C++

125 Top C++ Interview Questions and Answers 2017

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C++ Interview Questions and Answers:-

1. What is C++?
Released in 1985, C++ is an object-oriented programming language created by Bjarne Stroustrup. C++ maintains almost all aspects of the C language while simplifying memory management and adding several features – including a new data type known as a class (you will learn more about these later) – to allow object-oriented programming. C++ maintains the features of C which allowed for low-level memory access but also gives the programmer new tools to simplify memory management.

2. C++ used for:
C++ is a powerful general-purpose programming language. It can be used to create small programs or large applications. It can be used to make CGI scripts or console-only DOS programs. C++ allows you to create programs to do almost anything you need to do. The creator of C++, Bjarne Stroustrup, has put together a partial list of applications written in C++.

3. What is a modifier in C++?
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. Example: The function mod is a modifier in the following code snippet:

class test
{
int x,y;
public:
test()
{
x=0; y=0;
}
void mod()
{
x=10;
y=15;
}
};

4. What is an accessor in C++?
An accessor is a class operation that does not modify the state of an object in C++. The accessor functions need to be declared as const operations

5. Differentiate between a template class and class template in C++?
Template class: A generic definition or a parametrized 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.

6. When does a name clash occur in C++?
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.

7. Define namespace in C++?
It is a feature in C++ to minimize name collisions in the global namespace. 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.

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

9. What is an Iterator class in C++?
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 an 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.

10. What is an incomplete type in C++?
Incomplete types refer to pointers in which there is no 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.

11. What is a dangling pointer in C++?
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. 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.

12. Differentiate between the message and method in C++?
Message in C++ :

  • Objects communicate by sending messages to each other.
  • A message is sent to invoke a method in C++.

A method in C++ :

  • Provides a response to a message.
  • It is an implementation of operation in C++.

13. What is an adaptor class or Wrapper class in C++?
A class that has no functionality of its own is an Adaptor class in C++. 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.

14. What is a Null object in C++?
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.

15. What is class invariant in C++?
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.

16. What do you mean by Stack unwinding in C++?
Stack unwinding in C++ 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.

17. Define precondition and post-condition to a member function in C++?
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. 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 is() 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 is empty() must necessarily hold. This is a post-condition of the push operation.

18. 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.

19. What are proxy objects in C++?
Objects that stand for other objects are called proxy objects or surrogates.
template <class t=””>
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:

Array2D<float>data(10,20);
cout<<data[3][6]; // fine

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.

20. Name some pure object oriented languages?
pure object-oriented languages are Smalltalk, Java, Eiffel, Sather.

21. What is a node class in c++?
A node class is a class that,

  • relies on the base class for services and implementation,
  • provides a wider interface to the users than its base class,
  • relies primarily on virtual functions in its public interface
  • depends on all its direct and indirect base class
  • can be understood only in the context of the base class
  • can be used as a base for further derivation
  • 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.

22. What is an orthogonal base class in C++?
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.

23. What is a container class? What are the types of container classes in C++?
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.

24. How do you write a function that can reverse a linked-list in C++?
void reverselist(void)
{
if(head==0)
return;
if(head-<next==0)
return;
if(head-<next==tail)
{
head-<next = 0;
tail-<next = head;
}
else
{
node* pre = head;
node* cur = head-<next;
node* curnext = cur-<next;
head-<next = 0;
cur-<next = head;

for(; curnext!=0; )
{
cur-<next = pre;
pre = cur;
cur = curnext;
curnext = curnext-<next;
}

curnext-<next = cur;
}
}

25. What is polymorphism in C++?
Polymorphism in C++ 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.

26. How do you find out if a linked-list has an end? (i.e. the list is not a cycle)
You can find out by using 2 pointers. One of them goes 2 nodes each time. The second one goes at 1 node each time. If there is a cycle, the one that goes 2 nodes each time will eventually meet the one that goes slower. If that is the case, then you will know the linked-list is a cycle.

27. How can you tell what shell you are running on a UNIX system?
You can do the Echo $RANDOM. It will return an undefined variable if you are from the C-Shell, just a return prompt if you are from the Bourne shell, and a 5 digit random numbers if you are from the Korn shell. You could also do a ps -l and look for the shell with the highest PID.

