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std::has_virtual_destructor

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

std::has_virtual_destructor is a 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.

If the program adds specializations for std::has_virtual_destructor or std::has_virtual_destructor_v, the behavior is undefined.

Contents

[edit] Template parameters

T - a type to check

[edit] 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>

[edit] 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.

[edit] 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;
}

[edit] 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

[edit] See also

checks if a type has a non-deleted destructor
(class template) [edit]
checks if a type is a polymorphic class type
(class template) [edit]