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 datatype 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
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++.
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 nodes 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.
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
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).
What is the difference between declaration and definition?
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
What are the advantages of inheritance?
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
How do you write a function that can reverse a linked-list?
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
Write a program that ask for user input from 5 to 9 then calculate the average
cout << "Please enter your input between 5 and 9: ";
cout << "Invalid input, please re-enter: ";
cout << "The average number is: " << average << "\n";
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++ )
What is public, protected, private?
Public, protected and private are three access specifier 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.
Write a function that swaps the values of two integers, using int* as the argument type.
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:
pointer2 = pointer2->next; if (pointer2) pointer2=pointer2->next;
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.
What is virtual constructors/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 declare 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.
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 – declare 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
Virtual constructor: Constructors cannot be virtual. Declaring a constructor as a virtual
function is a syntax error. Does c++ support multilevel and multiple inheritance?
What are the advantages of inheritance?
• 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.
What is the difference between declaration and definition?
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
What is the difference between an ARRAY and a LIST?
Array is collection of homogeneous elements.
List is 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.
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:
for( it = list.begin() ; it != list.end() ; it++ )
Does c++ support multilevel and multiple inheritance?
Templates allow to create 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 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>
The only difference between both prototypes is the use of keyword class or typename, its use is
indistinct since both expressions have exactly the same meaning and behave exactly the same
Define a constructor - What it is and how it might be called (2 methods).
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.
1) Implicitly: automatically by complier when an object is created.
2) Calling the constructors explicitly is possible, but it makes the code unverifiable.
public Point2D() : x(0) , y(0) {} //default (no argument) constructor
Point2D MyPoint; // Implicit Constructor call. In order to allocate memory on stack, the default
constructor is implicitly called.
Point2D * pPoint = new Point2D(); // Explicit Constructor call. In order to allocate memory on
HEAP we call the default constructor.
You have two pairs: new() and delete() and another pair : alloc() and free().
Explain differences between eg. new() and malloc()
1.) "new and delete" are preprocessors while "malloc() and free()" are functions. [we dont use
brackets will calling new or delete].
2.) no need of allocate the memory while using "new" but in "malloc()" we have to use
3.) "new" will initlize the new memory to 0 but "malloc()" gives random value in the new alloted
memory location [better to use calloc()]
new() allocates continous space for the object instace
malloc() allocates distributed space.
new() is castless, meaning that allocates memory for this specific type,
malloc(), calloc() allocate space for void * that is cated to the specific class type pointer.
What is the difference between class and structure?
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.
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 Interview
Questions - Homegrown versions with a solid, consistent approach.
Packaging an object's variables within its methods is called encapsulation.
Explain term POLIMORPHISM and give an example using eg. SHAPE object: If I have a
base class SHAPE, how would I define DRAW methods for two objects CIRCLE and
POLYMORPHISM : A phenomenon which enables an object to react differently to the same
in C++ it is attained by using a keyword virtual
public virtual void SHAPE::DRAW()=0;
Note here the function DRAW() is pure virtual which means the sub classes must implement the
DRAW() method and SHAPE cannot be instatiated
public class CIRCLE::public SHAPE
public class SQUARE::public SHAPE
now from the user class the calls would be like
public void MENU::OnClickDrawCircle(){
public void MENU::OnClickDrawCircle(){
public void CANVAS::OnMouseOperations(){
public virtual Draw() = 0; //abstract class with a pure virtual method
public virtual Draw() { this->drawCircle(0,0,r); }
public virtual Draw() { this->drawRectangular(0,0,a,a); }
Each object is driven down from SHAPE implementing Draw() function in its own way.
Object is a software bundle of variables and related methods. Objects have state and behavior.
How can you tell what shell you are running on UNIX system?
You can do the Echo $RANDOM. It will return a 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.
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.
Describe PRIVATE, PROTECTED and PUBLIC – the differences and give examples.
public Point2D() : x(0) , y(0) {} //default (no argument) constructor
You cannot directly access private data members when they are declared (implicitly) private:
MyPoint.x = 5; // Compiler will issue a compile ERROR
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
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 in 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 to 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:
object or function can have the same name than another one, causing a redefinition error.
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:
public Point2D() : x(0) , y(0) {} //default (no argument) constructor
public Point2D( const Point2D & ) ;
Point2D::Point2D( const Point2D & p )
Point2D AnotherPoint = Point2D( MyPoint ); // now AnotherPoint has color = 345
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-> , where a and b is a subset of R, at least one of the
* a- > b is a trivial functional dependency (b is a subset of a)
* a is a superkey for schema R
What is 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.
