C++ interview questions with answers

C++ Interview questions Part 13

noreply@blogger.com (Anonymous) — Mon, 8 Mar 2010 10:37:00 -0800

C++ interview question:List out some of the object-oriented methodologies?
Answer:

Ø Object Oriented Development (OOD) (Booch 1991,1994).
Ø Object Oriented Analysis and Design (OOA/D) (Coad and Yourdon 1991).
Ø Object Modelling Techniques (OMT) (Rumbaugh 1991).
Ø Object Oriented Software Engineering (Objectory) (Jacobson 1992).
Ø Object Oriented Analysis (OOA) (Shlaer and Mellor 1992). The Fusion Method (Coleman 1991)

C++ interview question: Name some pure object oriented languages?
Answer:
Ø Smalltalk,
Ø Java,
Ø Eiffel,
Ø Sather.

C++ interview question: What is an USECASE? Why it is needed?

Answer:Use Case is a description of a set of sequence of actions that a system performs that yields an observable result of value to a particular action. In SSAD process <=> In OOAD USECASE. It is represented elliptically.

C++ interview question :Can we generate a C++ source code from the binary file?
Answer: Technically this is possible, but in my knowledge their no such software available yet. Why this is possible? In program flow we do like this to generate binary file. High level language programming code -low level programming code- hex code- binary code. How we can do reverse can be illustrated with this example. When I type 0 on screen the ASCII equivalent is 65 and so the binary code will be by converting 65 (01010 0101) so I can recognize this and decode this. Same technique can be used. Some secret mission defense org. I heard have this code splitter from binary to assembly language (low level language)/ Converter type devices available, they use them for secret national purpose.

C++ interview question : What is a memory leak? How can we avoid it?

Answer :A memory leak can be avoided by making sure that whatever memory has been dynamically allocated will be cleared after the use of the same. for example

int main()
{ char *myCharData[20];
for (int nLoop =0;nLoop < 20; ++nLoop) { myCharData[nLoop ] = new char[256];
strcpy(myCharData[nLoop],"SABITH");
......
}
........................
/*Some manipulations here using myCharData*/
/*Now here we have to clear the data. The place can vary according to ur program. This being a simple program,u can clear at the end*/
for(int nLoop =0;nLoop < 20; ++nLoop)
{
delete[] myCharData[nLoop ];
}
return 0;

C++ interview question: What is virtual class and friend class?

Answer: Friend classes are used when two or more classes are designed to work together and virtual base class aids in multiple inheritance

C++ interview question:Why does the function arguments are called as "signatures"?
Answer: The arguments distinguish functions with the same name (functional polymorphism). The name alone does not necessarily identify a unique function. However, the name and its arguments (signatures) will uniquely identify a function.In real life we see suppose, in class there are two guys with same name, but they can be easily identified by their signatures. The same concept is applied here.

ex: class person
{
public:
char getsex();
void setsex(char);
void setsex(int);
};
In the above example we see that there is a function setsex() with same name but with different signature.

C++ Interview questions Part 12

noreply@blogger.com (Anonymous) — Tue, 2 Feb 2010 11:12:00 -0800

C++ interview question:What is cloning?

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

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

C++ interview question:Will the inline function be compiled as the inline function always?Justify.
Answer:An inline function is a request and not a command. Hence it won't be compiled as an inline function always.
Explanation:

Inline-expansion could fail if the inline function contains loops, the address of an inline function is used, or an inline function is called in a complex expression. The rules for inlining are compiler dependent.

C++ interview question:Define a way other than using the keyword inline to make a function inline.
Answer:The function must be defined inside the class.

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

C++ interview question:What is placement new?
Answer:When you want to call a constructor directly, you use the placement new. Sometimes you have some raw memory that's already been allocated, and you need to construct an object in the memory you have. Operator new's special version placement new allows you to do it.

class Widget
{

public :
Widget(int widgetsize);

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

C++ interview question:What do you mean by analysis and design?
Answer:
Analysis:
Basically, it is the process of determining what needs to be done before how it should be done. In order to accomplish this, the developer refers the existing systems and documents. So, simply it is an art of discovery.
Design:
It is the process of adopting/choosing the one among the many, which best accomplishes the users needs. So, simply, it is compromising mechanism.

