passing that function to a linker. This is how the linker differentiates between different functions with the same name. Q26. What is the difference between a pointer and a reference? A26. A reference must always refer to some object and, therefore, must always be initialized; pointers do not have such restrictions. A pointer can be reassigned to point to different objects while a reference always refers to an object with which it was initialized.Q27. How can you access the static member of a class? A27. <ClassName>::<StaticMemberName>. Q28. How are prefix and postfix versions of operator++() differentiated?

A28. The postfix version of operator++() has a dummy parameter of type int. The prefix version does not have dummy parameter. Q29. What functions does C++ silently write and call? A29. Constructors, destructors, copy constructors, assignment operators, and address-of operators. Q30. What is the difference between new/delete and malloc/free?A30. Malloc/free do not know about constructors and destructors. New and delete create and destroy objects, while malloc and free allocate and deallocate memory. Q31. What is the difference between delete and delete[ ]? A31. Delete deletes one object; delete[ ] deletes an array of objects. Q32. Name two cases where you MUST use initialization list as opposed to assignment in constructors. A32. Both non-static const data members and reference data members cannot be assigned values; instead, you should use initialization list to initialize them. Q33. What is the difference between const char *myPointer and char *const myPointer? A33. Const char *myPointer is a non constant pointer to constant data; while char *const myPointer is a constant pointer to non constant data. Q34. Suppose that objects A, B, and C are instances of class MyClass (MyClass A, B, C;). How should you design an assignment operator so that the "A=B=C;" statement would be allowed by a compiler but "(A=B)=C;" would not be allowed by a compiler? A34. Make operator=return a reference to a const object. Q35. Is there any problem with the following: char *a=NULL; char& p = *a;? A35. The result is undefined. You should never do this. A reference must always refer to some object. Q36. Class B is derived from class A. Function f is A's friend. Is f B's friend as well? A36. No. Friendship cannot be inherited.Q37. What issue do auto_ptr objects address? A37. If you use auto_ptr objects you would not have to be concerned with heap objects not being deleted even if the exception is thrown. Q38. What happens when a function throws an exception that was not specified by an exception specification for this function? A38. Unexpected() is called, which, by default, will eventually trigger abort(). Q39. Why should you prefer throw/catch mechanism to setjmp/longjmp? A39. The main problem with longjmp() is that it does not destroy local objects properly. Q40. Can you think of a situation where your program would crash without reaching the breakpoint which you set at the beginning of main()?A40. C++ allows for dynamic initialization of global variables before main() is invoked. It is possible that initialization of global will invoke some function. If this function crashes the crash will occur before main() is entered. If you feel comfortable answering these questions, then rest assured that your chances of impressing any interviewer are very high. Be prepared to know basic computer science concepts such as data structures, search and sort algorithms, basic database concepts, etc. The client's needs will determine what particular branch of computer science you have to be familiar with, but you should always be ready to implement the stock, the queue, and the linked list data structures with either C or C++ programming languages. And know how to write your own version of strcpy (string copy) in C programming language since very often they ask you to do that.

Microsoft Interview Questions & Answers I recently visited Microsoft's Silicon Valley campus and interviewed with the Hotmail group. If you've never had a Microsoft interview, realize that they are very different than the standard interview. You won't be asked any of those questions like, "What is your greatest weakness," or, "Where do you want to be in five years?" Rather, a Microsoft interview typically contains a number of brain teasers and coding questions. In fact, you can read interview questions from my internship interviews. Here are the questions I was asked, accompanied with the answers right below the question! So, once you reach the end of the question, don't read any further unless you want to immediately know the answer! Anyway, here goes: Question: How could you determine if a linked list contains a cycle in it, and, at what node the cycle starts? Answer: There are a number of approaches. The approach I shared is in time N (where N is the number of nodes in your linked list). Assume that the node definition contains a boolean flag, bVisited.

