client.c

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

void error(const char *msg)
{
    perror(msg);
    exit(1);
}

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(1);
    }
    portno = atoi(argv[2]);
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0)
        error("ERROR opening socket");
    server = gethostbyname(argv[1]);
    if (server == NULL) {
        fprintf(stderr, "ERROR, no such host\n");
        exit(1);
    }
    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    memcpy(&serv_addr.sin_addr.s_addr, server->h_addr, server->h_length);
    serv_addr.sin_port = htons(portno);
    if (connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
        error("ERROR connecting");
    printf("Please enter the message: ");
    memset(buffer, 0, 256);
    if (fgets(buffer, 255, stdin) == NULL)
        error("ERROR no message entered");
    n = write(sockfd, buffer, strlen(buffer));
    if (n < 0)
        error("ERROR writing to socket");
    memset(buffer, 0, 256);
    n = read(sockfd, buffer, 255);
    if (n < 0)
        error("ERROR reading from socket");
    printf("%s\n", buffer);
    close(sockfd);
    return 0;
}