C++ interview question:What are the steps involved in designing?
Answer:Before getting into the design the designer should go through the SRS prepared by the System Analyst.
The main tasks of design are Architectural Design and Detailed Design.
In Architectural Design we find what are the main modules in the problem domain.
In Detailed Design we find what should be done within each module.

C++ interview question:What are the main underlying concepts of object orientation?
Answer:Objects, messages, class, inheritance and polymorphism are the main concepts of object orientation.

C++ interview question:What do u meant by "SBI" of an object?
Answer:SBI stands for State, Behavior and Identity. Since every object has the above three.
Ø State:
It is just a value to the attribute of an object at a particular time.
Ø Behaviour:
It describes the actions and their reactions of that object.
Ø Identity
An object has an identity that characterizes its own existence. The identity makes it possible to distinguish any object in an unambiguous way, and independently from its state.

C++ interview question:Differentiate persistent & non-persistent objects?
Answer:Persistent refers to an object's ability to transcend time or space. A persistent object stores/saves its state in a permanent storage system with out losing the information represented by the object.
A non-persistent object is said to be transient or ephemeral. By default objects are considered as non-persistent.

C++ interview question:What do you meant by active and passive objects?
Answer:Active objects are one which instigate an interaction which owns a thread and they are responsible for handling control to other objects. In simple words it can be referred as client. Passive objects are one, which passively waits for the message to be processed. It waits for another object that requires its services. In simple words it can be referred as server.

C++ interview Question:What is meant by software development method?
Answer:Software development method describes how to model and build software systems in a reliable and reproducible way. To put it simple, methods that are used to represent ones' thinking using graphical notations.

C++ Interview questions Part 11

noreply@blogger.com (Anonymous) — Sat, 1 Aug 2009 10:58:00 -0700

C++ interview question:What is slicing?

Answer:Slicing means that the data added by a subclass are discarded when an object of the subclass is passed or returned by value or from a function expecting a base class object.

Explanation:

Consider the following class declaration:

class base

{

...

base& operator =(const base&);

base (const base&);

}

void fun( )

{

base e=m;

e=m;

}

As base copy functions don't know anything about the derived only the base part of the derived is copied. This is commonly referred to as slicing. One reason to pass objects of classes in a hierarchy is to avoid slicing. Other reasons are to preserve polymorphic behavior and to gain efficiency.

C++ interview question:What is name mangling?
Answer:Name mangling is the process through which your c++ compilers give each function in your program a unique name. In C++, all programs have at-least a few functions with the same name. Name mangling is a concession to the fact that linker always insists on all function names being unique.
Example:

In general, member names are made unique by concatenating the name of the member with that of the class e.g. given the declaration:

class Bar

{

public:

int ival;

...

};

ival becomes something like:

// a possible member name mangling

ival__3Bar

Consider this derivation:

class Foo : public Bar

{

public:

int ival;

...

}

The internal representation of a Foo object is the concatenation of its base and derived class members.

// Pseudo C++ code

// Internal representation of Foo

class Foo

{

public:

int ival__3Bar;

int ival__3Foo;

...

};

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

C++ interview question:What are proxy objects?

Answer:Objects that points to other objects are called proxy objects or surrogates. Its an object that provides the same interface as its server object but does not have any functionality. During a method invocation, it routes data to the true server object and sends back the return value to the object.

C++ interview question:Differentiate between declaration and definition in C++.
Answer:A declaration introduces a name into the program; a definition provides a unique description of an entity (e.g. type, instance, and function). Declarations can be repeated in a given scope, it introduces a name in a given scope. There must be exactly one definition of every object, function or class used in a C++ program.

A declaration is a definition unless:

Ø it declares a function without specifying its body,

Ø it contains an extern specifier and no initializer or function body,

Ø it is the declaration of a static class data member without a class definition,

Ø it is a class name definition,

Ø it is a typedef declaration.

A definition is a declaration unless:

Ø it defines a static class data member,

Ø it defines a non-inline member function.

