February 2017
Intermediate to advanced
368 pages
8h 21m
Japanese
Content preview from Optimized C++ ―最適化、高速化のためのプログラミングテクニック
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214
10 章 データ構造を最適化する
std::vector
は動的サイズ変更可能配列（図
10-1
参照）だ。配列要素は、テンプレート型引数
T
のインスタンスで、ベクトルにコピーコンストラクトされて入れられる。要素のコピーコンスト
ラクタがメンバにメモリ割り当てする可能性があるが、
std::vector
呼び出しだけが、要素追加
に際してメモリマネージャに内部バッファの再割り当てを要求する。このフラットな構造により、
std::vector
は異常なほど効率的になる。
C++
開発者のストラウストラップは特別な理由がない限
りコンテナクラスに
std::vector
を勧めている。その理由を本節の後で述べる。■
std::vector
の多くの演算は、
O
表記で定数時間で実行される。そのような演算には、ベクトル
末尾への新要素追加、
i
番目の要素参照取得等がある。ベクトルの単純な内部構造により、演算は
絶対的に高速となる。
std::vector
のイテレータは、ランダムアクセスイテレータで、同じベクト
ルの
2
つのイテレータの距離が定数時間で計算できる。この性質から、
std::vector
の分割統治探
索や整列を効率的に行える。
10.2.1
再割り当ての性能結果
std::vector
には、現在要素がどれだけあるかのサイズと、要素を保持する内部バッファの大き
さを表す容量がある。サイズ
==
容量なら、挿入によって内部バッファの再割り当て、ベクトル要
素の新ストレージへのコピー、古いバッファへの全イテレータと参照の無効化という高価な拡張作 ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.