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Varianti

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

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C++
 
Utilità libreria
Tipo di supporto (basic types, RTTI, type traits)
Gestione della memoria dinamica
La gestione degli errori
Programma di utilità
Funzioni variadic
Data e ora
Funzione oggetti
initializer_list(C++11)
bitset
hash(C++11)
Gli operatori relazionali
Original:
Relational operators
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rel_ops::operator!=
rel_ops::operator>
rel_ops::operator<=
rel_ops::operator>=
Coppie e tuple
Original:
Pairs and tuples
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pair
tuple(C++11)
piecewise_construct_t(C++11)
piecewise_construct(C++11)
Swap, in avanti e spostare
Original:
Swap, forward and move
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swap
forward(C++11)
move(C++11)
move_if_noexcept(C++11)
declval(C++11)
 
Tipo di supporto
Tipi base
Original:
Basic types
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Tipi fondamentali
Larghezza fissa interi tipi (C++11)
Limiti numerici
Original:
Numeric limits
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numeric_limits
C numerico limita interfaccia
Informazioni sul tipo di runtime
Original:
Runtime type information
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Tipo tratti
Original:
Type traits
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Categorie di tipo primario
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)
Proprietà del tipo
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)
Operazioni supportate
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)
I rapporti e le query di proprietà
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)
Tipo modifiche
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)
Tipo di trasformazioni
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)
Digitare costanti tratto
Original:
Type trait constants
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integral_constant(C++11)
 
Elemento definito nell'header <type_traits>
template< class T >
struct is_default_constructible;
 (1) (dal C++11)
template< class T >
struct is_trivially_default_constructible;
 (2) (dal C++11)
template< class T >
struct is_nothrow_default_constructible;
 (3) (dal C++11)
1)
Verifica se un tipo è DefaultConstructible, cioè ha un costruttore di default accessibile esplicita o implicita. Se la condizione è soddisfatta, un membro costante value true parità è previsto, in caso contrario è value 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)
Uguale a 1), ma l'espressione costruttore non chiama qualsiasi operazione che non è banale.
Original:
Same as 1), but the constructor expression does not call any operation that is not trivial.
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3)
Uguale a 1), ma l'espressione costruttore è noexcept.
Original:
Same as 1), but the constructor expression is noexcept.
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Indice

Inherited from std::integral_constant

Member constants

value
[statico]
true se T is default-constructible , false altrimenti
Original:
true if T is default-constructible , false otherwise
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(pubblico membro statico costante)

Member functions

operator bool
converte l'oggetto in bool, restituisce value
Original:
converts the object to bool, returns value
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(metodo pubblico)

Member types

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

[modifica] Possibile implementazione

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> {};

[modifica] Esempio

#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

[modifica] Vedi anche

(C++11)
(C++11)
(C++11)
Verifica se un tipo ha un costruttore per argomenti specifici
Original:
checks if a type has a constructor for specific arguments
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(classe template) [modifica]
(C++11)
(C++11)
(C++11)
Verifica se un tipo ha un costruttore di copia
Original:
checks if a type has a copy constructor
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(classe template) [modifica]
(C++11)
(C++11)
(C++11)
Verifica se un tipo ha un costruttore mossa
Original:
checks if a type has a move constructor
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(classe template) [modifica]
Estratto da "https://it.cppreference.com/mwiki/index.php?title=cpp/types/is_default_constructible&oldid=27026"