C++ Interview questions Part 10

noreply@blogger.com (Anonymous) — Tue, 26 May 2009 10:53:00 -0700

C++ interview question:When can you tell that a memory leak will occur?

Answer:A memory leak occurs when a program loses the ability to free a block of dynamically allocated memory.

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

C++ interview question:Differentiate between a deep copy and a shallow copy?
Answer:Deep copy involves using the contents of one object to create another instance of the same class. In a deep copy, the two objects may contain ht same information but the target object will have its own buffers and resources. the destruction of either object will not affect the remaining object. The overloaded assignment operator would create a deep copy of objects.

Shallow copy involves copying the contents of one object into another instance of the same class thus creating a mirror image. Owing to straight copying of references and pointers, the two objects will share the same externally contained contents of the other object to be unpredictable.

Explanation:

Using a copy constructor we simply copy the data values member by member. This method of copying is called shallow copy. If the object is a simple class, comprised of built in types and no pointers this would be acceptable. This function would use the values and the objects and its behavior would not be altered with a shallow copy, only the addresses of pointers that are members are copied and not the value the address is pointing to. The data values of the object would then be inadvertently altered by the function. When the function goes out of scope, the copy of the object with all its data is popped off the stack.

If the object has any pointers a deep copy needs to be executed. With the deep copy of an object, memory is allocated for the object in free store and the elements pointed to are copied. A deep copy is used for objects that are returned from a function.

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

C++ interview question:What is a smart pointer?
Answer:A smart pointer is an object that acts, looks and feels like a normal pointer but offers more functionality. In C++, smart pointers are implemented as template classes that encapsulate a pointer and override standard pointer operators. They have a number of advantages over regular pointers. They are guaranteed to be initialized as either null pointers or pointers to a heap object. Indirection through a null pointer is checked. No delete is ever necessary. Objects are automatically freed when the last pointer to them has gone away. One significant problem with these smart pointers is that unlike regular pointers, they don't respect inheritance. Smart pointers are unattractive for polymorphic code. Given below is an example for the implementation of smart pointers.

Example:

template

class smart_pointer

{

public:

smart_pointer(); // makes a null pointer

smart_pointer(const X& x) // makes pointer to copy of x

X& operator *( );

const X& operator*( ) const;

X* operator->() const;

smart_pointer(const smart_pointer &);

const smart_pointer & operator =(const smart_pointer&);

~smart_pointer():

private:

//...

};

This class implement a smart pointer to an object of type X. The object itself is located on the heap. Here is how to use it:

smart_pointer p= employee("Harris",1333);

Like other overloaded operators, p will behave like a regular pointer,

cout<<*p;

p->raise_salary(0.5);

C++ interview question:What is reflexive association?

Answer:The 'is-a' is called a reflexive association because the reflexive association permits classes to bear the is-a association not only with their super-classes but also with themselves. It differs from a 'specializes-from' as 'specializes-from' is usually used to describe the association between a super-class and a sub-class. For example:

Printer is-a printer.

C++ Interview questions Part 9

noreply@blogger.com (Anonymous) — Sun, 10 May 2009 10:50:00 -0700

C++ interview question: What is a node class?

Answer:A node class is a class that,

Ø relies on the base class for services and implementation,

Ø provides a wider interface to te users than its base class,

Ø relies primarily on virtual functions in its public interface

Ø depends on all its direct and indirect base class

Ø can be understood only in the context of the base class

Ø can be used as base for further derivation

Ø can be used to create objects.

A node class is a class that has added new services or functionality beyond the services inherited from its base class.

C++ interview question: What is an orthogonal base class?

Answer: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.

C++ interview question:What is a container class? What are the types of container classes?

Answer: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.

C++ interview question:What is a protocol class?

Answer:An abstract class is a protocol class if:

Ø it neither contains nor inherits from classes that contain member data, non-virtual functions, or private (or protected) members of any kind.

Ø it has a non-inline virtual destructor defined with an empty implementation,

Ø all member functions other than the destructor including inherited functions, are declared pure virtual functions and left undefined.

C++ interview question:What is a mixin class?

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

C++ interview question:What is a concrete class?

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

C++ interview question:What is the handle class?

