Destructors

Destructors

A destructor is the mirror image of a constructor: it runs when an object is destroyed. Its job is cleaning up - freeing heap memory, closing a file, or releasing anything the object owned.

class Car {
public:
  Car() { cout << "created\n"; }   // constructor
  ~Car() { cout << "destroyed\n"; }  // destructor
};

Rules

• The name is the class name with a tilde (~) in front.
• It returns nothing - not even void.
• A class has exactly one destructor, and it takes no parameters.

When does it run?

The destructor fires when the object's lifetime ends:

void func() {
  Car myCar;        // exists here
}                   // destroyed as the scope ends

• A local (stack) object is destroyed when the scope ends.
• An object created with new is destroyed when you call delete.
• A global object dies when the program ends.

Cleaning up

If the constructor allocated memory with new, the destructor is the place to free it with delete - otherwise the memory leaks.

TL;DR

• A destructor looks like ~ClassName() with no return type.
• It runs automatically when the object is destroyed.
• Stack objects run it at scope end; heap objects run it at delete.
• Use it to release resources the object owns.