Top 85 C++ Interview Questions & Answers

C++ INTERVIEW QUESTIONS & ANSWERS

  1. What is a class?
    Ans: The objects with the same data structure (attributes) and
    behaviour(operations) are called class.

  2. What is an object?
    Ans: It is an entity which may correspond to real-world entities such as students,
    employees, bank account. It may be concrete such as file system or conceptual such
    as scheduling policies in multiprocessor operating system. Every object will have
    data structures called attributes and behavior called operations.

  3. What is the difference between an object and a class?
    Ans: All objects possessing similar properties are grouped into class. Eg –person is a
    class,ram,hari are objects of person class . All have similar attributes like name, age,
    sex and similar operations like speak, walk.
    Class person
    { private: char name[20];
    int age;
    char sex;
    public: speak();
    walk();
    };

  4. What is the difference between class and structure?
    Ans: In class the data members by default are private but in structure they are by
    default public

  5. Define object based programming language ?
    Ans: Object based programming language support encapsulation and object identity
    without supporting some important features of OOPs language.eg-ada.
    Object based language=Encapsulation + object Identity

  6. Define object oriented language ?
    Ans: Object-oriented language incorporates all the features of object based
    programming languages along with inherentance and polymorphism.eg-c++,java.

  7. Define OOPs?
    Ans: OOP is a method of implementation in which programs are organized as cooperative collection of objects,each of which represents an instance of some class
    and whose classes are all member of a hierarchy of classes united through the
    property of inheritance.

  8. What is public, protected, private?
    Ans: These are access specifier or visibility lebels .The class members that has been
    declared as private can be accessed only from within the class.public members can
    be accessed from outside the class also.Within the class or from the object of a class
    Protected access limit is same as that of private but it plays a prominent role in case
    of inheritance

  9. What is a scope resolution operator?
    Ans: The scope resolution operator permits a program to reference an identifier in
    the global scope that has been hidden by another identifier with the same name in
    the local scope.

  10. What do you mean by inheritance?
    Ans: The mechanism of deriving a new class(derived) from an old class(base class)
    is called inheritance. It allows the extension and reuse of existing code without
    having to rewrite the code from scratch.

  11. What is abstraction?
    Ans: The technique of creating user-defined data types ,having the properties of
    built-in data types and a set of permitted operators that are well suited to the
    application to be programmed is known as data abstraction. Class is a construct for
    abstract data types(ADT).

  12. What is encapsulation?
    Ans: It is the mechanism that wraps the data and function it manipulates into single
    unit and keeps it safe from external interference.

13 .How variable declaration in c++ differs that in c ?
Ans: C requires all the variables to be declared at the beginning of a scope but in c++
we can declare variables anywhere in the scope.This makes the programmer easier
to understand because the variables are declared in the context of their use.

  1. What are the c++ tokens ?
    Ans: c++ has the following tokens
    I. keywords
    II. identifiers
    III. constants
    IV. strings
    V. operators

  2. What do you mean by reference variable in c++ ?
    Ans: A reference variable provides an alias to a previously defined variable.
    data type & reference-name = variable name

  3. What do you mean by implicit conversion ?
    Ans: Whenever data types are mixed in an expression then c++ performs the
    conversion automatically.
    Here smaller type is converted to wider type.
    Ex- in case of integer and float integer is converted into float type.

  4. What is the difference between method overloading and method
    overriding?
    Ans: Overloading a method (or function) in C++ is the ability for functions of the
    same name to be defined as long as these methods have different signatures
    (different set of parameters). Method overriding is the ability of the inherited class
    rewriting the virtual method of the base class.

  5. What are the defining traits of an object-oriented language?
    The defining traits of an object-oriented language are:
    encapsulation
    inheritance
    polymorphism
    Ans:
    Polymorphism: is a feature of OOPL that at run time depending upon the type of
    object the appropriate method is called.
    Inheritance: is a feature of OOPL that represents the “is a” relationship between
    different objects (classes). Say in real life a manager is a employee. So in OOPL
    manger class is inherited from the employee class.
    Encapsulation: is a feature of OOPL that is used to hide the information.

