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发信人: czliao@csie.nctu (snOOPy), 信区: programming
标  题: 问一下UNIX programming 的基本问题
发信站: 交大资工 News Server (Mon Nov  6 00:15:30 1995)
转信站: star!news.ee.nthu!news.csie.nctu!czliao

     底下有几个问题想请问一下懂UNIX programming 的人
        while (fgets(buf, MAXLINE, stdin) != NULL) {
                buf[strlen(buf) - 1] = 0;       /* replace newline with null *.

                if ( (pid = fork()) < 0)
                        err_sys("fork error");

                else if (pid == 0) {            /* child */
                        execlp(buf, buf, (char *) 0);
                        err_ret("couldn't execute: %s", buf);
                        exit(127);
                }

                /*这是Advanced Programming in UNIX Environment 中的一个
                  程式,我有点搞不懂的是,这其中所指的parent 和 child,
                  是不是由 fork()所产生的 process 且其值等於0的都是
                  child process 其值大於0的都是parent process ?
                  另外照这个程式看来,似乎要等parent 或 child 其中一个 process
                  完全执行完,才会执行下一个 process ,这样一来,好像就没
                  有多工的情形了*/

                /* parent */
                if ( (pid = waitpid(pid, &status, 0)) < 0)
                        err_sys("waitpid error");
                printf("%% ");
        }

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发信人: letitbe.bbs@cis.nctu (Let It Be), 信区: programming
标  题: Re: 问一下UNIX programming 的基本问题
发信站: 交大资科_BBS (Mon Nov  6 01:44:35 1995)
转信站: star!news.ee.nthu!news.cis.nctu!cis_nctu

It's a basic problem for fork(2V),
I think you should `man 2 fork` first,
then you will see:

     fork() creates a new process.  The new process  (child  pro-
     cess) is an exact copy of the calling process except for the
     following:
     .......[cut].....

Well, when child is running, his parent is also running,
they just get a different pid = fork() value. So they
will choose different way to continue running program...

One will choose: if (pid == 0) , it's child
the other will choose: if (pid > 0), it's parent

They run in the same time!
(in your case, parent just wait wait wait wait child return value..
it seems parent not work, but in fact, WAIT is also a job)

Anyway, you should man fork to get some useful information first.

PS: sorry, I can only read but can't write Chinese now... :~~
    I can't find a good chinese keyin method for my CXterm

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