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std::integral_constant

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C++
 
Utilities-Bibliothek
 
Geben Sie Unterstützung
Grundtypen
Original:
Basic types
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Grundtypen
Feste Breite Integer-Typen (C++11)
Numerische Grenzen
Original:
Numeric limits
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numeric_limits
C numerische begrenzt Schnittstelle
Laufzeit-Typinformationen
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Runtime type information
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Exterieur
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Type traits
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Primären Typ Kategorien
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)
Typ Eigenschaften
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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)
Unterstützte Operationen
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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)
Beziehungen und Eigentum Abfragen
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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)
Typ Modifikationen
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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)
Typ Transformationen
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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)
Typ-Trait-Konstanten
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Type trait constants
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integral_constant(C++11)
 
Defined 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.
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Zwei Spezialisierungen für die Art bool sind vorgesehen:
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Two specializations for the type bool are provided:
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Defined in header <type_traits>
Type
Original:
Type
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 Definition
true_type std::integral_constant<bool, true>
false_type std::integral_constant<bool, false>

Inhaltsverzeichnis

[Bearbeiten] Mitglied Typen

Type
Original:
Type
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 Definition
value_type T
type std::integral_constant<T,v>

[Bearbeiten] Mitglied Konstanten

Name
Original:
Name
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 Value
value
statische Konstante Ausdruck des Typs T mit dem Wert v
Original:
static constant expression of type T with value v
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[Bearbeiten] Member-Funktionen

operator value_type
wandelt das Objekt value_type, gibt value
Original:
converts the object to value_type, returns value
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(öffentliche Elementfunktion)

[Bearbeiten] 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; }
};

[Bearbeiten] 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");
}


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