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std::ignore

提供: cppreference.com
< cpp‎ | utility‎ | tuple

 
 
ユーティリティライブラリ
支援を入力します (basic types, RTTI, type traits)
動的なメモリ管理
エラー処理
プログラムユーティリティ
可変個引数関数
日付と時刻
関数オブジェクト
initializer_list(C++11)
bitset
hash(C++11)
関係演算子
Original:
Relational operators
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rel_ops::operator!=
rel_ops::operator>
rel_ops::operator<=
rel_ops::operator>=
ペアとタプル
Original:
Pairs and tuples
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pair
tuple(C++11)
piecewise_construct_t(C++11)
piecewise_construct(C++11)
フォワード、スワップ、および移動
Original:
Swap, forward and move
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swap
forward(C++11)
move(C++11)
move_if_noexcept(C++11)
declval(C++11)
 
std::tuple
メンバ関数
Original:
Member functions
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tuple::tuple
tuple::operator=
tuple::swap
非メンバ関数
Original:
Non-member functions
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make_tuple
tie
forward_as_tuple
None
operator=
operator!=
operator<
operator<=
operator>
operator>=
std::swap
get
ヘルパークラス
Original:
Helper classes
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tuple_size
tuple_element
uses_allocator
ignore
 
Defined in header <tuple>
const /*unspecified*/ ignore;
(C++11およびそれ以降)
任意の値が影響を与えることなく、それに割り当てることができるように不特定の型のオブジェクト。使用されていない引数のプレースホルダとして、std::tieを展開する時にstd::tupleで使用するためのもの。
Original:
An object of unspecified type such that any value can be assigned to it with no effect. Intended for use with std::tie when unpacking a std::tuple, as a placeholder for the arguments that are not used.
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[編集]

set.insert()で返されるペアをアンパックだけ、booleanを保存.
Original:
unpack a pair returned by set.insert(), but only save the boolean.
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#include <iostream>
#include <string>
#include <set>
#include <tuple>
 
int main()
{
    std::set<std::string> set_of_str;
    bool inserted;
    std::tie(std::ignore, inserted) = set_of_str.insert("Test");
    if (inserted) {
        std::cout << "Value was inserted sucessfully\n";
    }
}

Output:

Value was inserted sucessfully
左辺値参照またはアンパックのtupleは、個々のオブジェクトにタプルが作成されます
Original:
creates a tuple of lvalue references or unpacks a tuple into individual objects
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(関数テンプレート) [edit]