28. What is Boyce Codd Normal form?
A relation schema R is in BCNF with respect to a set F of functional dependencies if for all functional dependencies in F+ of the form a->b, where a and b is a subset of R, at least one of the following holds:

  • a->b is a trivial functional dependency (b is a subset of a)
  • a is a superkey for schema R

29. What is a pure virtual function?
A class is made abstract by declaring one or more of its virtual functions to be pure. A pure virtual function is one with an initializer of = 0 in its declaration

30. Write a Struct Time where integer m, h, s are its members
struct Time
{
int m;
int h;
int s;
};

31. How do you traverse a Btree in Backward in-order?

  • Process the node in the right subtree
  • Process the root
  • Process the node in the left subtree

32. What are the two main roles of the Operating System?

  1. As a resource manager
  2. As a virtual machine

33.In the derived class, which data member of the base class is visible?
In the public and protected sections.

34. How do you find out if a linked-list has an end? (i.e. the list is not a cycle)
You can find out by using 2 pointers. One of them goes 2 nodes each time. The second one goes at 1 node each time. If there is a cycle, the one that goes 2 nodes each time will eventually meet the one that goes slower. If that is the case, then you will know the linked-list is a cycle.

35. What is the difference between realloc() and free()?
The free subroutine frees a block of memory previously allocated by the malloc subroutine. Undefined results occur if the Pointer parameter is not a valid pointer. If the Pointer parameter is a null value, no action will occur. The realloc subroutine changes the size of the block of memory pointed to by the Pointer parameter to the number of bytes specified by the Size parameter and returns a new pointer to the block. The pointer specified by the Pointer parameter must have been created with the malloc, calloc, or realloc subroutines and not been deallocated with the free or realloc subroutines. Undefined results occur if the Pointer parameter is not a valid pointer.

36. What is function overloading and operator overloading?
Function overloading: C++ enables several functions of the same name to be defined, as long as these functions have different sets of parameters (at least as far as their types are concerned). This capability is called function overloading. When an overloaded function is called, the C++ compiler selects the proper function by examining the number, types, and order of the arguments in the call. Function overloading is commonly used to create several functions of the same name that perform similar tasks but on different data types.
Operator overloading allows existing C++ operators to be redefined so that they work on objects of user-defined classes. Overloaded operators are syntactic sugar for equivalent function calls. They form a pleasant facade that doesn’t add anything fundamental to the language (but they can improve understandability and reduce maintenance costs).

37. What is the difference between declaration and definition?
The declaration tells the compiler that at some later point we plan to present the definition of this declaration.
E.g.: void stars () //function declaration
The definition contains the actual implementation.
E.g.: void stars () // declarator
{
for(int j=10; j > =0; j–) //function body
cout << *;
cout << endl; }

38. What are the advantages of inheritance in C++?
It permits code reusability. Reusability saves time in program development. It encourages the reuse of proven and debugged high-quality software, thus reducing problem after a system becomes functional.

39. How do you write a function that can reverse a linked-list?
void reverselist(void)
{
if(head==0)
return;
if(head->next==0)
return;
if(head->next==tail)
{
head->next = 0;
tail->next = head;
}
else
{
node* pre = head;
node* cur = head->next;
node* curnext = cur->next;
head->next = 0;
cur-> next = head;

for(; curnext!=0; )
{
cur->next = pre;
pre = cur;
cur = curnext;
curnext = curnext->next;
}

curnext->next = cur;
}
}

40. What do you mean by inline function?
The idea behind inline functions is to insert the code of a called function at the point where the function is called. If done carefully, this can improve the application’s performance in exchange for increased compile time and possibly (but not always) an increase in the size of the generated binary executables.

