#include	"unp.h"voidsig_alrm(int signo){}intmain(int argc, char **argv){	int					sockfd, n;	struct sockaddr_in	servaddr;	struct itimerval	val;	fd_set				rset, wset;	if (argc != 2)		err_quit("usage: a.out <IPaddress>");	if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)		err_sys("socket error");	bzero(&servaddr, sizeof(servaddr));	servaddr.sin_family = AF_INET;	servaddr.sin_port   = htons(13);	/* echo server */	Inet_pton(AF_INET, argv[1], &servaddr.sin_addr);		/* Set interval timer to go off before 3WHS completes */	Signal(SIGALRM, sig_alrm);	val.it_interval.tv_sec  = 0;	val.it_interval.tv_usec = 0;	val.it_value.tv_sec  = 0;	val.it_value.tv_usec = 50000;	/* 50 ms */	if (setitimer(ITIMER_REAL, &val, NULL) == -1)		err_sys("setitimer error");again:	if (connect(sockfd, (SA *) &servaddr, sizeof(servaddr)) < 0) {		if (errno == EINTR) {#ifdef	notdef			goto again;	/* second call to connect() -> EADDRINUSE */#endif#ifdef	notdef			printf("interrupted system call\n");			exit(0);#endif		} else			err_sys("connect error");	}	FD_ZERO(&rset);	FD_SET(sockfd, &rset);	wset = rset;sleep(4);	n = Select(sockfd+1, &rset, &wset, NULL, NULL);	printf("select returned %d\n", n);	if (FD_ISSET(sockfd, &rset))		printf("socket is readable\n");	if (FD_ISSET(sockfd, &wset))		printf("socket is writable\n");	str_cli(stdin, sockfd);		/* do it all */	exit(0);}