Answer:A handle is a class that maintains a pointer to an object that is programmatically accessible through the public interface of the handle class.

Explanation:

In case of abstract classes, unless one manipulates the objects of these classes through pointers and references, the benefits of the virtual functions are lost. User code may become dependent on details of implementation classes because an abstract type cannot be allocated statistically or on the stack without its size being known. Using pointers or references implies that the burden of memory management falls on the user. Another limitation of abstract class object is of fixed size. Classes however are used to represent concepts that require varying amounts of storage to implement them.

A popular technique for dealing with these issues is to separate what is used as a single object in two parts: a handle providing the user interface and a representation holding all or most of the object's state. The connection between the handle and the representation is typically a pointer in the handle. Often, handles have a bit more data than the simple representation pointer, but not much more. Hence the layout of the handle is typically stable, even when the representation changes and also that handles are small enough to move around relatively freely so that the user needn’t use the pointers and the references.

C++ interview question:What is an action class?

Answer:The simplest and most obvious way to specify an action in C++ is to write a function. However, if the action has to be delayed, has to be transmitted 'elsewhere' before being performed, requires its own data, has to be combined with other actions, etc then it often becomes attractive to provide the action in the form of a class that can execute the desired action and provide other services as well. Manipulators used with iostreams is an obvious example.

Explanation:

A common form of action class is a simple class containing just one virtual function.

class Action

{

public:

virtual int do_it( int )=0;

virtual ~Action( );

}

Given this, we can write code say a member that can store actions for later execution without using pointers to functions, without knowing anything about the objects involved, and without even knowing the name of the operation it invokes. For example:

class write_file : public Action

{

File& f;

public:

int do_it(int)

{

return fwrite( ).suceed( );

}

};

class error_message: public Action

{

response_box db(message.cstr( ),"Continue","Cancel","Retry");

switch (db.getresponse( ))

{

case 0: return 0;

case 1: abort();

case 2: current_operation.redo( );return 1;

}

};

A user of the Action class will be completely isolated from any knowledge of derived classes such as write_file and error_message.

C++ Interview questions Part 8

noreply@blogger.com (Anonymous) — Sat, 25 Apr 2009 10:44:00 -0700

C++ interview question:What is a Null object?

Answer: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.

C++ interview question:What is class invariant?

Answer: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.

C++ interview question:What do you mean by Stack unwinding?

Answers: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.

C++ interview question:Define precondition and post-condition to a member function.

Answers:

Precondition:

A precondition is a condition that must be true on entry to a member function. A class is used correctly if preconditions are never false. An operation is not responsible for doing anything sensible if its precondition fails to hold.

For example, the interface invariants of stack class say nothing about pushing yet another element on a stack that is already full. We say that isful() is a precondition of the push operation.

Post-condition:

A post-condition is a condition that must be true on exit from a member function if the precondition was valid on entry to that function. A class is implemented correctly if post-conditions are never false.

For example, after pushing an element on the stack, we know that isempty() must necessarily hold. This is a post-condition of the push operation.

C++ interview question:What are the conditions that have to be met for a condition to be an invariant of the class?

Answers:

Ø The condition should hold at the end of every constructor.

Ø The condition should hold at the end of every mutator(non-const) operation.

C++ interview question:What are proxy objects?

Answer:Objects that stand for other objects are called proxy objects or surrogates.

Example:

template

class Array2D

{

public:

class Array1D

{

public:

T& operator[] (int index);

const T& operator[] (int index) const;

};

Array1D operator[] (int index);

const Array1D operator[] (int index) const;

...

};

The following then becomes legal:

Array2Ddata(10,20);

........

cout<

Here data[3] yields an Array1D object and the operator [] invocation on that object yields the float in position(3,6) of the original two dimensional array. Clients of the Array2D class need not be aware of the presence of the Array1D class. Objects of this latter class stand for one-dimensional array objects that, conceptually, do not exist for clients of Array2D. Such clients program as if they were using real, live, 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.

C++ interview question:Name some pure object oriented languages.

Answer:

Ø Smalltalk,

Ø Java,

Ø Eiffel,

Ø Sather.

