cpp


All C++ Language Interview Questions


Link: http://www.freejobalert.com/cpp-interview-questions/2893/
1. What is a class?
Ans: The objects with the same data structure (attributes) and behavior (operations) are called class.
2. What is an object?
Ans: It is an entity which may correspond to real-world entities such as students, employees, bank account. It may be concrete such as file system or conceptual such as scheduling policies in multiprocessor operating system.
Every object will have data structures called attributes and behavior called operations.
3. What is the difference between an object and a class?
Ans: All objects possessing similar properties are grouped into class.
Example :–person is a class, ram, hari are objects of person class. All have similar attributes like name, age, sex and similar operations like speak, walk.
Class person
{
private:
char name[20];
int age;
char sex;
public: speak();
walk();
};
4. What is the difference between class and structure?
Ans: In class the data members by default are private but in structure they are by default public
5. Define object based programming language?
Ans: Object based programming language support encapsulation and object identity without supporting some important features of OOPs language.
Object based language=Encapsulation + object Identity
6. Define object oriented language?
Ans: Object-oriented language incorporates all the features of object basedprogramming languages along with inheritance and polymorphism.
Example: – c++, java.
7. Define OOPs?
Ans: OOP is a method of implementation in which programs are organized as co-operative collection of objects, each of which represents an instance of some class and whose classes are all member of a hierarchy of classes united through the property of inheritance.
8. What is public, protected, and private?
Ans: These are access specifier or a visibility lebels .The class member that has been declared as private can be accessed only from within the class. Public members can be accessed from outside the class also. Within the class or from the object of a class protected access limit is same as that of private but it plays a prominent role in case of inheritance
9. What is a scope resolution operator?
Ans: The scope resolution operator permits a program to reference an identifier in the global scope that has been hidden by another identifier with the same name in the local scope.
10. What do you mean by inheritance?
Ans: The mechanism of deriving a new class (derived) from an old class (base class) is called inheritance. It allows the extension and reuse of existing code without having to rewrite the code from scratch.
11. What is abstraction?
Ans: The technique of creating user-defined data types, having the properties of built-in data types and a set of permitted operators that are well suited to the application to be programmed is known as data abstraction. Class is a construct for abstract data types (ADT).
12. What is encapsulation?
Ans: It is the mechanism that wraps the data and function it manipulates into single unit and keeps it safe from external interference.
13. How variable declaration in c++ differs that in c?
Ans: C requires all the variables to be declared at the beginning of a scope but in c++ we can declare variables anywhere in the scope. This makes the programmer easier to understand because the variables are declared in the context of their use.
14. What are the c++ tokens?
Ans: c++ has the following tokens
I. keywords
II. Identifiers
III. Constants
IV. Strings
V. operators
15. What do you mean by reference variable in c++?
Ans: A reference variable provides an alias to a previously defined variable.
Data type & reference-name = variable name
16. What do you mean by implicit conversion?
Ans: Whenever data types are mixed in an expression then c++ performs the conversion automatically.
Here smaller type is converted to wider type.
Example- in case of integer and float integer is converted into float type.
17. What is the difference between method overloading and method overriding?
Ans: Overloading a method (or function) in C++ is the ability for functions of the same name to be defined as long as these methods have different signatures (different set of parameters). Method overriding is the ability of the inherited class rewriting the virtual method of the base class.
18. What are the defining traits of an object-oriented language?
The defining traits of an object-oriented language are:
encapsulation
inheritance
polymorphism
Ans: 
Polymorphism: is a feature of OOPL that at run time depending upon the type of object the appropriate method is called.
Inheritance: is a feature of OOPL that represents the “is a” relationship between different objects (classes). Say in real life a manager is a employee. So in OOPL manger class is inherited from the employee class.
Encapsulation: is a feature of OOPL that is used to hide the information.
19. What is polymorphism?
Ans: Polymorphism is the idea that a base class can be inherited by several classes. A base class pointer can point to its child class and a base class array can store different child class objects.
