std::underlying_type

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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
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Numeric limits
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numeric_limits
C numerico limita interfaccia
Informazioni sul tipo di runtime
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Runtime type information
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Tipo tratti
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Type traits
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Categorie di tipo primario
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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_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
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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)
Operazioni supportate
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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)
I rapporti e le query di proprietà
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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)
Tipo modifiche
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Type modifications
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Tipo di trasformazioni
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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)
Digitare costanti tratto
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Type trait constants
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integral_constant(C++11)
 
Elemento definito nell'header <type_traits>
template<class T >
struct underlying_type;
(dal C++11)
Definisce un membro type typedef del tipo che è il tipo di base per l'enumerazione T.
Original:
Defines a member typedef type of type that is the underlying type for the enumeration T.
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[modifica]Membri tipi

Nome
Original:
Name
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 Definition
type
il tipo di base per T
Original:
the underlying type for T
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[modifica]Note

Ogni tipo di enumerazione ha un tipo sottostante, che può essere
Original:
Each enumeration type has an underlying type, which can be
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1. Specificato esplicitamente (sia ambito e le enumerazioni senza ambito)
Original:
1. Specified explicitly (both scoped and unscoped enumerations)
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2. Omissis, nel qual caso è int per le enumerazioni ambito o una implementazione definito di tipo integrale in grado di rappresentare tutti i valori della enum (per le enumerazioni senza ambito)
Original:
2. Omitted, in which case it is int for scoped enumerations or an implementation-defined integral type capable of representing all values of the enum (for unscoped enumerations)
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[modifica]Esempio

#include <iostream>#include <type_traits>   enum e1 {};enumclass e2:int{};   int main(){bool e1_type =std::is_same<unsigned ,typename std::underlying_type<e1>::type>::value;   bool e2_type =std::is_same<int ,typename std::underlying_type<e2>::type>::value;   std::cout<<"underlying type for 'e1' is "<<(e1_type?"unsigned":"non-unsigned")<<'\n'<<"underlying type for 'e2' is "<<(e2_type?"int":"non-int")<<'\n';}

Output: 

underlying type for 'e1' is unsigned underlying type for 'e2' is int
Estratto da "https://it.cppreference.com/mwiki/index.php?title=cpp/types/underlying_type&oldid=27118"
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