13 daemon实现

#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
class Daemon {
 public:
  Daemon(bool changeDir = false, bool closeStd = true) {
    int fd;
    if (fork() != 0) {
      exit(0);
    }
    setsid();
    if (changeDir) {
      chdir("/");
    }
    if (closeStd && (fd = open("/dev/null", O_RDWR, 0)) != -1) {
      dup2(fd, STDIN_FILENO);
      dup2(fd, STDOUT_FILENO);
      dup2(fd, STDERR_FILENO);
      if (fd > STDERR_FILENO) {
        close(fd);
      }
    }
  }
};