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What is an object in C++?
An object is a package that contains related data and instructions. The data relates to what the object represents, while the instructions define how this object relates to other objects and itself.
What is a message?
A message is a signal from one object to another requesting that a computation take place. It is roughly equivalent to a function call in other languages.
What is a class?
A class defines the characteristics of a certain type of object. It defines what its members will remember, the messages to which they will respond, and what form the response will take.
What is an instance?
An individual object that is a member of some class.
What is a super-class?
Given a class, a super-class is the basis of the class under consideration. The given class is defined as a subset (in some respects) of the super-class. Objects of the given class potentially posses all the characteristics belonging to objects of the super-class.
What is inheritance?
Inheritance is property such that a parent (or super) class passes the characteristics of itself to children (or sub) classes that are derived from it. The sub-class has the option of modifying these characteristics in order to make a different but fundamentally related class from the super-class.
To what does message protocol refer?
An object’s message protocol is the exact form of the set of messages to which the object can respond.
What is polymorphism?
Polymorphism refers to the ability of an object to respond in a logically identical fashion to messages of the same protocol, containing differing types of objects. Consider 1 + 5 and 1 + 5.1. In the former, the message “+ 5″ is sent to an object of class integer (1). In the later, the message “+ 5.1″ is sent to the same integer object. The form of the message (its protocol) is identical in both cases. What differs is the type of object on the right-hand side of these messages. The former is an integer object (5) while the later is a floating point object (5.1). The receiver (1) appears (to other objects) to respond in the same way to both messages. Internally, however, it knows that it must treat the two types of objects differently in order to obtain the same overall response.
What are instance variables?
These represent an object’s private memory. They are defined in an object’s class.
What are class variables?
These represent a class’s memory which it shares with each of its instances.
What is a method?
A method is a class’s procedural response to a given message protocol. It is like the definition of a procedure in other languages.
In C++ what is a constructor? A destructor?
A constructors and destructors are methods defined in a class that are invoked automatically when an object is created or destroyed. They are used to initialize a newly allocated object and to cleanup behind an object about to be removed.
Compare and contrast C and C++.
Comparison: C++ is an extension to the C language. When C++ is used as a procedural language, there are only minor syntactical differences between them.
Contrast: When used as a procedural language, C++ is a better C because:
It vigorously enforces data typing conventions.
It allows variables to be defined where they are used.
It allows the definition of real (semantically significant) constants.
It allows for automatic pointer dereferencing.
It supports call-by-reference in addition to call-by-value in functions.
It supports tentative variable declarations (when the type and location of a variable cannot be known before hand.
As an object oriented language, C++ introduces much of the OOP paradigm while allowing a mixture of OOP and procedural styles.
What is operator overloading?
It is the process of, and ability to redefine the way an object responds to a C++ operator symbol. This would be done in the object’s class definition.
What is cin and cout?
They are objects corresponding to a program’s default input and output files.
What are the differences between a C++ struct and C++ class?
The default member and base class access specifiers are different.
This is one of the commonly misunderstood aspects of C++. Believe it or not, many programmers think that a C++ struct is just like a C struct, while a C++ class has inheritance, access specifiers, member functions, overloaded operators, and so on. Some of them have even written books about C++. Actually, the C++ struct has all the features of the class. The only differences are that a struct defaults to public member access and public base class inheritance, and a class defaults to the private access specifier and private base class inheritance. Getting this question wrong does not necessarily disqualify you because you will be in plenty of good company. Getting it right is a definite plus.
What is a default constructor?
A constructor that has no arguments or one where all the arguments have default argument values.
If you don’t code a default constructor, the compiler provides one if there are no other constructors. If you are going to instantiate an array of objects of the class, the class must have a default constructor.
What is a conversion constructor?
A constructor that accepts one argument of a different type.
The compiler uses this idiom as one way to infer conversion rules for a class. A constructor with more than one argument and with default argument values can be interpreted by the compiler as a conversion constructor when the compiler is looking for an object of the type and sees an object of the type of the constructor’s first argument.
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.
First, you must know that a copy constructor is one that has only one argument, which is a reference to the same type as the constructor. The compiler invokes a copy constructor wherever it needs to make a copy of the object, for example to pass an argument by value. If you do not provide a copy constructor, the compiler creates a member-by-member copy constructor for you.
