How to check if stdin is still opened without blocking?

Question

I need my program written in pure C to stop execution when stdin is closed.

There is indefinite work done in program main cycle, and there is no way I can use blocki

Answer 1

select() does exactly what you want: signal that an operation (read, in this case) on a file descriptor (file, socket, whatever) will not block.

#include 
#include 

int is_ready(int fd) {
    fd_set fdset;
    struct timeval timeout;
    int ret;
    FD_ZERO(&fdset);
    FD_SET(fd, &fdset);
    timeout.tv_sec = 0;
    timeout.tv_usec = 1;
    //int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
     struct timeval *timeout);
    return select(fd+1, &fdset, NULL, NULL, &timeout) == 1 ? 1 : 0;
}

You can now check a file descriptor before use, for instance in order to empty the file descriptor:

void empty_fd(int fd) {
    char buffer[1024];
    while (is_ready(fd)) {
        read(fd, buffer, sizeof(buffer));
    }
}

In your case, use fileno(stdin) to get the file descriptor of stdin:

if (is_ready(fileno(stdin))) {
    /* read stuff from stdin will not block */
}