struct Node{ ... bool bVisited;};Then, to determine whether a node has a loop, you could first set this flag to false for all of the nodes: // Detect cycle// Note: pHead points to the head of the list (assume already exists)Node *pCurrent = pHead;while (pCurrent){ pCurrent->bVisited = false; pCurrent = pCurrent->pNext;}Then, to determine whether or not a cycle existed, loop through each node. After visiting a node, set bVisited to true. When you first visit a node, check to see if the node has already been visited (i.e., test bVisited == true). If it has, you've hit the start of the cycle! bool bCycle = false;pCurrent = pHead;while (pCurrent && !pCycle){ if (pCurrent->bVisited == true) // cycle! pCycle = true; else { pCurrent->bVisited = true; pCurrent = pCurrent->pNext; }} A much better approach was submitted by 4Guys visitor George R., a Microsoft interviewer/employee. He recommended using the following technique, which is in time O(N) and space O(1).

Use two pointers. // error checking and checking for NULL at end of list omitted

p1 = p2 = head;

do {p1 = p1->next;p2 = p2->next->next;

} while (p1 != p2);

p2 is moving through the list twice as fast as p1. If the list is circular, (i.e. a cycle exists) it will eventually get around to that sluggard, p1.

Thanks George!

Question: How would you reverse a doubly-linked list? Answer: This problem isn't too hard. You just need to start at the head of the list, and iterate to the end. At each node, swap the values of pNext and pPrev. Finally, set pHead to the last node in the list. Node * pCurrent = pHead, *pTemp;while (pCurrent){ pTemp = pCurrent->pNext;

pCurrent->pNext = pCurrent->pPrev; pCurrent->pPrev = temp; pHead = pCurrent;

pCurrent = temp;}

Question: Assume you have an array that contains a number of strings (perhaps char * a[100]). Each string is a word from the dictionary. Your task, described in high-level terms, is to devise a way to determine and display all of the anagrams within the array (two words are anagrams if they contain the same characters; for example, tales and slate are anagrams.) Answer: Begin by sorting each element in the array in alphabetical order. So, if one element of your array was slate, it would be rearranged to form aelst (use some mechanism to know that the particular instance of aelst maps to slate). At this point, you slate and tales would be identical: aelst. Next, sort the entire array of these modified dictionary words. Now, all of the anagrams are grouped together. Finally, step through the array and display duplicate terms, mapping the sorted letters (aelst) back to the word (slate or tales).

Question: Given the following prototype: int compact(int * p, int size); write a function that will take a sorted array, possibly with duplicates, and compact the array, returning the new length of the array. That is, if p points to an array containing: 1, 3, 7, 7, 8, 9, 9, 9, 10, when the function returns, the contents of p should be: 1, 3, 7, 8, 9, 10, with a length of 5 returned. Answer: A single loop will accomplish this. int compact(int * p, int size){ int current, insert = 1; for (current=1; current < size; current++) if (p[current] != p[insert-1]) { p[insert] = p[current]; current++; insert++; } else current++;}

Passing the C++ TestSecuring success in an interviewDr. Dobb's Journal Spring 1998

By Al StevensAl, a contributing editor for Dr. Dobb's Journal, can be contacted at astevens@ddj.com.

In my August 1996 Dr. Dobb's Journal "C Programming" column, I reported that someone with two to five years experience programming C++ can, according to a report in ComputerWorld, command $70,000 on either coast and $65,000 in the central part of the country. The opportunities seem even better for programmers with Win32

programming experience, particularly Windows NT C++ and Microsoft Foundation Classes (MFC) programming experience.http://ads.ddj.com/redirect/132/973585052http://ads.ddj.com/redirect/132/973585052

