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http://www.freebsd.org/doc/en_US.ISO8859-1/books/developers-handbook/sockets-ess
ential-functions.html

Client:
/*
 * daytime.c
 *
 * Programmed by G. Adam Stanislav
 */
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

int main() {
  register int s;
  register int bytes;
  struct sockaddr_in sa;
  char buffer[BUFSIZ+1];

  if ((s = socket(PF_INET, SOCK_STREAM, 0)) < 0) {
    perror("socket");
    return 1;
  }

  bzero(&sa, sizeof sa);

  sa.sin_family = AF_INET;
  sa.sin_port = htons(13);
  sa.sin_addr.s_addr = htonl((((((192 << 8) | 43) << 8) | 244) << 8) | 18);
  if (connect(s, (struct sockaddr *)&sa, sizeof sa) < 0) {
    perror("connect");
    close(s);
    return 2;
  }

  while ((bytes = read(s, buffer, BUFSIZ)) > 0)
    write(1, buffer, bytes);

  close(s);
  return 0;
}

Server:
/*
 * daytimed - a port 13 server
 *
 * Programmed by G. Adam Stanislav
 * June 19, 2001
 */
#include <stdio.h>
#include <time.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define BACKLOG 4

int main() {
    register int s, c;
    int b;
    struct sockaddr_in sa;
    time_t t;
    struct tm *tm;
    FILE *client;

    if ((s = socket(PF_INET, SOCK_STREAM, 0)) < 0) {
        perror("socket");
        return 1;
    }

    bzero(&sa, sizeof sa);

    sa.sin_family = AF_INET;
    sa.sin_port   = htons(13);

    if (INADDR_ANY)
        sa.sin_addr.s_addr = htonl(INADDR_ANY);

    if (bind(s, (struct sockaddr *)&sa, sizeof sa) < 0) {
        perror("bind");
        return 2;
    }

    switch (fork()) {
        case -1:
            perror("fork");
            return 3;
            break;
        default:
            close(s);
            return 0;
            break;
        case 0:
            break;
    }

    listen(s, BACKLOG);

    for (;;) {
        b = sizeof sa;

        if ((c = accept(s, (struct sockaddr *)&sa, &b)) < 0) {
            perror("daytimed accept");
            return 4;
        }

        if ((client = fdopen(c, "w")) == NULL) {
            perror("daytimed fdopen");
            return 5;
        }

        if ((t = time(NULL)) < 0) {
            perror("daytimed time");

            return 6;
        }

        tm = gmtime(&t);
        fprintf(client, "%.4i-%.2i-%.2iT%.2i:%.2i:%.2iZ\n",
            tm->tm_year + 1900,
            tm->tm_mon + 1,
            tm->tm_mday,
            tm->tm_hour,
            tm->tm_min,
            tm->tm_sec);

        fclose(client);
    }
}

Посмотри в "Эффективное программирование TCP/IP" Йона Снейдера. Хорошая и недорогая книжка (около 150 рублей).