I searched but did not get a relevant answer to this question, i am working on a linux machine, i wanted to check if the standard input stream contains any character, without removing the characters from the stream.
Expression feof(stdin) is true if an attempt to read the standard input has been done, and the standard input was found to have nothing left in it. Be cautious with eof. It does not ask whether there is anything left in the standard input. It only returns true if you have already tried to read past the end of the file.
You might want to try select() function, and wait for having data into the input stream.
Description:
select() and pselect() allow a program to monitor multiple file descriptors, waiting until one or more of the file descriptors become "ready" for some class of I/O operation (e.g., input possible). A file descriptor is considered ready if it is possible to perform the corresponding I/O operation (e.g., read(2)) without blocking.
In your case, the file descriptor will be stdin
void yourFunction(){
fd_set fds;
struct timeval timeout;
int selectRetVal;
/* Set time limit you want to WAIT for the fdescriptor to have data,
or not( you can set it to ZERO if you want) */
timeout.tv_sec = 0;
timeout.tv_usec = 1;
/* Create a descriptor set containing our remote socket
(the one that connects with the remote troll at the client side). */
FD_ZERO(&fds);
FD_SET(stdin, &fds);
selectRetVal = select(sizeof(fds)*8, &fds, NULL, NULL, &timeout);
if (selectRetVal == -1) {
/* error occurred in select(), */
printf("select failed()\n");
} else if (selectRetVal == 0) {
printf("Timeout occurred!!! No data to fetch().\n");
//do some other stuff
} else {
/* The descriptor has data, fetch it. */
if (FD_ISSET(stdin, &fds)) {
//do whatever you want with the data
}
}
}
Hope it helps.
cacho was on the right path, however select
is only necessary if you're dealing with more than one file descriptor, and stdin
is not a POSIX file descriptor (int
); It's a FILE *
. You'd want to use STDIN_FILENO
, if you go that route.
It's not a very clean route to take, either. I'd prefer to use poll
. By specifying 0 as the timeout
, poll will return immediately.
If none of the defined events have occurred on any selected file descriptor, poll() shall wait at least timeout milliseconds for an event to occur on any of the selected file descriptors. If the value of timeout is 0, poll() shall return immediately. If the value of timeout is -1, poll() shall block until a requested event occurs or until the call is interrupted.
struct pollfd stdin_poll = { .fd = STDIN_FILENO
, .events = POLLIN | POLLRDBAND | POLLRDNORM | POLLPRI };
if (poll(&stdin_poll, 1, 0) == 1) {
/* Data waiting on stdin. Process it. */
}
/* Do other processing. */
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