Of course, no one expects the typical college graduate to have two or more years of solid experience programming a particular platform. The range of your experience depends on how your time was distributed between the usual class workload, lab time, research projects, and any part-time jobs you might have had. Nonetheless, there is a demand for qualified people and a shortage of qualified people. Employers will be looking to entry-level recent graduates to take up the slack. That's where you come in. You'll be competing with all those other grads for those jobs, and, if the ComputerWorld report is a forecast of what's coming, in two years, this summer's entry-level programmers will be the veterans knocking down those respectable salaries. The trick is to get your foot in the door now. Let's see if we can help prepare you to impress the folks who are interviewing new programmers.Windows NT programming is Win32 programming, which, unless you are writing deep systems-level code, is the same thing as Windows 95 programming. If you don't have an NT system handy, latch onto a Windows 95 PC and a copy of Visual C++ 4.0 or later. I don't want you to neglect your studies these last few months -- you have to get through finals before anyone talks to you about a job -- but there are a few things you can do to prepare to demonstrate an understanding of the programming environments that employers want to discuss. That demonstration could be just the advantage that edges out the competition.You need to show in a brief interview that you understand and can work with C++ in the Win32 development environment. Those are two different curves, both of which are steep. Let's start with C++.I put together a list of questions that employers can ask potential programming employees to qualify them as to the extent of their C++ knowledge. These, I think, are representative of the kinds of things that you will be asked. I published the questions and my opinions about appropriate answers in my column. From the response I got from readers, I learned that many practicing C++ programmers cannot answer some of these questions. The pop quiz, as one reader labeled it, sent many programmers back to their reference books. They had fallen into a rut, using a comfortable subset of the language, and, as a consequence, were not using C++ to its full potential. Other readers suggested more questions and a broader approach to qualifying an applicant. Those suggestions caused me to evaluate my approach and adjust it.I divided applicants into three groups: those who understand C++ well enough to use it as an improved C; those who have experience designing C++ classes; and those who are so motivated that they keep up with the recently approved specification of standard C++.I will state here that anyone who has read and understands my book, Teach Yourself C++ (MIS Press, about to be released in its 5th edition), or who has completed the tutorials on The Al Stevens Cram Course on C/C++ CD-ROM (available from Dr. Dobb's Journal), can ace all three parts of this quiz. If you consider that statement to be a shameless plug, then you fully understand my motives. It's true, nonetheless. Let's get on with it.A lot of what follows was taken directly from my August and September 1996 "C Programming" columns in Dr. Dobb's Journal. I reworded some of it to reflect your concerns and to incorporate some changes and corrections that other readers sent to me.

Questions for All C++ ApplicantsHere's the first group of C++ questions and my opinions about what some acceptable answers would be. These questions do not cover C++ wall-to-wall, of course. I selected them as being typical of the kinds of things that all C++ programmers should be expected to know. There are five questions. Three correct answers is a good score.Q: How do you link a C++ program to C functions?A: By using the extern "C" linkage specification around the C function declarations.You should know about mangled function names and type-safe linkages. Then you should explain how the extern "C" linkage specification statement turns that feature off during compilation so that the linker properly links function calls to C functions. Another acceptable answer is "I don't know. We never had to do that." Merely describing what a linker does would indicate to me that you do not understand the issue that underlies the question.Q: Explain the scope resolution operator.A: 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.