What is the word you will use when defining a function in base class to allow this function
What do you mean by binding of data and functions?
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
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.
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
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.
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);
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.
its private and protected members. A friend function is not a member of the class. But it must be
listed in the class definition.
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.
Abstraction is of the process of hiding unwanted details from the user.
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.
What is the difference between an external iterator and an internal iterator? Describe an
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.
What is a scope resolution operator?
A scope resolution operator (::), can be used to define the member functions of a class outside
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
class Shape { public: virtual void draw() = 0; };
What is polymorphism? 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.
What's the output of the following program? Why?
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)
output = (X & Y) | (X & Z) | (Y & Z)
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 a 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.
Answer: 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.
Explain which of the following declarations will compile and what will be constant - a
pointer or the value pointed at: * const char *
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
You're given a simple code for the class Bank Customer. Write the following functions:
* + operator overload (customers' balances should be added up, as an example of 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
What problems might the following macro bring to the application?
Anything wrong with this code?
deleted, but only the first element destructor will be called.
Anything wrong with this code?
Yes, the program will crash in an attempt to delete a null pointer.
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.
integer (though not necessarily), a long is a 4-byte integer, and a long long is a 8-byte integer.
What does extern mean in a function declaration?
Using extern in a function declaration we can make a function such that it can used outside the
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
exists at file scope, the identifier has external linkage.
What can I safely assume about the initial values of variables which are not explicitly
It depends on complier which may assign any garbage value to a variable if it is not initialized.
What is the difference between char a[] = "string"; and char *p = "string";?
if *p is assigned to some other value the allocate memory can change.
What's the auto keyword good for?
Not much. It declares an object with automatic storage duration. Which means the object will be
and not dynamically allocated have automatic storage duration by default.
{ int a; //this is the same as writing "
Local variables occur within a scope; they are "local" 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 as an auto
What is the difference between char a[] = "string"; and char *p = "string"; ?
p is pointing to a constant string, you can never safely say
however you can always say a[3]='x';
char a[]="string"; - character array initialization.
pointer in C++ to preserve backward compatibility with C.)
a[] will have 7 bytes. However, p is only 4 bytes. P is pointing to an adress is either BSS or the
data section (depending on which compiler — GNU for the former and CC for the latter).
for char a[]…….using the array notation 7 bytes of storage in the static memory block are taken
up, one for each character and one for the terminating nul character.
But, in the pointer notation char *p………….the same 7 bytes required, plus N bytes to store the
pointer variable "p" (where N depends on the system but is usually a minimum of 2 bytes and
How do I declare an array of N pointers to functions returning pointers to functions returning
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
Here a is that array. And according to question no function will not take any parameter value.
What does extern mean in a function declaration?
the file currently being compiled. This variable or function may be defined in another file or
further down in the current file.
How do I initialize a pointer to a function?
This is the way to initialize a pointer to a function
How do you link a C++ program to C functions?
By using the extern "C" linkage specification around the C function declarations.
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.
What are the differences between a C++ struct and C++ class?
The default member and base-class access specifier are different.
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.
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
What is a default constructor?
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; }
What is a conversion constructor?
A constructor that accepts one argument of a different type.
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
When should you use multiple inheritance?
There are three acceptable answers: "Never," "Rarely," and "When the problem domain cannot
be accurately modeled any other way."
Explain the ISA and HASA class relationships. How would you implement each in a class
A specialized class "is" a specialization of another class and, therefore, has the ISA relationship
with the other class. An Employee ISA Person. This relationship is best implemented with
inheritance. 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 the HASA relationship
with the Salary class. This relationship is best implemented by embedding an object of the Salary
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 generosity) to the
designer of the container or manager class.
One that can be modified by the class even when the object of the class or the member function
doing the modification is const.
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
What is the Standard Template Library (STL)?
A library of container templates approved by the ANSI committee for inclusion in the standard
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.
Describe run-time type identification.
The ability to determine at run time the type of an object by using the typeid operator or the
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
This solution assumes that two library vendors don't use the same namespace identifier, of
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.
Will the following program execute?
void *vptr = (void *) malloc(sizeof(void));
It will throw an error, as arithmetic operations cannot be performed on void pointers.
