/*** talker.c -- a datagram "client" demo*/#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <errno.h>#include <string.h>#include <sys/types.h>#include <sys/socket.h>#include <netinet/in.h>#include <arpa/inet.h>#include <netdb.h>#define MYPORT 4950    // the port users will be connecting toint main(int argc, char *argv[]){    int sockfd;    struct sockaddr_in their_addr; // connector's address information    struct hostent *he;    int numbytes;    char send_buf[256];    /* parameters check */    if (argc != 2) {        fprintf(stderr,"usage: talker hostname\n");        exit(1);    }    /* argv[1] = server ip address */    if ((he=gethostbyname(argv[1])) == NULL) {  // get the host info        perror("gethostbyname");        exit(1);    }    /* setup socket */    if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {        perror("socket");        exit(1);    }        /* receive string from console and send it to the server */    while(1)    {	char * ptr;        their_addr.sin_family = AF_INET;     // host byte order        their_addr.sin_port = htons(MYPORT); // short, network byte order        their_addr.sin_addr = *((struct in_addr *)he->h_addr);        memset(&(their_addr.sin_zero), '\0', 8);  // zero the rest of the struct	/* get string from console */	printf("send to server:");	ptr = send_buf;	do	{		*ptr = getchar();		ptr ++;	}while(*(ptr-1) != '\n');	*ptr = 0;	/* send the string to server */        if ((numbytes=sendto(sockfd, send_buf, strlen(send_buf), 0,		     (struct sockaddr *)&their_addr, sizeof(struct sockaddr))) == -1) {            perror("sendto");            exit(1);        }    }    close(sockfd);    return 0;}