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std::is_void

From cppreference.com
< cpp‎ | types
 
 
Metaprogramming library
Type traits
Type categories
is_void
(C++11)
(C++14)  
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
Type properties
(C++11)
(C++11)
(C++14)
(C++11)
(C++11)(until C++20*)
(C++11)(deprecated in C++20)
(C++11)
Type trait constants
Metafunctions
(C++17)
Supported operations
Relationships and property queries
Type modifications
(C++11)(C++11)(C++11)
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(C++11)(deprecated in C++23)
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(C++11)(until C++20*)(C++17)
Compile-time rational arithmetic
Compile-time integer sequences
 
Defined in header <type_traits>
template< class T >
struct is_void;
(since C++11)

std::is_void is a UnaryTypeTrait.

Checks whether T is a void type. Provides the member constant value that is equal to true, if T is the type void, const void, volatile void, or const volatile void. Otherwise, value is equal to false.

If the program adds specializations for std::is_void or std::is_void_v, the behavior is undefined.

Contents

[edit] Template parameters

T - a type to check

[edit] Helper variable template

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

Inherited from std::integral_constant

Member constants

value
[static]
true if T is the type void (possibly cv-qualified), 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] Possible implementation

template<class T>
struct is_void : std::is_same<void, typename std::remove_cv<T>::type> {};

[edit] Example

#include <type_traits>
 
void foo();
 
static_assert
(
    std::is_void_v<void> == true and
    std::is_void_v<const void> == true and
    std::is_void_v<volatile void> == true and
    std::is_void_v<void*> == false and
    std::is_void_v<int> == false and
    std::is_void_v<decltype(foo)> == false and
    std::is_void_v<std::is_void<void>> == false
);
 
int main() {}

[edit] See also

(C++11)
checks if a type is an array type
(class template) [edit]
checks if a type is a pointer type
(class template) [edit]
(C++11)
checks if a type is an enumeration type
(class template) [edit]
(C++11)
checks if a type is a union type
(class template) [edit]
(C++11)
checks if a type is a non-union class type
(class template) [edit]
checks if a type is a function type
(class template) [edit]
(C++11)
checks if a type is an object type
(class template) [edit]