September 2015
Intermediate to advanced
364 pages
10h 33m
Japanese
Content preview from Effective Modern C++ ―C++11/14プログラムを進化させる42項目
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128
｜
4 章 スマートポインタ
トが複数回破棄されることを意味します（1 レファレンスカウントにつき 1 度）。次のようなコード
はダメダメダメです。
auto pw = new Widget; // pw is raw ptr
pw は raw ポインタ
…
std::shared_ptr<Widget> spw1(pw, loggingDel); // create control
// block for *pw
*pw のコントロール
ブロック作成
…
std::shared_ptr<Widget> spw2(pw, loggingDel); // create 2nd
// control block
// for *pw!
*pw の 2 つ目のコント
ロールブロック作成！
上例ではダイナミックに割り当てたオブジェクトを指す raw ポインタ pw を作成していますが、
これは悪手です。本章全体で述べている内容、raw ポインタよりもスマートポインタを優先する、
に反しています（この背景を覚えていなければ、項目 17 の「重要ポイント」（113 ページ）から読み
直すこと）。まぁ、それは置いておきましょう。pw を作成する行は見た目も醜悪ですが、それでも
プログラムが未定義動作を起こすことはありません。
さて、raw ポインタを与え spw1 のコンストラクタを呼び出しているため、この対象オブジェク
ト用のコントロールブロックが作成されます（レファレンスカウントも作成される）。この場合の対
象オブジェクトは ...
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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.
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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.