std::pointer_traits - cppreference.com

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Definido no cabeçalho `<memory>`

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

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

O modelo de classe pointer_traits fornece a maneira padronizada para acessar certas propriedades do ponteiro-como tipos. O std::allocator_traits modelo padrão depende pointer_traits para determinar os padrões para vários typedefs requer por 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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O pointer_traits não especializado declara os seguintes tipos:

Original:

The non-specialized pointer_traits declares the following types:

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Tipos de membro


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. Caso contrário `T` se `Ptr` é um `Template<T, Args...>` instanciação do modelo 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, caso contrário 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.

Membros apelido modelos


Modelo 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 existir, caso contrário `Tempate<U, Args...>` se `Ptr` é um `Template<T, Args...>` instanciação do modelo 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.

Funções de membro


	obtém um ponteiro dereferencable a sua tese 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. (função public static membro)

A especialização é fornecido para tipos de ponteiro, T*, que declara os seguintes tipos

Original:

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

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Tipos de membro


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

Membros apelido modelos


Modelo 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*`

Funções de membro


	obtém um ponteiro dereferencable ao seu argumento} 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. (função public static membro)

Notas

O alias modelo religar membros torna possível, dado um tipo de ponteiro-como que aponta para T, para obter o tipo de ponteiro-like mesmo que aponta para U. por exemplo,

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>> :: reativação <double>, std :: unique_ptr <double>> :: value), "")

Original:

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

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Exemplo

#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';
}

Saída:

Veja também


	fornece informações sobre os tipos de alocador 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. (modelo de classe) [edit]

	obtém o endereço real de um objeto, mesmo se o operador &' está sobrecarregado 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. (modelo de função) [edit]