20. What do you mean by inline function?
Ans: An inline function is a function that is expanded inline when invoked.ie. the compiler replaces the function call with the corresponding function code. An inline function is a function that is expanded in line when it is invoked. That is the compiler replaces the function call with the corresponding function code (similar to macro).
21 What is the difference between a NULL pointer and a void pointer?
Ans: A NULL pointer is a pointer of any type whose value is zero. A void pointer is a pointer to an object of an unknown type, and is guaranteed to have enough bits to hold a pointer to any object. A void pointer is not guaranteed to have enough bits to point to a function (though in general practice it does).
22. What is difference between C++ and Java?
Ans: C++ has pointers Java does not.
Java is platform independent C++ is not.
Java has garbage collection C++ does not.
23. What do you mean by multiple inheritance in C++ ?
Ans: Multiple inheritance is a feature in C++ by which one class can be of different types. Say class teaching Assistant is inherited from two classes say teacher and Student.
24. What do you mean by virtual methods?
Ans: virtual methods are used to use the polymorphism feature in C++. Say class A is inherited from class B. If we declare say function f() as virtual in class B and override the same function in class A then at runtime appropriate method of the class will be called depending upon the type of the object.
25. What do you mean by static methods?
Ans: By using the static method there is no need creating an object of that class to use that method. We can directly call that method on that class. For example, say class A has static function f(), then we can call f() function as A.f(). There is no need of creating an object of class A.
26. How many ways are there to initialize an int with a constant?
Ans: Two.
There are two formats for initializers in C++ as shown in the example that follows. The first format uses the traditional C notation. The second format uses constructor notation.
int foo = 123;
int bar (123);
27. What is a constructor?
Ans: Constructor is a special member function of a class, which is invoked automatically whenever an instance of the class is created. It has the same name as its class.
28. What is destructor?
Ans: Destructor is a special member function of a class, which is invoked automatically whenever an object goes out of the scope. It has the same name as its class with a tilde character prefixed.
29. What is an explicit constructor?
Ans: A conversion constructor declared with the explicit keyword. The compiler does not use an explicit constructor to implement an implied conversion of types. It’s purpose is reserved explicitly for construction.
30 What is the Standard Template Library?
Ans: A library of container templates approved by the ANSI committee for inclusion in the standard C++ specification. A programmer who then launches into a discussion of the generic programming model, iterators, allocators, algorithms, and such, has a higher than average understanding of the new technology that STL brings to C++ programming.
31. What problem does the namespace feature solve?
Ans: Multiple providers of libraries might use common global identifiers causing a name collision when an application tries to link with two or more such libraries. Thenamespace feature surrounds a library’s external declarations with a uniquenamespace that eliminates the potential for those collisions. This solution assumes that two library vendors don’t use the same namespace identifier, of course.
32. What is the use of ‘using’ declaration?
Ans: A using declaration makes it possible to use a name from a namespace
33. What is a template?
Ans: Templates allow us to create generic functions that admit any data type as parameters and return a value without having to overload the function with all the possible data types. Until certain point they fulfill the functionality of a macro. Its prototype is any of the two following ones:
template function_declaration;
template function_declaration;
34. Differentiate between a template class and class template?
Ans:
Template class:
A generic definition or a parameterized class not instantiated until the client provides the needed information. It’s jargon for plain templates.
Class template:
A class template specifies how individual classes can be constructed much like the way a class specifies how individual objects can be constructed. It’s jargon for plain classes.
35. What is the difference between a copy constructor and an overloaded assignment operator?
Ans: A copy constructor constructs a new object by using the content of the argument object. An overloaded assignment operator assigns the contents of an existing object to another existing object of the same class.
36. What is a virtual destructor?
Ans: The simple answer is that a virtual destructor is one that is declared with the virtual attribute.
37. What is an incomplete type?
Ans: Incomplete type refers to pointers in which there is non availability of the implementation of the referenced location or it points to some location whose value is not available for modification.
