The 10 most important C++ interview questions and answers for 2023

Class: A class is a user-defined data type with data members and member functions specified by the user. The data members are the variables that make up the data, and the member functions are the functions used to manipulate them.

Object: A class instance is defined as an object. Because a class is a user-defined data type, it's possible to refer to an object as a variable of that data type. Fields, methods, and constructors may all be found in an object.

• C++ allows the use of references; however, C does not.
• C++ has available features, such as friend functions, function overloading, inheritance, templates, and virtual functions. On the other hand, C does not have any such features available.
• The classic if-else technique of exception handling is used in C. C++, on the other hand, provides exception handling functionality at the language level.
• In C, scanf() and printf() are the most often used input and output functions. The standard input stream in C++ is cin, while the standard output stream is cout.
• C++ supports both procedural and object-oriented programming techniques, whereas C is a procedural programming language.

The equal to operator == compares two values to see if they are equal. If they're equal, it's true; otherwise, it's untrue.

The assignment operator = assigns the right operand's value to the left operand.

Through C++ interview questions like this, the interviewer is trying to gauge your detail orientation.

In simple terms, polymorphism means to have many forms. Polymorphism refers to the existence of many functions with the same name but differing functionality. Polymorphism occurs due to having multiple classes related to each other because of inheritance. Therefore, it behaves differently in different situations. In C++, there are two types of polymorphism:

Compile-time polymorphism

Compile-time polymorphism is achieved through function and operator overloading. Due to it being identified at compile-time, it has a faster execution time. In this type of polymorphism, which method will be called is known at the compile time. Additionally, the call is also resolved by the compiler.

Runtime polymorphism

Runtime polymorphism is achieved through virtual functions and pointers. Compared to compile-time polymorphism, runtime polymorphism provides a much slower execution time due to it being identified during runtime. In runtime polymorphism, the method will be called during the runtime; therefore, the compiler cannot resolve the call.

You provide copies of actual arguments to the function's formal parameters when using the call by value approach. This implies that any changes to the values within the function will have no effect on the real values.

The reference or address of actual parameters is provided to the function's formal parameters via the call-by-reference approach. This means that any change in the function's values will be reflected in the real values.

The current object's memory location is held by the 'this' pointer, which is a constant pointer. All nonstatic member function calls get it as a hidden argument. It may also be found as a local variable in the body of all nonstatic functions.

The 'this' pointer is not available for static member functions since they can be called without any object, i.e., with the class name.

vTable is a table that contains the function pointers. Additionally, vptr is a singular pointer to a vTable. Every class has a vTable; therefore, every object contains a vptr. The C++ compiler, to maintain and use vptr and vTable, adds some additional code to two places:

• Constructor

vptr is set up by this code in every constructor: Of the object that is being made to point to the class's vTable

• Polymorphic Function Call

The compiler adds code to look for vptr using the base class pointer or reference at every site where a polymorphic call is performed. Once the vptr has been properly obtained, the vTable of a derived class may be accessed. The vTable is used to obtain and call the address of the derived class method display().

This C++ interview question can show the interviewer the depth of your knowledge in the language.

In C++, a copy function Object() { [native code] } is a member function that uses another object of the same class to instantiate an object. It's also possible to make Copy Constructor private. When one of the following four circumstances occurs, a call to the Copy Constructor is made:

• A temporary object generated by the compiler
• If an object is created based on a different object of the same class
• If the object of a class is returned by value
• If the object of a class is passed by value as an argument

A virtual function is a base class member function that you redefine in a derived class. To declare a virtual function, a virtual keyword is used. When a function is made virtual, C++ uses the type of object referenced by the base class pointer to determine which function should be executed at runtime.

A virtual function can be called from a constructor; however, there is a small difference in its behavior in such a case. The virtual call is resolved at runtime, and always the member function of the present class is called.

The above is an important C++ interview question. There are two pieces to the derived class: a base part and a derived part. When C++ creates derived objects, it works in stages. The most-base class (at the very top of the inheritance tree) gets created first. Then, in sequence, each child class is built until the most-child class is built last. As a result, the constructor of class B will be invoked first, followed by the constructor of class D.

During the demolition, everything is done in the exact opposite sequence. Destructors begin at the most derived class and work their way down to the base class.

As a result, the destructor of class D will be invoked first, followed by the destructor of class B.