C++ Interview questions Part 8

C++ interview question:What is a Null object?

Answer:It is an object of some class whose purpose is to indicate that a real object of that class does not exist. One common use for a null object is a return value from a member function that is supposed to return an object with some specified properties but cannot find such an object. 

C++ interview question:What is class invariant?

Answer:A class invariant is a condition that defines all valid states for an object. It is a logical condition to ensure the correct working of a class. Class invariants must hold when an object is created, and they must be preserved under all operations of the class. In particular all class invariants are both preconditions and post-conditions for all operations or member functions of the class. 

C++ interview question:What do you mean by Stack unwinding?

Answers:It is a process during exception handling when the destructor is called for all local objects between the place where the exception was thrown and where it is caught. 

C++ interview question:Define precondition and post-condition to a member function.

Answers:

Precondition:

       A precondition is a condition that must be true on entry to a member function. A class is used correctly if preconditions are never false. An operation is not responsible for doing anything sensible if its precondition fails to hold. 

       For example, the interface invariants of stack class say nothing about pushing yet another element on a stack that is already full. We say that isful() is a precondition of the push operation.

Post-condition:

        A post-condition is a condition that must be true on exit from a member function if the precondition was valid on entry to that function. A class is implemented correctly if post-conditions are never false.

        For example, after pushing an element on the stack, we know that isempty() must necessarily hold. This is a post-condition of the push operation. 

C++ interview question:What are the conditions that have to be met for a condition to be an invariant of the class?

Answers:

Ø The condition should hold at the end of every constructor.

Ø The condition should hold at the end of every mutator(non-const) operation. 

C++ interview question:What are proxy objects?

Answer:Objects that stand for other objects are called proxy objects or surrogates.

Example:

template

class Array2D 

{

public:

class Array1D

{

public:

T& operator[] (int index);

const T& operator[] (int index) const;

..

};

Array1D operator[] (int index);

const Array1D operator[] (int index) const;

...

};

The following then becomes legal:

Array2Ddata(10,20);

........

cout<

Here data[3] yields an Array1D object and the operator [] invocation on that object yields the float in position(3,6) of the original two dimensional array. Clients of the Array2D class need not be aware of the presence of the Array1D class. Objects of this latter class stand for one-dimensional array objects that, conceptually, do not exist for clients of Array2D. Such clients program as if they were using real, live, two-dimensional arrays. Each Array1D object stands for a one-dimensional array that is absent from a conceptual model used by the clients of Array2D. In the above example, Array1D is a proxy class. Its instances stand for one-dimensional arrays that, conceptually, do not exist. 

C++ interview question:Name some pure object oriented languages.

Answer:

Ø Smalltalk, 

Ø Java, 

Ø Eiffel, 

Ø Sather. 

C++ interview question:Name the operators that cannot be overloaded.

Answers:sizeof . .* .-> :: ?:

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C++ Interview Questions Part 7

C++ interview question:Define namespace.

Answer:It is a feature in c++ to minimize name collisions in the global name space. This namespace keyword assigns a distinct name to a library that allows other libraries to use the same identifier names without creating any name collisions. Furthermore, the compiler uses the namespace signature for differentiating the definitions. 

C++ interview question:What is the use of ‘using’ declaration.

Answer:A using declaration makes it possible to use a name from a namespace without the scope operator. 

C++ interview question:What is an Iterator class?

Answer:A class that is used to traverse through the objects maintained by a container class. There are five categories of iterators: 

Ø input iterators,

Ø output iterators,

Ø forward iterators,

Ø bidirectional iterators,

Ø random access.

             An iterator is an entity that gives access to the contents of a container object without violating encapsulation constraints. Access to the contents is granted on a one-at-a-time basis in order. The order can be storage order (as in lists and queues) or some arbitrary order (as in array indices) or according to some ordering relation (as in an ordered binary tree). The iterator is a construct, which provides an interface that, when called, yields either the next element in the container, or some value denoting the fact that there are no more elements to examine. Iterators hide the details of access to and update of the elements of a container class.

               The simplest and safest iterators are those that permit read-only access to the contents of a container class. The following code fragment shows how an iterator might appear in code:

cont_iter:=new cont_iterator();

x:=cont_iter.next();

while x/=none do

..

s(x);

...

x:=cont_iter.next();

end;

In this example, cont_iter is the name of the iterator. It is created on the first line by instantiation of cont_iterator class, an iterator class defined to iterate over some container class, cont. Succesive elements from the container are carried to x. The loop terminates when x is bound to some empty value. (Here, none)In the middle of the loop, there is s(x) an operation on x, the current element from the container. The next element of the container is obtained at the bottom of the loop. 

C++ interview question::List out some of the OODBMS available.

Answer:

Ø GEMSTONE/OPAL of Gemstone systems.

Ø ONTOS of Ontos.

Ø Objectivity of Objectivity inc.

Ø Versant of Versant object technology.

Ø Object store of Object Design

Ø ARDENT of ARDENT software.

Ø POET of POET software.

C++ interview question:What is an incomplete type?

Answer:Incomplete types refers to pointers in which there is non availability of the implementation of the referenced location or it points to some location whose value is not available for modification.

Example:

int *i=0x400 // i points to address 400

*i=0; //set the value of memory location pointed by i.

Incomplete types are otherwise called uninitialized pointers.

C++ interview Question:What is a dangling pointer?

Answer:A dangling pointer arises when you use the address of an object after its lifetime is over.This may occur in situations like returning addresses of the automatic variables from a function or using the address of the memory block after it is freed.

C++ interview question:Differentiate between the message and method 

Answer:

Message Method

1.Objects communicate by sending messages Provides response to a message to each other.

2.A message is sent to invoke a method. It is an implementation of an operation.

C++ interview question:What is an adaptor class or Wrapper class?

Answer:A class that has no functionality of its own. Its member functions hide the use of a third party software component or an object with the non-compatible interface or a non- object- oriented implementation.

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