Destructors in C++

What is destructor? 
Destructor is a member function which destructs or deletes an object.

Syntax:

~constructor-name();

Properties of Destructor:

  • Destructor function is automatically invoked when the objects are destroyed.
  • It cannot be declared static or const.
  • The destructor does not have arguments.
  • It has no return type not even void.
  • An object of a class with a Destructor cannot become a member of the union.
  • A destructor should be declared in the public section of the class.
  • The programmer cannot access the address of destructor.

When is destructor called? 
A destructor function is called automatically when the object goes out of scope: 
(1) the function ends 
(2) the program ends 
(3) a block containing local variables ends 
(4) a delete operator is called  

How destructors are different from a normal member function? 
Destructors have same name as the class preceded by a tilde (~) 
Destructors don’t take any argument and don’t return anything



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class String {
private:
    char* s;
    int size;
 
public:
    String(char*); // constructor
    ~String(); // destructor
};
 
String::String(char* c)
{
    size = strlen(c);
    s = new char[size + 1];
    strcpy(s, c);
}
String::~String() { delete[] s; }

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Can there be more than one destructor in a class? 
No, there can only one destructor in a class with classname preceded by ~, no parameters and no return type.

When do we need to write a user-defined destructor? 
If we do not write our own destructor in class, compiler creates a default destructor for us. The default destructor works fine unless we have dynamically allocated memory or pointer in class. When a class contains a pointer to memory allocated in class, we should write a destructor to release memory before the class instance is destroyed. This must be done to avoid memory leak.

Can a destructor be virtual? 
Yes, In fact, it is always a good idea to make destructors virtual in base class when we have a virtual function. See virtual destructor for more details. 
You may like to take a quiz on destructors.

Related Articles : 
Constructors in C++ 
Virtual Destructor 
Pure virtual destructor in C++
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