C++ interview question:Name the operators that cannot be overloaded.

Answers:sizeof . .* .-> :: ?:

C++ Interview Questions Part 7

noreply@blogger.com (Anonymous) — Sun, 5 Apr 2009 03:10:00 -0700

C++ interview question:Define namespace.

Answer: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.

C++ interview question:What is the use of ‘using’ declaration.

Answer:A using declaration makes it possible to use a name from a namespace without the scope operator.

C++ interview question:What is an Iterator class?

Answer:A class that is used to traverse through the objects maintained by a container class. There are five categories of iterators:

Ø input iterators,

Ø output iterators,

Ø forward iterators,

Ø bidirectional iterators,

Ø random access.

An iterator is an entity that gives access to the contents of a container object without violating encapsulation constraints. Access to the contents is granted on a one-at-a-time basis in order. The order can be storage order (as in lists and queues) or some arbitrary order (as in array indices) or according to some ordering relation (as in an ordered binary tree). The iterator is a construct, which provides an interface that, when called, yields either the next element in the container, or some value denoting the fact that there are no more elements to examine. Iterators hide the details of access to and update of the elements of a container class.

The simplest and safest iterators are those that permit read-only access to the contents of a container class. The following code fragment shows how an iterator might appear in code:

cont_iter:=new cont_iterator();

x:=cont_iter.next();

while x/=none do

s(x);

...

x:=cont_iter.next();

end;

In this example, cont_iter is the name of the iterator. It is created on the first line by instantiation of cont_iterator class, an iterator class defined to iterate over some container class, cont. Succesive elements from the container are carried to x. The loop terminates when x is bound to some empty value. (Here, none)In the middle of the loop, there is s(x) an operation on x, the current element from the container. The next element of the container is obtained at the bottom of the loop.

C++ interview question::List out some of the OODBMS available.

Answer:

Ø GEMSTONE/OPAL of Gemstone systems.

Ø ONTOS of Ontos.

Ø Objectivity of Objectivity inc.

Ø Versant of Versant object technology.

Ø Object store of Object Design

Ø ARDENT of ARDENT software.

Ø POET of POET software.

C++ interview question:What is an incomplete type?

Answer:Incomplete types refers to pointers in which there is non availability of the implementation of the referenced location or it points to some location whose value is not available for modification.

Example:

int *i=0x400 // i points to address 400

*i=0; //set the value of memory location pointed by i.

Incomplete types are otherwise called uninitialized pointers.

C++ interview Question:What is a dangling pointer?

Answer: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.

C++ interview question:Differentiate between the message and method

Answer:

Message Method

1.Objects communicate by sending messages Provides response to a message to each other.

2.A message is sent to invoke a method. It is an implementation of an operation.

C++ interview question:What is an adaptor class or Wrapper class?

Answer:A class that has no functionality of its own. Its member functions hide the use of a third party software component or an object with the non-compatible interface or a non- object- oriented implementation.

C++ Interview Questions Part 6

noreply@blogger.com (Anonymous) — Fri, 20 Mar 2009 02:38:00 -0700

C++ interview question: What are virtual functions?

Answer: C++ virtual function is a member function of a class, whose functionality can be over-ridden in its derived classes.

C++ virtual function is,

* A member function of a class

* Declared with virtual keyword

* usually has a different functionality in the derived class

* A function call is resolved at run-time

C++ interview question: We can overload assignment operator as a normal function.But we can not overload assignment operator as friend function why?

Answer :If the operation modifies the state of the class object, it operates on, it must be a member function, not a friend fucntionThus all operator such as =, *=, +=, etc are naturally defined as member functions not friend functions Conversely, if the operator does not modify any of its operands, but needs only a representation of the object, it does not have to be a member function and often less confusing. This is the reason why binary operators are often implemented as friend functions such as + , *, -, etc..

C++ interview question: What is the difference between class and structure?

Answer: 1:By default, the members of structures are public while that for class is private

2: structures doesn't provide something like data hiding which is provided by the classes

3: structures contains only data while class bind both data and member functions

C++ interview question: What is virtual class and friend class?

Answer: Friend classes are used when two or more classes are designed to work together and virtual base class aids in multiple inheritance.

