Varianti

    NULL

    Da cppreference.com.

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    <metanoindex/>

     
    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
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    Relational operators
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    rel_ops::operator!=
    rel_ops::operator>
    rel_ops::operator<=
    rel_ops::operator>=
    Coppie e tuple
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    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
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    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
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    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_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
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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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    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
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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)
     
    <tbody> </tbody>
    Elemento definito nell'header <cstddef>
    Elemento definito nell'header <cstring>
    Elemento definito nell'header <cwchar>
    Elemento definito nell'header <ctime>
    Elemento definito nell'header <clocale>
    Elemento definito nell'header <cstdio>
    #define NULL /*implementation-defined*/
    Definisce la costante di puntatore nullo, che è un prvalue integrante un'espressione costante di tipo intero che restituisce zero o un prvalue di std::nullptr_t tipo. Il puntatore nullo costante può essere conversione implicita a qualsiasi tipo di puntatore, i risultati di conversione tipo nel puntatore nullo valore di quel tipo. Se la costante puntatore nullo è di tipo intero, esso può essere convertito in un tipo di prvalue std::nullptr_t.
    Original:
    Defines the null pointer constant, which is an integral constant expression prvalue of integer type that evaluates to zero or a prvalue of type std::nullptr_t. The null pointer constant may be conversione implicita to any pointer type; such conversion results in the null pointer value of that type. If the null pointer constant has integer type, it may be converted to a prvalue of type std::nullptr_t.
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    Possibile implementazione

    #define NULL 0
//since C++11
#define NULL nullptr

    Esempio

    #include <cstddef>
class S;
int main()
{
    int* p = NULL;
    int* p2 = static_cast<std::nullptr_t>(NULL);
    void(*f)(int) = NULL;
    int S::*mp = NULL;
    void(S::*mfp)(int) = NULL;
}


    Vedi anche

    nullptr
    il puntatore letterale che specifica un valore nullo (C++11) valore del puntatore
    Original:
    the pointer literal which specifies a null pointer value (C++11)
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    [modifica]
    (C++11)
    il tipo di puntatore nullo nullptr letterale
    Original:
    the type of the null pointer literal nullptr
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    (typedef) [modifica]