1 #include <sys/socket.h> 2 #include <netinet/in.h> 3 #include <netinet/tcp.h> 4 #include <arpa/inet.h> 5 #include <inttypes.h> 6 #include <errno.h> 7 #include <stdio.h> 8 #include <unistd.h> 9 10 int main(int argc, char *argv[]) { 11 int s; 12 struct sockaddr_storage sa; 13 socklen_t salen; 14 uint16_t port; 15 16 if ((s = socket(PF_INET6, SOCK_STREAM, 0)) < 0) { 17 if (errno == EAFNOSUPPORT) 18 s = socket(PF_INET, SOCK_STREAM, 0); 19 20 if (s < 0) { 21 perror("socket()"); 22 return 1; 23 } 24 } 25 26 if (listen(s, 2) < 0) { 27 perror("listen()"); 28 return 2; 29 } 30 31 salen = sizeof(sa); 32 if (getsockname(s, (struct sockaddr*) &sa, &salen) < 0) { 33 perror("getsockname()"); 34 return 3; 35 } 36 37 if (((struct sockaddr*) &sa)->sa_family == AF_INET) 38 port = ((struct sockaddr_in*) &sa)->sin_port; 39 else 40 port = ((struct sockaddr_in6*) &sa)->sin6_port; 41 42 printf("Selected port number %u\n", ntohs(port)); 43 44 /* ... hic sunt leones ... */ 45 46 sleep(60); 47 48 return 0; 49 } 50
