What do you mean by C++ access specifiers ?

Access specifiers are used to define how the members (functions and variables) can be accessed outside the class. There are three access specifiers defined which are public, private, and protected.

private:
Members declared as private are accessible only with in the same class and they cannot be accessed outside the class they are declared.
public:
Members declared as public are accessible from any where.
protected:
Members declared as protected can not be accessed from outside the class except a child class. This access specifier has significance in the context of inheritance.

What is the difference between a NULL pointer and a void pointer?

A NULL pointer is a pointer of any type whose value is zero. A void pointer is a pointer to an object of an unknown type, and is guaranteed to have enough bits to hold a pointer to any object. A void pointer is not guaranteed to have enough bits to point to a function (though in general practice it does).

What is difference between C++ and Java?

C++ has pointers Java does not.
Java is platform independent C++ is not.
Java has garbage collection C++ does not.

What do you mean by virtual methods?

virtual methods are used to use the polymorphism feature in C++. Say class A is inherited from class B. If we declare say function f() as virtual in class B and override the same function in class A then at runtime appropriate method of the class will be called depending upon the type of the object.

What is an explicit constructor?

Ans: A conversion constructor declared with the explicit keyword. The compiler does not use an explicit constructor to implement an implied conversion of types. It’s purpose is reserved explicitly for construction.

What is the Standard Template Library?

Ans: A library of container templates approved by the ANSI committee for inclusion in the standard C++ specification. A programmer 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.

What is an iterator?

Iterators are like pointers. They are used to access the elements of containers thus providing a link between algorithms and containers. Iterators are defined for specific containers and used as arguments to algorithms.