tighten up code to reduce wasted paper

[unix-history] / usr / src / share / doc / psd / 20.ipctut / dgramread.c

.\" Copyright (c) 1986 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"     @(#)dgramread.c 6.2 (Berkeley) %G%
.\"
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>

/*
* In the included file <netinet/in.h> a sockaddr_in is defined as follows:
* struct sockaddr_in {
*      short   sin_family;
*      u_short sin_port;
*      struct in_addr sin_addr;
*      char    sin_zero[8];
* }; 
*
* This program creates a datagram socket, binds a name to it, then reads
* from the socket.  
*/
main()
{
       int             sock, length;
       struct sockaddr_in name;
       char            buf[1024];

       /* Create socket from which to read. */
       sock = socket(AF_INET, SOCK_DGRAM, 0);
       if (sock < 0) {
               perror("opening datagram socket");
               exit(-1);
       }
       /* Create name with wildcards. */
       name.sin_family = AF_INET;
       name.sin_addr.s_addr = INADDR_ANY;
       name.sin_port = 0;
       if (bind(sock, &name, sizeof(name))) {
               close(sock);
               perror("binding datagram socket");
       }
       /* Find assigned port value and print it out. */
       length = sizeof(name);
       if (getsockname(sock, &name, &length)) {
               close(sock);
               perror("getting socket name");
       }
       printf("Socket has port #%d\en", ntohs(name.sin_port));
       /* Read from the socket */
       if (read(sock, buf, 1024, 0) < 0)
               perror("receiving datagram packet");
       printf("-->%s\en", buf);
       close(sock);
}