I am trying to read a number character with character, but I don't know if the stdin buffer is empty or not.
My first solution whas to look for '\n' character in stdin buffer, but this is no good if I what to enter multiple numbers separated with ' '(blank space).
How can I know if in stdin buffer I have characters or not?
I nead to do it in C and to be portable.
There are a lot of soutions:
feof is preferred one for checking if buffer is empty.
if (!feof(stdin)) // Check if the stdin is empty // read stuff
poll or select with timeout of 0 - these would return immediately and result is either -1 with errno
EAGAIN if no data available or number of descriptors with data (one, since you're checking only stdin).
ioctl is a swiss army knife of using descriptors. The request you need is
if (ioctl(0, I_NREAD, &n) == 0 && n > 0) // we have exactly n bytes to read
However the correct solution is to read everything you got (using
scanf) as a line, then process the result - and this works good enough with
char buf; // large enough scanf("%79s", buf); // read everything we have in stdin if (sscanf(buf, "%d", &number) == 1) // we have a number
... as long as you properly handle re-reading, strings that are longer than your buffer, and other real-life complications.