  6. What is polymorphism?
    Ans: Polymorphism is the idea that a base class can be inherited by several classes.
    A base class pointer can point to its child class and a base class array can store
    different child class objects.

  7. What do you mean by inline function?
    Ans: An inline function is a function that is expanded inline when invoked.ie. the
    compiler replaces the function call with the corresponding function code. An inline
    function is a function that is expanded in line when it is invoked. That is the compiler
    replaces the function call with the corresponding function code(similar to macro).

21 What is the difference between a NULL pointer and a void pointer?
Ans: 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).

  1. What is difference between C++ and Java?
    Ans: C++ has pointers Java does not.
    Java is platform independent C++ is not.
    Java has garbage collection C++ does not.

  2. What do you mean by multiple inheritance in C++ ?
    Ans: Multiple inheritance is a feature in C++ by which one class can be of different
    types. Say class teachingAssistant is inherited from two classes say teacher and
    Student.

  3. What do you mean by virtual methods?
    Ans: virtual methods are used to use the polymorhism feature in C++. Say class A is
    inherited from class B. If we declare say fuction 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.

  4. What do you mean by static methods?
    Ans: By using the static method there is no need creating an object of that class to
    use that method. We can directly call that method on that class. For example, say
    class A has static function f(), then we can call f() function as A.f(). There is no need
    of creating an object of class A.

  5. How many ways are there to initialize an int with a constant?
    Ans: Two.
    There are two formats for initializers in C++ as shown in the example that follows.
    The first format uses the traditional C notation. The second format uses constructor
    notation.
    int foo = 123;
    int bar (123);

  6. What is constructors?
    Ans: Constructor is a special member function of a class ,which is invoked
    automatically whenever an instance of the class is created. It has the same name as
    its class.

  7. What are destructors?
    Ans: Destructor is a special member function of a class , which is invoked
    automatically whenever an object goes out of the scope.It has the same name as its
    class with a tilde character prefixed.

  8. 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. Its
    purpose is reserved explicitly for construction.

  9. 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.

  10. What problem does the namespace feature solve?
    Ans: Multiple providers of libraries might use common global identifiers causing a
    name collision when an application tries to link with two or more such libraries. The
    namespace feature surrounds a library’s external declarations with a unique
    namespace that eliminates the potential for those collisions. This solution assumes
    that two library vendors don’t use the same namespace identifier, of course.

  11. What is the use of ‘using’ declaration ?
    Ans: A using declaration makes it possible to use a name from a namespace

33.What is a template ?
Ans: Templates allow to create generic functions that admit any data type as
parameters and return a value without having to overload the function with all the
possible data types. Until certain point they fulfill the functionality of a macro. Its
prototype is any of the two following ones:
template function_declaration;
template function_declaration;

  1. Differentiate between a template class and class template ?
    Ans:
    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.

  2. What is the difference between a copy constructor and an overloaded
    assignment operator?
    Ans: 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.

  3. What is a virtual destructor?
    Ans: The simple answer is that a virtual destructor is one that is declared with the
    virtual attribute.

  4. What is an incomplete type?
    Ans: 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=0×400 // i points to address 400
    *i=0; //set the value of memory location pointed by i.
    Incomplete types are otherwise called uninitialized pointers.

  5. [imp] What do you mean by Stack unwinding?
    Ans: 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.

  6. What is a container class? What are the types of container classes?
    Ans: A container class is a class that is used to hold objects in memory or external
    storage. A container class acts as a generic holder. A container class has a predefined
    behavior and a well-known interface. A container class is a supporting class whose
    purpose is to hide the topology used for maintaining the list of objects in memory.
    When a container class contains a group of mixed objects, the container is called a
    heterogeneous container; when the container is holding a group of objects that are
    all the same, the container is called a homogeneous container

  1. Name some pure object oriented languages ?
    Ans: Smalltalk, Java, Eiffel, Sather.

  2. Name the operators that cannot be overloaded ?
    Ans: sizeof, ., .*, .->, ::, ?:

  3. What is an adaptor class or Wrapper class?
    Ans: 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.

  4. What is a Null object?
    Ans: 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.

  5. [imp] What is class invariant?
    Ans: 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.

