When do I need to declare my own destructor?

Question

class Point    
{
public:
    float x,y;
    Point() {}
    Point(float,float);
    Point operator + (Point);
    Point operator * (double);
    void rotate_p(float)         


        

Answer 1

Introduction

Since data-members with automatic-storage duration have their lifetime bound to that of the instance having them, there's no need for you to call their destructor explicitly; they will always be destroyed whenever the instance of the class is.

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When do I normally need to declare my own destructor?

Normally you will have to explicitly declare your own destructor if:

• You are declaring a class which is supposed to serve as a base for inheritance involving polymorphism, if you do you'll need a virtual destructor to make sure that the destructor of a Derived class is called upon destroying it through a pointer/reference to Base.

• You need to release resourced aquired by the class during its leftime

  • Example 1: The class has a handle to a file, this needs to be closed when the object destructs; the destructor is the perfect location.

  • Exempel 2: The class owns an object with dynamic-storage duration, since the lifetime of the object can potentially live on long after the class instance has been destroyed you'll need to explicitly destroy it in the destructor.

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The implicitly generated destructor

Unless you explicitly declare your own destructor, an implicitly generated destructor will be created for you by the compiler.

14.4p4 Destructors [class.dtor]

If a class has no user-declared destructor, a destructor is implicitly declares as defaulted (8.4). An implicitly declared destructor is an inline public member of its class.

^{src: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3337.pdf}

There are however some rare/advanced cases where the compiler will refuse to generate a destructor for you, under these cases you must explicitly declare your own, or make sure that the destructor for your class instance is never called; because in order to destroy an object, a destructor is neccessary.

14.4p5 Destructors [class.dtor]

A default destructor for a class X is defined as delete if:

• X is a union-like class that has a variant member with a non-trivial destructor,

• any of the non-static data members has class type M (or array thereof) and M has a deleted destructor or a destructor that is inaccessible from the default destructor,

• any direct or virtual base class has a deleted destructor or a destructor that is inaccessible from the default destructor,

• or, for a virtual destructor, lookup of the non-array deallocation function results in an ambiguity or in a function that is deleted or inaccessible from the default destructor.

^{src: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3337.pdf}

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More can be read under the following link:

• cppreference.com - Destructors