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std::is_default_constructible, std::is_trivially_default_constructible, std::is_nothrow_default_constructible

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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
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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)
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 >
struct is_default_constructible;
(1) (seit C++11)
template< class T >
struct is_trivially_default_constructible;
(2) (seit C++11)
template< class T >
struct is_nothrow_default_constructible;
(3) (seit C++11)
1)
Prüft, ob eine Art DefaultConstructible ist, dh eine zugängliche explizite oder implizite Standardkonstruktor. Wenn die Bedingung erfüllt ist, ein Mitglied konstanten value gleich true bereitgestellt wird, sonst value ist false .
Original:
Checks whether a type is DefaultConstructible, i.e. has an accessible explicit or implicit default constructor. If the requirement is met, a member constant value equal true is provided, otherwise value is false.
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2)
Gleiche wie 1), aber der Konstruktor Ausdruck nicht nennen jede Operation, die nicht trivial ist .
Original:
Same as 1), but the constructor expression does not call any operation that is not trivial.
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3)
Wie 1), aber der Konstruktor Expression noexcept .
Original:
Same as 1), but the constructor expression is noexcept.
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Inhaltsverzeichnis

Inherited from std::integral_constant

Member constants

value
[statisch]
true wenn T is default-constructible , false anders
Original:
true if T is default-constructible , false otherwise
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(public static Mitglied konstanten)

Member functions

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

Member types

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

[Bearbeiten] Mögliche Implementierung

template< class T>
struct is_default_constructible : std::is_constructible<T> {};
 
template< class T>
struct is_trivially_default_constructible : std::is_trivially_constructible<T> {};
 
template< class T>
struct is_nothrow_default_constructible : std::is_nothrow_constructible<T> {};

[Bearbeiten] Beispiel

#include <iostream>
#include <type_traits>
 
struct Ex1 {
    std::string str; // member has a non-trivial default ctor
};
struct Ex2 {
    int n;
    Ex2() = default; // trivial and non-throwing
};
 
int main() {
    std::cout << std::boolalpha << "Ex1 is default-constructible? "
              << std::is_default_constructible<Ex1>::value << '\n'
              << "Ex1 is trivially default-constructible? "
              << std::is_trivially_default_constructible<Ex1>::value << '\n'
              << "Ex2 is trivially default-constructible? "
              << std::is_trivially_default_constructible<Ex2>::value << '\n';
              << "Ex2 is nothrow default-constructible? "
              << std::is_nothrow_default_constructible<Ex2>::value << '\n';
}

Output:

Ex1 is default-constructible? true
Ex1 is trivially default-constructible? false
Ex2 is trivially default-constructible? true
Ex2 is nothrow default-constructible? true

[Bearbeiten] Siehe auch

prüft, ob ein Typ hat einen Konstruktor für Argumente
Original:
checks if a type has a constructor for specific arguments
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(Klassen-Template) [edit]
prüft, ob ein Typ hat einen Copy-Konstruktor
Original:
checks if a type has a copy constructor
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(Klassen-Template) [edit]
prüft, ob ein Typ hat einen Umzug Konstruktor
Original:
checks if a type has a move constructor
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(Klassen-Template) [edit]