The answer can get complicated. It should start with "colon-colon," however. (Some readers had not heard the term, "scope resolution operator," but they knew what :: means. You should know the formal names of such things so that you can understand all communication about them.) If you claim to be well into the design or use of classes that employ inheritance, you tend to address overriding virtual function overrides to explicitly call a function higher in the hierarchy. That's good knowledge to demonstrate, but address your comments specifically to global scope resolution. Describe C++'s ability to override the particular C behavior where identifiers in the global scope are always hidden by similar identifiers in a local scope.Q: What are the differences between a C++ struct and C++ class?A: The default member and base class access specifiers are different.This is one of the commonly misunderstood aspects of C++. Believe it or not, many programmers think that a C++ struct is just like a C struct, while a C++ class has inheritance, access specifiers, member functions, overloaded operators, and so on. Some of them have even written books about C++. Actually, the C++ struct has all the features of the class. The only differences are that a struct defaults to public member access and public base class inheritance, and a class defaults to the private access specifier and private base class inheritance. Getting this question wrong does not necessarily disqualify you because you will be in plenty of good company. Getting it right is a definite plus.Q: How many ways are there to initialize an int with a constant?A: Two.There are two formats for initializers in C++ as shown in Example 1. Example 1(a) uses the traditional C notation, while Example 1(b) uses constructor notation. Many programmers do not know about the notation in Example 1(b), although they should certainly know about the first one. Many old-timer C programmers who made the switch to C++ never use the second idiom, although some wise heads of C++ profess to prefer it.A reader wrote to tell me of two other ways, as shown in Examples 2(a) and 2(b), which made me think that maybe the answer could be extended even further to include the initialization of an int function parameter with a constant argument from the caller.Q: How does throwing and catching exceptions differ from using setjmp and longjmp?A: The throw operation calls the destructors for automatic objects instantiated since entry to the try block.Exceptions are in the mainstream of C++ now, so most programmers, if they are familiar with setjmp and longjmp, should know the difference. Both idioms return a program from the nested depths of multiple function calls to a defined position higher in the program. The program stack is "unwound" so that the state of the program with respect to function calls and pushed arguments is restored as if the calls had not been made. C++ exception handling adds to that behavior the orderly calls to the destructors of automatic objects that were instantiated as the program proceeded from within the try block toward where the throw expression is evaluated.It's okay to discuss the notational differences between the two idioms. Explain the syntax of try blocks, catch exception handlers, and throw expressions. Then specifically address what happens in a throw that does not happen in a longjmp. Your answer should reflect an understanding of the behavior described in the answer just given.One valid reason for not knowing about exception handling is that your experience is exclusively with older C++ compilers that do not implement exception handling. I would prefer that you have at least heard of exception handling, though.It is not unusual for C and C++ programmers to be unfamiliar with setjmp/ longjmp. Those constructs are not particularly intuitive. A C programmer who has written recursive descent parsing algorithms will certainly be familiar with setjmp/ longjmp. Others might not, and that's acceptable. In that case, you won't be able to discuss how setjmp/longjmp differs from C++ exception handling, but let the interview turn into a discussion of C++ exception handling in general. That conversation will reveal to the interviewer a lot about your overall understanding of C++.

Questions for Class DesignersThe next group of questions explores your knowledge of class design. There are eight questions. Five out of eight is a good score.Q: What is your reaction to this line of code?

delete this;A: It's not a good practice.A good programmer will insist that the statement is never to be used if the class is to be used by other programmers and instantiated as static, extern, or automatic objects. That much should be obvious.The code has two built-in pitfalls. First, if it executes in a member function for an extern, static, or automatic object, the program will probably crash as soon as the delete statement executes. There is no portable way for an object to

