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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15.4
条件コンパイル
265
めに
#undef
指令を使う。
#undef
指令では、定義を取り消すマクロに引数があっても引数リ
ストを指定する必要はない。例を挙げる。
#include <ctype.h>
#undef isdigit //
この名前のマクロ定義を削除
/* ... */
if (isdigit(c)) //
関数
isdigit()
呼び出し
{
/* ... */
}
マクロのスコープは、最初の
#undef
指令か、合致する
#undef
指令がなければ、定義され
た翻訳単位の終わりまでだ。
15.3
型総称マクロ
C11標準は、データ型について
switch
文に似た働きをする総称選択を導入した。総称
選択は、他の式の型に基づいて候補リストから式を選択することと等価だ（正確な機構は
「5.1.1 総称選択（C11）」で述べている）。これは Cプログラマが、C99がヘッダ t
gmath.h
の数学関数で提供しているような型総称マクロを自分で定義する手段を提供する。
総称選択は、新キーワード
_Generic
から始まる。次の例は、tgmath.hの型総称マクロ
log10(
x
)
の実装例を示す。
#define log10(X) _Generic((X), \
long double: log10l, \
float: log10f, \
default: log10 \
)(X)
コンパイラが式
X
の型に応じて式
log10l
,
log10f
,
log10
のいずれかを選ぶ。マクロが型
double
または整数型の引数
arg
で呼 ...
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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.