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offsetof

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C++
 
Утилиты библиотеки
 
Поддержка типов
Основные типы
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Basic types
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Основные типы
Исправлены типы целых ширину (C++11)
nullptr_t(C++11)
offsetof
NULL
Числовые пределы
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Numeric limits
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numeric_limits
С числовым ограничивает интерфейс
Время тип информации
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Runtime type information
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Тип черты
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Type traits
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Первичные категории типа
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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)
Тип свойства
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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)
Поддерживаемые операции
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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)
Отношения собственности и запросов
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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)
Тип модификаций
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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)
Тип преобразования
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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)
Введите черта констант
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Type trait constants
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integral_constant(C++11)
 
Заголовочный файл <cstddef>
#define offsetof(type, member) /*implementation-defined*/
offsetof макрос заменяется на константу типа std::size_t, значение которой является смещение в байтах от начала объекта заданного типа в своем указанного члена, в том числе обивка если таковые имеются.
Original:
The macro offsetof expands to a constant of type std::size_t, the value of which is the offset, in bytes, from the beginning of an object of specified type to its specified member, including padding if any.
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Содержание

[править] Notes

Если type не является стандартной верстки типа, поведение не определено.
Original:
If type is not a standard-layout type, the behavior is undefined.
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Если member является статическим членом или функции-члена, поведение не определено.
Original:
If member is a static member or a function member, the behavior is undefined.
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Смещение первого члена стандартной верстки типа всегда равна нулю (пустой базой оптимизации является обязательным)
Original:
The offset of the first member of a standard-layout type is always zero (пустой базой оптимизации is mandatory)
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[править] Возможная реализация

#define offsetof(type,member) ((std::size_t) &(((type*)0)->member))

[править] Пример

#include <iostream>
#include <cstddef>
struct S {
    char c;
    double d;
};
int main()
{
    std::cout << "the first element is at offset " << offsetof(S, c) << '\n'
              << "the double is at offset " << offsetof(S, d) << '\n';
}

Вывод: 

the first element is at offset 0
the double is at offset 8

[править] См. также
беззнаковое целое число типа возвращаемого sizeof оператора
Original:
unsigned integer type returned by the sizeof operator
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(определение типа) [edit]
(C++11)
проверяет, является ли тип нормативно-макета типа
Original:
checks if a type is standard-layout type
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(шаблон класса) [edit]
Источник — «http://ru.cppreference.com/mwiki/index.php?title=cpp/types/offsetof&oldid=31437»