std:: is_integral

std::is_integral is a 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 .

If the program adds specializations for std::is_integral or std::is_integral_v , the behavior is undefined.

Template parameters

Helper variable template

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 <type_traits>
 
static_assert
(
    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
);
 
class A {};
static_assert(std::is_integral_v<A> == false);
 
struct B { int x:4; };
static_assert(std::is_integral_v<B> == false);
using BF = decltype(B::x); // bit-field's type
static_assert(std::is_integral_v<BF> == true);
 
enum E : int {};
static_assert(std::is_integral_v<E> == false);
 
template <class T>
constexpr T same(T i)
{
    static_assert(std::is_integral<T>::value, "Integral required.");
    return i;
}
static_assert(same('"') == 042);
 
int main() {}

See also