41. Write a program that ask for user input from 5 to 9 then calculate the average
#include “iostream.h”
int main() {
int MAX = 4;
int total = 0;
int average;
int numb;

for (int i=0; i<MAX; i++) {
cout <<
“Please enter your input between 5 and 9: “;
cin >> numb;
while ( numb<5 || numb>9) {
cout << “Invalid input, please re-enter: “;
cin >> numb;
}
total = total + numb;
}
average = total/MAX;
cout << “The average number is: ”
<< average << “n”;
return 0;
}

41. Write a short code using C++ to print out all odd number from 1 to 100 using a for loop
for( unsigned int i = 1; i < = 100; i++ )

if( i & 0x00000001 )

cout << i << “,”;

42. What is public, protected, private in C++?

  • Public, protected and private are three access specifiers in C++.
  • Public data members and member functions are accessible outside the class.
  • Protected data members and member functions are only available to derived classes.
  • Private data members and member functions can’t be accessed outside the class. However, there is an exception can be using friend classes.

43. Write a function that swaps the values of two integers, using int* as the argument type.
void swap(int* a, int*b) {
int t;
t = *a;
*a = *b;
*b = t;
}

44. Tell how to check whether a linked list is circular.
Create two pointers, each set to the start of the list. Update each as follows:
while (pointer1) {
pointer1 = pointer1->next;
pointer2 = pointer2->next; if (pointer2) pointer2=pointer2->next;
if (pointer1 == pointer2) {
print (“circularn”);
}
}

OK, why does this work?
If a list is circular, at some point pointer2 will wrap around and be either at the item just before pointer1, or the item before that. Either way, it’s either 1 or 2 jumps until they meet.

45. What are virtual constructors/destructors?
Answer1
Virtual destructors:
If an object (with a non-virtual destructor) is destroyed explicitly by applying the delete operator to a base-class pointer to the object, the base class destructor function (matching the pointer type) is called on the object.
There is a simple solution to this problem declares a virtual base-class destructor.
This makes all derived-class destructors virtual even though they don’t have the same name as the base-class destructor. Now, if the object in the hierarchy is destroyed explicitly by applying the delete operator to a base-class pointer to a derived-class object, the destructor for the appropriate class is called. Virtual constructor: Constructors cannot be virtual. Declaring a constructor as a virtual function is a syntax error.

Answer2
Virtual destructors: If an object (with a non-virtual destructor) is destroyed explicitly by applying the delete operator to a base-class pointer to the object, the base class destructor function (matching the pointer type) is called on the object.
There is a simple solution to this problem declares a virtual base-class destructor. This makes all derived-class destructors virtual even though they don’t have the same name as the base-class destructor. Now, if the object in the hierarchy is destroyed explicitly by applying the delete operator to a base-class pointer to a derived-class object, the destructor for the appropriate class is called.

46. What is the difference between an ARRAY and a LIST?
Answer1
An array is a collection of homogeneous elements.
The list is a collection of heterogeneous elements.

For Array memory allocated is static and continuous.
For List memory allocated is dynamic and Random.

Array: User need not have to keep in track of next memory allocation.
List: User has to keep in Track of next location where memory is allocated.

Answer2
Array uses direct access of stored members, list uses sequencial access for members.

//With Array you have direct access to memory position 5
Object x = a[5]; // x takes directly a reference to 5th element of array

//With the list you have to cross all previous nodes in order to get the 5th node:
list mylist;
list::iterator it;

for( it = list.begin() ; it != list.end() ; it++ )
{
if( i==5)
{
x = *it;
break;
}
i++;
}

47. Does c++ support multilevel and multiple inheritance?
Yes.

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

template <class indetifier> function_declaration; template <typename indetifier> function_declaration;

The only difference between both prototypes is the use of keyword class or type name, its use is indistinct since both expressions have exactly the same meaning and behave exactly the same way.

49. Define a constructor – What it is and how it might be called (2 methods).
Answer1
the constructor is a member function of the class, with the name of the function being the same as the class name. It also specifies how the object should be initialized.

Ways of calling constructor:
1) Implicitly: automatically by the compiler when an object is created.
2) Calling the constructors explicitly is possible, but it makes the code unverifiable.

Answer2
class Point2D{
int x; int y;
public Point2D() : x(0) , y(0) {} //default (no argument) constructor
};

main(){

Point2D MyPoint; // Implicit Constructor call. In order to allocate memory on stack, the default constructor is implicitly called.

