C++ Tutorial Index

C++ Tutorial C++ History C++ Installation C++ First Program C++ cin and cout C++ Data type C++ Variable C++ operator C++ Keywords

C++ Control Statements

C++ If C++ Nested if C++ If-else C++ If-else-if C++ Switch C++ Break C++ Continue C++ Goto C++ For loop C++ While loop C++ Do while loop

C++ Functions

C++ Call by Value C++ Call by Reference C++ Recursion Function C++ Inline function C++ Friend function

C++ Arrays

Single dimension array Two dimension array

C++ Strings

C++ Strings

C++ Inheritance

C++ Inheritance Single level Inheritance Multilevel Inheritance Multiple Inheritance Hierarchical Inheritance Hybrid Inheritance

C++ Polymorphism

C++ Polymorphism C++ Overloading C++ Overriding C++ Virtual Function

C++ Pointers

C++ Pointers C++ this pointer

C++ Exception Handling

C++ Exception Handling

C++ Constructors

C++ Constructors Default Constructor Parameterize Constructor Copy constructor Constructor Overloading Destructor

C++ File Handling

C++ File Handling C++ Writing to file C++ Reading file C++ Close file

Miscellaneous

C Vs C++ C++ Comments C++ Data Abstraction C++ Identifier C++ Memory Management C++ Storage Classes C++ Void Pointer C++ Array To Function C++ Expressions C++ Features C++ Interfaces C++ Encapsulation std::min in C++ External merge sort in C++ Remove duplicates from sorted array in C++ Precision of floating point numbers Using these functions floor(), ceil(), trunc(), round() and setprecision() in C++ C++ References C++ Friend Functions C++ Mutable keyword Unary Operators in C++ Initialize Array of objects with parameterized constructors in C++ Differences between #define & const in C/C++ C++ Program to Implement Shell Sort C++ Program to Implement Merge Sort Storage Classes in C Vector resize() in C++ Passing by Reference Vs. Passing by the pointer in C++ Free vs delete() in C++ goto statement in C and C++ C++ program to read string using cin.getline() C++ String Concatenation Heap Sort in C++ Swap numbers in C++ Input Iterators in C++ Fibonacci Series in C++ C ++ Program: Alphabet Triangle and Number Triangle C++ Program: Matrix Multiplication C++ Program to Print Fibonacci Triangle Stack in C++ Maps in C++ Queue in C++ C++ Bitset C++ Algorithms Priority Queue in C++ C++ Multimap C++ Deque Function Pointer in C++ Sizeof() Operators in C++ C++ array of Pointers free() Vs delete in C Timsort Implementation Using C++ CPP Templates C++ Aggregation C++ Enumeration C++ Math Functions C++ Object Class C++ Queue Initialize Vector in C++ Vector in C++ C++ STL Components Function overloading in C++ C++ Maximum Index Problem C++ find missing in the second array C++ Program to find the product array puzzle C++ Program To Find Largest Subarray With 0 Sum C++ Program To Move All Zeros To The End Of The Array C++ Program to find the element that occurs once C++ Program to find the largest number formed from an array Constructor Vs Destructor C++ Namespaces C++ OOPs Concept C++ Static C++ Structs C++ Try-Catch C++ User Defined Exceptions C++ Virtual Destructor C++ vs C# Malloc() and new in C++ Palindrome Number Program in C++ Snake Code in C++ Splitting a string in C++ Structure Vs Class in C++ Virtual Function Vs Pure Virtual Function C++ Bidirectional Iterators C++ Forward Iterators C++ Iterators C++ Output Iterators C++ Range-based For Loop Converting string into integer in C++ LCM Program in C++ Type conversion in C++ Add two numbers using the function in C++ Advantage and disadvantage friend function C++ Armstrong Number Program in C++ ATM machine program in C++ using functions Binary to Decimal in C++ Bit Manipulation in C++ C++ Constructor C++ Dijkstra Algorithm Using the Priority Queue C++ int into String C++ Signal Handling Decimal to Binary in C++ Decimal to Hexadecimal in C++ Decimal to Octal in C++ Factorial Program in C++ Function in C++ Hexadecimal to Decimal in C++ Octal to Decimal in C++ Reverse a Number in C++ Structure Vs Class in C++ C++ Forward Iterators C++ Output Iterators C++ Prime number program Constructor Overloading in C++ Different Ways to Compare Strings in C++ Program to convert infix to postfix expression in C++ SET Data Structure in C++ Upcasting and Downcasting in C++ Reverse an Array in C++ Fast Input and Output in C++ Delete Operator in C++ Copy elision in C++ C++ Date and Time C++ Bitwise XOR Operator Array of sets in C++ Binary Operator Overloading in C++ Binary Search in C++ Implementing the sets without C++ STL containers Scope Resolution Operator in C++ Smart pointers in C++ Types of polymorphism in C++