tell that it was instantiated on the heap, so the class cannot assert that its object is properly instantiated. Second, when an object commits suicide this way, the using program might not know about its demise. As far as the instantiating program is concerned, the object remains in scope and continues to exist even though the object did itself in. Subsequent dereferencing of the pointer can and usually does lead to disaster.A reader pointed out that a class can ensure that its objects are instantiated on the heap by making its destructor private. This idiom necessitates a kludgy DeleteMe kind of function because the instantiator cannot call the delete operator for objects of the class. The DeleteMe function would then use "delete this."I got a lot of mail about this issue. Many programmers believe that delete this is a valid construct. In my experience, classes that use delete this when objects are instantiated by users usually spawn bugs related to the idiom, most often when a program dereferences a pointer to an object that has already deleted itself.Q: What is a default constructor?A: A constructor that has no arguments or one where all the arguments have default argument values.If you don't 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.Q: What is a conversion constructor?A: 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 constructor's first argument.Q: What is the difference between a copy constructor and an overloaded assignment operator?A: 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.Q: When should you use multiple inheritance?A: There are three acceptable answers: "Never," "Rarely," and "When the problem domain cannot be accurately modeled any other way."There are some famous C++ pundits and luminaries who disagree with that third answer, so be careful.Let's digress to consider this issue lest your interview turn into a religious debate. Consider an Asset class, Building class, Vehicle class, and CompanyCar class. All company cars are vehicles. Some company cars are assets because the organizations own them. Others might be leased. Not all assets are vehicles. Money accounts are assets. Real-estate holdings are assets. Some real-estate holdings are buildings. Not all buildings are assets. Ad infinitum. When you diagram these relationships, it becomes apparent that multiple inheritance is an intuitive way to model this common problem domain. You should understand, however, that multiple inheritance, like a chainsaw, is a useful tool that has its perils, needs respect, and is best avoided except when nothing else will do. Stress this understanding because your interviewer might share the common bias against multiple inheritance that many object-oriented designers hold.Q: What is a virtual destructor?A: 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.Q: Explain the ISA and HASA class relationships. How would you implement each in a class design?A: 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 employee's name onscreen, for example. But if you get ISA and HASA right, you usually don't need to go any further.Q: When is a template a better solution than a base class?A: 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 ApplicantsThere 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.Q: What is a mutable member?A: 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 don't 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.Q: What is an explicit constructor?A: 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.Q: What is the Standard Template Library?A: A library of container templates approved by the ANSI committee for inclusion in the standard C++ specification.An applicant who then launches into a discussion of the generic programming model, iterators, allocators, algorithms, and such, has a higher than average understanding of the new technology that STL brings to C++ programming.Q: Describe run-time type identification.A: The ability to determine at run time the type of an object by using the typeid operator or the dynamic_cast operator.Q: What problem does the namespace feature solve?A: 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 library's external declarations with a unique namespace that eliminates the potential for those collisions.This solution assumes that two library vendors don't use the same namespace, of course.Q: Are there any new intrinsic (built-in) data types?A: 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.Other apparent new types (string, complex, and so forth) are implemented as classes in the Standard C++ Library rather than as intrinsic types.In my original column, I left out wchar_t even though I should have known about it. Several readers wrote to correct me. I tell you this now to emphasize that even I would not have scored 100 percent on my own test.

Understanding Win32I haven't put together a list of questions that you should know about the Win32 API because the subject is way too broad to cover that way. There's no way that I could guess what an interviewer is likely to ask. Instead, I'm going to tell you how to become expert enough to get through an interview. You'll have to cram this work into your

otherwise busy student's schedule. I don't know how to tell you where to find the time, but if you can do it, it's worth it. Forsake the social life for the next several months. Try to get by without sleeping. (It's easy. You do all the things you would otherwise do, but you do them tired.) You are investing in your future, and this might be the most profitable time you'll ever spend. Don't, of course, neglect your other studies.You'll need a Windows 95 (or NT) system with Visual C++. Run the tutorials that the VC++ online books include. Get comfortable with the programming environment -- the editor, the debugger, the online documentation, the class wizard, the resource editor, and so on.Next, you need two good books about Windows and MFC programming. These books are the classic Programming Windows 95, by Charles Petzold, and Programming Windows 95 with MFC, by Jeff Prosise (both published by Microsoft Press). Read the Petzold book cover to cover. Do it at your computer and run the programs that Charles includes. Step through them with the VC++ debugger. Get a solid foundation in the Win32 API, the Windows event-driven, message-based programming model, and the Windows way of using resources -- menus, dialog boxes, controls, and so on.Now, read Prosise. Learn the MFC application/document/view architecture. Learn how the MFC class library encapsulates those things and the Windows resources. Run all of Jeff's programs with the debugger just as you did Charles's. Be aware that the debugger steps into all the MFC code. If you find yourself in the depths of an MFC constructor, for example, use the "Step out of" command to get back to the example. Eventually you'll learn to anticipate that and step over statements that would lead you into the vapor.Here's the best advice I can give you. With both these books, when you are running the example programs through the debugger, never step out of a line of code until you fully understand what the line of code is doing and why. If the book is unclear about it, and if, after wracking your brain and exhausting all your resources, you can't figure it out, send me a message at astevens@ddj.com. If I can't figure it out, I'll find someone who can.This offer is good until December 24, 1999. If you don't have a job by then, you can have mine, because that's when I plan to get out of this business to avoid the Year 2000 fiasco.