  6. What is a dangling pointer?
    Ans: 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.
    Example: The following code snippet shows this:
    class Sample
    { public: int *ptr;
    Sample(int i)
    { ptr = new int(i);
    }
    ~Sample()
    { delete ptr;
    }
    void PrintVal()
    { cout << “The value is ” << *ptr;
    }
    };
    void SomeFunc(Sample x)
    { cout << “Say i am in someFunc ” << endl;
    }
    int main()
    { Sample s1= 10;
    SomeFunc(s1);
    s1.PrintVal();
    }
    In the above example when PrintVal() function is called it is called by the pointer
    that has been freed by the destructor in SomeFunc.

  7. Differentiate between the message and method ?
    Ans:
    Message: Objects communicate by sending messages to each other. A message is
    sent to invoke a method.
    Method: Provides response to a message. It is an implementation of an operation

  8. How can we access protected and private members of a class ?
    Ans: In the case of members protected and private, these could not be accessed from
    outside the same class at which they are declared. This rule can be transgressed with
    the use of the friend keyword in a class, so we can allow an external function to gain
    access to the protected and private members of a class.

  9. Can you handle exception in C++ ?
    Ans: Yes we can handle exception in C++ using keyword :try,catch and throw.
    Program statements that we want to monitor for exceptions are contained in a try
    block. If an exception occurs within the try block,it is thrown (using throw).The
    exception is caught,using catch,and processed.

  10. What is virtual function ?
    Ans: A virtual function is a member function that is declared within a base class and
    redefined by a derived class .To create a virtual function,the function declaration in
    the base class is preceded by the keyword virtual.

  11. What do you mean by early binding ?
    Ans: Early binding refers to the events that occur at compile time. Early binding
    occurs when all information needed to call a function is known at compile time.
    Examples of early binding include normal function calls, overloaded function calls,
    and overloaded operators. The advantages of early binding are efficiency.

  12. What do you mean by late binding ?
    Ans: Late binding refers to function calls that are not resolved until run time. Virtual
    functions are used to achieve late binding. When access is via a base pointer or
    reference,the virtual function actually called is determined by the type of object
    pointed to by the pointer.

  13. What is a modifier?
    Ans: 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’.

  14. What is an accessor?
    Ans: 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

  15. When does a name clash occur?
    Ans: 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

  16. Define namespace.
    Ans: 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.

  17. What is the use of ‘using’ declaration.
    Ans: A using declaration makes it possible to use a name from a namespace without
    the scope operator.

  18. What is an Iterator class?
    Ans: A class that is used to traverse through the objects maintained by a container
    C++ INTERVIEW QUESTIONS
    durgesh.tripathi2@gmail.com Page 10
    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-atime 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.

  19. List out some of the OODBMS available.
    Ans:
    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.

  20. List out some of the object-oriented methodologies.
    Ans:
    Ø Object Oriented Development (OOD) (Booch 1991,1994).
    Ø Object Oriented Analysis and Design (OOA/D) (Coad and Yourdon 1991).
    Ø Object Modelling Techniques (OMT) (Rumbaugh 1991).
    Ø Object Oriented Software Engineering (Objectory) (Jacobson 1992).
    Ø Object Oriented Analysis (OOA) (Shlaer and Mellor 1992).
    Ø The Fusion Method (Coleman 1991).

  21. What is an incomplete type?
    Ans: 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.

  22. Define precondition and post-condition to a member function.
    Ans:
    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.

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

  24. What are proxy objects?
    Ans: 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, twodimensional 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.

  1. Name some pure object oriented languages.
    Ans:
    Ø Smalltalk,
    Ø Java,
    Ø Eiffel,
    Ø Sather.

  2. Name the operators that cannot be overloaded.
    Ans: sizeof . .* .-> :: ?:

  3. What is a node class?
    Ans: A node class is a class that,
    Ø relies on the base class for services and implementation,
    Ø provides a wider interface to te users than its base class,
    Ø relies primarily on virtual functions in its public interface
    Ø depends on all its direct and indirect base class
    Ø can be understood only in the context of the base class
    Ø can be used as base for further derivation
    Ø 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.

