integral_constant Class, bool_constant Class
The latest version of this topic can be found at integral_constant Class, bool_constant Class.
Makes an integral constant from a type and value.
Syntax
struct integral_constant {
static constexpr T value = v;
typedef T value_type;
typedef integral_constant<T, v>
type;
constexpr operator value_type() const noexcept { return (value); }
constexpr value_type operator()() const noexcept { return (value); }
};
Parameters
T
The type of the constant.
v
The value of the constant.
Remarks
The integral_constant template class, 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 template class 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