Example: 
int *i=0×400 // i points to address 400
*i=0; //set the value of memory location pointed by i.
Incomplete types are otherwise called uninitialized pointers.
38. What do you mean by Stack unwinding?
Ans: It is a process during exception handling when the destructor is called for all local objects between the place where the exception was thrown and where it is caught.
39. What is a container class? What are the types of container classes?
Ans: A container class is a class that is used to hold objects in memory or external storage. A container class acts as a generic holder. A container class has a predefined behavior and a well-known interface. A container class is a supporting class whose purpose is to hide the topology used for maintaining the list of objects in memory. When a container class contains a group of mixed objects, the container is called a heterogeneous container; when the container is holding a group of objects that are all the same, the container is called a homogeneous container
40. Name some pure object oriented languages?
Ans: Smalltalk, Java, Eiffel, Sather.
41. Name the operators that cannot be overloaded?
Ans: sizeof, ., .*, .->, ::, ?:
42. What is an adaptor class or Wrapper class?
Ans: A class that has no functionality of its own. Its member functions hide the use of a third party software component or an object with the non-compatible interface or a non-object-oriented implementation.
43. What is a Null object?
Ans: It is an object of some class whose purpose is to indicate that a real object of that class does not exist. One common use for a null object is a return value from a member function that is supposed to return an object with some specified properties but cannot find such an object.
44. What is class invariant?
Ans: A class invariant is a condition that defines all valid states for an object. It is a logical condition to ensure the correct working of a class. Class invariants must hold when an object is created, and they must be preserved under all operations of the class. In particular all class invariants are both preconditions and post-conditions for all operations or member functions of the class.
45. What is a dangling pointer?
Ans: A dangling pointer arises when you use the address of an object after its lifetime is over. This may occur in situations like returning addresses of the automatic variables from a function or using the address of the memory block after it is freed. Example: The following code snippet shows this:
class Sample
{
public:
int *ptr;
Sample(int i)
{
ptr = new int(i);
}
~Sample()
{
delete ptr;
}
void PrintVal()
{
cout << “The value is ” << *ptr;
}
};
void SomeFunc(Sample x)
{
cout << “Say i am in someFunc ” << endl;
}
int main()
{
Sample s1= 10;
SomeFunc(s1);
s1.PrintVal();
}
In the above example when PrintVal() function is called it is called by the pointer that has been freed by the destructor in SomeFunc.
46. Differentiate between the message and method?
Ans: 
Message: 
Objects communicate by sending messages to each other.
A message is sent to invoke a method.
Method
Provides response to a message and it is an implementation of an operation
47. How can we access protected and private members of a class?
Ans: In the case of members protected and private, these could not be accessed from outside the same class at which they are declared. This rule can be transgressed with the use of the friend keyword in a class, so we can allow an external function to gain access to the protected and private members of a class.
48. Can you handle exception in C++?
Ans: Yes we can handle exception in C++ using keyword: try, catch and throw. Program statements that we want to monitor for exceptions are contained in a try block. If an exception occurs within the try block, it is thrown (using throw).The exception is caught, using catch, and processed.
49. What is virtual function?
Ans: A virtual function is a member function that is declared within a base class and
redefined by a derived class .To create a virtual function, the function declaration in the base class is preceded by the keyword virtual.
50. What do you mean by early binding?
Ans:Early binding refers to the events that occur at compile time. Early binding occurs when
all information needed to call a function is known at compile time. Examples of early binding include normal function calls, overloaded function calls, and overloaded operators. The advantage of early binding is efficiency.
51. What do you mean by late binding?
Ans: Late binding refers to function calls that are not resolved until run time. Virtual functions are used to achieve late binding. When access is via a base pointer or reference, the virtual function actually called is determined by the type of object pointed to by the pointer.




---------



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 following initializations.