Point2D * point = new Point2D(); // Explicit Constructor call. In order to allocate memory on HEAP, we call the default constructor.

50. You have two pairs: new() and delete() and another pair : malloc() and free(). Explain differences between eg. new() and malloc()
Answer1
1.) new and delete are preprocessors while malloc() and free() are functions. [we don’t use brackets will calling new or delete].
2.) no need of allocating the memory while using new but in malloc() we have to use sizeof
3.) new will initialize the new memory to 0 but malloc() gives random value in the newly allocated memory location [better to use malloc()]

Answer2
new() allocates continuous space for the object instance
malloc() allocates distributed space.
new() is castless, meaning that allocates memory for this specific type,
malloc(), calloc() allocate space for void * that is created to the specific class type pointer.

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51. What is the difference between class and structure in C++?
Structure: Initially (in C) a structure was used to bundle different type of data types together to perform a particular functionality. But C++ extended the structure to contain functions also. The major difference is that all declarations inside a structure are by default public.
Class: Class is a successor of Structure. By default all the members inside the class are private.

52. What is RTTI in C++?
Runtime type identification (RTTI) lets you find the dynamic type of an object when you have only a pointer or a reference to the base type. RTTI is the official way in standard C++ to discover the type of an object and to convert the type of a pointer or reference (that is, dynamic typing). The need came from practical experience with C++. RTTI replaces many homegrown versions with a solid, consistent approach.

53. What is encapsulation in C++?
Packaging an object’s variables within its methods is called encapsulation.

54. What is a C++ object?
Object is a software bundle of variables and related methods. Objects have state and behavior.

55. Describe PRIVATE, PROTECTED and PUBLIC the differences and give examples.
class Point2D{
int x; int y;

public int color;
protected bool pinned;
public Point2D() : x(0) , y(0) {} //default (no argument) constructor
};

Point2D MyPoint;

You cannot directly access private data members when they are declared (implicitly) private:

MyPoint.x = 5; // Compiler will issue a compile ERROR
//Nor yoy can see them:
int x_dim = MyPoint.x; // Compiler will issue a compile ERROR

On the other hand, you can assign and read the public data members:

MyPoint.color = 255; // no problem
int col = MyPoint.color; // no problem

With protected data members you can read them but not write them: MyPoint.pinned = true; // Compiler will issue a compile ERROR

bool isPinned = MyPoint.pinned; // no problem

56. What is C++ namespace?
Namespaces allow us to group a set of global classes, objects and/or functions under a name. To say it somehow, they serve to split the global scope into sub-scopes known as namespaces.
The form to use namespaces is:
namespace identifier { namespace-body }
Where identifier is any valid identifier and namespace-body is the set of classes, objects, and functions that are included within the namespace. For example:
namespace general { int a, b; } In this case, a and b are normal variables integrated within the general namespace. In order to access these variables from outside the namespace we have to use the scope operator::. For example, to access the previous variables we would have to put:
general::a general::b
The functionality of namespaces is especially useful in case there is a possibility that a global object or function can have the same name than another one, causing a redefinition error.

57. What do you mean by inheritance?
Inheritance is the process of creating new classes, called derived classes, from existing classes or base classes. The derived class inherits all the capabilities of the base class but can add embellishments and refinements of its own.

58. What is a COPY CONSTRUCTOR and when is it called?
A copy constructor is a method that accepts an object of the same class and copies it’s data members to the object on the left part of assignement:

class Point2D{
int x; int y;

public int color;
protected bool pinned;
public Point2D() : x(0) , y(0) {} //default (no argument) constructor
public Point2D( const Point2D & ) ;
};

Point2D::Point2D( const Point2D & p )
{
this->x = p.x;
this->y = p.y;
this->color = p.color;
this->pinned = p.pinned;
}

main(){
Point2D MyPoint;
MyPoint.color = 345;
Point2D AnotherPoint = Point2D( MyPoint ); // now AnotherPoint has color = 345

59. What is Boyce Codd Normal form in C++?
A relation schema R is in BCNF with respect to a set F of functional dependencies if for all functional dependencies in F+ of the form a->, where a and b is a subset of R, at least one of the following holds:
* a- > b is a trivial functional dependency (b is a subset of a)
* a is a superkey for schema R

60. What is the virtual class and friend class?
Friend classes are used when two or more classes are designed to work together and need access to each other’s implementation in ways that the rest of the world shouldn’t be allowed to have. In other words, they help keep private things private. For instance, it may be desirable for class DatabaseCursor to have more privilege to the internals of class Database than main() has.