C++ interview question: Is there any way to write a class such that no class can be inherited from it. Please include code

Answer: Simple, make all constructors of the class private.

C++ interview question: Why can’t we overload the sizeof, :?, :: ., .* operators in c++

Answer: The restriction is for safety. For example if we overload. Operator then we can’t access member in normal way for that we have to use ->.

C++ interview question :What is importance of const. pointer in copy constructor?

Answer :Because otherwise you will pass the object to copy as an argument of copy constructor as pass by value which by definition creates a copy and so on... an infinite call chain

C++ Interview Questions Part 5

noreply@blogger.com (Anonymous) — Wed, 4 Mar 2009 02:34:00 -0800

C++ interview question: What will happen if I say delete this

Answer: if you say "delete this", you are effectively calling the destructor twice, which could well be a disaster if your class uses heap. The destructor will be called when you say “delete this” and again when that object goes out of scope. Since this is the language behavior, there is no way to prevent the destructor from being called twice. Please refrain from forcibly calling a destructor or using clause like this.

C++ interview question: What is the output of printf ("%d")

Answer :Usually the output value cannot be predicted. It will not give any error. It will print a garbage value. But if the situation is

main()

{

int a=1,b=2,c=3;

printf("%d");

}

The output will be the value of the last variable, ie. 3

C++ interview question: # what is an algorithm (in terms of the STL/C++ standard library)?

Answer: Algorithm in STL consist different searching and sorting algos implementation, which takes start and end iterators of STL container on which algo is going to work.

C++ interview question: How can you force instantiation of a template?

Answer: you can instantiate a template in two ways. 1. Implicit instantiation and 2. Explicit Instantiation implicit instatanitioan can be done by the following ways:

template

class A

{

public:

A(){}

~A(){}

void x();

void z();

};

void main()

{

A ai;

A af;

}

External Instantion can be done the following way:

int main()

{

template class A;

}

C++ interview question: What is the difference between operator new and the new operator?

Answer: This is what happens when you create a new object: 1. the memory for the object is allocated using "operator new". 2. the constructor of the class is invoked to properly initialize this memory. As you can see, the new operator does both 1 and 2. The operator new merely allocates memory, it does not initialize it. Where as the new operator also initializes it properly by calling the constructor.

C++ interview question: What is the Basic nature of "cin" and "cout" and what concept or principle we are using on those two?

Answer: Basically "cin and cout" are INSTANCES of istream and ostream classes respectively. And the concept which is used on cin and cout is operator overloading. Extraction and Insertion operators are overloaded for input and ouput operations.

C++ Interview Questions Part 4

noreply@blogger.com (Anonymous) — Wed, 18 Feb 2009 02:28:00 -0800

C++ Interview Question: What is "strstream”?

Answer: Class that reads and writes to an array in memory

C++ interview question: Can we generate a C++ source code from the binary file?

Answer: Technically this is possible, but in my knowledge their no such software available yet. Why this is possible? In program flow we do like this to generate binary file. High level language programming code -low level programming code- hex code- binary code. How we can do reverse can be illustrated with this example. When I type 0 on screen the ASCII equivalent is 65 and so the binary code will be by converting 65 (01010 0101) so I can recognize this and decode this. Same technique can be used. Some secret mission defense org. I heard have this code splitter from binary to assembly language (low level language)/ Converter type devices available, they use them for secret national purpose.

C++ interview question: Explain "passing by value", "passing by pointer" and "passing by reference"

Answer: There is major difference between these three are when we want to avoid making the copy of variable and we want to change value of actual argument on calling function. There are we use passing by pointer, passing the reference. We can not perform arithmetic operation on reference.

C++ interview question: Difference between "vector" and "array"?

Answer: Vector and Array List are very similar. Both of them represent a 'grow able array', where you access to the elements in it through an index.Array List it's part of the Java Collection Framework, and has been added with version 1.2, while Vector it's an object that is present since the first version of the JDK. Vector, anyway, has been retrofitted to implement the List interface.The main difference is that Vector it's a synchronized object, while Array List it's not.While the iterator that are returned by both classes are fail-fast (they cleanly throw Concurrent Modification Exception when the original object has been modified), the Enumeration returned by Vector are not.Unless you have strong reason to use a Vector, the suggestion is to use the Array List.