Destructor

Let’s discover the C++ destructor, virtual and pure virtual destructors, and when destructors are invoked and their rules in this lesson.

Destructors :

A member function that destroys an object is known as a destructor. Destructors acts in the reverse direction as of constructors but are specified similarly to constructors; they destroy class objects. It can be defined only one time in a class, that too with the same name as that of the class. It is called by itself, much like constructors. It however, uses a tilde symbol (~) as a prefix.

Syntax :

~className{


    // Content code
};

Destructors in C++ cannot have arguments and modifiers can't be used on destructors too.

Features of a Destructor :

The major characteristics of a destructor are as follows :

  • The destructor function is called itself on the destruction of the object.
  • It's not feasible to define a destructor as static or const.
  • No parameters are present for the destructor.
  • It does not have a void return type.
  • A member of the association can’t be an element of a class that contains a Destructor.
  • The declaration of a destructor is always required to take place in the public section of that class.
  • The location of destructor is unreachable by the programmer.

When is the destructor invoked?

When an object is no longer in scope, a destructor function is executed automatically:

  1. When a function is completed.
  2. At the conclusion of the program.
  3. When a scope containing local variables ({}-parenthesis) expires.
  4. When you use the delete operator.

What makes destructors distinct from regular member functions?

In the following respects, a destructor differs from regular functions:

  • The name of the destructor is the same as the class, but it is prefixed by a tilde (~).
  • Destructors are known for not taking in any kind of arguments and they also do not return anything itself.

Rules to define a Destructor :

  1. The name must start with a tilde symbol (~) and match the class name.
  2. A class cannot have more than one destructor.
  3. Unlike constructors, destructors do not accept any parameters.
  4. They, like constructors, do not have a return type.
  5. If you don't specify a destructor inside a class, the compiler creates one for you and places it in your code.

Example :

#include <iostream>
using namespace std;
class XYZ
{
    public:
        XYZ () //defining the constructor
       {
 	    cout << "This is inside constructor" << endl;
       }
       ~XYZ() //destructor defining the destructor
       {
             cout << "This is inside destructor" << endl;
       }
};
int main()
{
     XYZ obj1; //calling the constructor
     cout << "main function terminated." << endl;
     return 0;
}

Output:

This is inside constructor
main function terminated.
This is inside destructor

Explanation :

Firstly, class XYZ was created which further helped to define XYZ() constructor and ~XYZ() destructor. When the constructor is invoked, "This is inside constructor" is written, followed by "main function terminated.”, but the object obj1 that was defined previously goes out of scope, and the ~XYZ() destructor is called to de-allocate the memory occupied by obj1.

