这个错误如何修改啊

gudeng

编译错误如下：
# gcc -o multiserver multiserver.c
/tmp/ccUtqeFc.o(.text+0x17f): In function `main':
: undefined reference to `pthread_create'
collect2: ld returned 1 exit status
这个提示是什么意思，请教各位大侠。

原程序：
#include<stdio.h>
#include<string.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<pthread.h>

#define PORT 1234
#define BACKLOG 5
#define MAXDATASIZE 1000

void process_cli(int connectfd,struct sockaddr_in client);

void *start_routine(void *arg);
struct ARG
{
int connfd;
struct sockaddr_in client;
};

main()
{
int listenfd,connectfd;
struct sockaddr_in server;
struct sockaddr_in client;
int sin_size;
pthread_t thread;
struct ARG *arg;


if((listenfd=socket(AF_INET,SOCK_STREAM,0))==-1)
{
perror("Creating socket failed!\n");
exit(1);
}

int opt=SO_REUSEADDR;
setsockopt(listenfd,SOL_SOCKET,SO_REUSEADDR,&opt,sizeof(opt));
bzero(&server,sizeof(server));
server.sin_family=AF_INET;
server.sin_port=htons(PORT);
server.sin_addr.s_addr=htonl(INADDR_ANY);
if(bind(listenfd,(struct sockaddr *)&server,sizeof(struct sockaddr))==-1)
{
perror("bind error\n");
exit(1);
}

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

sin_size=sizeof(struct sockaddr_in);

while(1)
{
if((connectfd=accept(listenfd,(struct sockaddr *)&client,&sin_size))==-1)
{
perror("accept error\n");
exit(1);
}

arg=(struct ARG *)malloc(sizeof(struct ARG));
arg->connfd=connectfd;
memcpy((void *)&arg->client,&client,sizeof(client));

if(pthread_create(&thread,NULL,start_routine,(void *)arg))
{
perror("pthread_create() error\n");
exit(1);
}
}
close(listenfd);
}

void process_cli(int connectfd,struct sockaddr_in client)
{
int num,i;
char recvbuf[MAXDATASIZE],sendbuf[MAXDATASIZE],cli_name[MAXDATASIZE];

printf("you got a connection from %s. ",inet_ntoa(client.sin_addr));
num=recv(connectfd,cli_name,MAXDATASIZE,0);
if(num==0)
{
close(connectfd);
printf("client disconnected.\n");
return;
}
cli_name[num-1]='\0';
printf("client's name is %s.\n",cli_name);

while(num=recv(connectfd,recvbuf,MAXDATASIZE,0))
{
recvbuf[num]='\0';

printf("Received client(%s) message:%s",cli_name,recvbuf);
for(i=0;i<num-1;i++)
{
sendbuf=recvbuf[num-i-2];
}
sendbuf[num-1]='\0';
send(connectfd,sendbuf,strlen(sendbuf),0);
}
close(connectfd);
}

void *start_routine(void *arg)
{
struct ARG *info;
info=(struct ARG *)arg;
process_cli(info->connfd,info->client);
free(arg);
pthread_exit(NULL);
}

libinary

编译的时候加上pthread库

gudeng

该如何连接呢，能进一步说明么

kj501

gcc -o multiserver multiserver.c  -lpthread