std::is_integral

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

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.

The behavior of a program that adds specializations for std::is_integral or std::is_integral_v is undefined.

Template parameters

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; };
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

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

Docs

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