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 memory with the default base type value (depending upon compiler 2 compilers) because 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 variables 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.

C++ interview question: what is the difference between 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 begins) 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 are 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 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 constructor provided by the compiler in above case?
Answer: yes, if the designer of the class do not 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 million objects...so 4 megabyte memory will be lost...where all ptr do the same thing..... 

C++ interview question: Why can’t one make an object of abstract class? Give compiler view of statement 
Answer: we can’t make object of abstract class because, 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 creating the object. 

C++ interview question: In C++ has 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 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 cannot 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 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;
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 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 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 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 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 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 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 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++ Questions
Note : All the programs are tested under Turbo C++ 3.0, 4.5 and Microsoft VC++ 6.0
compilers.
It is assumed that,
􀂾 Programs run under Windows environment,
􀂾 The underlying machine is an x86 based system,
􀂾 Program is compiled using Turbo C/C++ compiler.
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The program output may depend on the information based on this assumptions (for
example sizeof(int) == 2 may be assumed).
1) class Sample
{
public:
int *ptr;
Sample(int i)
{
ptr = new int(i);
}
~Sample()
{
delete ptr;
}
void PrintVal()
{
cout << "The value is " << *ptr;
}
};
void SomeFunc(Sample x)
{
cout << "Say i am in someFunc " << endl;
}
int main()
{
Sample s1= 10;
SomeFunc(s1);
s1.PrintVal();
}
Answer:
Say i am in someFunc
Null pointer assignment(Run-time error)
Explanation:
As the object is passed by value to SomeFunc the destructor of the object is called
when the control returns from the function. So when PrintVal is called it meets up with ptr
that has been freed.The solution is to pass the Sample object by reference to SomeFunc:
void SomeFunc(Sample &x)
{
cout << "Say i am in someFunc " << endl;
}
because when we pass objects by refernece that object is not destroyed. while returning
from the function.
2) Which is the parameter that is added to every non-static member function when it is
called?
Answer:
‘this’ pointer
3) class base
{
public:
int bval;
base(){ bval=0;}
};
class deri:public base
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{
public:
int dval;
deri(){ dval=1;}
};
void SomeFunc(base *arr,int size)
{
for(int i=0; i<size; i++,arr++)
cout<<arr->bval;
cout<<endl;
}
int main()
{
base BaseArr[5];
SomeFunc(BaseArr,5);
deri DeriArr[5];
SomeFunc(DeriArr,5);
}
Answer:
00000
01010
Explanation:
The function SomeFunc expects two arguments.The first one is a pointer to an array
of base class objects and the second one is the sizeof the array.The first call of someFunc
calls it with an array of bae objects, so it works correctly and prints the bval of all the objects.
When Somefunc is called the second time the argument passed is the pointeer to an array of
derived class objects and not the array of base class objects. But that is what the function
expects to be sent. So the derived class pointer is promoted to base class pointer and the
address is sent to the function. SomeFunc() knows nothing about this and just treats the
pointer as an array of base class objects. So when arr++ is met, the size of base class object
is taken into consideration and is incremented by sizeof(int) bytes for bval (the deri class
objects have bval and dval as members and so is of size >= sizeof(int)+sizeof(int) ).
4) class base
{
public:
void baseFun(){ cout<<"from base"<<endl;}
};
class deri:public base
{
public:
void baseFun(){ cout<< "from derived"<<endl;}
};
void SomeFunc(base *baseObj)
{
baseObj->baseFun();
}
int main()
{
base baseObject;
SomeFunc(&baseObject);
deri deriObject;
SomeFunc(&deriObject);
}
Answer:
from base
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63
from base
Explanation:
As we have seen in the previous case, SomeFunc expects a pointer to a base class.
Since a pointer to a derived class object is passed, it treats the argument only as a base
class pointer and the corresponding base function is called.
