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std::is_empty

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< cpp‎ | types

 
 
 
Soutien aux types fondamentaux
Les types de base
Original:
Basic types
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Types fondamentaux
Fixe les types entiers largeur (C++11)
Limites numériques
Original:
Numeric limits
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numeric_limits
C numérique limite interface
Informations sur le type d'exécution
Original:
Runtime type information
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Caractères de type
Original:
Type traits
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Catégories de type primaire
Original:
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
Original:
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
Original:
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
Original:
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
Original:
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
Original:
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
Original:
Type trait constants
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integral_constant (C++11)
 
Defined in header <type_traits>
template< class T >
struct is_empty;
(depuis C++11)
Si T est en type vide (c'est à dire un type de classe non pas l'union avec les membres non statiques autres que les champs de bits de taille 0, pas de fonctions virtuelles, pas de classes de base virtuelles, et aucune classe de base non vides), fournit le membre de constante value true égale. Pour tout autre type, value est false .
Original:
If T is en empty type (that is, a non-union class type with no non-static members other than bit-fields of size 0, no virtual functions, no virtual base classes, and no non-empty base classes), provides the member constant value equal true. For any other type, value is false.
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Sommaire

Inherited from std::integral_constant

Member constants

value
[
statique
Original:
static
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]
true si T is an empty class type , false autrement
Original:
true if T is an empty class type , false otherwise
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(constante membre statique publique)

Member functions

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

Member types

Type d'
Original:
Type
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Definition
value_type bool
type std::integral_constant<bool, value>

[modifier] Notes

sizeof(T) retourne toujours 1 si T est vide, mais héritant de classes de base vides n'est généralement pas augmenter la taille d'une classe grâce à l'optimisation de base vide .
Original:
sizeof(T) always returns 1 if T is empty, but inheriting from empty base classes usually does not increase the size of a class due to empty base optimization.
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std::is_empty<T> et tous les autres caractères de classes vides sont .
Original:
std::is_empty<T> and all other type traits are empty classes.
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[modifier] Exemple

#include <iostream>
#include <type_traits>
 
struct A {};
 
struct B {
    int m;
};
 
struct C {
    virtual ~C();
};
 
int main()
{
    std::cout << std::boolalpha;
    std::cout << std::is_empty<A>::value << '\n';
    std::cout << std::is_empty<B>::value << '\n';
    std::cout << std::is_empty<C>::value << '\n';
}

Résultat :

true
false
false

[modifier] Voir aussi

(C++11)
checks if a type is a class type (but not union type)
(classe générique) [edit]