I want to add an example:
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
int main(int argc, char const *argv[]) {
char buf[20];
fcntl(0, F_SETFL, fcntl(0, F_GETFL) | O_NONBLOCK);
sleep(4);
int numRead = read(0, buf, 4);
if (numRead > 0) {
printf("You said: %s", buf);
}
}
When you run this program you have 4 seconds to provide input to standard in. If no input found, it will return.
2 sample executions:
$ ./a.out
fda
You said: fda
$ ./a.out
$