How to Comport Yourself in the InterviewBear with me now while I patronize you for a moment. I've sat through enough interviews to know what rings the chimes of an interviewer and what turns them cold. This is going to be like one of those motivational speeches that people buy on cassettes from late night TV pitchmen. Inasmuch as you already paid for the magazine, consider this one to be free.Remember, no one expects you to demonstrate the breadth of experience and judgement that comes with years of experience. You should not be expected to know the relative merits of every compiler, operating system, application framework, and so on. You should know what those things are, and, being a smart young person, you are expected to have and voice strong opinions based on your limited experience, but those opinions need not demonstrate anything more than the youthful exuberance and enthusiasm to which you are naturally entitled. You are bullet-proof, beer is food, and all's right with the world.Relax in the interview and be yourself. It is not an adversarial situation. The company really wants you to be the one. Most of us hate interviewing and hope above hope that the right person shows up in the first session so we can get out of having to do any more interviews.Above all, don't pretend to know more than you do. Be truthful when you do not know an answer. Don't try to guess what the interviewer wants to hear. Don't be afraid to ask, "What are you getting at?" Tell the interviewer that, given the chance, you can learn whatever you lack in plenty of time to be of useful service to the company. Most programming is intuitive to someone like yourself who has the aptitude. Make them know that you understand that concept and can apply it. The successful applicant is assured and confident. Make the interviewer feel that by hiring you, the company will solve its programming problems.Here's what else not to do. I know I just told you to be yourself, but, please, avoid making social and political statements with your appearance. You have no way of knowing what the interviewer's biases and prejudices are, and that's the person whose muster you must pass today, even if on the job you'd never see that person again. Sometimes the initial screening is done by personnel types who wouldn't know a byte if it bit them. Dress and groom yourself neatly and neutrally. Try to look capable and professional. You can retreat to your own style, slob or fop, after you get the job and prove your worth.Express a willingness to relocate anywhere and work long hours on any kind of application. Insist, however, that you want to design programs and write code. You are not a typist, shipping clerk, computer operator, data-entry person, manual writer, coffee maker, driver, gopher, or tech-support phone person. Those are fine professions, but not for you. You are a programmer. That's what you do best and that's what they need most. Emphasize that you

want to work with the best technical people that the company has so that you can learn. Interviewers like to hear that.Finally, don't get discouraged. You won't get an offer for every interview, and you'll get some offers that are unacceptable. Keep your spirits up, apply for every job that looks appealing, and spend your evenings sharpening your programming skills at home. If you see a job that you want, don't be dissuaded by an imposing list of qualifications that you do not possess. Chances are, the company won't find anyone with all the right skills anyway. Go for it and convince the interviewers that you can learn what you need to know.Do these things and the right job will find you.

C++ Questions What are the major differences between C and C++?

What are the differences between new and malloc? What is the difference between delete and delete[]? What are the differences between a struct in C and in C++? What are the advantages/disadvantages of using #define? What are the advantages/disadvantages of using inline and const?

What is the difference between a pointer and a reference? When would you use a pointer? A reference? What does it mean to take the address of a reference?

What does it mean to declare a function or variable as static? What is the order of initalization for data? What is name mangling/name decoration?

What kind of problems does name mangling cause? How do you work around them?

What is a class? What are the differences between a struct and a class in C++? What is the difference between public, private, and protected access? For class CFoo { }; what default methods will the compiler generate for you>? How can you force the compiler to not generate them? What is the purpose of a constructor? Destructor? What is a constructor initializer list? When must you use a constructor initializer list? What is a:

Constructor? Destructor? Default constructor? Copy constructor? Conversion constructor?

What does it mean to declare a... member function asvirtual? member function asstatic? member function asstatic? member varible as static? destructor as static?

Can you explain the term "resource acqusition is initialization?" What is a "pure virtual" member function? What is the difference between public, private, and protected inheritance? What is virtual inheritance? What is placement new? What is the difference between operator new and the new operator?

What is exception handling? Explain what happens when an exception is thrown in C++. What happens if an exception is not caught?

