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| C++ Interview Questions |
1. What is C++?
Released in 1985, C++ is an object-oriented programming language created by Bjarne Stroustrup. C++ maintains almost all aspects of the C language, while simplifying memory management and adding several features – including a new datatype known as a class (you will learn more about these later) – to allow object-oriented programming. C++ maintains the features of C which allowed for low-level memory access but also gives the programmer new tools to simplify memory management.
C++ is a powerful general-purpose programming language. It can be used to create small programs or large applications. It can be used to make CGI scripts or console-only DOS programs. C++ allows you to create programs to do almost anything you need to do. The creator of C++, Bjarne Stroustrup, has put together a partial list of applications written in C++.
2. How do you find out if a linked-list has an end? (i.e. the list is not a cycle)
You can find out by using 2 pointers. One of them goes 2 nodes each time. The second one goes at 1 nodes each time. If there is a cycle, the one that goes 2 nodes each time will eventually meet the one that goes slower. If that is the case, then you will know the linked-list is a cycle.
3. What is the difference between realloc() and free()?
The free subroutine frees a block of memory previously allocated by the malloc subroutine. Undefined results occur if the Pointer parameter is not a valid pointer. If the Pointer parameter is a null value, no action will occur. The realloc subroutine changes the size of the block of memory pointed to by the Pointer parameter to the number of bytes specified by the Size parameter and returns a new pointer to the block. The pointer specified by the Pointer parameter must have been created with the malloc, calloc, or realloc subroutines and not been deallocated with the free or realloc subroutines. Undefined results occur if the Pointer parameter is not a valid pointer.
4. What is function overloading and operator overloading?
Function overloading: C++ enables several functions of the same name to be defined, as long as these functions have different sets of parameters (at least as far as their types are concerned). This capability is called function overloading. When an overloaded function is called, the C++ compiler selects the proper function by examining the number, types and order of the arguments in the call. Function overloading is commonly used to create several functions of the same name that perform similar tasks but on different data types.
Operator overloading allows existing C++ operators to be redefined so that they work on objects of user-defined classes. Overloaded operators are syntactic sugar for equivalent function calls. They form a pleasant facade that doesn’t add anything fundamental to the language (but they can improve understandability and reduce maintenance costs).
5. What are the advantages of inheritance?
It permits code reusability. Reusability saves time in program development. It encourages the reuse of proven and debugged high-quality software, thus reducing problem after a system becomes functional.
6. What do you mean by inline function?
The idea behind inline functions is to insert the code of a called function at the point where the function is called. If done carefully, this can improve the application’s performance in exchange for increased compile time and possibly (but not always) an increase in the size of the generated binary executables.
7. What is public, protected, private?
Public, protected and private are three access specifier in C++.
Public data members and member functions are accessible outside the class.
Protected data members and member functions are only available to derived classes.
Private data members and member functions canโt be accessed outside the class. However there is an exception can be using friend classes.
8. Does c++ support multilevel and multiple inheritance?
Yes.
9. What are the advantages of inheritance?
a. It permits code reusability.
b. Reusability saves time in program development.
c. It encourages the reuse of proven and debugged high-quality software, thus reducing problem after a system becomes functional.
10. What is the difference between an ARRAY and a LIST?
Array is collection of homogeneous elements.
List is collection of heterogeneous elements.
For Array memory allocated is static and continuous.
For List memory allocated is dynamic and Random.
Array: User need not have to keep in track of next memory allocation.
List: User has to keep in Track of next location where memory is allocated.
Array uses direct access of stored members, list uses sequencial access for members.
11. What is a template?
Templates allow to create generic functions that admit any data type as parameters and return value without having to overload the function with all the possible data types.
12. Define a constructor – What it is and how it might be called?
Constructor is a member function of the class, with the name of the function being the same as the class name. It also specifies how the object should be initialized.
Ways of calling constructor:
i. Implicitly: automatically by complier when an object is created.
ii. Calling the constructors explicitly is possible, but it makes the code unverifiable.
