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Annotation of 43BSDReno/share/doc/ps1/07.ipctut/pipe.c, revision 1.1.1.1

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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