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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102
6 章 動的変数割り当てを最適化する
等しくない。式
string("Hello") + string("!")
の値は、
"Hello, World!"
に等しく、
"Hi"
に等しくない。値の意味は、ビットで決まり、プログラムでの使われ方で決まるのではない。
値は変更不可能
2
＋
2
＝
5
が成り立つように、
4
を
5
に変える演算は存在しない。整数変数の値を
4
から
5
に変
えることはできる。これは、名前が一意なエンティティである変数の値の変更だ。この変更は
4
という値を変えるものではない。
値はコピー可能
値のコピーには意味がある。
2
つの文字列変数の値が
"foo"
であっても、プログラムは正しい。
変数がエンティティオブジェクトか値オブジェクトかということが、コピーや等価比較が意味を
持つかどうかを決める。エンティティは、コピーや比較を行うべきでない。クラスメンバ変数がエ
ンティティか値かで、クラスのコピーコンストラクタを書くべきかどうかが決まる。クラスインス
タンスは、エンティティの所有権を共有するが、エンティティを正当にコピーすることはできな
い。エンティティオブジェクトと値オブジェクトの理解が重要なのは、エンティティとして振る舞
う変数が、多くの動的に割り当てられた変数を持つ構造体であるため、コピーがそもそも意味を持
つとしてもコピーが高価になるからだ。
6.2
C++
動的変数
API
の復習
C++
には、動的変数を管理する頑健なツールキットが用意されている。種類は、メモリ管理の
詳細な制御から動的に割り当てられた
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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.