integral_constant Class, bool_constant Class

Article
08/03/2021

Makes an integral constant from a type and value.

Syntax

template<class T, T v>
struct integral_constant {
   static constexpr T value = v;
   typedef T value_type;
   typedef integral_constant<T, v> type;
   constexpr operator value_type() const noexcept;
   constexpr value_type operator()() const noexcept;
   };

Parameters

T
The type of the constant.

v
The value of the constant.

Remarks

The integral_constant class template, when specialized with an integral type T and a value v of that type, represents an object that holds a constant of that integral type with the specified value. The member named type is an alias for the generated template specialization type, and the value member holds the value v used to create the specialization.

The bool_constant class template is an explicit partial specialization of integral_constant that uses bool as the T argument.

Example

// std__type_traits__integral_constant.cpp
// compile with: /EHsc
#include <type_traits>
#include <iostream>

int main()
    {
    std::cout << "integral_constant<int, 5> == "
        << std::integral_constant<int, 5>::value << std::endl;
    std::cout << "integral_constant<bool, false> == " << std::boolalpha
        << std::integral_constant<bool, false>::value << std::endl;

    return (0);
    }

integral_constant<int, 5> == 5
integral_constant<bool, false> == false

Requirements

Header: <type_traits>

Namespace: std