C++ Interview Questions

C++ Interview Questions

C++ is an object-oriented programming language and is meant for general purposes. It has imperative and generic programming features and it especially provides low-level memory manipulation facilities. The International Organization for Standardization (ISO) standardizes C++ and the latest version is C++20. Similar to C, the C++ language supports four types of memory management, namely static storage duration objects, automatic storage duration objects, thread storage duration objects, and dynamic storage duration objects.

It is widely used for partially or completely scripting and application development such as with Adobe Systems, Google apps, MySQL servers, Mozilla Firefox and Thunderbird, various media players and more. C++ also finds application in the development of Operating Systems as Apple OS X, Microsoft OS, Symbian OS and more. The development and evolution of C++ are guided by the principle that each program written in the programming language must be driven by actual problems and that its features should be used immediately in real-world programs. C++ is exceptionally compatible with many programming languages in order to foster a compatible and useful programming environment.

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Here are a few questions, which might be asked during a C++ interview:

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C++ Interview Questions

A class describes the behavior and properties common to any particular type of object. It is a user-defined data type, which holds its own data members and member functions, which can be accessed and used by creating an instance of that class. Defining a class means defining a blueprint for a data type or an object. A class definition begins with the keyword class followed by the class name and the class body, which is enclosed by a pair of curly braces. A class definition must always be followed either by a semicolon or a list of declarations for it to be valid.
The C language follows the procedural style programming.C++ is a multi-paradigm programming language. It supports both procedural and object-oriented styles of programming.
Data is less secure in C as compared to C++.In case of C++, you can use modifiers for class members to make it inaccessible for outside users. Thus, the data is more secure in C++.
The C language follows the top-down approach.The C++ language follows the bottom-up approach.
There is no scope for function overloading in C.C++ supports function overloading.
The user cannot use functions in structure in the case of C.In case of C++, the user can use functions in structure.
C also does not support reference variables.C++ supports use of reference variables.
In C, the methods scanf() and printf() are mainly used for input or output.The C++ language mainly uses streams cin and cout to perform the input and output operations.
A constructor is used to initialize the instance of a class or object.A destructor simply destroys the objects when they are no longer needed.
A constructor is called when a new instance of a class or object is created.A destructor is called when an instance of a class or object is deleted or released.
A constructor allocates the memory.A destructor releases or frees the memory.
Constructors can have arguments.A destructor cannot have any arguments.
Overloading of the constructor is possible in C++.Overloading of destructors is not possible.
A constructor has the same name as class name.A destructor also has the same name as class name but with (~) tiled operator.
Data abstraction is a mechanism of exposing only the interfaces and hiding the implementation details from the user. Encapsulation can merely be understood as wrapping up of data and methods in a capsule, which means just hiding properties and methods. Encapsulation is used for hiding the code and data in a single unit to protect the data from the outside the world. The class is the best example of encapsulation in C++. On the other hand, abstraction means showing only the necessary details to the intended user.
C++ facilitates the user to specify more than one definition for a function name or an operator in the same scope. This is called function overloading and operator overloading respectively. Function overloading is primarily a feature in C++ where two or more functions can have not only the same name but also different types and numbers of parameters. Operating overloading, on the other hand, allows the user to make operators work for user-defined classes. For example, we can overload an operator such as ‘+’ in a class like String so that we can concatenate two strings by just using + instead of other descriptive functions. Other example classes where the user may overload arithmetic operators are Complex Number, Fractional Number, Big Integer, and more.
Static is a keyword in C++ programming used to give unique characteristics to an element. The static elements are allocated storage only once in an entire program lifetime in the static storage area. Also, they have a scope for the span of the program lifetime. Static member functions do not have this pointer, and they cannot be of a virtual type.  Member method declarations with the same name and the name parameter-type-list cannot be overloaded if any of them is a static member function declaration. Furthermore, a static member function cannot be declared as const, volatile, or const volatile.

Polymorphism is a kind of runtime generalization that is enabled by the type system in object-oriented as well as functional programming languages like C++ and Haskell. Typically, we talk about two types of polymorphism in programming languages:

  • Subtype polymorphism – which allows a function that is defined over a formal parameter having one type also to be defined over subtypes of same.
  • Parametric polymorphism – which allows a template, already defined class over a template parameter having one type also to be defined over subtypes of same.

