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)
Type transformations
(C++11)(deprecated in C++23)
(C++11)(deprecated in C++23)
(C++11)
(C++11)
(C++17)

(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 an 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.

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

Template parameters

T - a type to check

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>

Possible implementation

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

Example

#include <iostream>
#include <type_traits>
 
int main() 
{
    std::cout << std::boolalpha;
    std::cout << std::is_void<void>::value << '\n';
    std::cout << std::is_void<int>::value << '\n';
}

Output:

true
false

See also

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