C++ interview question

C++ interview question

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  C++ INTERVIEW QUESTIONS C++ INTERVIEW QUESTION Ans: The objects with the same data structure (attributes) and 1. What is a class? behaviour(operations) are called class. Ans: It is an entity which may correspond to real-world entities such as students, 2. What is an object? 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. Ans: All objects possessing similar properties are grouped into class. Eg –person is a 3. What is the difference between an object and a class? 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(); }; Ans: In class the data members by default are private but in structure they are by 4. What is the difference between class and structure? default public Ans: Object based programming language support encapsulation and object identity 5. Define object based programming language ? without supporting some important features of OOPs language.eg-ada. Object based language=Encapsulation + object Identity Ans: Object-oriented language incorporates all the features of object based 6. Define object oriented language ? programming languages along with inherentance and polymorphism.eg-c++,java. Ans: OOP is a method of implementation in which programs are organized as co- 7. Define OOPs? operative collection of objects,each of which represents an instance of some class durgesh.tripathi2@gmail.com Page 1
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  C++ INTERVIEW QUESTIONS andwhose classes are all member of a hierarchy of classes united through the property of inheritance. Ans: These are access specifier or visibility lebels .The class members that has been 8. What is public, protected, private? 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 Ans: The scope resolution operator permits a program to reference an identifier in 9. What is a scope resolution operator? the global scope that has been hidden by another identifier with the same name in the local scope. Ans: The mechanism of deriving a new class(derived) from an old class(base class) 10. What do you mean by inheritance? is called inheritance. It allows the extension and reuse of existing code without having to rewrite the code from scratch. Ans: The technique of creating user-defined data types ,having the properties of 11. What is abstraction? 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). Ans: It is the mechanism that wraps the data and function it manipulates into single 12. What is encapsulation? unit and keeps it safe from external interference. Ans: C requires all the variables to be declared at the beginning of a scope but in c++ 13 .How variable declaration in c++ differs that 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. Ans: c++ has the following tokens 14. What are the c++ tokens ? I. keywords II. identifiers III. constants durgesh.tripathi2@gmail.com Page 2
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  C++ INTERVIEW QUESTIONS IV.strings V. operators Ans: A reference variable provides an alias to a previously defined variable. 15. What do you mean by reference variable in c++ ? data type & reference-name = variable name Ans: Whenever data types are mixed in an expression then c++ performs the 16. What do you mean by implicit conversion ? conversion automatically. Here smaller type is converted to wider type. Ex- in case of integer and float integer is converted into float type. 17. What is the difference between method overloading and method Ans: Overloading a method (or function) in C++ is the ability for functions of the overriding? 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. The defining traits of an object-oriented language are: 18. What are the defining traits of an object-oriented language? 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. Ans: Polymorphism is the idea that a base class can be inherited by several classes. 19. What is polymorphism? A base class pointer can point to its child class and a base class array can store different child class objects. durgesh.tripathi2@gmail.com Page 3
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  C++ INTERVIEW QUESTIONS Ans:An inline function is a function that is expanded inline when invoked.ie. the 20. What do you mean by inline function? 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). Ans: A NULL pointer is a pointer of any type whose value is zero. A void pointer is a 21 What is the difference between a NULL pointer and a void pointer? 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). Ans: C++ has pointers Java does not. 22. What is difference between C++ and Java? Java is platform independent C++ is not. Java has garbage collection C++ does not. Ans: Multiple inheritance is a feature in C++ by which one class can be of different 23. What do you mean by multiple inheritance in C++ ? types. Say class teachingAssistant is inherited from two classes say teacher and Student. Ans: virtual methods are used to use the polymorhism feature in C++. Say class A is 24. What do you mean by virtual methods? 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. Ans: By using the static method there is no need creating an object of that class to 25. What do you mean by static methods? 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. Ans: Two. 26. How many ways are there to initialize an int with a constant? 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. durgesh.tripathi2@gmail.com Page 4
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  C++ INTERVIEW QUESTIONS intfoo = 123; int bar (123); Ans: Constructor is a special member function of a class ,which is invoked 27. What is constructors? automatically whenever an instance of the class is created. It has the same name as its class. Ans: Destructor is a special member function of a class , which is invoked 28. What are destructors? automatically whenever an object goes out of the scope.It has the same name as its class with a tilde character prefixed. Ans: A conversion constructor declared with the explicit keyword. The compiler 29. What is an explicit constructor? does not use an explicit constructor to implement an implied conversion of types. Its purpose is reserved explicitly for construction. Ans: A library of container templates approved by the ANSI committee for inclusion 30. What is the Standard Template Library? 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. Ans: Multiple providers of libraries might use common global identifiers causing a 31. What problem does the namespace feature solve? 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. Ans: A using declaration makes it possible to use a name from a namespace 32. What is the use of ‘using’ declaration ? Ans: Templates allow to create generic functions that admit any data type as 33.What is a template ? 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: durgesh.tripathi2@gmail.com Page 5
