std::integral_constant – cppreference.com

Aus cppreference.com

definiert in Header `<type_traits>`

`template< class T, T v > struct integral_constant;`		(seit C++11)

std::integral_constant wickelt eine statische Konstante des angegebenen Typs. Es ist die Basisklasse für die C + + Exterieur .

Original:

std::integral_constant wraps a static constant of specified type. It is the base class for the C++ type traits.

The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.

Zwei Spezialisierungen für die Art bool sind vorgesehen:

Original:

Two specializations for the type bool are provided:

The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.

definiert in Header `<type_traits>`

Type Original: Type The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.	Definition

`true_type`	`std::integral_constant<bool, true>`

`false_type`	`std::integral_constant<bool, false>`

Mitglied Typen


Type Original: Type The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.	Definition

`value_type`	`T`

`type`	`std::integral_constant<T,v>`

Mitglied Konstanten


Name Original: Name The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.	Value

`value`	statische Konstante Ausdruck des Typs `T` mit dem Wert `v` Original: static constant expression of type `T` with value `v` The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

Member-Funktionen


	wandelt das Objekt `value_type`, gibt `value` Original: converts the object to `value_type`, returns `value` The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (öffentliche Elementfunktion)

Mögliche Implementierung

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

Beispiel

#include <iostream>
#include <type_traits>

int main() 
{
    typedef std::integral_constant<int, 2> two_t;
    typedef std::integral_constant<int, 4> four_t;

//  static_assert(std::is_same<two_t, four_t>::value,
//                "two_t and four_t are not equal!"); 
//  error: static assertion failed: "two_t and four_t are not a same types"

    static_assert(two_t::value*2 == four_t::value,
       "2*2 != 4"
    );

    enum class my_e {
       e1,
       e2
    };
    typedef std::integral_constant<my_e, my_e::e1> my_e_e1;
    typedef std::integral_constant<my_e, my_e::e2> my_e_e2;

//  static_assert(my_e_e1::value == my_e::e2,
//               "my_e_e1::value != my_e::e2");
//  error: static assertion failed: "my_e_e1::value != my_e::e2"

    static_assert(std::is_same<my_e_e2, my_e_e2>::value,
                  "my_e_e2 != my_e_e2");
}