5) class base
{
public:
virtual void baseFun(){ cout<<"from base"<<endl;}
};
class deri:public base
{
public:
void baseFun(){ cout<< "from derived"<<endl;}
};
void SomeFunc(base *baseObj)
{
baseObj->baseFun();
}
int main()
{
base baseObject;
SomeFunc(&baseObject);
deri deriObject;
SomeFunc(&deriObject);
}
Answer:
from base
from derived
Explanation:
Remember that baseFunc is a virtual function. That means that it supports run-time
polymorphism. So the function corresponding to the derived class object is called.
void main()
{
int a, *pa, &ra;
pa = &a;
ra = a;
cout <<"a="<<a <<"*pa="<<*pa <<"ra"<<ra ;
}
/*
Answer :
Compiler Error: 'ra',reference must be initialized
Explanation :
Pointers are different from references. One of the main
differences is that the pointers can be both initialized and assigned,
whereas references can only be initialized. So this code issues an error.
*/
const int size = 5;
void print(int *ptr)
{
cout<<ptr[0];
}
void print(int ptr[size])
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{
cout<<ptr[0];
}
void main()
{
int a[size] = {1,2,3,4,5};
int *b = new int(size);
print(a);
print(b);
}
/*
Answer:
Compiler Error : function 'void print(int *)' already has a body
Explanation:
Arrays cannot be passed to functions, only pointers (for arrays, base addresses)
can be passed. So the arguments int *ptr and int prt[size] have no difference
as function arguments. In other words, both the functoins have the same signature and
so cannot be overloaded.
*/
class some{
public:
~some()
{
cout<<"some's destructor"<<endl;
}
};
void main()
{
some s;
s.~some();
}
/*
Answer:
some's destructor
some's destructor
Explanation:
Destructors can be called explicitly. Here 's.~some()' explicitly calls the
destructor of 's'. When main() returns, destructor of s is called again,
hence the result.
*/
#include <iostream.h>
class fig2d
{
int dim1;
int dim2;
public:
fig2d() { dim1=5; dim2=6;}
virtual void operator<<(ostream & rhs);
};
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void fig2d::operator<<(ostream &rhs)
{
rhs <<this->dim1<<" "<<this->dim2<<" ";
}
/*class fig3d : public fig2d
{
int dim3;
public:
fig3d() { dim3=7;}
virtual void operator<<(ostream &rhs);
};
void fig3d::operator<<(ostream &rhs)
{
fig2d::operator <<(rhs);
rhs<<this->dim3;
}
*/
void main()
{
fig2d obj1;
// fig3d obj2;
obj1 << cout;
// obj2 << cout;
}
/*
Answer :
5 6
Explanation:
In this program, the << operator is overloaded with ostream as argument.
This enables the 'cout' to be present at the right-hand-side. Normally, 'cout'
is implemented as global function, but it doesn't mean that 'cout' is not possible
to be overloaded as member function.
Overloading << as virtual member function becomes handy when the class in which
it is overloaded is inherited, and this becomes available to be overrided. This is as opposed
to global friend functions, where friend's are not inherited.
*/
class opOverload{
public:
bool operator==(opOverload temp);
};
bool opOverload::operator==(opOverload temp){
if(*this == temp ){
cout<<"The both are same objects\n";
return true;
}
else{
cout<<"The both are different\n";
return false;
}
}
void main(){
opOverload a1, a2;
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a1= =a2;
}
Answer :
Runtime Error: Stack Overflow
Explanation :
Just like normal functions, operator functions can be called recursively. This program
just illustrates that point, by calling the operator == function recursively, leading to an infinite
loop.
class complex{
double re;
double im;
public:
complex() : re(1),im(0.5) {}
bool operator==(complex &rhs);
operator int(){}
};
bool complex::operator == (complex &rhs){
if((this->re == rhs.re) && (this->im == rhs.im))
return true;
else
return false;
}
int main(){
complex c1;
cout<< c1;
}
Answer : Garbage value
Explanation:
The programmer wishes to print the complex object using output
re-direction operator,which he has not defined for his lass.But the compiler instead of giving
an error sees the conversion function
and converts the user defined object to standard object and prints
some garbage value.
