client.c

/* 
 * Client program based on sample code
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h> 
#include <unistd.h>


int main(int argc, char* argv[])
{
	int sockfd, portno, n;
	struct sockaddr_in serv_addr;
	struct hostent *server;

	char buffer[256];

	if (argc < 3) 
	{
		fprintf(stderr,"usage %s hostname port\n", argv[0]);
		exit(0);
	}

	portno = atoi(argv[2]);

	
	/* Translate host name into peer's IP address ;
	 * This is name translation service by the operating system 
	 */
	server = gethostbyname(argv[1]);
	
	if (server == NULL) 
	{
		fprintf(stderr,"ERROR, no such host\n");
		exit(0);
	}
	
	/* Building data structures for socket */

	bzero((char *) &serv_addr, sizeof(serv_addr));

	serv_addr.sin_family = AF_INET;

	bcopy((char *)server->h_addr, 
			(char *)&serv_addr.sin_addr.s_addr,
			server->h_length);

	serv_addr.sin_port = htons(portno);

	/* Create TCP socket -- active open 
	* Preliminary steps: Setup: creation of active open socket
	*/
	
	sockfd = socket(AF_INET, SOCK_STREAM, 0);
	
	if (sockfd < 0) 
	{
		perror("ERROR opening socket");
		exit(0);
	}
	
	if (connect(sockfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr)) < 0) 
	{
		perror("ERROR connecting-");
		exit(0);
	}

	/* Do processing
	*/
	
	printf("Please enter the message: ");

	bzero(buffer,256);

	fgets(buffer,255,stdin);

	n = write(sockfd,buffer,strlen(buffer));

	if (n < 0) 
	{
		perror("ERROR writing to socket");
		exit(0);
	}
	
	bzero(buffer,256);

	n = read(sockfd,buffer,255);
	
	if (n < 0)
	{
		perror("ERROR reading from socket");
		exit(0);
	}

	printf("%s\n",buffer);

	return 0;
}