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  C++ INTERVIEW QUESTIONS templatefunction_declaration; template function_declaration; 34. Differentiate between a template class and class template ? Template class: A generic definition or a parameterized class not instantiated until Ans: 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. 35. What is the difference between a copy constructor and an overloaded Ans: A copy constructor constructs a new object by using the content of the assignment operator? argument object. An overloaded assignment operator assigns the contents of an existing object to another existing object of the same class. Ans: The simple answer is that a virtual destructor is one that is declared with the 36. What is a virtual destructor? virtual attribute. Ans: Incomplete types refers to pointers in which there is non availability of the 37. What is an incomplete type? implementation of the referenced location or it points to some location whose value is not available for modification. int *i=0×400 // i points to address 400 Example: *i=0; //set the value of memory location pointed by i. Incomplete types are otherwise called uninitialized pointers. Ans: It is a process during exception handling when the destructor is called for all 38. [imp] What do you mean by Stack unwinding? local objects between the place where the exception was thrown and where it is caught. Ans: A container class is a class that is used to hold objects in memory or external 39. What is a container class? What are the types of container classes? 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 durgesh.tripathi2@gmail.com Page 6
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  C++ INTERVIEW QUESTIONS heterogeneouscontainer; when the container is holding a group of objects that are all the same, the container is called a homogeneous container Ans: Smalltalk, Java, Eiffel, Sather. 40. Name some pure object oriented languages ? Ans: sizeof, ., .*, .->, ::, ?: 41. Name the operators that cannot be overloaded ? Ans: A class that has no functionality of its own. Its member functions hide the use of 42. What is an adaptor class or Wrapper class? a third party software component or an object with the non-compatible interface or a non-object-oriented implementation. Ans: It is an object of some class whose purpose is to indicate that a real object of 43. What is a Null object? 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. Ans: A class invariant is a condition that defines all valid states for an object. It is a 44. [imp] What is class invariant? 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. Ans: A dangling pointer arises when you use the address of an object after its 45. What is a dangling pointer? 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; durgesh.tripathi2@gmail.com Page 7
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  C++ INTERVIEW QUESTIONS } 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. 46. 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 Ans: In the case of members protected and private, these could not be accessed from 47. How can we access protected and private members of a class ? 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. Ans: Yes we can handle exception in C++ using keyword :try,catch and throw. 48. Can you handle exception in C++ ? 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. durgesh.tripathi2@gmail.com Page 8
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  C++ INTERVIEW QUESTIONS Ans:A virtual function is a member function that is declared within a base class and 49. What is virtual function ? redefined by a derived class .To create a virtual function,the function declaration in the base class is preceded by the keyword virtual. Ans: Early binding refers to the events that occur at compile time. Early binding 50. What do you mean by 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. Ans: Late binding refers to function calls that are not resolved until run time. Virtual 51. What do you mean by late binding ? 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. Ans: A modifier, also called a modifying function is a member function that changes 52. What is a modifier? 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’. Ans: An accessor is a class operation that does not modify the state of an object. The 53. What is an accessor? accessor functions need to be declared as const operations Ans: A name clash occurs when a name is defined in more than one place. For 54. When does a name clash occur? 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 Ans: It is a feature in c++ to minimize name collisions in the global name space. This 55. Define namespace. 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. Ans: A using declaration makes it possible to use a name from a namespace without 56. What is the use of ‘using’ declaration. the scope operator. Ans: A class that is used to traverse through the objects maintained by a container 57. What is an Iterator class? durgesh.tripathi2@gmail.com Page 9
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  C++ INTERVIEW QUESTIONS 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-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. 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. 58. List out some of the OODBMS available. Ø GEMSTONE/OPAL of Gemstone systems. Ans: 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. durgesh.tripathi2@gmail.com Page 10
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  C++ INTERVIEW QUESTIONS 59.List out some of the object-oriented methodologies. Ø Object Oriented Development (OOD) (Booch 1991,1994). Ans: 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). Ans: Incomplete types refers to pointers in which there is non availability of the 60. What is an incomplete type? 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 Example: *i=0; //set the value of memory location pointed by i. Incomplete types are otherwise called uninitialized pointers. 61. 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. 62. What are the conditions that have to be met for a condition to be an invariant of the class? Ø The condition should hold at the end of every constructor. Ans: Ø The condition should hold at the end of every mutator(non-const) operation. 63. What are proxy objects? Ans: Objects that stand for other objects are called proxy objects or surrogates. template Example: durgesh.tripathi2@gmail.com Page 11
