C Plus Plus Theory Questions Part 1 - Online Article

Question 1

What is a modifier?

Answer

A modifier, also called a modifying function is a member function that changes the value of at least one data member. In other words, an operation that modifies the state of an object. Modifiers are also known as 'mutators'.

Question 2

What is an accessor?

Answer

An accessor is a class operation that does not modify the state of an object. The accessor functions need to be declared as const operations.

Question 3

Differentiate between a template class and class template.

Answer

Template class: A generic definition or a parameterized class not instantiated until the client provides the needed information. It's jargon for plain templates. Class template: A class template specifies how individual classes can be constructed much like the way a class specifies how individual objects can be constructed. It's jargon for plain classes.

Question 4

When does a name clash occur?

Answer

A name clash occurs when a name is defined in more than one place. For example., two different class libraries could give two different classes the same name. If you try to use many class libraries at the same time, there is a fair chance that you will be unable to compile or link the program because of name clashes.

Question 5

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.

Question 6

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.

Question 7

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:

  • input iterators,
  • output iterators,
  • forward iterators,
  • bidirectional iterators,

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. Successive 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.

Question 8

What is an incomplete type?

Answer

Incomplete types refer 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.

Question 9

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.

Question 10

Differentiate between the message and method.

Answer

Message Method Objects communicate by sending messages Provides response to a message. to each other. A message is sent to invoke a method. It is an implementation of an operation.

Question 11

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.

Question 12

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.

Question 13

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.

Question 14

What do you mean by Stack unwinding?

Answer

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.

Question 15

Define precondition and post-condition to a member function.

Answer

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.

Question 16

What are the conditions that have to be met for a condition to be an invariant of the class?

Answer

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

Question 17

What are proxy objects?

Answer

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

Example:

template<class T>
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:

Array2D<float>data(10,20);
........
cout<<data[3][6]; // fine

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.

Question 18

Name some pure object oriented languages.

Answer

  • Smalltalk,
  • Java,
  • Eiffel,
  • Sather.

Question 19

Name the operators that cannot be overloaded.

Answer

sizeof . .* .-> :: ?:

Question 20

What is a node class?

Answer:

A node class is a class that,

  • relies on the base class for services and implementation,
  • provides a wider interface to te users than its base class,
  • relies primarily on virtual functions in its public interface,
  • depends on all its direct and indirect base class,
  • can be understood only in the context of the base class,
  • can be used as base for further derivation,
  • can be used to create objects. A node class is a class that has added new services or functionality beyond the services inherited from its base class.

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