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Annotation of 43BSDReno/share/doc/ps1/07.ipctut/pipe.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1986 The Regents of the University of California.
        !             3:  * All rights reserved.
        !             4:  *
        !             5:  * Redistribution and use in source and binary forms are permitted
        !             6:  * provided that the above copyright notice and this paragraph are
        !             7:  * duplicated in all such forms and that any documentation,
        !             8:  * advertising materials, and other materials related to such
        !             9:  * distribution and use acknowledge that the software was developed
        !            10:  * by the University of California, Berkeley.  The name of the
        !            11:  * University may not be used to endorse or promote products derived
        !            12:  * from this software without specific prior written permission.
        !            13:  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
        !            14:  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
        !            15:  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        !            16:  */
        !            17: 
        !            18: #ifndef lint
        !            19: char copyright[] =
        !            20: "@(#) Copyright (c) 1986 The Regents of the University of California.\n\
        !            21:  All rights reserved.\n";
        !            22: #endif /* not lint */
        !            23: 
        !            24: #ifndef lint
        !            25: static char sccsid[] = "@(#)pipe.c     6.3 (Berkeley) 3/7/89";
        !            26: #endif /* not lint */
        !            27: 
        !            28: #include <stdio.h>
        !            29: 
        !            30: #define DATA "Bright star, would I were steadfast as thou art . . ."
        !            31: 
        !            32: /*
        !            33:  * This program creates a pipe, then forks.  The child communicates to the
        !            34:  * parent over the pipe. Notice that a pipe is a one-way communications
        !            35:  * device.  I can write to the output socket (sockets[1], the second socket
        !            36:  * of the array returned by pipe()) and read from the input socket
        !            37:  * (sockets[0]), but not vice versa. 
        !            38:  */
        !            39: 
        !            40: main()
        !            41: {
        !            42:        int sockets[2], child;
        !            43: 
        !            44:        /* Create a pipe */
        !            45:        if (pipe(sockets) < 0) {
        !            46:                perror("opening stream socket pair");
        !            47:                exit(10);
        !            48:        }
        !            49: 
        !            50:        if ((child = fork()) == -1)
        !            51:                perror("fork");
        !            52:        else if (child) {
        !            53:                char buf[1024];
        !            54: 
        !            55:                /* This is still the parent.  It reads the child's message. */
        !            56:                close(sockets[1]);
        !            57:                if (read(sockets[0], buf, 1024) < 0)
        !            58:                        perror("reading message");
        !            59:                printf("-->%s\en", buf);
        !            60:                close(sockets[0]);
        !            61:        } else {
        !            62:                /* This is the child.  It writes a message to its parent. */
        !            63:                close(sockets[0]);
        !            64:                if (write(sockets[1], DATA, sizeof(DATA)) < 0)
        !            65:                        perror("writing message");
        !            66:                close(sockets[1]);
        !            67:        }
        !            68: }

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