class complex{
double re;
double im;
public:
complex() : re(0),im(0) {}
complex(double n) { re=n,im=n;};
complex(int m,int n) { re=m,im=n;}
void print() { cout<<re; cout<<im;}
};
void main(){
complex c3;
double i=5;
c3 = i;
c3.print();
}
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Answer:
5,5
Explanation:
Though no operator= function taking complex, double is defined, the double on the
rhs is converted into a temporary object using the single argument constructor taking double
and assigned to the lvalue.
void main()
{
int a, *pa, &ra;
pa = &a;
ra = a;
cout <<"a="<<a <<"*pa="<<*pa <<"ra"<<ra ;
}
Answer :
Compiler Error: 'ra',reference must be initialized
Explanation :
Pointers are different from references. One of the main
differences is that the pointers can be both initialized and assigned,
whereas references can only be initialized. So this code issues an error.
Try it Yourself
1) Determine the output of the 'C++' Codelet.
class base
{
public :
out()
{
cout<<"base ";
}
};
class deri{
public : out()
{
cout<<"deri ";
}
};
void main()
{ deri dp[3];
base *bp = (base*)dp;
for (int i=0; i<3;i++)
(bp++)->out();
}
2) Justify the use of virtual constructors and destructors in C++.
3) Each C++ object possesses the 4 member fns,(which can be declared by the
programmer explicitly or by the implementation if they are not available). What are those
4 functions?
4) What is wrong with this class declaration?
class something
{
char *str;
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68
public:
something(){
st = new char[10]; }
~something()
{
delete str;
}
};
5) Inheritance is also known as -------- relationship. Containership as ________
relationship.
6) When is it necessary to use member-wise initialization list (also known as header
initialization list) in C++?
7) Which is the only operator in C++ which can be overloaded but NOT inherited.
8) Is there anything wrong with this C++ class declaration?
class temp
{
int value1;
mutable int value2;
public :
void fun(int val)
const{
((temp*) this)->value1 = 10;
value2 = 10;
}
};
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1. What is a modifier?
Answer:
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’.
2. What is an accessor?
Answer:
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
3. Differentiate between a template class and class template.
Answer:
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.
4. When does a name clash occur?
Answer:
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.
5. 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.
6. 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.
7. 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:
􀂾 input iterators,
􀂾 output iterators,
􀂾 forward iterators,
􀂾 bidirectional iterators,
􀂾 random access.
An iterator is an entity that gives access to the contents of a container object without
violating encapsulation constraints. Access to the contents is granted on a one-at-a-time
basis in order. The order can be storage order (as in lists and queues) or some arbitrary
order (as in array indices) or according to some ordering relation (as in an ordered binary
tree). The iterator is a construct, which provides an interface that, when called, yields either
the next element in the container, or some value denoting the fact that there are no more
elements to examine. Iterators hide the details of access to and update of the elements of a
container class.
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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.
9. List out some of the OODBMS available.
Answer:
􀂾 GEMSTONE/OPAL of Gemstone systems.
􀂾 ONTOS of Ontos.
􀂾 Objectivity of Objectivity inc.
􀂾 Versant of Versant object technology.
􀂾 Object store of Object Design.
􀂾 ARDENT of ARDENT software.
􀂾 POET of POET software.
10. List out some of the object-oriented methodologies.
Answer:
􀂾 Object Oriented Development (OOD) (Booch 1991,1994).
􀂾 Object Oriented Analysis and Design (OOA/D) (Coad and Yourdon 1991).
􀂾 Object Modelling Techniques (OMT) (Rumbaugh 1991).
􀂾 Object Oriented Software Engineering (Objectory) (Jacobson 1992).
􀂾 Object Oriented Analysis (OOA) (Shlaer and Mellor 1992).
􀂾 The Fusion Method (Coleman 1991).