61. What problems might the following macro bring to the application?
#define sq(x) x*x

62. Anything wrong with this code?
T *p = new T[10];
delete p;
Everything is correct, Only the first element of the array will be deleted”, The entire array will be deleted, but only the first element destructor will be called.

63. Anything wrong with this code?
T *p = 0;
delete p;
Yes, the program will crash in an attempt to delete a null pointer.

64. How do you decide which integer type to use?
It depends on our requirement. When we are required an integer to be stored in 1 byte (means less than or equal to 255) we use short int, for 2 bytes we use int, for 8 bytes we use long int.

A char is for 1-byte integers, a short is for 2-byte integers, an int is generally a 2-byte or 4-byte integer (though not necessarily), along is a 4-byte integer, and a long is an 8-byte integer.

65. What is the best way to declare and define global variables?
The best way to declare global variables is to declare them after including all the files so that it can be used in all the functions.

66. What does extern mean in a function declaration?
Using extern in a function declaration we can make a function such that it can use outside the file in which it is defined.

An extern variable, function definition, or declaration also makes the described variable or function usable by the succeeding part of the current source file. This declaration does not replace the definition. The declaration is used to describe the variable that is externally defined.

If a declaration for an identifier already exists at file scope, any extern declaration of the same identifier found within a block refers to that same object. If no other declaration for the identifier exists at file scope, the identifier has external linkage.

67. What can I safely assume about the initial values of variables which are not explicitly initialized?
It depends on a compiler which may assign any garbage value to a variable if it is not initialized.

68. What is the difference between char a[] = string; and char *p = string;?
In the first case, 6 bytes are allocated to the variable a which is fixed, whereas in the second case if *p is assigned to some other value the allocate memory can change.

69. What is the auto keyword good for in C++?
Answer1
Not much. It declares an object with automatic storage duration. Which means the object will be destroyed at the end of the scope of the objects. All variables in functions that are not declared as static and not dynamically allocated have automatic storage duration by default.

For example
int main()
{
int a; //this is the same as writing “auto int a;”
}

Answer2
Local variables occur within a scope; they are œlocal to a function. They are often called automatic variables because they automatically come into being when the scope is entered and automatically go away when the scope closes. The keyword auto makes this explicit, but local variables default to auto auto auto auto so it is never necessary to declare something like an auto auto auto auto.

70. How do I declare an array of N pointers to functions returning pointers to functions returning pointers to characters?
Answer1
If you want the code to be even slightly readable, you will use typedefs.
typedef char* (*functiontype_one)(void);
typedef functiontype_one (*functiontype_two)(void);
functiontype_two myarray[N]; //assuming N is a const integral

Answer2
char* (* (*a[N])())()
Here a is that array. And according to question no function will not take any parameter value.

71. What does extern mean in a function declaration in C++?
It tells the compiler that a variable or a function exists, even if the compiler hasn’t yet seen it in the file currently being compiled. This variable or function may be defined in another file or further down in the current file.

72. How do I initialize a pointer to a function?
This is the way to initialize
a pointer to a function
void fun(int a)
{

}

void main()
{
void (*fp)(int);
fp=fun;
fp(1);

}

73. How do you link a C++ program to C functions?
By using the extern “C” linkage specification around the C function declarations.

74. Explain the scope resolution operator.
It 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.

75. What are the differences between a C++ struct and C++ class?
The default member and base-class access specifiers are different.

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

77. How does throwing and catching exceptions differ from using setjmp and longjmp?
The throw operation calls the destructors for automatic objects instantiated since entry to the try block.

