std::is_empty
From cppreference.com
| Defined in header <type_traits>
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| template< class T > struct is_empty; |
(since C++11) | |
If T is en empty type (that is, a non-union class type with no non-static members other than bit-fields of size 0, no virtual functions, no virtual base classes, and no non-empty base classes), provides the member constant value equal true. For any other type, value is false.
Contents |
Inherited from std::integral_constant
Member constants
| value [static] |
true if T is an empty class type , false otherwise (public static member constant) |
Member functions
| operator bool |
converts the object to bool, returns value (public member function) |
Member types
| Type | Definition |
| value_type | bool |
| type | std::integral_constant<bool, value> |
[edit] Notes
sizeof(T) always returns 1 if T is empty, but inheriting from empty base classes usually does not increase the size of a class due to empty base optimization.
std::is_empty<T> and all other type traits are empty classes.
[edit] Example
#include <iostream> #include <type_traits> struct A {}; struct B { int m; }; struct C { virtual ~C(); }; int main() { std::cout << std::boolalpha; std::cout << std::is_empty<A>::value << '\n'; std::cout << std::is_empty<B>::value << '\n'; std::cout << std::is_empty<C>::value << '\n'; }
Output:
true false false
[edit] See also
| (C++11) |
checks if a type is a class type (but not union type) (class template) |
