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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7.2
関数宣言
113
7.2
関数宣言
使う前に関数を宣言することで、コンパイラに型を知らせる。言い換えると、宣言は関
数のインタフェースを記述する。宣言は最低限、関数の戻り値の型を次のように示さねば
ならない。
int rename();
これは、
int
型の値を返す関数
rename()
を定義する。関数名がデフォルトで外部識別子
なので、これは次と等価である。
extern int rename();
この宣言は、関数引数の個数や型の情報を含まない。結果として、コンパイラは、この
関数への呼び出しが正しいかどうかをテストできない。関数を定義と異なる個数や型の引
数で呼び出すと、結果は致命的な実行時エラーとなる。このようなエラーを防ぐには、関
数引数を常に宣言しておく。言い換えると、関数宣言は関数プロトタイプであるべきだ。
例えば、ファイル名を変更する標準ライブラリ関数
rename()
のプロトタイプは次の通り。
int rename(const char* oldname, const char* newname);
この関数は、
const char
へのポインタ型の2引数をとる。言い換えると、関数は
char
オ
ブジェクトを読むためだけにポインタを使う。引数は文字列リテラルでもよい。
プロトタイプ宣言では引数の識別子は省略できる。名前を含めたとき、そのスコープは
プロトタイプそのもののスコープとなる。コンパイラには意味がないので、実用上は、プロ
グラマに引数の目的は何であるかを伝えるコメントでしかない。
rename() ...
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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.