客户端

#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>
#define PORT 3490 /* the port client will be connecting to */
#define MAXDATASIZE 100 /* max number of bytes we can get at once */
int main(int argc, char *argv[])
{
int sockfd, numbytes;
char buf[MAXDATASIZE] ;

struct hostent *he;
struct sockaddr_in their_addr; /* connector's address information */
if(argc != 2)
{
   fprintf(stderr,"usage: client hostname\n");
   exit(1);
}

if((he=gethostbyname(argv[1])) == NULL)
{
   /* get the host info */
   herror("get host by name" ) ;
         exit(1);
}

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

their_addr.sin_family = AF_INET; /* host byte order */
their_addr.sin_port = htons(PORT); /* short, network byte order */
their_addr.sin_addr = *((struct in_addr *)he->h_addr);
bzero(&(their_addr.sin_zero), 8); /* zero the rest of the struct */
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;
}

服务端:

#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>
#define MYPORT 3490 /* the port users will be connecting to */
#define BACKLOG 10 /* how many pending connections queue will hold */
main()
{
int sockfd, new_fd; /* listen on sock_fd, new connection on new_fd */
struct sockaddr_in my_addr; /* my address information */
struct sockaddr_in their_addr; /* connector's address information */
int sin_size;

if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
{
   perror("socket error") ;
   exit(1) ;
}
my_addr.sin_family = AF_INET; /* host byte order */
my_addr.sin_port = htons(MYPORT); /* short, network byte order */
my_addr.sin_addr.s_addr = INADDR_ANY; /* auto-fill with my IP */
bzero(&(my_addr.sin_zero), 8); /* zero the rest of the struct */

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

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

while(1)
{
   /* main accept() loop */
   sin_size = sizeof(struct sockaddr_in);
  
   if ((new_fd = accept(sockfd, (struct sockaddr *)&their_addr,&sin_size)) == -1)
   {
    perror("accept error");
    continue;
   }

   printf("server: got connection from %s\n", inet_ntoa(their_addr.sin_addr));
  
   if (!fork())
   {
    /* this is the child process */
    if (send(new_fd, "Hello, world!\n", 14, 0) == -1)
     perror("send error");
    close(new_fd);
    exit(0);
   }
   close(new_fd); /* parent doesn't need this */
   while(waitpid(-1,NULL,WNOHANG) > 0); /* clean up child processes */
}
}