What happens if an exception is throws from an object's constructor? What happens if an exception is throws from an object's destructor? What are the costs and benefits of using exceptions? When would you choose to return an error code rather than throw an exception?

What is a template? What is partial specialization or template specialization? How can you force instantiation of a template? What is an iterator? What is an algorithm (in terms of the STL/C++ standard library)? What is std::auto_ptr? What is wrong with this statement? std::auto_ptr ptr(new char[10]); It is possible to build a C++ compiler on top of a C compiler. How would you do this? (Note: I've only

asked this question once; and yes, he understood that I was asking him how cfront was put together. We hired him.)/i>

Code SnippetsI like to put these up on a whiteboard, and ask questiosn about them.

What output does the following code generate? Why?What output does it generate if you make A::Foo() a pure virtual function?

class A {A() { this->Foo(); }virtual void Foo() { cout << "A::Foo()" << endl; }

};

class B : public A {B() { this->Foo(); }virtual void Foo() { cout << "A::Foo()" << endl; }

};

int main(int, char**){

A objectA;B objectB;

return 0;}

What output does this program generate as shown? Why?class A {

A() { cout << "A::A()" << endl; }~A() { cout << "A::~A()" << endl; throw

"A::exception"; }};

class B {B() { cout << "B::B()" << endl; throw

"B::exception"; }~B() { cout << "B::~B()"; }

};

int main(int, char**){

try

{cout << "Entering try...catch block" << endl;

A objectA;B objectB;

cout << "Exiting try...catch block" << endl;}catch (char* ex){

cout << ex << endl;}

return 0;}

Misc. Questions What's the difference between SQL, DDL, and DML? What's a join? An inner join? An outer join? Describe HTTP. What's a design pattern? Can you explain the singleton, vistor, facade, or handle class design pattern?

C++ Test / Typical Interview QuestionsCheck out the following links for interview help.http://www.collegegrad.com/intv/intrview.htmlLevel 2What is the output of the following code segment and why?#include <stdio.h>void main ( void ){unsigned number = 100;if (number > (unsigned) -1 )printf("Hello");elseprintf("There");}

Output : There Reason : When -1 is converted to unsigned it is converted to the largerst unsigned number, 4294967295 in Visual C++ version 5.0.

Level 1

Describe the output from the following code segment.

#include <stdio.h>void main ( void ){for ( int i=0; i<100; ++i);{

printf("%d", i);}}

Output : 100

Reason : The for loop has a ";" at the end of it, so the block of codethat follows is executed after the for loop is run 100 times.

Level 1

What is the output of the following code segment?#include <stdio.h>

void main ( void ){int value1, value2;int * retValue;

value1 = -1;value2 = value1 + 4;

*retValue = value1 * value2;printf("%d", retValue);}

Output : Could be anything

Reason : We are printing the address of retValue not the value of retVale.

Level 3What is the output of the following code?#include <iostream.h>

class TValue {protected:int value;public:TValue (int n) { value = n; }int GetValue (void) { return value; }virtual int GetData (void) { return value; }};

class TMult: public TValue {protected:int multiplier;public:TMult (int n, int m): TValue (n) {multiplier = m;}int GetValue(void) { return value * multiplier;}virtual int GetData(void) { return value * multiplier;}};

void main(void){

TValue tVal(10);TMult tMul(10, 2);TValue *pVal, *pVal2;

pVal = new TMult(10,2);pVal2 = new TMult(10,2);

cout << "tVal : " << tVal.GetValue() << endl;cout << "tMult: " << tMul.GetValue() << endl;cout << "pVal GetValue() : " << pVal->GetValue() << endl;

cout << "pVal2 GetData(): " << pVal->GetData() << endl;

}Output:tVal : 10tMult: 20pVal GetValue() : 10pVal2 GetData(): 20

Reason: See the definition of virtual member below.What is the result of the following bit shifting segment of code?

What is serialization?