78. What is a default constructor in C++?
Default constructor WITH arguments

class B {
public:
B (int m = 0) : n (m) {}
int n;
};

int main(int argc, char *argv[])
{
B b;
return 0;
}

79. What is a conversion constructor C++?
A constructor that accepts one argument of a different type.

80. 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.

81. When should you use multiple inheritances?
There are three acceptable answers: “Never,” “Rarely,” and “When the problem domain cannot be accurately modeled any other way.”

82. Explain the ISA and HASA class relationships. How would you implement each in a class design?
A specialized class “is” a specialization of another class and, therefore, has an ISA relationship with the other class. An Employee ISA Person. This relationship is best implemented with inheritance. An employee is derived from Person. A class may have an instance of another class. For example, an employee “has” a salary, therefore the Employee class has a HASA relationship with the Salary class. This relationship is best implemented by embedding an object of the Salary class in the Employee class.

83. When is a template a better solution than a base class?
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 genericity) to the designer of the container or manager class.

84. What is a mutable member?
One that can be modified by the class even when the object of the class or the member function doing the modification is const.

85. What is an explicit constructor?
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.

86. What is the Standard Template Library (STL)?
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.

87. Describe run-time type identification.
The ability to determine at run time the type of an object by using the typeid operator or the dynamic_cast operator.

88. What problem does the namespace feature solve?
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.

89. Are there any new intrinsic (built-in) data types?
Yes. The ANSI committee added the bool intrinsic type and its true and false value keywords.

90. Will the following program execute?
Will the following program execute?
void main()
{
void *vptr = (void *) malloc(sizeof(void));
vptr++;
}

Answer1
It will throw an error, as arithmetic operations cannot be performed on void pointers.

Answer2
It will not build as size cannot be applied to void* ( error Unknown size )

Answer3
How can it execute if it won™t even compile? It needs to be int main, not void main. Also, cannot increment a void *.

Answer4
According to gcc compiler, it won™t show any error, simply it executes. but in general we can’t do arthematic operation on the void, and gives the size of a void as 1

Answer5
The program compiles in GNU C while giving a warning for œvoid main”. The program runs without a crash. sizeof(void) is 1? hence when vptr++, the address is incremented by 1.

Answer6
Regarding arguments about GCC, be aware that this is a C++ question, not C. So gcc will compile and execute, g++ cannot. g++ complains that the return type cannot be void and the argument of sizeof() cannot be void. It also reports that ISO C++ forbids incrementing a pointer of type void*™.

Answer7
in C++
voidp.c: In function `int main()™:
voidp.c:4: error: invalid application of `sizeof™ to a void type
voidp.c:4: error: `malloc™ undeclared (first use this function)
voidp.c:4: error: (Each undeclared identifier is reported only once for each function it appears in.)
voidp.c:6: error: ISO C++ forbids incrementing a pointer of type `void*™

But in c, it work without problems

91. Will this C++ program execute or not?
void main()
{
char *cptr = 0?2000;
long *lptr = 0?2000;
cptr++;
lptr++;
printf(%x %x, cptr, lptr);
}Will it execute or not?

Answer1
For Q2: As above, won’t compile because main must return it. Also, 0—2000 cannot be implicitly converted to a pointer (I assume you meant 0—2000 and not 0?2000.)

Answer2
Not Execute.
Compile with VC7 results following errors:
error C2440: initializing ™: cannot convert from int™ to char *™
error C2440: initializing ™: cannot convert from int™ to long *™

Not Execute if it is C++, but Execute in C.
The printout:
2001 2004

Answer3
In C++
[$]> g++ point.c
point.c: In function `int main()™:
point.c:4: error: invalid conversion from `int™ to `char*™
point.c:5: error: invalid conversion from `int™ to `long int*™

in C
[$] etc > gcc point.c
point.c: In function `main™:
point.c:4: warning: initialization makes pointer from integer without a cast
point.c:5: warning: initialization makes pointer from integer without a cast
[$] etc > ./a.exe
2001 2004

92. What is the difference between Mutex and Binary semaphore?
semaphore is used to synchronize processes. whereas mutex is used to provide synchronization between threads running in the same process.

