3 Error Executing Socket Function Call Read Timeout

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Socket Read Timeout C

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Select Timeout

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Linux Select Example

timeout in read function call? up vote 29 down vote favorite 14 I want to use serial com port for communication and I want to implement a timeout every time I call the read function call. int filedesc = open( "dev/ttyS0", O_RDWR ); read( filedesc, buff, len ); EDIT: I'm using Linux OS. How to implement using select function call? c linux share|improve this question select linux edited Apr 24 at 20:49 Alexis Wilke 6,89512046 asked May 27 '10 at 1:06 domlao 5,1161960106 3 See linux.die.net/man/2/select –sizzzzlerz May 27 '10 at 1:29 add a comment| 5 Answers 5 active oldest votes up vote 51 down vote accepted select() takes 5 parameters, first the highest file descriptor + 1, then a fd_set for read, one for write and one for exceptions. The last paramter is a struct timeval, used for timeout. It return -1 on error, 0 on timeout or the number of file descriptors in the sets that are set. #include #include #include #include #include int main(void) { fd_set set; struct timeval timeout; int rv; char buff[100]; int len = 100; int filedesc = open( "dev/ttyS0", O_RDWR ); FD_ZERO(&set); /* clear the set */ FD_SET(filedesc, &set); /* add our file descriptor to the set */ timeout.tv_sec = 0; timeout.tv_usec = 10000; rv = select(filedesc + 1, &set, NULL, NULL, &timeout); if(rv == -1) perror("select"); /* an error accured */ else if(rv == 0) printf("timeout"); /* a timeout occured */ else read( filedesc, buff, len ); /* there was data to read */ } share|impro

top select, pselect, FD_CLR, FD_ISSET, FD_SET, FD_ZERO - synchronous I/O multiplexing SYNOPSIS fd_set top /* According to POSIX.1-2001, POSIX.1-2008 */ #include fd_isset /* According to earlier standards */ #include #include #include int select(int nfds, fd_set *readfds, linux read command timeout fd_set *writefds, fd_set *exceptfds, struct timeval *timeout); void FD_CLR(int fd, fd_set *set); int FD_ISSET(int fd, fd_set *set); void FD_SET(int fd, fd_set *set); void FD_ZERO(fd_set *set); #include int http://stackoverflow.com/questions/2917881/how-to-implement-a-timeout-in-read-function-call pselect(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, const struct timespec *timeout, const sigset_t *sigmask); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): pselect(): _POSIX_C_SOURCE >= 200112L DESCRIPTION top select() and pselect() allow a program to monitor multiple file descriptors, waiting until one or more of the file descriptors become "ready" http://man7.org/linux/man-pages/man2/select.2.html for some class of I/O operation (e.g., input possible). A file descriptor is considered ready if it is possible to perform a corresponding I/O operation (e.g., read(2) without blocking, or a sufficiently small write(2)). select() can monitor only file descriptors numbers that are less than FD_SETSIZE; poll(2) does not have this limitation. See BUGS. The operation of select() and pselect() is identical, other than these three differences: (i) select() uses a timeout that is a struct timeval (with seconds and microseconds), while pselect() uses a struct timespec (with seconds and nanoseconds). (ii) select() may update the timeout argument to indicate how much time was left. pselect() does not change this argument. (iii) select() has no sigmask argument, and behaves as pselect() called with NULL sigmask. Three independent sets of file descriptors are watched. Those listed in readfds will be watched to see if characters become available for reading (more precisely, to see if a read will not block; in particular, a file descriptor is

*buf, size_t len, int flags, struct sockaddr *src_addr, socklen_t *addrlen); ssize_t recvmsg(int sockfd, struct msghdr *msg, int flags); Description The recvfrom() and recvmsg() calls are used to https://linux.die.net/man/2/recv receive messages from a socket, and may be used to receive data on a socket whether or not it is connection-oriented. If src_addr is not NULL, and the underlying protocol provides the source address, this source address is filled in. When src_addr is NULL, nothing is filled in; in this case, addrlen is not used, and should also be read timeout NULL. The argument addrlen is a value-result argument, which the caller should initialize before the call to the size of the buffer associated with src_addr, and modified on return to indicate the actual size of the source address. The returned address is truncated if the buffer provided is too small; in this case, addrlen will return a value greater than 3 error executing was supplied to the call. The recv() call is normally used only on a connected socket (see connect(2)) and is identical to recvfrom() with a NULL src_addr argument. All three routines return the length of the message on successful completion. If a message is too long to fit in the supplied buffer, excess bytes may be discarded depending on the type of socket the message is received from. If no messages are available at the socket, the receive calls wait for a message to arrive, unless the socket is nonblocking (see fcntl(2)), in which case the value -1 is returned and the external variable errno is set to EAGAIN or EWOULDBLOCK. The receive calls normally return any data available, up to the requested amount, rather than waiting for receipt of the full amount requested. The select(2) or poll(2) call may be used to determine when more data arrives. The flags argument to a recv() call is formed by ORing one or more of the following values: MSG_CMSG_CLOEXEC (recvmsg() only; since Linux 2.6.23) Set the close-on-exec flag fo