std::has_virtual_destructor

< cpp‎ | types

Defined in header `<type_traits>`
template< class T > struct has_virtual_destructor;		(since C++11)

std::has_virtual_destructor is an UnaryTypeTrait.

If T is a type with a virtual destructor, the base characteristic is std::true_type. For any other type, the base characteristic is std::false_type.

If T is an incomplete non-union class type, the behavior is undefined.

The behavior of a program that adds specializations for std::has_virtual_destructor or std::has_virtual_destructor_v (since C++17) is undefined.

Template parameters

a type to check

Helper variable template

template< class T > inline constexpr bool has_virtual_destructor_v = has_virtual_destructor<T>::value;		(since C++17)

Inherited from std::integral_constant

Member constants

value

[static]

true if T has a virtual destructor, false otherwise
(public static member constant)

Member functions

operator bool	converts the object to bool, returns value (public member function)
operator() (C++14)	returns value (public member function)

Member types

Type	Definition
`value_type`	bool
`type`	std::integral_constant<bool, value>

Notes

If a class C has a public virtual destructor, it can be derived from, and the derived object can be safely deleted through a pointer to the base object (GotW #18). In this case, std::is_polymorphic<C>::value is true.

Example

#include <type_traits>
 
struct S {};
static_assert(!std::has_virtual_destructor_v<S>);
 
struct B { virtual ~B() {} };
static_assert(std::has_virtual_destructor_v<B>);
 
struct D : B { ~D() {} };
static_assert(std::has_virtual_destructor_v<D>);
 
int main()
{
    B* pd = new D;
    delete pd;
}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 2015	C++11	the behavior was undefined if `T` is an incomplete union type	the base characteristic is std::false_type in this case

is_destructibleis_trivially_destructibleis_nothrow_destructible (C++11)(C++11)(C++11)	checks if a type has a non-deleted destructor (class template)
is_polymorphic (C++11)	checks if a type is a polymorphic class type (class template)