std::pointer_traits - cppreference.com

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Elemento definito nell'header `<memory>`

`template< class Ptr > struct pointer_traits;`	(1)	(dal C++11)

`template< class T > struct pointer_traits<T*>;`	(2)	(dal C++11)

Il modello di classe pointer_traits fornisce il modo standard per accedere alle proprietà di alcuni tipi di puntatore di tipo. Il std::allocator_traits modello standard si basa su pointer_traits per determinare le impostazioni predefinite per diversi typedef richiede da Allocator.

Original:

The pointer_traits class template provides the standardized way to access certain properties of pointer-like types. The standard template std::allocator_traits relies on pointer_traits to determine the defaults for various typedefs requires by Allocator.

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Il non specializzato pointer_traits dichiara i seguenti tipi:

Original:

The non-specialized pointer_traits declares the following types:

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Membri tipi


Tipo Original: Type The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.	Definition

`pointer`	`Ptr`

`element_type`	`Ptr::element_type` se presente. In caso contrario, se `T` `Ptr` è un `Template<T, Args...>` istanziazione di template Original: `Ptr::element_type` if present. Otherwise `T` if `Ptr` is a template instantiation `Template<T, Args...>` The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

`difference_type`	`Ptr::difference_type` se presente, altrimenti std::ptrdiff_t Original: `Ptr::difference_type` if present, otherwise std::ptrdiff_t The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

Membri alias modelli


Template Original: Template The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.	Definition

template <class U> using rebind	`Ptr::rebind<U>` se esiste, altrimenti se `Tempate<U, Args...>` `Ptr` è un `Template<T, Args...>` istanziazione di template Original: `Ptr::rebind<U>` if exists, otherwise `Tempate<U, Args...>` if `Ptr` is a template instantiation `Template<T, Args...>` The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

Membri funzioni


	ottiene un puntatore dereferencable al suo argomento Original: obtains a dereferencable pointer to its argument The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (metodo pubblico statico)

Una specializzazione è previsto per i tipi di puntatore, T*, che dichiara i seguenti tipi

Original:

A specialization is provided for pointer types, T*, which declares the following types

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Membri tipi


Tipo Original: Type The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.	Definition

`pointer`	`T*`

`element_type`	`T`

`difference_type`	std::ptrdiff_t

Membri alias modelli


Template Original: Template The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.	Definition

template< class U > using rebind	`U*`

Membri funzioni


	ottiene un puntatore dereferencable al suo argomento} Original: obtains a dereferencable pointer to its argument} The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (metodo pubblico statico)

Note

Le riassociare alias modello utente permette, dato un puntatore come tipo che punta a T, per ottenere lo stesso puntatore come tipo che punta a U. Per esempio,

Original:

The rebind member template alias makes it possible, given a pointer-like type that points to T, to obtain the same pointer-like type that points to U. For example,

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std :: is_same <std :: pointer_traits <std :: shared_ptr <int>> :: Rebind <double>, std :: unique_ptr <double>> :: valore), "")

Original:

std::is_same<std::pointer_traits< std::shared_ptr<int>>::rebind<double>, std::unique_ptr<double> >::value), "")

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Esempio

#include <memory>
#include <iostream>

template <class Ptr>
struct BlockList
{
   // Predefine a memory block 
   struct block;
   
   // Define a pointer to a memory block from the kind of pointer Ptr s
   // If Ptr is any kind of T*, block_ptr_t is block*
   // If Ptr is smart_ptr<T>, block_ptr_t is smart_ptr<block>
   typedef typename std::pointer_traits<Ptr>::template rebind<block> block_ptr_t;
            
   struct block
   {
      std::size_t size;
      block_ptr_t next_block;
   }; 
   
   block_ptr_t free_blocks;
}; 

int main()
{
    BlockList<int*> bl1;
    // The type of bl1.free_blocks is block*

    BlockList<std::shared_ptr<char>> bl2;
    // The type of bl2.free_blocks is std::shared_ptr<block>
    std::cout << bl2.free_blocks.use_count() << '\n';
}

Output:

Vedi anche


	fornisce informazioni sui tipi di allocatore Original: provides information about allocator types The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (classe template) [modifica]

	ottiene l'indirizzo reale di un oggetto, anche se l'operatore &' è sovraccarico Original: obtains actual address of an object, even if the & operator is overloaded The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (funzione di modello) [modifica]