How to use select and accept to communicate with clients properly? - c

Question

I have read some example and manual about select and accept but I still can't figure out where I did wrong.
I tried to let server communicate with multiple clients. But when I execute server first, then execute client, server will immediately cause segmentation fault( when i == sockfd in server.c). And I tried to print some strings to check which statement cause wrong, it even no print anything after if (i == sockfd). So I really have no idea how to move on, are there any suggestion?
Server.c
char inputBuffer[140] = {};
char message[] = {"Hi,this is server.\n"};
int sockfd = 0,forClientSockfd = 0;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd == -1)
{
printf("Fail to create a socket.");
}
//socket creation
struct sockaddr_in serverInfo,clientInfo;
socklen_t addrlen = sizeof(clientInfo);
serverInfo.sin_family = PF_INET;
serverInfo.sin_addr.s_addr = INADDR_ANY;
serverInfo.sin_port = htons(PORT);
bind(sockfd,(struct sockaddr *)&serverInfo,sizeof(serverInfo));
listen(sockfd,5);
fd_set active_fd_set, read_fd_set;
int i;
struct sockaddr_in clientname;
size_t size;
/* Initialize the set of active sockets. */
FD_ZERO (&active_fd_set);
FD_SET (sockfd, &active_fd_set);
int fd_max = sockfd;
while (1)
{
/* Block until input arrives on one or more active sockets. */
//FD_ZERO (&active_fd_set);
//FD_SET (sockfd, &active_fd_set);
read_fd_set = active_fd_set;
if (select (fd_max+1, &read_fd_set, NULL, NULL, NULL) < 0)
{
printf("select fail\n");
}
/* Service all the sockets with input pending. */
for (i = 0; i <= fd_max; ++i)
{
//printf("%d\n",i);
if (FD_ISSET (i, &read_fd_set))
{
//printf("inner :%d %d\n",i,sockfd);
if (i == sockfd)
{
/* Connection request on original socket. */
//printf("A");
int new;
size = sizeof (clientname);
new = accept (sockfd,(struct sockaddr *) &clientname,&size);
if (new < 0)
{
printf("accept fail\n");
}
else
{
printf (
"Server: connect from host %s, port %hd.\n",
inet_ntoa (clientname.sin_addr),
ntohs (clientname.sin_port));
FD_SET (new, &active_fd_set);
if(new > fd_max)
{
fd_max = new;
}
}
}
else
{
/* Data arriving on an already-connected socket. */
if (read_from_client (i) < 0)
{
close (i);
FD_CLR (i, &active_fd_set);
}
}
}
}
}
return 0;
}
int read_from_client (int filedes)
{
char buffer[140];
int nbytes;
nbytes = recv (filedes, buffer, sizeof(buffer),0);
if (nbytes < 0)
{
/* Read error. */
perror ("read");
exit (EXIT_FAILURE);
}
else if (nbytes == 0)
/* End-of-file. */
return -1;
else
{
/* Data read. */
printf ("Server: got message: `%s'\n", buffer);
return 0;
}
}
client.c
int sockfd = 0;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd == -1)
{
printf("Fail to create a socket.");
}
//socket connnection
struct sockaddr_in info;
bzero(&info,sizeof(info));
info.sin_family = PF_INET;
//localhost test
info.sin_addr.s_addr = inet_addr(LOCALHOST);
info.sin_port = htons(PORT);
int err;
char *p;
//Send a message to server
err = connect(sockfd,(struct sockaddr *)&info,sizeof(info));
if(err==-1)
printf("Connection error");
while(1)
{
char message[140];
char receiveMessage[140] = {};
fgets(message,140,stdin);
//scanf("%*[^\n]",message);
//printf("%s",message);
/*if(p=strchr(message,'\n')){
*p = 0;
}else{
scanf("%*[^\n]");
scanf("%c");
}
fgets(message,140,stdin);*/
//scanf("%s",message);
send(sockfd,message,sizeof(message),0);
//printf("RCV");
//recv(sockfd,receiveMessage,sizeof(receiveMessage),0);
//printf("%s\n",receiveMessage);
}
thanks !!