11. 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.
12. 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.
13. Differentiate between the message and method.
Answer:
Message Method
Objects communicate by sending messages Provides response to a message.
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71
to each other.
A message is sent to invoke a method. It is an implementation of an operation.
14. 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 nonobject-
oriented implementation.
15. 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.
16. 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.
17. What do you mean by Stack unwinding?
Answer:
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.
18. Define precondition and post-condition to a member function.
Answer:
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 postconditions
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.
19. What are the conditions that have to be met for a condition to be an invariant of the
class?
Answer:
􀂾 The condition should hold at the end of every constructor.
􀂾 The condition should hold at the end of every mutator(non-const) operation.
20. What are proxy objects?
Answer:
Objects that stand for other objects are called proxy objects or surrogates.
Example:
template<class T>
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class Array2D
{
public:
class Array1D
{
public:
T& operator[] (int index);
const T& operator[] (int index) const;
...
};
Array1D operator[] (int index);
const Array1D operator[] (int index) const;
...
};
The following then becomes legal:
Array2D<float>data(10,20);
........
cout<<data[3][6]; // fine
Here data[3] yields an Array1D object and the operator [] invocation on that object
yields the float in position(3,6) of the original two dimensional array. Clients of the Array2D
class need not be aware of the presence of the Array1D class. Objects of this latter class
stand for one-dimensional array objects that, conceptually, do not exist for clients of
Array2D. Such clients program as if they were using real, live, two-dimensional arrays. Each
Array1D object stands for a one-dimensional array that is absent from a conceptual model
used by the clients of Array2D. In the above example, Array1D is a proxy class. Its instances
stand for one-dimensional arrays that, conceptually, do not exist.
21. Name some pure object oriented languages.
Answer:
􀂾 Smalltalk,
􀂾 Java,
􀂾 Eiffel,
􀂾 Sather.
22. Name the operators that cannot be overloaded.
Answer:
sizeof . .* .-> :: ?:
23. What is a node class?
Answer:
A node class is a class that,
􀂾 relies on the base class for services and implementation,
􀂾 provides a wider interface to te 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 from its base class.
24. 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
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73
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.
25. 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.
26. What is a protocol class?
Answer:
An abstract class is a protocol class if:
􀂾 it neither contains nor inherits from classes that contain member data, non-virtual
functions, or private (or protected) members of any kind.
􀂾 it has a non-inline virtual destructor defined with an empty implementation,
􀂾 all member functions other than the destructor including inherited functions, are
declared pure virtual functions and left undefined.
27. 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.
28. 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.
29.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.
30. What is an action class?
Answer:
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74
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.
31. 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.
32.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.
33. 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
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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.
34. 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.
35. 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 X>
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 <X> &);
const smart_pointer <X> & operator =(const smart_pointer<X>&);
~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 <employee> p= employee("Harris",1333);
Like other overloaded operators, p will behave like a regular pointer,
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76
cout<<*p;
p->raise_salary(0.5);
36. 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.
37. 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.
38. 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;
...
}
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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).
39. 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.
40. 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:
􀂾 it declares a function without specifying its body,
􀂾 it contains an extern specifier and no initializer or function body,
􀂾 it is the declaration of a static class data member without a class definition,
􀂾 it is a class name definition,
􀂾 it is a typedef declaration.
A definition is a declaration unless:
􀂾 it defines a static class data member,
􀂾 it defines a non-inline member function.
41. 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.
42. Describe the main characteristics of static functions.
Answer:
The main characteristics of static functions include,
􀂾 It is without the a this pointer,
􀂾 It can't directly access the non-static members of its class
􀂾 It can't be declared const, volatile or virtual.
􀂾 It doesn't need to be invoked through an object of its class, although for
convenience, it may.
43. 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.
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78
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.
44. Define a way other than using the keyword inline to make a function inline.
Answer:
The function must be defined inside the class.
45. 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.
46. 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.
 



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