  4. What is an orthogonal base class?
    Ans: If two base classes have no overlapping methods or data they are said to be
    independent of, or orthogonal to each other. Orthogonal in the sense means that two
    classes operate in different dimensions and do not interfere with each other in any
    way. The same derived class may inherit such classes with no difficulty.

  5. What is a container class? What are the types of container classes?
    Ans: A container class is a class that is used to hold objects in memory or external
    storage. A container class acts as a generic holder. A container class has a predefined
    behavior and a well-known interface. A container class is a supporting class whose
    purpose is to hide the topology used for maintaining the list of objects in memory.
    When a container class contains a group of mixed objects, the container is called a
    heterogeneous container; when the container is holding a group of objects that are
    all the same, the container is called a homogeneous container.

  6. What is a protocol class?
    Ans: An abstract class is a protocol class if:
    Ø it neither contains nor inherits from classes that contain member data, nonvirtual functions, or private (or protected) members of any kind.
    Ø it has a non-inline virtual destructor defined with an empty implementation,
    Ø all member functions other than the destructor including inherited functions, are
    declared pure virtual functions and left undefined.

  7. What is a mixin class?
    Ans: A class that provides some but not all of the implementation for a virtual base
    class is often called mixin. Derivation done just for the purpose of redefining the
    virtual functions in the base classes is often called mixin inheritance. Mixin classes
    typically don’t share common bases.

  8. What is a concrete class?
    Ans: A concrete class is used to define a useful object that can be instantiated as an
    automatic variable on the program stack. The implementation of a concrete class is
    defined. The concrete class is not intended to be a base class and no attempt to
    minimize dependency on other classes in the implementation or behavior of the
    class.

  9. What is the handle class?
    Ans: A handle is a class that maintains a pointer to an object that is
    programmatically accessible through the public interface of the handle class.
    Explanation: In case of abstract classes, unless one manipulates the objects of these
    classes through pointers and references, the benefits of the virtual functions are lost.
    User code may become dependent on details of implementation classes because an
    abstract type cannot be allocated statistically or on the stack without its size being
    known. Using pointers or references implies that the burden of memory
    management falls on the user. Another limitation of abstract class object is of fixed
    size. Classes however are used to represent concepts that require varying amounts
    of storage to implement them.
    A popular technique for dealing with these issues is to separate what is used as a
    single object in two parts: a handle providing the user interface and a representation
    holding all or most of the object’s state. The connection between the handle and the
    representation is typically a pointer in the handle. Often, handles have a bit more
    data than the simple representation pointer, but not much more. Hence the layout of
    the handle is typically stable, even when the representation changes and also that
    handles are small enough to move around relatively freely so that the user needn’t
    use the pointers and the references.

  10. What is an action class?
    Ans: The simplest and most obvious way to specify an action in C++ is to write a
    function. However, if the action has to be delayed, has to be transmitted ‘elsewhere’
    before being performed, requires its own data, has to be combined with other
    actions, etc then it often becomes attractive to provide the action in the form of a
    class that can execute the desired action and provide other services as well.
    Manipulators used with iostreams is an obvious example.
    Explanation: A common form of action class is a simple class containing just one
    virtual function.
    class Action
    { public: virtual int do_it( int )=0;
    virtual ~Action( );
    }
    Given this, we can write code say a member that can store actions for later execution
    without using pointers to functions, without knowing anything about the objects
    involved, and without even knowing the name of the operation it invokes. For
    example:
    class write_file : public Action
    { File& f;
    public: int do_it(int)
    { return fwrite( ).suceed( );
    }
    };
    class error_message: public Action
    { response_box db(message.cstr( ),”Continue”,”Cancel”,”Retry”);
    switch (db.getresponse( ))
    { case 0: return 0;
    case 1: abort();
    case 2: current_operation.redo( );return 1;
    }
    };
    A user of the Action class will be completely isolated from any knowledge of derived
    classes such as write_file and error_message.