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  C++ INTERVIEW QUESTIONS 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, 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. 64. Name some pure object oriented languages. Ø Smalltalk, Ans: Ø Java, Ø Eiffel, Ø Sather. Ans: sizeof . .* .-> :: ?: 65. Name the operators that cannot be overloaded. Ans: A node class is a class that, 66. What is a node class? 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. durgesh.tripathi2@gmail.com Page 12
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  C++ INTERVIEW QUESTIONS Anode class is a class that has added new services or functionality beyond the services inherited from its base class. Ans: If two base classes have no overlapping methods or data they are said to be 67. What is an orthogonal base class? 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. Ans: A container class is a class that is used to hold objects in memory or external 68. What is a container class? What are the types of container classes? 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. Ans: An abstract class is a protocol class if: 69. What is a protocol class? Ø it neither contains nor inherits from classes that contain member data, non- virtual 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. Ans: A class that provides some but not all of the implementation for a virtual base 70. What is a mixin class? 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. Ans: A concrete class is used to define a useful object that can be instantiated as an 71. What is a concrete class? 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. Ans: A handle is a class that maintains a pointer to an object that is 72. What is the handle class? 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 durgesh.tripathi2@gmail.com Page 13
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  C++ INTERVIEW QUESTIONS 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. Ans: The simplest and most obvious way to specify an action in C++ is to write a 73. What is an action class? 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 class write_file : public Action example: { 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; } }; durgesh.tripathi2@gmail.com Page 14
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  C++ INTERVIEW QUESTIONS Auser of the Action class will be completely isolated from any knowledge of derived classes such as write_file and error_message. Ans: A memory leak occurs when a program loses the ability to free a block of 74. When can you tell that a memory leak will occur? dynamically allocated memory. Ans: A template is a parameterized construct or type containing generic code that 75. What is a parameterized type? 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. Ans: Deep copy involves using the contents of one object to create another instance 76. Differentiate between a deep copy and a shallow copy? 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. Ans: A pointer is said to be opaque if the definition of the type to which it points to is 77. What is an opaque pointer? 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. Ans: A smart pointer is an object that acts, looks and feels like a normal pointer but 78. What is a smart pointer? offers more functionality. In C++, smart pointers are implemented as template durgesh.tripathi2@gmail.com Page 15
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  C++ INTERVIEW QUESTIONS classesthat 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. template Example: 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); Ans: The 'is-a' is called a reflexive association because the reflexive association 79. What is 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. Ans: Slicing means that the data added by a subclass are discarded when an object of 80. What is slicing? 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( ) durgesh.tripathi2@gmail.com Page 16
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  C++ INTERVIEW QUESTIONS { 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. Ans: Name mangling is the process through which your c++ compilers give each 81. What is name mangling? 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 class Foo : public Bar Consider this derivation: { 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). Ans: A declaration introduces a name into the program; a definition provides a 82. Differentiate between declaration and definition in C++. 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 durgesh.tripathi2@gmail.com Page 17
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  C++ INTERVIEW QUESTIONS exactlyone definition of every object, function or class used in a C++ program. Ø it declares a function without specifying its body, A declaration is a definition unless: 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. Ø it defines a static class data member, A definition is a declaration unless: Ø it defines a non-inline member function. Ans: An object can carry out copying in two ways i.e. it can set itself to be a copy of 83. What is cloning? another object, or it can return a copy of itself. The latter process is called cloning. Ans: The main characteristics of static functions include, 84. Describe the main characteristics of static functions. 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. Ans: An inline function is a request and not a command. Hence it won't be compiled 85. Will the inline function be compiled as the inline function always? Justify. 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. Ans: The function must be defined inside the class. 86. Define a way other than using the keyword inline to make a function inline. Ans: The scope operator can be used to refer to members of the global namespace. 87. How can a '::' operator be used as unary operator? 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. Ans: When you want to call a constructor directly, you use the placement new. 88. What is 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 durgesh.tripathi2@gmail.com Page 18
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  C++ INTERVIEW QUESTIONS placementnew 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. …………………………………….00000000000000000000000000000000000000……………………………. durgesh.tripathi2@gmail.com Page 19