(Paper) C++ Aptitude Questions and Answers Set - 2

C/C++ Aptitude Questions and Answers Set - 2


What is a modifier?
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?.

What is an accessor?
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

Differentiate between a template class and class template.
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.

When does a name clash occur?
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

Define namespace.
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.

What is the use of ?using? declaration.
A using declaration makes it possible to use a name from a namespace without the scope operator.

What is an Iterator class?
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();
           while x/=none do
         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.

List out some of the OODBMS available.

?      GEMSTONE/OPAL of Gemstone systems.
?      ONTOS of Ontos.
?      Objectivity of  Objectivity inc.
?      Versant of Versant object technology.
?      Object store of Object Design.
?      ARDENT of ARDENT software.
?      POET of POET software.

List out some of the object-oriented methodologies.

?       Object Oriented Development  (OOD) (Booch 1991,1994).
?       Object Oriented Analysis and Design  (OOA/D) (Coad and Yourdon 1991).
?       Object Modelling Techniques  (OMT)  (Rumbaugh 1991).
?       Object Oriented Software Engineering  (Objectory) (Jacobson 1992).
?       Object Oriented Analysis  (OOA) (Shlaer and Mellor 1992).
?       The Fusion Method  (Coleman 1991).

What is an incomplete type?
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.
                 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.

What is a dangling pointer?
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.

Differentiate between the message and method.
             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.

What is an adaptor class or Wrapper class?
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.

What is a Null object?
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.

What is class invariant?
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.

What do you mean by Stack unwinding?
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.

Define precondition and post-condition to a member function.
            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.
            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.

What are the conditions that have to be met for a condition to be an invariant of the class?
?  The condition should hold at the end of every constructor.
?  The condition should hold at the end of every mutator(non-const) operation.