Kod programy Serwer:
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <signal.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/resource.h>
#include <sys/wait.h>
#include <sys/time.h>

#define MAX 4096
#define LISTENQ 1024
#define SIZE 2

void err_sys(char *s)
{
	printf("%s\n",s);
	exit (-1);
}
union val
{
	int i_val;
	long l_val;
	char c_val[10];
	struct linger linger_val;
	struct timeval timeval_val;
} val;
static char *sock_str_int(union val *, int);
struct sock_opts
{
	char *opt_str;
	int opt_level;
	int opt_name;
	char *(*opt_val_str)(union val *,int);
}
sock_opts[] = {
"SO_RCVBUF", SOL_SOCKET, SO_RCVBUF, sock_str_int,
"SO_SNDBUF", SOL_SOCKET, SO_SNDBUF, sock_str_int,
};

static char strres[128];
static char *
sock_str_int (union val *ptr, int len)
{
	if(len != sizeof(int))
		snprintf(strres, sizeof(strres), "size (%d) not sizeof(int)", len);
	else
		snprintf(strres, sizeof(strres), "%d", ptr->i_val);
	return(strres);
}

int main(int arg, char **argv)
{
	int connfd, listenfd, sockfd, i, j=0, liczba[2], wynik=0, tmp=0, maxfd, maxi, nready, client[SIZE];
	int fd,len;
	int a = 6666;
	struct sock_opts *ptr;
	ssize_t n;
	fd_set rset, allset;
	struct sockaddr_in servaddr, cliaddr;
	socklen_t clilen;
	char bufor[MAX], bufortmp[MAX], tmpchar, tabtmp[MAX];
	if((listenfd=socket(AF_INET, SOCK_STREAM, 0))<0)
		err_sys("Błąd otwierania socketa");
	bzero(&servaddr, sizeof(servaddr));
	servaddr.sin_family=AF_INET;
	servaddr.sin_addr.s_addr=htonl(INADDR_ANY);
	servaddr.sin_port = htons(50001);
	if(bind(listenfd,(struct sockaddr *)&servaddr, sizeof(servaddr))<0)
		err_sys("Błąd przybicia gniazda");
	if(listen(listenfd,LISTENQ)<0)
		err_sys("Błąd nasłuchu");
	maxfd = listenfd;
	maxi=-1;
	for(i=0; i<SIZE;i++)
		client[i] = -1;
	FD_ZERO(&allset);
	FD_SET(listenfd, &allset);
	while(1)
	{
		rset = allset;
		puts("Oczekiwanie na klienta, bądź dane");
		nready = select(maxfd+1, &rset, NULL,NULL,NULL);
		if(FD_ISSET(listenfd, &rset))
		{
			clilen = sizeof(cliaddr);
			connfd = accept(listenfd,(struct sockaddr *) &cliaddr, &clilen);
			for(i=0; i<SIZE;i++)
				if(client[i]<0)
				{
					client[i]=connfd;
					break;
				}
			if(i == SIZE)
				err_sys("za duzo klientow");
			FD_SET(connfd,&allset);
			if(connfd>maxfd)
				maxfd=connfd;
			if(i>maxi)
				maxi = i;
			if(--nready <= 0)
				continue;
		}
		for(i=0;i<=maxi;i++)
		{
			if((sockfd=client[i])<0)
				continue;
			if(FD_ISSET(sockfd, &rset))
			{
				if ((n=read(sockfd,bufor,MAX)) < 0)
				{
					perror("Błąd w odczycie");
					exit(-1);
				}
				if(bufor[0] == 'q')
				{
					close(sockfd);
					FD_CLR(sockfd,&allset);
					client[i]=-1;
				}
				else
				{
					puts("Wysłano do klienta");
					--n;
					write(sockfd, &n, sizeof(n));
					if(--nready<=0)
						break;
				} //end else
			} //end if
		} //end for
				fd = socket(AF_INET, SOCK_STREAM, 0);
				for (ptr = sock_opts; ptr->opt_str != NULL; ptr++)
				{
					printf("%s: ", ptr->opt_str);
				if (ptr->opt_val_str ==NULL)
					printf("(undefined)\n");
				else
				{
				len = sizeof(val);
				a = 32222222;
				if (setsockopt(fd, ptr->opt_level, ptr->opt_name, &val, a) == -1)
				{
			    	fprintf(stderr, "Error setting socket opts: %s\n", strerror(errno));
				close (fd);
				}
				if (getsockopt(fd, ptr->opt_level, ptr->opt_name, &val, &len) == -1)
				{
					err_sys("getsockopt error");
				}
				else
				{
					printf("default = %s\n", (*ptr->opt_val_str)(&val,len));
				}
			}
		}
	} //end for
} //end main

Kod programy Klient:
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>
#include <sys/types.h>

#define MAX_LINE 4096

int err (char*s)
{
	printf("%s\n",s);
	printf("Errno:%d\n",errno);
	fprintf(stderr,"%s\n",strerror(errno));
	exit(-1);
}

void wyslij (int sockfd,const char *c)
{
	if (send(sockfd, c, strlen(c),MSG_NOSIGNAL)<=0)
		err("Błąd wysyłki");
}

int main(int argc, char *argv[])
{
	if (argc != 3)
		err("Format: ./klient adres_ip port");
	struct sockaddr_in adres_strukt;
        int sockfd = socket(AF_INET,SOCK_STREAM,0);
        bzero(&adres_strukt,sizeof(adres_strukt));
        adres_strukt.sin_family=AF_INET;
	if (inet_pton(AF_INET,argv[1],&adres_strukt.sin_addr)<0)
		err("Zly format adresu IP");
	if((adres_strukt.sin_port=htons(atoi(argv[2])))<0)
		err("Zly numer portu");

	if (connect(sockfd,(struct sockaddr*)&adres_strukt,sizeof(struct sockaddr_in)) != 0)
		err("Błąd w połączeniu");
	char znaki[MAX_LINE];
	int liczba;
	while(1)
	{
		puts("Wprowadz komunikat");
		fgets(znaki,MAX_LINE,stdin);
		wyslij(sockfd,znaki);
		if (znaki[0] != 'q')
		{
			if (read(sockfd,&liczba,sizeof(int)) == -1)
				err("Błąd w odczycie");
			else
				printf("Liczba znakow: %d\n",liczba);
		}
		else
		{
			puts("Koniec");
			break;
		}
	}
	if (close(sockfd) == -1)
		err("Błąd zamykania");
	return 0;}