C++ Interview Questions and Answers - DoAnswers.com

C++ is an enhanced version of the C language. C++ includes everything that is part of C and adds support for object- oriented programming (OOP). In addition, C++ also contains many improvements and features that make it a "better C", independent of object oriented programming. C++ is actually an extendible language since we can define new types in such a way that they act just like the predefined types which are part of the standard language. If you just use C++ as a better C, you will not be using all of its power. Like any quality tool, C++ must be used the way it was designed to be used to exploit its richness. Some of the new features include encapsulation, inline function calls, overloading operators, inheritance and polymorphism. I am not going to explain what they mean here as that would simply take me away from my purpose here, but you can refer to any good C++ book or the C++ FAQ for more information.

C++ Language Interviews are getting tough these days as the technology grows faster. To get through the C++ Language interview one needs to update him/herself in a regular manner. Having said that, just before the interview, it is very important to have a quick glance of the reputed C++ Language questions and answers to make yourself comfortable during the interview process. This is where DoAnswers.com helps you in renewing yourself on C++ Language and various other technologies interview preparation.

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.

The run time type identification comes at a cost of performance penalty. Compiler maintains the class.

The abstract class whose pure virtual method has to be implemented by all the classes which derive on these. Otherwise it would result in a compilation error. This construct should be used when one wants to ensure that all the derived classes implement the method defined as pure virtual in base class.

44. 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.

Malloc/free do not know about constructors and destructors. New and delete create and destroy objects, while malloc and free allocate and deallocate memory.

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

It is not a good programming Practice. A good programmer will insist that you should absolutely never use the statement 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 baller can and usually does lead to disaster. I think that the language rules should disallow the idiom, but that's another matter.

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.

A name clash occurswhen 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.

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 generality) to the designer of the container or manager class.