Example-2 :

#include<iostream>
using namespace std;
 
class exmpl
{
    public:
        int x=50;
         
        exmpl() //constructor is created
        {
            cout<<"It is the Constructor of exmpl !"<<endl;
        }
         
        ~exmpl() //destructor is defined
        {
            cout<<"It is the Destructor of exmpl !"<<endl;
        }
         
        void print_exmpl() // void function
        {
            cout<<"exmpl is printed"<<endl;
        }
};
 
int main()
{
    exmpl exmpl_obj; // created the example object for the class exmpl
    cout<<exmpl_obj.x<<endl;
    exmpl_obj.print_exmpl(); //calling the function
    return 0;
}

Output :

It is the Constructor of exmpl !
50
exmpl is printed
It is the Destructor of exmpl !

Explanation :

We've set up a variable called a=50 and a method called print_exmpl() inside the exmpl class. We've also defined the exmpl() and ~exmpl() constructors and destructors, respectively .

We constructed an object exmpl_obj that corresponds to the exmpl class above within the main() method. As a result, the constructor exmpl() is requested.

Then we did certain activities on it, such as executing the object's print_exmpl() function.

The destructor for the object exmpl_obj is called instantly after the main() function ends. As may be seen from the output above.

C++ Virtual Destructors

Destructing an object of derived class with non-virtual destructor using a reference of base class can cause unclear behavior. A virtual destructor should be provided in the base class to provide a solution to this problem of unclear behavior.

Virtual destructors are allowed in the Base class. These base class Destructors must be made virtual if upcasting is used to ensure that the object is properly destroyed when the application finishes.

Example :

#include<iostream>
using namespace std;
 
class BaseClass 
{
    public:
         
        BaseClass()
        {
            cout<<"Base Constructor!"<<endl;
        }
       virtual ~BaseClass()
        {
            cout<<"Base Destructor!"<<endl;
        }
};
 
class DerivedClass : public BaseClass 
{
    public:
        DerivedClass()
        {
            cout<<"Derived Constructor!"<<endl;
        }
        ~DerivedClass()
        {
            cout<<"Derived Destructor!"<<endl;
        }
};
int main()
{
    BaseClass * obj = new DerivedClass;
    delete obj;
}

Output :

Base Constructor!
Derived Constructor!
Derived Destructor!
Base Destructor!

Explanation :

The virtual keyword is being used in this example before the basic destructor this time.

The result shows that the instruction BaseClass *obj = new DerivedClass , inside the main() method calls the constructors BaseClass() and DerivedClass(), respectively.

Since a virtual destructor is present in this base class while the object obj is being deleted, first the destructor of Derived class is called and then the Base class's destructor.

C++ Pure Virtual Destructors :

When the value of a destructor is set to zero, the virtual destructor is defined in the base class. Pure virtual destructor is also feasible, as is virtual destructor. However, the base class should define this Virtual destructor inside itself.

  • The one and only major difference between a Virtual and a Pure Virtual Destructor is that a Pure Virtual Destructor makes its Base class Abstract, thus the programmer can't construct any object of that class.
  • Pure virtual destructors are not a requirement in the in derived classes.

Example :

#include <iostream>
using namespace std;


// declare a class
class BaseClass {
   public:
    virtual ~BaseClass() = 0; // it is the Pure Virtual Destructor
};
// Defining the Pure Virtual Destructor
BaseClass :: ~BaseClass() {


    cout << "The Pure virtual destructor is being called.\n";
}
class DerivedClass : public BaseClass {
    public:
    ~DerivedClass() {
        cout << "The Derived Destructor is being called." << endl;
    }
}
int main() {


    BaseClass* obj = new DerivedClass;
    delete obj;


    return 0;
}

Output :

The Pure virtual destructor is being called.
The Derived Destructor is being called.

Explanation :

The result shows that the instruction BaseClass *obj = new DerivedClass , inside the main() method calls the constructors BaseClass() and DerivedClass(), respectively.

Because a pure virtual destructor is present inside the base class when removing object obj, the Derived class's pure virtual destructor is called first, followed by the Base class's derived destructor. Since it is a pure virtual destructor, thus it is not required in the derived class.



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