13. Explain differences between eg. new() and malloc()
โnew and deleteโ are preprocessors while โmalloc() and free()โ are functions. [we dont use brackets will calling new or delete].
no need of allocate the memory while using โnewโ but in โmalloc()โ we have to use โsizeof()โ.
โnewโ will initlize the new memory to 0 but โmalloc()โ gives random value in the new alloted memory location [better to use calloc()]
new() allocates continous space for the object instace where as malloc() allocates distributed space.
new() is castless, meaning that allocates memory for this specific type, malloc(), calloc() allocate space for void * that is limited to the specific class type pointer.
14. What is the difference between class and structure?
Structure: Initially (in C) a structure was used to bundle different type of data types together to perform a particular functionality. But C++ extended the structure to contain functions also. The major difference is that all declarations inside a structure are by default public.
Class: Class is a successor of Structure. By default all the members inside the class are private.
15. What is RTTI?
Runtime type identification (RTTI) lets you find the dynamic type of an object when you have only a pointer or a reference to the base type. RTTI is the official way in standard C++ to discover the type of an object and to convert the type of a pointer or reference (that is, dynamic typing). The need came from practical experience with C++. RTTI replaces many Interview Questions – Homegrown versions with a solid, consistent approach.
16. What is encapsulation?
Packaging an objectโs variables within its methods is called encapsulation.
17. What is an object?
Object is a software bundle of variables and related methods. Objects have state and behavior.
18. How can you tell what shell you are running on UNIX system?
You can do the Echo $RANDOM. It will return a undefined variable if you are from the C-Shell, just a return prompt if you are from the Bourne shell, and a 5 digit random numbers if you are from the Korn shell. You could also do a ps -l and look for the shell with the highest PID.
19. What do you mean by inheritance?
Inheritance is the process of creating new classes, called derived classes, from existing classes or base classes. The derived class inherits all the capabilities of the base class, but can add embellishments and refinements of its own.
20. What is a COPY CONSTRUCTOR and when is it called?
A copy constructor is a method that accepts an object of the same class and copies itโs data members to the object on the left part of assignment:
21. What is virtual class and friend class?
Friend classes are used when two or more classes are designed to work together and need access to each other’s implementation in ways that the rest of the world shouldn’t be allowed to have. In other words, they help keep private things private. For instance, it may be desirable for class DatabaseCursor to have more privilege to the internals of class Database than main() has.
22. What is the word you will use when defining a function in base class to allow this function to be a polymorphic function?
Virtual
23. What do you mean by binding of data and functions?
Encapsulation.
24. What are 2 ways of exporting a function from a DLL?
1.Taking a reference to the function from the DLL instance.
2. Using the DLL โs Type Library
25. What is the difference between an object and a class?
Classes and objects are separate but related concepts. Every object belongs to a class and every class contains one or more related objects.
A Class is static. All of the attributes of a class are fixed before, during, and after the execution of a program. The attributes of a class don’t change.
The class to which an object belongs is also (usually) static. If a particular object belongs to a certain class at the time that it is created then it almost certainly will still belong to that class right up until the time that it is destroyed.
An Object on the other hand has a limited lifespan. Objects are created and eventually destroyed. Also during that lifetime, the attributes of the object may undergo significant change.
26. What is a class?
Class is a user-defined data type in C++. It can be created to solve a particular kind of problem. After creation the user need not know the specifics of the working of a class.
27. What is friend function?
As the name suggests, the function acts as a friend to a class. As a friend of a class, it can access its private and protected members. A friend function is not a member of the class. But it must be listed in the class definition.
28. Which recursive sorting technique always makes recursive calls to sort subarrays that are about half size of the original array?
Mergesort always makes recursive calls to sort subarrays that are about half size of the original array, resulting in O(n log n) time.
29. What is abstraction?
Abstraction is of the process of hiding unwanted details from the user.
