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std::integral_constant

提供: cppreference.com
< cpp‎ | types

 
 
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initializer_list(C++11)
bitset
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関係演算子
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Relational operators
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pair
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Swap, forward and move
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swap
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基本的なタイプ
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Basic types
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基本的なタイプ
固定幅の整数型 (C++11)
数値の限界
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Numeric limits
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numeric_limits
Cの数値は、インターフェイスを制限します
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Runtime type information
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型の特徴
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Type traits
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Primary type categories
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is_void(C++11)
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Supported operations
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is_constructible
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is_move_constructible
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is_assignable
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is_copy_assignable
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is_move_assignable
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is_destructible
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(C++11)
(C++11)
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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)
形質定数を入力します
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Type trait constants
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integral_constant(C++11)
 
Defined in header <type_traits>
template< class T, T v >
struct integral_constant;
(C + + 11以来)
std::integral_constant指定された型の静的定数をラップします。これは、C + +型の特徴の基本クラスです.
Original:
std::integral_constant wraps a static constant of specified type. It is the base class for the C++ type traits.
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タイプboolための2つの専門分野が用意されています
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Two specializations for the type bool are provided:
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Defined in header <type_traits>
タイプ
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Type
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Definition
true_type std::integral_constant<bool, true>
false_type std::integral_constant<bool, false>

目次

[編集] メンバータイプ

タイプ
Original:
Type
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Definition
value_type T
type std::integral_constant<T,v>

[編集] メンバー定数

名前
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Name
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Value
value
T持つ型vの静的な定数式
Original:
static constant expression of type T with value v
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[編集] メンバ関数

operator value_type
value_typeにオブジェクトは、value返しに変換します
Original:
converts the object to value_type, returns value
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(パブリックメンバ関数)

[編集] 可能な実装

template<class T, T v>
struct integral_constant {
    static constexpr T value = v;
    typedef T value_type;
    typedef integral_constant type;
    constexpr operator value_type() const { return value; }
};

[編集]

#include <iostream>
#include <type_traits>
 
int main() 
{
    typedef std::integral_constant<int, 2> two_t;
    typedef std::integral_constant<int, 4> four_t;
 
//  static_assert(std::is_same<two_t, four_t>::value,
//                "two_t and four_t are not equal!"); 
//  error: static assertion failed: "two_t and four_t are not a same types"
 
    static_assert(two_t::value*2 == four_t::value,
       "2*2 != 4"
    );
 
    enum class my_e {
       e1,
       e2
    };
    typedef std::integral_constant<my_e, my_e::e1> my_e_e1;
    typedef std::integral_constant<my_e, my_e::e2> my_e_e2;
 
//  static_assert(my_e_e1::value == my_e::e2,
//               "my_e_e1::value != my_e::e2");
//  error: static assertion failed: "my_e_e1::value != my_e::e2"
 
    static_assert(std::is_same<my_e_e2, my_e_e2>::value,
                  "my_e_e2 != my_e_e2");
}