strerror() should do it. http://linux.die.net/man/3/strerror
FYI, so that you can find these things more easily, yourself: If you type man errno (or whatever function you’re investigating), and look at the very bottom of the man page, you’ll see a list of related functions. If you man each of those (taking a guess about which one(s) to do first based on their names) you’ll often find the answer to similar questions.