November 2016
Beginner to intermediate
816 pages
19h 58m
Japanese
Content preview from Cクイックリファレンス 第2版
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15.8
_Pragma
演算子
269
プリプロセッサが指定トークンを認識したら、そのための必要な動作をしたり、情報を
コンパイラに渡したりする。プリプロセッサがトークンを理解しなければ、
#pragma
指令を
無視しなければならない。
例えば、GNU CコンパイラとMicrosoft Visual Cコンパイラの最近の版はともに、コン
パイラに構造体メンバをあるバイト境界でアラインメント指示するプラグマ
pack(n)
を認識
する。次の例は
pack(1)
を用いて各構造体メンバがバイト境界でアラインメントするよう指
定する。
#if defined(__GNUC__ ) || defined( _MSC_VER)
#pragma pack(1) //
バイトアラインメント
:
パディングなし
#endif
単一バイトアラインメントは、構造体メンバ間にギャップがないことを保証する。
pack
プラグマの引数
n
は通常は2の小さなべき乗である。例えば、
pack(2)
は構造体メンバを偶
数バイトアドレスに、
pack(4)
は4バイト境界にアラインメントする。引数のない
pack()
は、
アラインメントを実装のデフォルト値にリセットする。
C99は次の3つの標準プラグマを導入した。
#pragma STDC FP_CONTRACT on_off_switch
#pragma STDC FENV_ACCESS on_off_switch
#pragma STDC CX_LIMITED_RANGE on_off_switch
on_off_switch ...
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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.