decltype specifier

 

C++

言語

コンセプト

ユーティリティライブラリ

ストリングスライブラリ

コンテナライブラリ

アルゴリズムライブラリ

イテレータライブラリ

ニューメリックスライブラリ

入力/出力ライブラリ

ローカライゼーションライブラリ

正規表現ライブラリ (C++11)

アトミック操作ライブラリ (C++11)

スレッドのサポートライブラリ (C++11)

 

C + +言語

一般的なトピック Original: General topics The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
プリプロセッサ コメント キーワード	ASCIIチャート エスケープシーケンスを の歴史、C + +
フロー制御 Original: Flow control The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
条件付き実行文 Original: Conditional execution statements The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
if statement	switch statement
繰り返し文 Original: Iteration statements The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
for loop range-for loop (C++11)	while loop do-while loop
文をジャンプします Original: Jump statements The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
continue statement break statement	goto statement return statement
機能します Original: Functions The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
関数の宣言
ラムダ関数の宣言
関数テンプレート
の歴史。インライン指定
例外仕様 (廃止予定)
noexcept指定子 (C++11)
例外 Original: Exceptions The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
式を投げる	try-catchブロック
名前空間 Original: Namespaces The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
名前空間の宣言	名前空間のエイリアス
タイプ Original: Types The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
基本的なタイプ 複合型 列挙型	union型 関数型
decltype specifier (C++11)
指定子 Original: Specifiers The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
CV指定
貯蔵期間指定
constexprの指定子 (C++11)
自動指定 (C++11)
alignas指定子 (C++11)
初期化 Original: Initialization The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
デフォルトの初期化 値の初期化 ゼロ初期化 初期設定をコピーします 直接初期化	集約の初期化 リストの初期化 (C++11) 定数の初期化 リファレンスの初期化

リテラル Original: Literals The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
整数リテラル 文字リテラル 浮動小数点リテラル 文字列リテラル	ブールリテラル nullptrを (C++11) ユーザーが定義します (C++11)
式 Original: Expressions The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
値カテゴリ 評価の順序	演算子 演算子の優先順位
代替表現
ユーティリティ Original: Utilities The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
タイプ Original: Types The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
typedef declaration
型の別名宣言 (C++11)
属性 (C++11)
キャストします Original: Casts The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
暗黙の型変換
const_cast conversion
static_cast conversion
dynamic_cast conversion
reinterpret_cast conversion
Cスタイルキャストと機能
メモリの割り当て Original: Memory allocation The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
new expression	delete expression
クラス Original: Classes The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
クラス宣言 this pointer 指定子にアクセスします	友人指定子 初期化リスト
クラス固有の機能特性 Original: Class-specific function properties The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
仮想関数 指定子をオーバーライドします (C++11) 最後の子 (C++11)	明示 (C++11) 静的
特殊なメンバ関数 Original: Special member functions The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
デフォルトのコンストラクタです コンストラクタをコピーしてください コンストラクタに移動します (C++11)	割り当てをコピーしてください 割り当てを移動します (C++11) デストラクタです
テンプレート Original: Templates The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
クラステンプレート
関数テンプレート
テンプレートの特殊化
パラメーターパック (C++11)
その他 Original: Miscellaneous The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
インラインアセンブリ

 

エンティティの宣言された型を検査または式の戻り値の型を照会.

Original:

Inspects the declared type of an entity or queries the return type of an expression.

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

構文

decltype ( entity )	(1)	(C + + 11以来)
decltype ( expression )	(2)	(C + + 11以来)

説明

1)

引数がいずれかのオブジェクト/関数のunparenthesised名前であるか、またはメンバアクセス式（object.memberまたはpointer->member）ならば、decltypeは、この式で指定されたentityの宣言された型を指定します.

Original:

If the argument is either the unparenthesised name of an object/function, or is a member access expression (object.member or pointer->member), then the decltype specifies the declared type of the entity specified by this expression.

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

2)

引数がタイプTの他の表現である場合

Original:

If the argument is any other expression of type T, then

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

a)

値カテゴリのexpressionである場合はxValue'は、その後、decltypeはT&&指定します

Original:

if the 値カテゴリ of expression is xvalue, then the decltype specifies T&&

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

b)

expressionの値カテゴリがある場合左辺値はとすると、decltypeはT&を指定します

Original:

if the value category of expression is lvalue, then the decltype specifies T&

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

c)

そうでなければ、decltypeはT指定します

Original:

otherwise, decltype specifies T

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

従って、オブジェクトの名前が括弧で括られている場合、それは左辺値式になることに注意してくださいdecltype(arg)とdecltype((arg))しばしば異なる種類があります.

Original:

Note that if the name of an object is parenthesised, it becomes an lvalue expression, thus decltype(arg) and decltype((arg)) are often different types.

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

decltypeテンプレートパラメータに依存してラムダに関連するタイプまたは型と同様に、標準の表記法を使用して宣言することはほとんど不可能であり、型を宣言する場合に便利です.

Original:

decltype is useful when declaring types that are difficult or impossible to declare using standard notation, like lambda-related types or types that depend on template parameters.

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

キーワード

decltype

例

#include <iostream>
 
struct A {
   double x;
};
const A* a = new A();
 
decltype( a->x ) x3;       // type of x3 is double (declared type)
decltype((a->x)) x4 = x3;  // type of x4 is const double& (lvalue expression)
 
template <class T, class U>
auto add(T t, U u) -> decltype(t + u); // return type depends on template parameters
 
int main() 
{
    int i = 33;
    decltype(i) j = i*2;
 
    std::cout << "i = " << i << ", "
              << "j = " << j << '\n';
 
    auto f = [](int a, int b) -> int {
       return a*b;
    };
 
    decltype(f) f2{f}; // the type of a lambda function is unique and unnamed
    i = f(2, 2);
    j = f2(3, 3);
 
    std::cout << "i = " << i << ", "
              << "j = " << j << '\n';
}

Output:

i = 33, j = 66
i = 4, j = 9

も参照してください

declval (C++11)	未評価のコンテキストで、式の型を取得します Original: obtains the type of expression in unevaluated context The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (関数テンプレート)