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std::initializer_list

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C++
 
Утилиты библиотеки
 
std::initializer_list
Член функций
Original:
Member functions
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initializer_list::initializer_list
Потенциала
Original:
Capacity
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initializer_list::size
Итераторы
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Iterators
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initializer_list::begin
initializer_list::end
Не являющиеся членами функций
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Non-member functions
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std::begin
std::end
 
Заголовочный файл <initializer_list>
template< class T >
class initializer_list;
 (начиная с C++11)
объект типа std::initializer_list<T> это легкий объект прокси-сервер, который обеспечивает доступ к массиву объектов типа T, выделенных реализации в неопределенных хранения (который может быть автоматическим, временные, или статический только для чтения памяти, в зависимости от ситуации )
Original:
An object of type std::initializer_list<T> is a lightweight proxy object, which provides access to an array of objects of type T, allocated by the implementation in unspecified storage (which could be automatic, temporary, or static read-only memory, depending on the situation)
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Этот массив инициализируется и std::initializer_list объект построен, когда приготовился-Init-лист используется в Список инициализации, в том числе вызова функции инициализации списка и выражения присваивания (не путать с инициализации конструктора списка), или когда приготовился-Init-лист связан с auto, в том числе в дальнюю цикла.
Original:
This array is initialized and a std::initializer_list object is constructed when a braced-init-list is used in Список инициализации, including function-call list initialization and assignment expression (not to be confused with инициализации конструктора списка), or when braced-init-list is bound to auto, including in a ranged for loop.
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Initializer список может быть реализован как пара указателей или указателя и длины. Копирование std::initializer_list не копирует основные объекты. основной массив не гарантирует существование после жизни оригинального объекта списке инициализаторов закончилось.
Original:
Initializer list may be implemented as a pair of pointers or pointer and length. Copying a std::initializer_list does not copy the underlying objects. The underlying array is not guaranteed to exist after the lifetime of the original initializer list object has ended.
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Содержание

[править] Член типов

Член типа
Original:
Member type
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 Definition
value_type T
reference const T&
const_reference const T&
size_type size_t
iterator const T*
const_iterator const T*

[править] Член функций
создает пустой список инициализации
Original:
creates an empty initializer list
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(public функция-член) [edit]
Потенциала
Original:
Capacity
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возвращает количество элементов в списке инициализаторов
Original:
returns the number of elements in the initializer list
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(public функция-член) [edit]
Итераторы
Original:
Iterators
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возвращает указатель на первый элемент
Original:
returns a pointer the first element
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(public функция-член) [edit]
возвращает указатель на следующий за последним элементом
Original:
returns a pointer to one past the last element
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(public функция-член) [edit]

[править] Не являющиеся членами функций

(C++11)
Специализируется std::begin
Original:
specializes std::begin
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(шаблон функции) [edit]
(C++11)
Специализируется std::end
Original:
specializes std::end
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(шаблон функции) [edit]

[править] Пример

#include <iostream>
#include <vector>
#include <initializer_list>
 
template<class T>
struct S {
    std::vector<T> v;
    S(std::initializer_list<T> l) : v(l) {
         std::cout << "constructed with a " << l.size() << "-element list\n";
    }
    void append(std::initializer_list<T> l) {
        v.insert(v.end(), l.begin(), l.end());
    }
    std::pair<const int*, size_t> c_arr() const {
        return {&v[0], v.size()};  // list-initialization in return statement
    }
};
 
template<typename T>
void templated_fn(T) { }
 
int main()
{
    S<int> s = {1,2,3,4,5}; // direct list-initialization
    s.append({6,7,8});      // list-initialization in function call
    std::cout << "The vector size is now " << s.c_arr().second << " ints:\n";
    for(auto n : s.v) std::cout << ' ' << n;
    std::cout << '\n';
 
    std::cout << "range-for over brace-init-list: \n";
    for(int x : {-1, -2, -3}) // the rule for auto makes this ranged for work
        std::cout << x << ' ';
    std::cout << '\n';
 
    auto al = {10, 11, 12};   // special rule for auto
    std::cout << "The list bound to auto has size() = " << al.size() << '\n';
 
//    templated_fn({1,2,3}); // compiler error! "{1,2,3}" is not an expression,
                             // it has no type, and so T cannot be deduced
    templated_fn<std::initializer_list<int>>({1,2,3}); // OK
    templated_fn<std::vector<int>>({1,2,3});           // also OK
}

Вывод: 

The vector size is now 8 ints:
 1 2 3 4 5 6 7 8
range-for over brace-init-list:
-1 -2 -3
The list bound to auto has size() = 3
Источник — «http://ru.cppreference.com/mwiki/index.php?title=cpp/utility/initializer_list&oldid=27465»