//客戶端程序 

/******* 客戶端程序 client.c ************/ 
#include  <stdio.h>
#include  <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include  <string.h>
#include <netinet/in.h>
#include <errno.h>
#include <netdb.h>

int main(int argc, char *argv[]) 
{ 
int sockfd; 
char buffer[1024]; 
struct sockaddr_in server_addr; 
struct hostent *host; 
int portnumber,nbytes; 

if(argc!=3) 
{ 
fprintf(stderr,"Usage:%s hostname portnumber\a\n",argv[0]); 
exit(1); 
} 

if((host=gethostbyname(argv[1]))==NULL) 
{ 
fprintf(stderr,"Gethostname error\n"); 
exit(1); 
} 

if((portnumber=atoi(argv[2]))<0) 
{ 
fprintf(stderr,"Usage:%s hostname portnumber\a\n",argv[0]); 
exit(1); 
} 

/* 客戶程序開始建立 sockfd描述符 */ 
if((sockfd=socket(AF_INET,SOCK_STREAM,0))==-1) 
{ 
fprintf(stderr,"Socket Error:%s\a\n",strerror(errno)); 
exit(1); 
} 

/* 客戶程序填充服務端的資料 */ 
bzero(&server_addr,sizeof(server_addr)); 
server_addr.sin_family=AF_INET; 
server_addr.sin_port=htons(portnumber); 
server_addr.sin_addr=*((struct in_addr *)host->h_addr); 

/* 客戶程序發起連接請求 */ 
if(connect(sockfd,(struct sockaddr *)(&server_addr),sizeof(struct sockaddr))==-1) 
{ 
fprintf(stderr,"Connect Error:%s\a\n",strerror(errno)); 
exit(1); 
} 

/* 連接成功了 */ 
if((nbytes=read(sockfd,buffer,1024))==-1) 
{ 
fprintf(stderr,"Read Error:%s\n",strerror(errno)); 
exit(1); 
} 
buffer[nbytes]='\0'; 
printf("I have received:%s\n",buffer); 
/* 結束通訊 */ 
close(sockfd); 
exit(0); 
}