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POShould every class have a virtual destructor?
 

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    <p>Java and C# support the notion of classes that can't be used as base classes with the <code>final</code> and <code>sealed</code> keywords. In C++ however there is no good way to prevent a class from being derived from which leaves the class's author with a dilemma, should every class have a virtual destructor or not?</p> <hr> <p><strong>Edit:</strong> Since C++11 this is no longer true, you can specify that a class is <a href="http://en.cppreference.com/w/cpp/language/final" rel="noreferrer"><code>final</code></a>.</p> <hr> <p>On the one hand giving an object a virtual destructor means it will have a <code>vtable</code> and therefore consume 4 (or 8 on 64 bit machines) additional bytes per-object for the <code>vptr</code>.</p> <p>On the other hand if someone later derives from this class and deletes a derived class via a pointer to the base class the program will be ill-defined (due to the absence of a virtual destructor), and frankly optimizing for a pointer per object is ridiculous. </p> <p>On the <a href="http://en.wikipedia.org/wiki/Gripping_hand" rel="noreferrer">gripping hand </a> having a virtual destructor (arguably) advertises that this type is meant to be used polymorphically.</p> <p>Some people think you need an explicit reason to not use a virtual destructor (as is the subtext of <a href="https://stackoverflow.com/questions/300986">this question</a>) and others say that you should use them only when you have reason to believe that your class is to be derived from, what do <em>you</em> think?</p>
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    1. COThere are already questions asking for the pros an cons - is this a duplicate, or is it intended as an opinion poll? If the latter, maybe you should create "yes" and "no" answers for voting, then close the question? I think that's the recommended way of implementing a multiple-choice poll on SO.
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    2. CODuplicates: http://stackoverflow.com/questions/270917/why-should-i-declare-a-virtual-destructor-for-an-abstract-class-in-c, http://stackoverflow.com/questions/300986/when-should-you-not-use-virtual-destructors
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    3. CO"and frankly optimizing for a pointer per object is ridiculous. " - Its not ridiculous for small objects. C++0x is adding a container forward_list, precisely because sometimes one pointer per object overhead is too much - from the space and time requirements.
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      1. USGreg Rogers
 

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