# std::has_virtual_destructor

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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

T | - | 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

Run this code

    #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

### See also

is_destructible is_trivially_destructible is_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)

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