C++ interview question: What are the types of STL containers?

Answer: deque

hash_map

hash_multimap

hash_multiset

hash_set

list

map

multimap

multiset

set

vector

C++ interview question:Difference between a "assignment operator" and a "copy constructor"

Answer :Copy constructor is called every time a copy of an object is made. When you pass an object by value, either into a function or as a function's return value, a temporary copy of that object is made. Assignment operator is called whenever you assign to an object. Assignment operator must check to see if the right-hand side of the assignment operator is the object itself. It executes only the two sides are not equal

C++ interview question: Can we have "Virtual Constructors"?

Answer: No, we cannot have virtual constructors. But if the need arises, we can simulate the implementation of virtual constructor by calling a Init method from the constructor which, should be a virtual function.

C++ interview question: Explain the need for "Virtual Destructor".

Answer: In case of inheritance, objects should be destructed exactly the opposite way of their construction. If virtual keyword is not added before base class destructor declaration, then derived class destructor will not at all be called. Hence there will be memory leakage if allocated for derived class members while constructing the object.

C++ Interview Questions Part 3

noreply@blogger.com (Anonymous) — Mon, 2 Feb 2009 02:24:00 -0800

C++ interview question: what is memory leaking in c++ ?

Answer: When a class uses dynamically allocated memory internally, all sorts of problems arise. If not properly used or handled, they can lead to memory leaks & corrupts Data Structures.

A memory leak is the situation that occurs when dynamically allocated memory is lost to the program.

Char * p;

p= new char[10000];

...

p= new char[5000];

Initially, 10000 bytes are dynamically allocated & the the address of those bytes is stored in p. later 5000 bytes are dynamically allocated & the address is stored in p. However, the original 10000 bytes’ve not been returned to the system using delete [] operator.

Memory leak actually depends on the nature of the program.

Question:

class A()

{

};

int main()

{

A a;

}

Whether there will be a default contructor provided by the compiler in above case ?

Answer :yes, if the designer of the class donot define any constructor in the class. then the compiler provides the default constructor in the class.

C++ interview question: what is the use of virtual destructor?

Answer :virtual destructor is very useful....everyone should use that......if there is no any strong reason for not using virtual destructor....like...One class having two char variable...........so it's size is two byte........if u use virtual destructor it's size will be 6 bytes....4 byte for virtual ptr....Now if this class have 1 millions objects...so 4 magabyte memory will be lost...where all ptr do the same thing.....

C++ interview question: Why cant one make an object of abstract class?Give compiler view of statement

Answer :we cant make object of abstract class becoz, in the vtable the vtable entry for the abstract class functions will be NULL, which ever are defined as pure virtual functions.Even if there is a single pure virtual function in the class the class becomes as abstract class.If there is a virtual function in your class the compiler automatically creates a table called virtual function table .. to store the virtual function addresses.... if the function is a pure virtual function the vtable entry for that function will be NULL.Even if there is a single NULL entry in the function table the compiler does not allow to create the object.

C++ interview question: In c++ have a default constructor?

Answer: Yes C++ does have a default constructor provided by the compiler. In this case all the members of the class are initialized to null values. These values act as the default values. For eg: My Class me; In the above case since the object is not initialized to any value so the default constructor will be called which will initialize the class with the default values.

C++ interview question: Have you heard of "mutable" keyword?

Answer :The mutable keyword can only be applied to non-static and non-const data members of a class. If a data member is declared mutable, then it is legal to assign a value to this data member from a const member function.

SEE FOLLOWING CODE :-

********************************************

class Mutable

{

private :

int m_iNonMutVar;

mutable int m_iMutVar;

public:

Mutable();

void TryChange() const;

};

Mutable::Mutable():m_iNonMutVar(10),m_iMutVar(20) {};

void Mutable::TryChange() const

{

m_iNonMutVar = 100; // THis will give ERROR

m_iMutVar = 200; // This will WORK coz it is mutable

}

C++ Interview Questions Part 2

noreply@blogger.com (Anonymous) — Sun, 18 Jan 2009 21:11:00 -0800

C++ interview question :what is the difference betwen wait() and delay()?

