std::is_integral

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

std::is_integral is an UnaryTypeTrait.

Checks whether T is an integral type. Provides the member constant value which is equal to true, if T is the type bool, char, char8_t (since C++20), char16_t, char32_t, wchar_t, short, int, long, long long, or any implementation-defined extended integer types, including any signed, unsigned, and cv-qualified variants. Otherwise, value is equal to false.

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

Template parameters

T - a type to check

Helper variable template

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

Inherited from std::integral_constant

Member constants

value
[static]
 true if T is an integral type, 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

// Note: this implementation uses C++20 facilities
template<class T>
struct is_integral : std::bool_constant<
    requires (T t, T* p, void (*f)(T)) // T* parameter excludes reference types
    {
        reinterpret_cast<T>(t); // Exclude class types
        f(0); // Exclude enumeration types
        p + t; // Exclude everything not yet excluded but integral types
    }> {};

Example

#include <iomanip>
#include <iostream>
#include <type_traits>
 
class A {};
 
struct B { int x:4{2}; };
using BF = decltype(B::x); // bit-field's type
 
enum E : int {};
 
template <class T>
T f(T i)
{
    static_assert(std::is_integral<T>::value, "Integral required.");
    return i;
}
 
#define SHOW(...) \
    std::cout << std::setw(29) << #__VA_ARGS__ << " == " << __VA_ARGS__ << '\n'
 
int main()
{
    std::cout << std::boolalpha;
 
    SHOW(std::is_integral<A>::value);
    SHOW(std::is_integral_v<E>);
    SHOW(std::is_integral_v<float>);
    SHOW(std::is_integral_v<int*>);
    SHOW(std::is_integral_v<int>);
    SHOW(std::is_integral_v<const int>);
    SHOW(std::is_integral_v<bool>);
    SHOW(std::is_integral_v<char>);
    SHOW(std::is_integral_v<BF>);
    SHOW(f(123));
}

Output:

   std::is_integral<A>::value == false
        std::is_integral_v<E> == false
    std::is_integral_v<float> == false
     std::is_integral_v<int*> == false
      std::is_integral_v<int> == true
std::is_integral_v<const int> == true
     std::is_integral_v<bool> == true
     std::is_integral_v<char> == true
       std::is_integral_v<BF> == true
                       f(123) == 123

See also

(C++20)
 specifies that a type is an integral type
(concept)
[static]
 identifies integer types
(public static member constant of std::numeric_limits<T>)
(C++11)
 checks if a type is a floating-point type
(class template)
(C++11)
 checks if a type is an arithmetic type
(class template)
(C++11)
 checks if a type is an enumeration type
(class template)