poll and if
in [Unix Programming]
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From: Bill Cunningham on 4 May 2010 07:48 Rainer Weikusat wrote: > "Bill Cunningham" <nospam(a)nspam.invalid> writes: >>> Rainer Weikusat wrote: >>> >>>> po[1] is the same as *(po + 1) which would access the second >>>> element of the array po. But your array has only one element. >> >> I changed the code to static struct pollfd *po; >> >> and renamed the arrays po[0] and re-compiled and got a smooth >> compilation. > > This should result in a segfault at runtime because you are now trying > to derefences a null pointer. You need to declare a structure, not a > pointer to a structure. And access the revents-member like this: > > po.revents > > NB: This is only true for a single struct pollfd, as in your example. This compiled cleanly- #include "main.h" static struct pollfd *po; static struct addrinfo ad, *p; static int rv, sock, con; int client(char *ip, char *port, char msg[1024]) { memset(&ad, 0, sizeof ad); ad.ai_family = PF_INET; ad.ai_socktype = SOCK_STREAM; ad.ai_protocol = IPPROTO_TCP; getaddrinfo(ip, port, &ad, &p); sock = socket(p->ai_family, p->ai_socktype, p->ai_protocol); fcntl(sock, F_SETFL, O_NONBLOCK); po[0].fd = sock; po[0].events = POLLOUT; rv = poll(po, 1, 3500); if (rv == -1) { perror("poll error"); return -1; } if (rv == 0) { puts("timout error"); return 1; } if (po[0].revents & POLLOUT) { send(sock, msg, strlen(msg) + 1, 0); puts("success"); return 0; } return 0; }
From: Bill Cunningham on 4 May 2010 08:06 Rainer Weikusat wrote: > "Bill Cunningham" <nospam(a)nspam.invalid> writes: >>> Rainer Weikusat wrote: >>> >>>> po[1] is the same as *(po + 1) which would access the second >>>> element of the array po. But your array has only one element. >> >> I changed the code to static struct pollfd *po; >> >> and renamed the arrays po[0] and re-compiled and got a smooth >> compilation. > > This should result in a segfault at runtime because you are now trying > to derefences a null pointer. You need to declare a structure, not a > pointer to a structure. And access the revents-member like this: > > po.revents > > NB: This is only true for a single struct pollfd, as in your example. Yes I did get a seg fault at runtime. It compiled into an object file fine but when I tried calling the client function from main; I got the seg fault. Bill
From: Rainer Weikusat on 4 May 2010 08:43
"Bill Cunningham" <nospam(a)nspam.invalid> writes: > Rainer Weikusat wrote: > #include "main.h" > > static struct pollfd *po; static struct pollfd po; > static struct addrinfo ad, *p; > static int rv, sock, con; > > int client(char *ip, char *port, char msg[1024]) > { > memset(&ad, 0, sizeof ad); > ad.ai_family = PF_INET; > ad.ai_socktype = SOCK_STREAM; > ad.ai_protocol = IPPROTO_TCP; > getaddrinfo(ip, port, &ad, &p); > sock = socket(p->ai_family, p->ai_socktype, p->ai_protocol); > fcntl(sock, F_SETFL, O_NONBLOCK); > po[0].fd = sock; > po[0].events = POLLOUT; po.fd = sock; po.events = POLLOUT; > rv = poll(po, 1, 3500); rv = poll(&po, 1, 3500); > if (rv == -1) { > perror("poll error"); > return -1; > } > if (rv == 0) { > puts("timout error"); > return 1; > } > if (po[0].revents & POLLOUT) { if (po.revents & POLLOUT) { > send(sock, msg, strlen(msg) + 1, 0); > puts("success"); > return 0; > } > return 0; > } |