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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107
6.2 C++ 動的変数 API の復習
unique_ptr
の導入前は、標準ライブラリコンテナは
C
スタイルポインタ、ディープオブジェクト
コピー、または
shared_ptr
を使ってプログラムするしかなかった。これらにはそれぞれ問題が
あった。
C
スタイルポインタではエラーやメモリリークの危険があり、ディープオブジェクトコ
ピーは大きなオブジェクトで効率が悪く、
shared_ptr
は本質的にコストがかかる。プロジェクト
によっては、コンテナクラスのための特別な安全でないスマートポインタを実装して、コピーコン
ストラクタが
std::swap()
を使って所有しているポインタをコンストラクタに移すような、ムーブ
のような演算を行うことがある。これにより、すべてではないが、多くのコンテナクラスメンバ関
数が期待通りに動作する。これは効率的だが、安全でなくデバッグが困難だ。
C++11
以前は、標準ライブラリコンテナクラスインスタンスの値型に
std::shared_ptr
がよく
使われた。これは正しくてデバッグもしやすいコードになるが、非効率な
shared_ptr
というコス
トを払うという欠点がある。
6.2.2
動的変数には実行時のコストがかかる
C++
はネイティブマシンコードにコンパイルされ、直接マシン実行されるので、ほとんどの
C++
の文のコストは高々数回のメモリアクセスになる。しかし、動的変数のためのメモリ割り当
ては、何千ものメモリアクセスを伴う。このコストは、平均して非常に大きいので、メモリマネー
ジャ呼び出しを ...
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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.