C - プロセスとシステムサービス - 限界を超える(unistd.hヘッダーファイル、fork関数、プロセスID、親プロセス、子プロセス)

Head First C
原著

開発環境

• OS: macOS High Sierra - Apple
• Text Editor: Emacs
• コンパイラー: LLVM/Clang, GCC(gcc)
• プログラミング言語: C

Head First C ―頭とからだで覚えるCの基本 (David Griffiths (著)、Dawn Griffiths (著)、中田 秀基 (監修)、木下 哲也 (翻訳)、オライリージャパン)の9章(プロセスとシステムサービス - 限界を超える)、コードマグネット(p. 422)を取り組んでみる。

コードマグネット(p. 422)

コード

#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

int main(int argc, char *argv[]) {
  char *feeds[] = {"http://rss.cnn.com/rss/edition.rss",
                   "http://rss.cnn.com/rss/edition_world.rss",
                   "http://rss.cnn.com/rss/edition_asia.rss"};
  int times = 3;
  char *phrase = argv[1];

  for (int i = 0; i < times; i++) {
    puts(feeds[i]);
    char var[255];
    sprintf(var, "RSS_FEED=%s", feeds[i]);
    char *vars[] = {var, NULL};
    pid_t pid = fork();
    if (pid == -1) {
      fprintf(stderr, "プロセスをフォークできません: %s\n", strerror(errno));
      return 1;
    }
    if (!pid) {
      if (execle("/usr/bin/python", "/usr/bin/python", "rssgossip.py", phrase,
                 NULL, vars) == -1) {
        fprintf(stderr, "スクリプトを実行できません: %s\n", strerror(errno));
        return 1;
      }
    }
  }
}

入出力結果(Terminal)

$ cc sample.c -o sample
$ ./sample us > rss.txt
$ cat rss.txt 
http://rss.cnn.com/rss/edition.rss
http://rss.cnn.com/rss/edition_world.rss
http://rss.cnn.com/rss/edition_asia.rss
Princess Ayako introduces her future husband to Japan
US trying to make friends, counter China with massive naval exercise
Businesses have 22 Brexit questions no one can answer
US moves to keep China Mobile out
Trump admin. to reverse guidance on use of race in college admissions
Airbus unveils new Beluga XL
Justin Trudeau rejects groping claim from 2000
US moves to keep China Mobile out
Australian scientists successfully map koala genome
The darkest year in modern US history?
British divers who found teens are pros at perilous rescues
Wait for freedom will take dangerous toll on boys' health
US Senate panel agrees with intel community: Putin was trying to help Trump
Paul Callan: Michael Cohen's road ahead is perilous and uncertain
$