電子書在這裡，見6.8.1 和6.8.2 章節，書中的程式碼有很多錯誤，包括#include、socket 描述符賦值等，正確的程式碼在這裡

Server 程式碼：

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <arpa/inet.h>
#include <unistd.h>

#define MYPORT 4000

#define BACKLOG 10 

int main(int argc, char* argv[])
{
int sock_fd, new_fd ;
struct sockaddr_in my_addr;
struct sockaddr_in peer_addr;
int sin_size;

if((sock_fd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
{
perror("socket");
exit(1);
}

my_addr.sin_family = AF_INET;
my_addr.sin_port = htons(MYPORT);
my_addr.sin_addr.s_addr = INADDR_ANY;// 使用INADDR_ANY，則會監聽本地所有IP，包括lo, eth0, eth1, eth0:0……
//my_addr.sin_addr.s_addr = inet_addr("127.0.0.1");// 這樣做可以只指定的IP，如127.0.0.1
bzero(&(my_addr.sin_zero), sizeof(my_addr.sin_zero));

if (bind(sock_fd, (struct sockaddr *)&my_addr, sizeof(struct sockaddr)) == -1)
{
perror("bind");
exit(1);
}

if (listen(sock_fd, BACKLOG) == -1)
{
perror("listen");
exit(1);
}

while(1)
{ 
sin_size = sizeof(struct sockaddr_in);
if ((new_fd = accept(sock_fd, (struct sockaddr *)&peer_addr, (socklen_t*)&sin_size)) == -1)
{
perror("accept");
continue;
}
printf("server: got connection from %s\n", inet_ntoa(peer_addr.sin_addr));


if (!fork())
{
if (send(new_fd,  "Hello, world!\n" , 14, 0) == -1)
{
perror("send");
close(new_fd);
exit(0);
}
close(new_fd);
}
}
while(waitpid(-1,NULL,WNOHANG) > 0);


return 0;
}

Client 程式碼：

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

#define PORT 4000
#define MAXDATASIZE 100

int main(int argc, char *argv[])
{
int sockfd, numbytes;
char buf[MAXDATASIZE];
struct hostent *he;
struct sockaddr_in their_addr;


if (argc != 2)
{
fprintf(stderr,"usage: client hostname\n");
exit(1);
}


if ((he=gethostbyname(argv[1])) == NULL)
{
herror("gethostbyname");
exit(1);
}

if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) 
{
perror("socket");
exit(1);
}

their_addr.sin_family = AF_INET;
their_addr.sin_port = htons(PORT);
their_addr.sin_addr = *((struct in_addr *)he->h_addr);
bzero(&(their_addr.sin_zero), 8);

if(connect(sockfd, (struct sockaddr *)&their_addr, sizeof(struct sockaddr)) == -1)
{
perror("connect");
exit(1);
}

if((numbytes=recv(sockfd, buf, MAXDATASIZE, 0)) == -1)
{
perror("recv");
exit(1);
}

buf[numbytes] = '\0';
printf("Received: %s",buf);
close(sockfd);
return 0;
}