fork2.c

unix环境高级编程一书源代码 本书全面介绍了UNIX系统的程序设计界面—系统调用界面和标准C库提供的许多函数。 本书的前15章着重于理论知识的阐述

#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);
}