Noob question: what is going to happen if length is 0?

Hmm, why doesn't this code work?

It's quite possible that we have an off by one error here.

while (message[length] == '\0')
    length--;

will cutoff the last character, e.g. if we have "abcd\0" then only "abc" will be printed. More conservative trimming algorithm will look something like this

while (message[length - 1] == '\n' || message[length - 1] == '\r')
    --length;

while (length && isspace(message[length - 1])
    --length;

this one is a bit more safer