93. In C++, what is the difference between method overloading and method overriding?
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 (a different set of parameters). Method overriding is the ability of the inherited class rewriting the virtual method of the base class.

94. What methods can be overridden in Java?
In C++ terminology, all public methods in Java are virtual. Therefore, all Java methods can be overwritten in subclasses except those that are declared final, static, and private.

95. What are the defining traits of an object-oriented language?
The defining traits of an object-oriented language are:
* encapsulation
* inheritance
* polymorphism

96. Can you be able to identify between Straight- through and Cross- over cable wiring? and in what case do you use Straight- through and Cross-over?
Straight-through is a type of wiring that is one to connection, Cross- over is a type of wiring which those wires are got switched
We use Straight-through cable when we connect between NIC Adapter and Hub. Using Cross-over cable when connecting between two NIC Adapters or sometime between two hubs.

97. If you hear the CPU fan is running and the monitor power is still on, but you did not see anything show up in the monitor screen. What would you do to find out what is going wrong?
I would use the ping command to check whether the machine is still alive(connect to the network) or it is dead.

98. Assignment Operator – What is the difference between an “assignment operator” and a “copy constructor”?
Answer1.
In the assignment operator, you are assigning a value to an existing object. But in copy constructor, you are creating a new object and then assigning a value to that object. For example:

complex c1,c2;
c1=c2; //this is assignment
complex c3=c2; //copy constructor

Answer2.
A copy constructor is used to initialize a newly declared variable from an existing variable. This makes a deep copy like assignment, but it is somewhat simpler:

There is no need to test to see if it is being initialized from itself.
There is no need to clean up (eg, delete) an existing value (there is none).
A reference to itself is not returned.

99. RTTI – What is RTTI in C++?
Answer1.
RTTI stands for “Run Time Type Identification”. In an inheritance hierarchy, we can find out the exact type of the object of which it is a member. It can be done by using:

1) dynamic id operator
2) typecast operator

Answer2.
RTTI is defined as follows: Run Time Type Information, a facility that allows an object to be queried at runtime to determine its type. One of the fundamental principles of object technology is polymorphism, which is the ability of an object to dynamically change at runtime.

100. STL Containers – What are the types of STL containers?
There are 3 types of STL containers:

1. Adaptive containers like a queue, stack
2. Associative containers like set, map
3. Sequence containers like vector, deque

101. What is the word you will use when defining a function in the base class to allow this function to be a polymorphic function?
virtual

102. What do you mean by binding of data and functions?
Encapsulation.

103. What are 2 ways of exporting a function from a DLL?
1.Taking a reference to the function from the DLL instance.
2. Using the DLL s Type Library

104. What is the difference between an object and a class?
Classes and objects are separate but related concepts. Every object belongs to a class and every class contains one or more related objects.
– A Class is static. All of the attributes of a class are fixed before, during, and after the execution of a program. The attributes of a class don’t change.
– The class to which an object belongs is also (usually) static. If a particular object belongs to a certain class at the time that it is created then it almost certainly will still belong to that class right up until the time that it is destroyed.
– An Object, on the other hand, has a limited lifespan. Objects are created and eventually destroyed. Also during that lifetime, the attributes of the object may undergo significant change.

105. Suppose that data is an array of 1000 integers. Write a single function call that will sort the 100 elements data [222] through data [321].
quicksort ((data + 222), 100);

106. What is the C++ class?
Class is a user-defined data type in C++. It can be created to solve a particular kind of problem. After creation, the user need not know the specifics of the working of a class.

107. What is friend function in C++?
As the name suggests, the function acts as a friend to a class. As a friend of a class, it can access its private and protected members. A friend function is not a member of the class. But it must be listed in the class definition.

108. Which recursive sorting technique always makes recursive calls to sort subarrays that are about half size of the original array?
Mergesort always makes recursive calls to sort subarrays that are about half size of the original array, resulting in O(n log n) time.

