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std::integral_constant

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< cpp‎ | types

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C++
 
Bibliothèque d'utilitaires
 
Soutien aux types fondamentaux
Les types de base
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Basic types
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Types fondamentaux
Fixe les types entiers largeur (C++11)
Limites numériques
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Numeric limits
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numeric_limits
C numérique limite interface
Informations sur le type d'exécution
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Runtime type information
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Caractères de type
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Type traits
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Catégories de type primaire
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Primary type categories
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is_void (C++11)
is_array (C++11)
is_pointer (C++11)
is_enum (C++11)
is_union (C++11)
is_class (C++11)
is_function (C++11)
is_object (C++11)
is_scalar (C++11)
is_compound (C++11)
is_integral (C++11)
is_floating_point (C++11)
is_fundamental (C++11)
is_arithmetic (C++11)
is_reference (C++11)
is_lvalue_reference (C++11)
is_rvalue_reference (C++11)
is_member_pointer (C++11)
is_member_object_pointer (C++11)
is_member_function_pointer (C++11)
Les propriétés du type
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Type properties
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is_const (C++11)
is_volatile (C++11)
is_pod (C++11)
is_empty (C++11)
is_polymorphic (C++11)
is_abstract (C++11)
Opérations prises en charge
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Supported operations
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is_constructible
is_trivially_constructible
is_nothrow_constructible		 (C++11)
(C++11)
(C++11)
is_default_constructible
is_trivially_default_constructible
is_nothrow_default_constructible		 (C++11)
(C++11)
(C++11)
is_copy_constructible
is_trivially_copy_constructible
is_nothrow_copy_constructible		 (C++11)
(C++11)
(C++11)
is_move_constructible
is_trivially_move_constructible
is_nothrow_move_constructible		 (C++11)
(C++11)
(C++11)
is_assignable
is_trivially_assignable
is_nothrow_assignable		 (C++11)
(C++11)
(C++11)
is_copy_assignable
is_trivially_copy_assignable
is_nothrow_copy_assignable		 (C++11)
(C++11)
(C++11)
is_move_assignable
is_trivially_move_assignable
is_nothrow_move_assignable		 (C++11)
(C++11)
(C++11)
is_destructible
is_trivially_destructible
is_nothrow_destructible		 (C++11)
(C++11)
(C++11)
has_virtual_destructor (C++11)
Les relations et les requêtes de propriété
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Relationships and property queries
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is_same (C++11)
is_base_of (C++11)
is_convertible (C++11)
alignment_of (C++11)
rank (C++11)
extent (C++11)
Modifications de type
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Type modifications
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remove_cv
remove_const
remove_volatile		 (C++11)
(C++11)
(C++11)
add_cv
add_const
add_volatile		 (C++11)
(C++11)
(C++11)
make_signed (C++11)
make_unsigned (C++11)
Transformations de type
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Type transformations
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aligned_storage (C++11)
aligned_union (C++11)
decay (C++11)
enable_if (C++11)
conditional (C++11)
common_type (C++11)
underlying_type (C++11)
result_of (C++11)
Tapez constantes traits
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Type trait constants
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integral_constant (C++11)
 
Déclaré dans l'en-tête <type_traits>
template< class T, T v >
struct integral_constant;
 (depuis C++11)
std::integral_constant encapsule une constante statique du type spécifié. Il s'agit de la classe de base pour les caractères de C + + .
Original:
std::integral_constant wraps a static constant of specified type. It is the base class for the C++ type traits.
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Deux spécialisations pour la bool type sont fournis:
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Two specializations for the type bool are provided:
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Defined in header <type_traits>
Type d'
Original:
Type
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 Definition
true_type std::integral_constant<bool, true>
false_type std::integral_constant<bool, false>

Sommaire

[modifier] Types de membres

Type d'
Original:
Type
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 Definition
value_type T
type std::integral_constant<T,v>

[modifier] Constantes membres

Nom
Original:
Name
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 Value
value
statique expression constante de type avec T v valeur
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static constant expression of type T with value v
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[modifier] Fonctions membres

operator value_type
convertit l'objet en value_type, retourne value
Original:
converts the object to value_type, returns value
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(fonction membre publique)

[modifier] Mise en œuvre possible

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; }
};

[modifier] Exemple

#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");
}


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