tcp_client.c

/* 
 *  tcpclient.c - A simple TCP client
 *  usage: tcpclient <host> <port>
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h> 

#define BUFSIZE 1024

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

    /* check command line arguments */
    if (argc != 4) {
        fprintf(stderr,"usage: %s <hostname> <port> <value>\n", argv[0]);
        exit(0);
    }
    hostname = argv[1];
    portno = atoi(argv[2]);

    /* socket: create the socket */
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) 
        printf("ERROR opening socket");

    /* gethostbyname: get the server's DNS entry */
    server = gethostbyname(hostname);
    if (server == NULL) {
        fprintf(stderr,"ERROR, no such host as %s\n", hostname);
        exit(0);
    }

    /* build the server's Internet address */
    bzero((char *) &serveraddr, sizeof(serveraddr));
    serveraddr.sin_family = AF_INET;
    bcopy((char *)server->h_addr, 
            (char *)&serveraddr.sin_addr.s_addr, server->h_length);
    serveraddr.sin_port = htons(portno);

    /* connect: create a connection with the server */
    if (connect(sockfd, (const struct sockaddr *)&serveraddr, sizeof(serveraddr)) < 0) {
        printf("ERROR connecting\n");
        exit(1);
    }

    /* get message line from the user */
    printf("Sending 0 1 0\n");

    buf[0] = 0;
    buf[1] = 1;
    buf[2] = atoi(argv[3]);

    n = write(sockfd, buf, 3);
    if (n < 0)  {
        printf("ERROR writing to socket\n");
        exit(1);
    }

    int temp;

    buf[0] = 1;
    buf[1] = 0;

    n = write(sockfd, buf, 2);
    if (n < 0)  {
        printf("ERROR writing to socket\n");
        exit(1);
    }

    n = read(sockfd, temp, sizeof(temp));
    if (n < 0)  {
        printf("ERROR writing to socket\n");
        exit(1);
    }

    printf("Temperature %d\n", temp);

    /* print the server's reply */
#if 0
    bzero(buf, BUFSIZE);
    n = read(sockfd, buf, BUFSIZE);
    if (n < 0) 
        printf("ERROR reading from socket");
    printf("Echo from server: %s", buf);
#endif

    close(sockfd);

    return 0;
}