Answer :Wait() and delay() works same but works on different platforms. Wait(2) will wait processing fro 2 second on Linux/Unix while delay(2000) with wait for 2 second but on DOS or Windows. so wait(2) on linux == delay(2000) on DOS Delay() is under while one can directly use wait in his/her program.

C++ interview question :Why always array starts with index 0

Answer :Array name is a constant pointer pointing to the base address(address of the first byte where the array begin) of the memory allocated. When you use arr[i], the compiler manipulates it as *(arr + i). Since arr is the address of the first element, the value of i must be 0 for accessing it. Hence all arrays begin with an index of 0.

C++ interview question: Can main() be overridden

Answer : In any application, there can be only one main function. In c++, main is not a member of any class. There is no chance of overriding

C++ interview question :What is the difference between macro and inline()?

Answer :

1. Inline follows strict parameter type checking, macros do not.

2. Macros are always expanded by preprocessor, whereas compiler may or may not replace the inline definitions.

C++ interview question: How can double dimensional arrays be dynamically initialized in C++?

Answer :example of how to dynamically initialize double dimensional arrays:

int num[2][3] = {34,32,30,24,22,20};

num[1][1] = 34

num[1][2] = 32

num[1][3] = 30

num[2][1] = 24

num[2][2] = 22

num[2][3] = 20

C++ interview question: Can destructor be private?

Answer: Yes destructors can be private. But according to Standard Programming practice it is not advisable to have destructors to be private.

C++ Interview Questions Part 1

noreply@blogger.com (Anonymous) — Fri, 2 Jan 2009 21:05:00 -0800

C++ interview question: What is a memory leak? How can we avoid it?

Answer :A memory leak can be avoided by making sure that whatever memory has been dynamically allocated will be cleared after the use of the same. for example

int main()

{ char *myCharData[20];

for (int nLoop =0;nLoop < 20; ++nLoop) { myCharData[nLoop ] = new char[256];

strcpy(myCharData[nLoop],"SABITH");

......

}

........................

/*Some manipulations here using myCharData*/

/*Now here we have to clear the data. The place can vary according to ur program. This being a simple program,u can clear at the end*/

for(int nLoop =0;nLoop < 20; ++nLoop)

{

delete[] myCharData[nLoop ];

}

return 0;

C++ interview question: How do you write a program which produces its own source code as its output?

Answer :write this program and save it as pro.c....run....it will show the program to the consol and write the source code into data.txt file...................

#include

void main()

{

FILE *fp,*ft;

char buff[100];

fp=fopen("pro.c","r");

if(fp==NULL)

{

printf("ERROR");

}

ft=fopen("data.txt","w+");

if(ft==NULL)

{

printf("ERROR");

}

while(getc(fp)!=EOF)

{

fscanf(fp,"%s",buff);

printf("%s\n",buff);

fprintf(ft,"%s\n",buff);

}

C++ interview question: What are the things contains in .obj file ? ( compiled result of .cpp file )

Answer :C++ .obj file holds code and data suitable for linking with other object files to create an executable or a shared object file.

C++ interview question :What is difference between followin intialization.

int iVar1;

int iVar2 = int();

and which one of two should we prefer always and why?

Answer :In first case a variable will be create in memeory with the default base type value (depending upon compiler 2 compiler) bcoz it is not initialized. in second case the variable will be created in the memory with the value retuned by the function int() (if int is a user define function) the second statement should have been int *i = new int();

C++ interview question :What is the difference between Object and Instance?

Answer :An instance of a user-defined type (i.e., a class) is called an object. We can instantiate many objects from one class.An object is an instance or occurrence of a class.

C++ interview question: How is static variable stored in the memory?

(if there are 2 functions in a file, and the static variable name is same (ex var) in both the function. how is it keep separately in the memory).

Answer: C++ uses name mangling when storing both local and global static varibales at the same place. The local static variables have function name and the global variables will have file name. Essentially the compiler uses namespace to distinguish between local and global static variables.

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