There are a considerable amount of difference between c and c++ :

Objective CC++
The classes in Objective C allow a method or function and a variable with the exact same name.In case of C++, they must be different.
Objective C does not support a constructor or destructor. Instead, it has init and dealloc methods, which must be called explicitly when needed.C++ supports constructors and destructors.
Objective C uses the signs + and – to differentiate between class methods (which are also known as factory methods in Java) and instance methods.On the other hand, C++ uses static to specify a factory method.
Multiple inheritances is not allowed in Objective C, however, a user can use a protocol to some extent.Multiple inheritances are allowed in C++.
Objective C does not directly allow for method overloading and has a workaround, but that is not the case for operator overloading.C++ directly allows for method overloading.
Objective C does not allow stack-based objects either. Each object must be a pointer to a block of memory for it to exist.C++ can use stack based objects which is automatically allocated, instantiated and deallocated on the stack.
In Objective C the message overloading is somehow faked by naming the parameters. The user is required to mangle the names manually.C++ actually does the same but the compiler does the name mangling for the user instead of having to do it himself.
Objective C doesn’t allow automatic type coercion.C++ allows automatic type coercion.
Objective C has references. But as pointers can be used wherever a reference is employed, there isn’t any specific need for references in general.C++ has references as the language requires.
Objective C doesn’t have templates.The users of C++ need templates because the programming language has a strong typing and static binding that prevents generic classes, such as Lists and Arrays.
An accessor method is a method that fetches private data that is stored within an object. An accessor provides the means by which to obtain the state of an object from other program parts. This is a preferred method in object-oriented paradigms as it provides an abstraction layer that hides the implementation details of functionality sets. An accessor doesn’t need arguments and it has the same type as the retrieved variable. The name of the accessor begins with the Get prefix and a naming convention is necessary while defining accessor methods.
Though a new dependent code is contained within accessor methods, yet they directly access state data. Furthermore, within a database fetch, the dependent code need not be changed. This is also an advantage of this type of object-oriented programming.

When comparing two data items, two access method calls are necessary in order to make the comparison. Accessors seek underlying data such as data creation, data retrieval, initialization, as well as modification. The accessor method is basically a type of instance method that contains a sequence of programming statements for the purpose of performing an action, customizing those actions with a parameter and producing a return value of some sort. An accessor function or method must be called to access a private object member.

If a user inherits a class into a derived class and provides a definition for one of the base class’s function again inside the derived class, then this function is called an overridden function, and this mechanism is known as function overriding. When the member function exists in both classes (base and derived) is called in the case of overridden functions, the member function of the derived class is invoked, and the function of the base class is ignored.

Object-oriented programming (OOP) is a type of computer programming, also more commonly known as software design, in which the programmers define the data type of a data structure and the types of operations or functions which can be applied to the data structure.

The data structure becomes an object that includes both data and functions. Additionally, programmers can create relationships between one object and another. Object-oriented programming basically aims to implement real-world entities in programming. These include data abstraction, data encapsulation, inheritance, polymorphism and more.

The keyword volatile informs the compiler that a variable may change without the compiler knowing it. Variables that are declared as volatile will not be cached by the compiler, and will therefore always be read from memory.

The keyword mutable can be used for class member variables. Mutable variables are allowed to change from within constant member functions of the class.

Abstraction is the process of providing only essential information regarding the standard features of objects and procedures while hiding the details from the user.

The class is a category of objects, which defines all the common properties of the various objects that belong to it.

Encapsulation is the process of combining or wrapping up of data or elements to create a single, new entity.

Information hiding is the process of hiding details of an object or function for reducing complexity.

Inheritance is a feature that represents the “is-a” relationship between the various classes.

The interface is the set of languages and codes that the applications or programs use to communicate with each other as well as with the hardware.

Messaging or message passing is a kind of communication used in parallel programming and OOP.

The object is a self-contained entity, which consists of both data and procedures employed to manipulate the data.

Polymorphism is a programming language’s ability to process objects differently depending on their data type or class.

The procedure is merely a section of a program that performs a specific task.

C++ is also considered as (but never proven to be) the superset of C. Since it is like an extension of C language is a mid-level programming language, and it acquires the features of both, low level as well as high-level programming languages.