You can write overloaded assignment operators that take arguments of other classes, but that behavior is usually implemented with implicit conversion constructors. If you do not provide an overloaded assignment operator for the class, the compiler creates a default member-by-member assignment operator.
What is a virtual destructor?
The simple answer is that a virtual destructor is one that is declared with the virtual attribute.
The behavior of a virtual destructor is what is important. If you destroy an object through a pointer or reference to a base class, and the base-class destructor is not virtual, the derived-class destructors are not executed, and the destruction might not be complete.
When is a template a better solution than a base class?
When you are designing a generic class to contain or otherwise manage objects of other types, when the format and behavior of those other types are unimportant to their containment or management, and particularly when those other types are unknown (thus the genericity) to the designer of the container or manager class.
Prior to templates, you had to use inheritance; your design might include a generic List container class and an application-specific Employee class. To put employees in a list, a ListedEmployee class is multiply derived (contrived) from the Employee and List classes. These solutions were unwieldy and error-prone. Templates solved that problem.
What is the difference between C and C++ ? Would you prefer to use one over the other ?
C is based on structured programming whereas C++ supports the object-oriented programming paradigm.Due to the advantages inherent in object-oriented programs such as modularity and reuse, C++ is preferred. However almost anything that can be built using C++ can also be built using C.
What are the access privileges in C++ ? What is the default access level ?
The access privileges in C++ are private, public and protected. The default access level assigned to members of a class is private. Private members of a class are accessible only within the class and by friends of the class. Protected members are accessible by the class itself and it’s sub-classes. Public members of a class can be accessed by anyone.
What is data encapsulation ?
Data Encapsulation is also known as data hiding. The most important advantage of encapsulation is that it lets the programmer create an object and then provide an interface to the object that other objects can use to call the methods provided by the object. The programmer can change the internal workings of an object but this transparent to other interfacing programs as long as the interface remains unchanged.
What is inheritance ?
Inheritance is the process of deriving classes from other classes. In such a case, the sub-class has an ‘is-a’ relationship with the super class. For e.g. vehicle can be a super-class and car can be a sub-class derived from vehicle. In this case a car is a vehicle. The super class ‘is not a’ sub-class as the sub- class is more specialized and may contain additional members as compared to the super class. The greatest advantage of inheritance is that it promotes generic design and code reuse.
What is multiple inheritance ? What are it’s advantages and disadvantages ?
Multiple Inheritance is the process whereby a sub-class can be derived from more than one super class. The advantage of multiple inheritance is that it allows a class to inherit the functionality of more than one base class thus allowing for modeling of complex relationships. The disadvantage of multiple inheritance is that it can lead to a lot of confusion when two base classes implement a method with the same name.
What is polymorphism?
Polymorphism refers to the ability to have more than one method with the same signature in an inheritance hierarchy. The correct method is invoked at run-time based on the context (object) on which the method is invoked. Polymorphism allows for a generic use of method names while providing specialized implementations for them.
What do the keyword static and const signify ?
When a class member is declared to be of a static type, it means that the member is not an instance variable but a class variable. Such a member is accessed using Classname.Membername (as opposed to Object.Membername). Const is a keyword used in C++ to specify that an object’s value cannot be changed.
How is memory allocated/deallocated in C ? How about C++ ?
Memory is allocated in C using malloc() and freed using free(). In C++ the new() operator is used to allocate memory to an object and the delete() operator is used to free the memory taken up by an object.
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. Its purpose is reserved explicitly for construction.
What is the Standard Template Library?
A library of container templates approved by the ANSI committee for inclusion in the standard C++ specification.
An applicant who then launches into a discussion of the generic programming model, iterators, allocators, algorithms, and such, has a higher than average understanding of the new technology that STL brings to C++ programming.
Describe run-time type identification.
The ability to determine at run time the type of an object by using the typeid operator or the dynamic_cast operator.
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 name-space feature surrounds a library’s external declarations with a unique namespace that eliminates the potential for those collisions.
This solution assumes that two library vendors don’t use the same namespace, of course.
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 and the wchar_t data type to support character sets wider than eight bits.
Other apparent new types (string, complex, and so forth) are implemented as classes in the Standard C++ Library rather than as intrinsic types
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