It will not build as sizeof cannot be applied to void* ( error "Unknown size" )
How can it execute if it won't even compile? It needs to be int main, not void main. Also, cannot
According to gcc compiler it won't show any error, simply it executes. but in general we can't do
arthematic operation on void, and gives size of void as 1
The program compiles in GNU C while giving a warning for "void main". The program runs
without a crash. sizeof(void) is "1? hence when vptr++, the address is incremented by 1.
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
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
voidp.c:6: error: ISO C++ forbids incrementing a pointer of type `void*'
But in c, it work without problems
For Q2: As above, won't compile because main must return int. Also, 0×2000 cannot be
implicitly converted to a pointer (I assume you meant 0×2000 and not 0?2000.)
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 Excute if it is C++, but Excute in 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*'
point.c:4: warning: initialization makes pointer from integer without a cast
point.c:5: warning: initialization makes pointer from integer without a cast
What is the difference between Mutex and Binary semaphore?
semaphore is used to synchronize processes. where as mutex is used to provide synchronization
between threads running in the same process.
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 (different set of parameters). Method
overriding is the ability of the inherited class rewriting the virtual method of the base class.
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.
What are the defining traits of an object-oriented language?
The defining traits of an object-oriented langauge are:
Write a program that ask for user input from 5 to 9 then calculate the average
cout<<"Please enter your input from 5 to 9";
cout<<"please re type your input";
} cout<<"The average number is"<<average<<endl;
Assignment Operator - What is the diffrence between a "assignment operator" and a
In 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 c3=c2; //copy constructor
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.
RTTI stands for "Run Time Type Identification". In an inheritance hierarchy, we can find out the
exact type of the objet of which it is member. It can be done by using:
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.
STL Containers - What are the types of STL containers?
There are 3 types of STL containers:
1. Adaptive containers like queue, stack
2. Associative containers like set, map
3. Sequence containers like vector, deque
What is the need for a Virtual Destructor ?
will be called before the derived class destructor and that will lead to memory leak because
derived class’s objects will not get freed.Destructors are declared virtual so as to bind objects
to the methods at runtime so that appropriate destructor is called.
"mutable" is a C++ keyword. When we declare const, none of its data members can change.
When we want one of its members to change, we declare it as mutable.
A "mutable" keyword is useful when we want to force a "logical const" data member to have its
value modified. A logical const can happen when we declare a data member as non-const, but we
have a const member function attempting to modify that data member. For example:
mutable bool validStatus_ = FALSE;
// logical const issue resolved
// data members become bitwise const
validStatus_ = TRUE; // fine to assign
"mutable" keyword in C++ is used to specify that the member may be updated or modified even
if it is member of constant object. Example:
const Animal Tiger(’Fulffy’,'antelope’,1);
// the age can be changed since its mutable
Could you write a small program that will compile in C but not in C++ ?
In C, if you can a const variable e.g.
you can use this variable in other module as follows
But for C++ compiler u must write
else error would be generated.
Bitwise Operations - 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);
C++ Object-Oriented Interview Questions And Answers
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
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
Differentiate between a template class and class template.
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.
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.
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.
What is the use of 'using' declaration. ?
A using declaration makes it possible to use a name from a namespace without the scope
A class that is used to traverse through the objects maintained by a container class. There are five
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
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.
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.
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
In the above example when PrintVal() function is
called it is called by the pointer that has been freed by the
Differentiate between the message and method.
* Objects communicate by sending messages to each other.
* A message is sent to invoke a method.
* Provides response to a message.
* It is an implementation of an operation.
What is an adaptor class or Wrapper class?
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
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.
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.
What do you mean by Stack unwinding?
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.
Define precondition and post-condition to a member function.
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
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.
Objects that stand for other objects are called proxy objects or surrogates.
const T& operator[] (int index)const;
Array1D operator[] (int index);
const Array1D operator[] (int index) const;
The following then becomes legal:
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 onedimensional
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.
Name some pure object oriented languages.
Smalltalk, Java, Eiffel, Sather.
What is an orthogonal base class?
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
* 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 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
What is a container class? What are the types of container classes?
A container class is a class that is used to hold objects in memory or external storage. A
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.
How do you write a function that can reverse a linked-list?
{ if(0==head || 0==head->next)
//if head->next ==0 should return head instead of 0;
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.
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 nodes 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.
How can you tell what shell you are running on UNIX system?
You can do the Echo $RANDOM. It will return a 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.