30. What are virtual functions?
A virtual function allows derived classes to replace the implementation provided by the base class. The compiler makes sure the replacement is always called whenever the object in question is actually of the derived class, even if the object is accessed by a base pointer rather than a derived pointer. This allows algorithms in the base class to be replaced in the derived class, even if users don’t know about the derived class.
31. What is the difference between an external iterator and an internal iterator? Describe an advantage of an external iterator.
An internal iterator is implemented with member functions of the class that has items to step through. .An external iterator is implemented as a separate class that can be “attach” to the object that has items to step through. .An external iterator has the advantage that many difference iterators can be active simultaneously on the same object.
32. What is a scope resolution operator?
A scope resolution operator (::), can be used to define the member functions of a class outside the class.
33. What do you mean by pure virtual functions?
A pure virtual member function is a member function that the base class forces derived classes to provide. Normally these member functions have no implementation. Pure virtual functions are equated to zero.
class Shape { public: virtual void draw() = 0; };
34. What is polymorphism? Explain with an example?
“Poly” means “many” and “morph” means “form”. Polymorphism is the ability of an object (or reference) to assume (be replaced by) or become many different forms of object.
Example: function overloading, function overriding, virtual functions. Another example can be a plus โ+โ sign, used for adding two integers or for using it to concatenate two strings.
35. Why are arrays usually processed with for loop?
The real power of arrays comes from their facility of using an index variable to traverse the array, accessing each element with the same expression a[i]. All the is needed to make this work is a iterated statement in which the variable i serves as a counter, incrementing from 0 to a.length -1. That is exactly what a loop does.
36. What is an HTML tag?
An HTML tag is a syntactical construct in the HTML language that abbreviates specific instructions to be executed when the HTML script is loaded into a Web browser. It is like a method in Java, a function in C++, a procedure in Pascal, or a subroutine in FORTRAN.
37. What is a conversion constructor?
A constructor that accepts one argument of a different type.
38. What is the difference between a copy constructor and an overloaded assignment operator?
A copy constructor constructs a new object by using the content of the argument object. An overloaded assignment operator assigns the contents of an existing object to another existing object of the same class.
39. When should you use multiple inheritance?
There are three acceptable answers: “Never,” “Rarely,” and “When the problem domain cannot be accurately modeled any other way.”
40. Explain the ISA and HASA class relationships. How would you implement each in a class design?
A specialized class “is” a specialization of another class and, therefore, has the ISA relationship with the other class. An Employee ISA Person. This relationship is best implemented with inheritance. Employee is derived from Person. A class may have an instance of another class. For example, an employee “has” a salary, therefore the Employee class has the HASA relationship with the Salary class. This relationship is best implemented by embedding an object of the Salary class in the Employee class.
41. When is a template a better solution than a base class?
When you are designing a generic class to contain or otherwise manage objects of other types, when the format and behavior of those other types are unimportant to their containment or management, and particularly when those other types are unknown (thus, the generosity) to the designer of the container or manager class.
42. What is a mutable member?
One that can be modified by the class even when the object of the class or the member function doing the modification is const.
43. What is an explicit constructor?
A conversion constructor declared with the explicit keyword. The compiler does not use an explicit constructor to implement an implied conversion of types. Itโs purpose is reserved explicitly for construction.
44. What is the Standard Template Library (STL)?
A library of container templates approved by the ANSI committee for inclusion in the standard C++ specification.
A programmer who then launches into a discussion of the generic programming model, iterators, allocators, algorithms, and such, has a higher than average understanding of the new technology that STL brings to C++ programming.
45. Describe run-time type identification.
The ability to determine at run time the type of an object by using the typeid operator or the dynamic_cast operator.
46. What problem does the namespace feature solve?
Multiple providers of libraries might use common global identifiers causing a name collision when an application tries to link with two or more such libraries. The namespace feature surrounds a libraryโs external declarations with a unique namespace that eliminates the potential for those collisions.
This solution assumes that two library vendors donโt use the same namespace identifier, of course.
47. Are there any new intrinsic (built-in) data types?
Yes. The ANSI committee added the bool intrinsic type and its true and false value keywords.
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