Linux select example.

select.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
 
#include <sys/select.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
 
#define PORT "9421"
 
/* function prototypes */
void die(const char*);
 
int main(int argc, char **argv)
{
        int sockfd, new, maxfd, on = 1, nready, i;
 
        struct addrinfo *res0, *res, hints;
 
        char buffer[BUFSIZ];
 
        fd_set master, readfds;
 
        ssize_t nbytes;
 
        (void)memset(&hints, '\0', sizeof(struct addrinfo));
 
        hints.ai_family = AF_INET;
        hints.ai_socktype = SOCK_STREAM;
        hints.ai_protocol = IPPROTO_TCP;
        hints.ai_flags = AI_PASSIVE;
 
        if(-1 == (getaddrinfo(NULL, PORT, &hints, &res0)))
                die("getaddrinfo()");
 
        for(res = res0; res; res = res->ai_next)
        {
                if(-1 == (sockfd = socket(res->ai_family, res->ai_socktype, res->ai_protocol)))
                {
                        perror("socket()");
                        continue;
                }
 
                if(-1 == (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, (char*)&on, sizeof(int))))
                {
                        perror("setsockopt()");
                        continue;
                }
 
                if(-1 == (bind(sockfd, res->ai_addr, res->ai_addrlen)))
                {
                        perror("bind");
                        continue;
                }
 
                break;
 
        }
 
        if(-1 == sockfd)
                exit(EXIT_FAILURE);
 
        freeaddrinfo(res0);
 
        if(-1 == (listen(sockfd, 32)))
                die("listen()");
 
        if(-1 == (fcntl(sockfd, F_SETFD, O_NONBLOCK)))
                die("fcntl()");
 
        FD_ZERO(&master);
        FD_ZERO(&readfds);
 
        FD_SET(sockfd, &master);
 
        maxfd = sockfd;
 
        for(;;)
        {
                memcpy(&readfds, &master, sizeof(master));
 
                (void)printf("running select()\n");
 
                if(-1 == (nready = select(maxfd+1, &readfds, NULL, NULL, NULL)))
                        die("select()");
 
                (void)printf("Number of ready descriptor: %d\n", nready);
 
                for(i=0; i<=maxfd && nready>0; i++)
                {
                        if(FD_ISSET(i, &readfds))
                        {
                                nready--;
 
                                if(i == sockfd)
                                {
                                        (void)printf("Trying to accept() new connection(s)\n");
 
                                        if(-1 == (new = accept(sockfd, NULL, NULL)))
                                        {
                                                if(EWOULDBLOCK != errno)
                                                        die("accept()");
 
                                                break;
                                        }
 
                                        else
                                        {
 
                                                if(-1 == (fcntl(new, F_SETFD, O_NONBLOCK)))
                                                        die("fcntl()");
 
                                                FD_SET(new, &master);
 
                                                if(maxfd < new)
                                                        maxfd = new;
                                        }
                                }
 
                                else
                                {
                                        (void)printf("recv() data from one of descriptors(s)\n");
 
                                        nbytes = recv(i, buffer, sizeof(buffer), 0);
 
                                        buffer[nbytes] = '\0';
                                        printf("%s", buffer);
 
                                        (void)printf("%zi bytes received.\n", nbytes);
 
                                        if(nbytes <= 0)
                                        {
                                                if(EWOULDBLOCK != errno)
                                                        die("recv()");
 
                                                break;
 
                                        }
 
 
                                        close(i);
                                        FD_CLR(i, &master);
 
                                }
                        }
 
                }
 
 
        }
 
 
        return 0;
}
 
void die(const char *msg)
{
        perror(msg);
        exit(EXIT_FAILURE);
}