109. What is an abstraction in C++?
Abstraction is of the process of hiding unwanted details from the user.

110. What are virtual functions in C++?
A virtual function allows derived classes to replace the implementation provided by the base class. The compiler makes sure the replacement is always called whenever the object in question is actually of the derived class, even if the object is accessed by a base pointer rather than a derived pointer. This allows algorithms in the base class to be replaced in the derived class, even if users don’t know about the derived class.

111. What is the difference between an external iterator and an internal iterator? Describe the advantage of an external iterator.
An internal iterator is implemented with member functions of the class that has items to step through. .An external iterator is implemented as a separate class that can be “attach” to the object that has items to step through. .An external iterator has the advantage that many difference iterators can be active simultaneously on the same object.

112. What is a scope resolution operator?
A scope resolution operator (::), can be used to define the member functions of a class outside the class.

113. What do you mean by pure virtual functions?
A pure virtual member function is a member function that the base class forces derived classes to provide. Normally these member functions have no implementation. Pure virtual functions are equated to zero.
class Shape { public: virtual void draw() = 0; };

114. What is polymorphism in C++? Explain with an example?
“Poly” means “many” and “morph” means “form”. Polymorphism is the ability of an object (or reference) to assume (be replaced by) or become many different forms of object.
Example: function overloading, function overriding, virtual functions. Another example can be a plus ‘+’ sign, used for adding two integers or for using it to concatenate two strings.

115. How can you quickly find the number of elements stored in a) static array b) dynamic array?
Why is it difficult to store a linked list in an array?
How can you find the nodes with respective data in a linked list?
Write a prog to accept a given string in any order and flash error if any of the characters are different. For example: If ABC is the input then ABC, BCA, cab, cab back are acceptable but aac or bad is unacceptable.
Write out a function that prints out all the permutations of a string. For example, abc would give you abc, acb, bac, bca, cab, cba. You can assume that all the characters will be unique.

116. What is the output of the following program? Why?
#include <stdio.h>
main()
{
typedef union
{
int a;
char b[10];
float c;
}
Union;

Union x,y = {100};
x.a = 50;
strcpy(x.b,”hello”);
x.c = 21.50;

printf(“Union x : %d %s %f n”,x.a,x.b,x.c );
printf(“Union y :%d %s%f n”,y.a,y.b,y.c);
}

Given inputs X, Y, Z and operations | and & (meaning bitwise OR and AND, respectively)
What is output equal to in
output = (X & Y) | (X & Z) | (Y & Z)

117. Why are arrays usually processed with for loop?
The real power of arrays comes from their facility of using an index variable to traverse the array, accessing each element with the same expression a[i]. All the is needed to make this work is an iterated statement in which the variable I serves as a counter, incrementing from 0 to a.length -1. That is exactly what a loop does.

118. What is an HTML tag?
An HTML tag is a syntactical construct in the HTML language that abbreviates specific instructions to be executed when the HTML script is loaded into a Web browser. It is like a method in Java, a function in C++, a procedure in Pascal, or a subroutine in FORTRAN.

119. Explain which of the following declarations will compile and what will be constant …
Explain which of the following declarations will compile and what will be constant – a pointer or the value pointed at * const char *
* char const *
* char * const

Note: Ask the candidate whether the first declaration is pointing to a string or a single character. Both explanations are correct, but if he says that it’s a single character pointer, ask why a whole string is initialized as char* in C++. If he says this is a string declaration, ask him to declare a pointer to a single character. Competent candidates should not have problems pointing out why const char* can be both a character and a string declaration, incompetent ones will come up with invalid reasons.

120. You are given a simple code for the class BankCustomer. Write the following functions …
You re given a simple code for the class BankCustomer. Write the following functions:
* Copy constructor
* = operator overload
* == operator overload
* + operator overload (customers’ balances should be added up, as an example of a joint account between husband and wife)

Note: Anyone confusing assignment and equality operators should be dismissed from the interview. The applicant might make a mistake of passing by value, not by reference. The candidate might also want to return a pointer, not a new object, from the addition operator. Slightly hint that you’d like the value to be changed outside the function, too, in the first case. Ask him whether the statement customer3 = customer1 + customer2 would work in the second case.

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