Answer: Serialization is the process of storing the state of an object for the purpose of loading it at another time. When an object is serialized, information about the type of object is written to the storage along with information and data about the object. When an object is deserialized, the same process happens in reverse, and the object is loaded and created from the input stream. What is a class?

A class allows data and functions to be bundled together and used as if they are a single element. Classes typically model real-world concepts that have both data and some sort of behavior.What is an instance of a class?Answer: An instance of a class, sometimes called an object, is an occurrence of a class. An instance of one of your classes can be used or manipulated inside your programs.Classes and instances of classes are not the same things -- think of a class as the description of an object; an instance of a class is a concrete occurrence of that class. What is the difference between TCP/IP and UDP/IP?TCP (Transport Control Protocol ) and UDP ( user datagram protocal) are both methods of transport protocols. IP stands for internet protocal. TCP/IP is like a telephone connection for communication to take place there must be a sender and receiver; there must be a connection made. UDP/IP does not require a connection to be made, similar to the mail system. You can post a letter without someone necessarily receiving it.TCP/IP is designed to solve modern computer communication problems by allowing different computers to communicate across multiple networks. IP or the "Internet Protocol" will provide the thread that allows data to find its way between two computers across multiple networks.TCP or the "Transport Control Protocol" will provide the "reliable transport" or assurance that data is sent and received between the two computers and their respective application programs.What is the difference between a class and a structure? In a class, members are private by default. In a structure, members are public by defaultWhich of the following operators are control structures: >= , <, &&, |, &, <=, || ?&& and || are short-circuit logical operators. ie. flag1 && flag2 evaluates toif (flag1) { if (flag2) { ... } }What was the ++ operator designed for originally?What is a binary tree?

A binary tree is an ordered tree in which each internal node has either zero or two children. Some definitions allow for simplyWhat is a binary search tree?Each internal node v stores an element e such that the elements stored in the left subtree of v are less than or equal to e, and the elements stored in the right subtree of v are greater than or equal to e.Name two string compression algorithms.Huffman Coding and Name two pattern matching algorithms.Knuth-Morris-Pratt Algorithm and Boyer-Moore AlgorithmAll Object Oriented Languages share three common defining traits explain theseEncapsulation, Polymorphism, and Inheritence. Inheritance is the process by which one object can acquire the properties of another, be more specific? An object can inherit a general set of properties to which it can add those features that are specific only to itself. Inheritance is important because it allows an object to support the concept of hierarchical classification. What is a Virtual Member Function?Calls to virtual member functions are linked at runtime (by a technique known as late binding). Calls to regular member functions are linked at compile time (early binding). Virtual member functions and late binding make it possible for objects to determine their own behavior at runtime - the chief characteristic of polymorphism.How many gas stations are there in Canada?What are you strengths?What are you weaknesses or areas for improvement?What is the most complicated data structure you have ever created?How do you deal with team members that don't do their share of the work? Specific examples.What are your carrer and education goals?What do you hope to get out of or learn from this job?Have you checked out our web page?What is your favorite / worst course this term?Why are you interested in working at our company?Do you have a web page? What kind of things are on it?What is class hierachi?What is a message map in MFC?How would you print out a singly linked list backwards?Answer: Use Recursion:void Reverse (Node *node){if (node->next != NULL)Reverse(node);cout << node->value << endl;}Is using the new operator fast or slow and why?How does stack memory allocation work?What are classes used for?1) Code reuse.2) Similar to real world.Why should I hire you over the other people being interviewed?Write the code for a function with the following prototype:isSubstring (char * source, char * substring);What test cases would you use to test it?What is the output of, int *p = "foo"; cout << sizeof (p) << endl;Write the code to bit shift the variable, int shift = 4; the bits to the right.What is the hexadecimal representation of the largest integer in a 32 bit system? The smallest integer.What is the purpose of the -> operator in C++? (cs342 page8)What is the difference between public, private and protected in C++? (page 572 C++ book)What is one thing that Java has that C++ does not? Answer: Garbage Collection What is a thing C++ has that Java does not? Answer: Preprocessor

Why might you want to use a Java application vs a Java applet?