fork2.c

unix环境下进程编程。

#include	<sys/types.h>
#include	<sys/wait.h>
#include	"ourhdr.h"

int
main(void)
{
	pid_t	pid;

	if ( (pid = fork()) < 0)
		err_sys("fork error");
	else if (pid == 0) {		/* first child */
		if ( (pid = fork()) < 0)
			err_sys("fork error");
		else if (pid > 0)
			exit(0);	/* parent from second fork == first child */

		/* We're the second child; our parent becomes init as soon
		   as our real parent calls exit() in the statement above.
		   Here's where we'd continue executing, knowing that when
		   we're done, init will reap our status. */

		sleep(2);
		printf("second child, parent pid = %d\n", getppid());
		exit(0);
	}

	if (waitpid(pid, NULL, 0) != pid)	/* wait for first child */
		err_sys("waitpid error");

	/* We're the parent (the original process); we continue executing,
	   knowing that we're not the parent of the second child. */

	exit(0);
}