  11. When can you tell that a memory leak will occur?
    Ans: A memory leak occurs when a program loses the ability to free a block of
    dynamically allocated memory.

  1. What is a parameterized type?
    Ans: A template is a parameterized construct or type containing generic code that
    can use or manipulate any type. It is called parameterized because an actual type is a
    parameter of the code body. Polymorphism may be achieved through parameterized
    types. This type of polymorphism is called parameteric polymorphism. Parameteric
    polymorphism is the mechanism by which the same code is used on different types
    passed as parameters.

  2. Differentiate between a deep copy and a shallow copy?
    Ans: Deep copy involves using the contents of one object to create another instance
    of the same class. In a deep copy, the two objects may contain ht same information
    but the target object will have its own buffers and resources. the destruction of
    either object will not affect the remaining object. The overloaded assignment
    operator would create a deep copy of objects.
    Shallow copy involves copying the contents of one object into another instance of
    the same class thus creating a mirror image. Owing to straight copying of references
    and pointers, the two objects will share the same externally contained contents of
    the other object to be unpredictable.
    Explanation: Using a copy constructor we simply copy the data values member by
    member. This method of copying is called shallow copy. If the object is a simple
    class, comprised of built in types and no pointers this would be acceptable. This
    function would use the values and the objects and its behavior would not be altered
    with a shallow copy, only the addresses of pointers that are members are copied and
    not the value the address is pointing to. The data values of the object would then be
    inadvertently altered by the function. When the function goes out of scope, the copy
    of the object with all its data is popped off the stack.
    If the object has any pointers a deep copy needs to be executed. With the deep copy
    of an object, memory is allocated for the object in free store and the elements
    pointed to are copied. A deep copy is used for objects that are returned from a
    function.

  3. What is an opaque pointer?
    Ans: A pointer is said to be opaque if the definition of the type to which it points to is
    not included in the current translation unit. A translation unit is the result of
    merging an implementation file with all its headers and header files.

  4. What is a smart pointer?
    Ans: A smart pointer is an object that acts, looks and feels like a normal pointer but
    offers more functionality. In C++, smart pointers are implemented as template
    classes that encapsulate a pointer and override standard pointer operators. They
    have a number of advantages over regular pointers. They are guaranteed to be
    initialized as either null pointers or pointers to a heap object. Indirection through a
    null pointer is checked. No delete is ever necessary. Objects are automatically freed
    when the last pointer to them has gone away. One significant problem with these
    smart pointers is that unlike regular pointers, they don’t respect inheritance. Smart
    pointers are unattractive for polymorphic code. Given below is an example for the
    implementation of smart pointers.
    Example:
    template
    class smart_pointer
    { public: smart_pointer(); // makes a null pointer
    smart_pointer(const X& x) // makes pointer to copy of x
    X& operator ( );
    const X& operator
    ( ) const;
    X* operator->() const;
    smart_pointer(const smart_pointer &);
    const smart_pointer & operator =(const smart_pointer&);
    ~smart_pointer();
    private: //…
    };
    This class implement a smart pointer to an object of type X. The object itself is
    located on the heap. Here is how to use it:
    smart_pointer p= employee(“Harris”,1333);
    Like other overloaded operators, p will behave like a regular pointer,
    cout<<*p;
    p->raise_salary(0.5);

  5. What is reflexive association?
    Ans: The ‘is-a’ is called a reflexive association because the reflexive association
    permits classes to bear the is-a association not only with their super-classes but also
    with themselves. It differs from a ‘specializes-from’ as ‘specializes-from’ is usually
    used to describe the association between a super-class and a sub-class. For example:
    Printer is-a printer.

  6. What is slicing?
    Ans: Slicing means that the data added by a subclass are discarded when an object of
    the subclass is passed or returned by value or from a function expecting a base class
    object.
    Explanation: Consider the following class declaration:
    class base
    { …
    base& operator =(const base&);
    base (const base&);
    }
    void fun( )
    C++ INTERVIEW QUESTIONS
    durgesh.tripathi2@gmail.com Page 17
    { base e=m;
    e=m;
    }
    As base copy functions don’t know anything about the derived only the base part of
    the derived is copied. This is commonly referred to as slicing. One reason to pass
    objects of classes in a hierarchy is to avoid slicing. Other reasons are to preserve
    polymorphic behavior and to gain efficiency.