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
* a->b is a trivial functional dependency (b is a subset of a)
* a is a superkey for schema R
What is 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
Write a Struct Time where integer m, h, s are its members
How do you traverse a Btree in Backward in-order?
Process the node in the right subtree
Process the node in the left subtree
What is the two main roles of Operating System?
In the derived class, which data member of the base class are visible?
In the public and protected sections.
Could you tell something about the Unix System Kernel?
The kernel is the heart of the UNIX openrating system, it's reponsible for controlling the
computer's resouces and scheduling user jobs so that each one gets its fair share of resources.
What are each of the standard files and what are they normally associated with?
They are the standard input file, the standard output file and the standard error file. The first is
usually associated with the keyboard, the second and third are usually associated with the
Detemine the code below, tell me exectly how many times is the operation sum++
for ( j = 100; j > 100 - i; j–)
The sum++ is performed 4950 times.
Give 4 examples which belongs application layer in TCP/IP architecture?
What's the meaning of ARP in TCP/IP?
The "ARP" stands for Address Resolution Protocol. The ARP standard defines two basic
message types: a request and a response. a request message contains an IP address and requests
the corresponding hardware address; a replay contains both the IP address, sent in the request,
Makefile is a utility in Unix to help compile large programs. It helps by only compiling the
portion of the program that has been changed.
A Makefile is the file and make uses to determine what rules to apply. make is useful for far
Deadlock is a situation when two or more processes prevent each other from running. Example:
if T1 is holding x and waiting for y to be free and T2 holding y and waiting for x to be free
Semaphore is a special variable, it has two methods: up and down. Semaphore performs atomic
operations, which means ones a semaphore is called it can not be inturrupted.
The internal counter (= #ups - #downs) can never be negative. If you execute the "down" method
when the internal counter is zero, it will block until some other thread calls the "up" method.
Semaphores are use for thread synchronization.
Is C an object-oriented language?
C is not an object-oriented language, but limited object-oriented programming can be done in C.
Name some major differences between C++ and Java.
C++ has pointers; Java does not. Java is platform-independent; C++ is not. Java has garbage
collection; C++ does not. Java does have pointers. In fact all variables in Java are pointers. The
difference is that Java does not allow you to manipulate the addresses of the pointer
C++ Networking Interview Questions and Answers
What is the difference between Stack and Queue?
Stack is a Last In First Out (LIFO) data structure.
Queue is a First In First Out (FIFO) data structure
Write a fucntion that will reverse a string.
if ((str = (char *)malloc(len+1)) == NULL)
What is the software Life-Cycle?
1) Analysis and specification of the task
2) Design of the algorithms and data structures
5) Maintenance and evolution of the system
What is the difference between a Java application and a Java applet?
The difference between a Java application and a Java applet is that a Java application is a
program that can be executed using the Java interpeter, and a JAVA applet can be transfered to
different networks and executed by using a web browser (transferable to the WWW).
Name 7 layers of the OSI Reference Model?
C++ Algorithm Interview Questions and Answers
What are the advantages and disadvantages of B-star trees over Binary trees?
write codes for B-start trees.
The major difference between B-tree and binary tres is that B-tree is a external data structure and
binary tree is a main memory data structure. The computational complexity of binary tree is
counted by the number of comparison operations at each node, while the computational
complexity of B-tree is determined by the disk I/O, that is, the number of node that will be
loaded from disk to main memory. The comparision of the different values in one node is not
Write the psuedo code for the Depth first Search.
For each vertex w such that edge vw is in G:
dfs(G, w); that is, explore vw, visit w, explore from there as much as possible, and backtrack
"Check" vw without visiting w. Mark v as "finished".
Describe one simple rehashing policy.
The simplest rehashing policy is linear probing. Suppose a key K hashes to location i. Suppose
other key occupies H[i]. The following function is used to generate alternative locations:
where j is the location most recently probed. Initially j = i, the hash code for K. Notice that this
version of rehash does not depend on K.
Describe Stacks and name a couple of places where stacks are useful.
A Stack is a linear structure in which insertions and deletions are always made at one end, called
some syntex errors, such as missing parentheses.
Suppose a 3-bit sequence number is used in the selective-reject ARQ, what is the maximum
number of frames that could be transmitted at a time?
If a 3-bit sequence number is used, then it could distinguish 8 different frames. Since the number
of frames that could be transmitted at a time is no greater half the numner of frames that could be
distinguished by the sequence number, so at most 4 frames can be transmitted at a time.
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