/* * This program creates a datagram socket, binds a name to it, and * then reads from the socket. */ #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <stdio.h> main() { int sock, length; struct sockaddr_in name; char buf[1024]; /* Create a socket from which to read. */ sock = socket(AF_INET, SOCK_DGRAM, 0); if (sock < 0) { perror("opening datagram socket"); exit(1); } /* Create name with wildcards. */ name.sin_family = AF_INET; name.sin_addr.s_addr = INADDR_ANY; name.sin_port = 0; if (bind(sock, (struct sockaddr *)&name, sizeof(name))) { perror("binding datagram socket"); exit(1); }
/* Find assigned port value and print it out. */ length = sizeof(name); if (getsockname(sock, (struct sockaddr *)&name, &length)) { perror("getting socket name"); exit(1); }
printf("Socket has port #%d\n", ntohs(name.sin_port)); /* Read from the socket. */ if (read(sock, buf, 1024) < 0) perror("receiving datagram packet"); printf("-->%s\n", buf); close(sock); }
/* * recvfrom() can also be used in place of the read. recvfrom() * provides an extra field for setting flags. More explanation * is available in Understanding Socket Data Transfer. */