  7. What is name mangling?
    Ans: Name mangling is the process through which your c++ compilers give each
    function in your program a unique name. In C++, all programs have at-least a few
    functions with the same name. Name mangling is a concession to the fact that linker
    always insists on all function names being unique.
    Example: In general, member names are made unique by concatenating the name of
    the member with that of the class e.g. given the declaration:
    class Bar
    { public:
    int ival;

    };
    ival becomes something like: // a possible member name mangling ival__3Bar
    Consider this derivation:
    class Foo : public Bar
    { public:
    int ival;

    }
    The internal representation of a Foo object is the concatenation of its base and
    derived class members.
    // Pseudo C++ code
    // Internal representation of Foo
    class Foo
    { public:
    int ival__3Bar;
    int ival__3Foo;

    };
    Unambiguous access of either ival members is achieved through name mangling.
    Member functions, because they can be overloaded, require an extensive mangling
    to provide each with a unique name. Here the compiler generates the same name for
    the two overloaded instances(Their argument lists make their instances unique).

  8. Differentiate between declaration and definition in C++.
    Ans: A declaration introduces a name into the program; a definition provides a
    unique description of an entity (e.g. type, instance, and function). Declarations can
    be repeated in a given scope, it introduces a name in a given scope. There must be
    exactly one definition of every object, function or class used in a C++ program.
    A declaration is a definition unless:
    Ø it declares a function without specifying its body,
    Ø it contains an extern specifier and no initializer or function body,
    Ø it is the declaration of a static class data member without a class definition,
    Ø it is a class name definition,
    Ø it is a typedef declaration.
    A definition is a declaration unless:
    Ø it defines a static class data member,
    Ø it defines a non-inline member function.

  9. What is cloning?
    Ans: An object can carry out copying in two ways i.e. it can set itself to be a copy of
    another object, or it can return a copy of itself. The latter process is called cloning.

  10. Describe the main characteristics of static functions.
    Ans: The main characteristics of static functions include,
    Ø It is without the a this pointer,
    Ø It can’t directly access the non-static members of its class
    Ø It can’t be declared const, volatile or virtual.
    Ø It doesn’t need to be invoked through an object of its class, although for
    convenience, it may.

  11. Will the inline function be compiled as the inline function always? Justify.
    Ans: An inline function is a request and not a command. Hence it won’t be compiled
    as an inline function always.
    Explanation: Inline-expansion could fail if the inline function contains loops, the
    address of an inline function is used, or an inline function is called in a complex
    expression. The rules for inlining are compiler dependent.

  12. Define a way other than using the keyword inline to make a function inline.
    Ans: The function must be defined inside the class.

  13. How can a ‘::’ operator be used as unary operator?
    Ans: The scope operator can be used to refer to members of the global namespace.
    Because the global namespace doesn’t have a name, the notation :: member-name
    refers to a member of the global namespace. This can be useful for referring to
    members of global namespace whose names have been hidden by names declared in
    nested local scope. Unless we specify to the compiler in which namespace to search
    for a declaration, the compiler simple searches the current scope, and any scopes in
    which the current scope is nested, to find the declaration for the name.

  14. What is placement new?
    Ans: When you want to call a constructor directly, you use the placement new.
    Sometimes you have some raw memory that’s already been allocated, and you need
    to construct an object in the memory you have. Operator new’s special version
    placement new allows you to do it.
    class Widget
    { public : Widget(int widgetsize);

    Widget* Construct_widget_int_buffer(void *buffer,int widgetsize)
    { return new(buffer) Widget(widgetsize);
    }
    };
    This function returns a pointer to a Widget object that’s constructed within the
    buffer passed to the function. Such a function might be useful for applications using
    shared memory or memory-mapped I/O, because objects in such applications must
    be placed at specific addresses or in memory allocated by special routines.

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