Like errno, but used by BSD1 host lookup functions such as gethostbyname. If you ever see a confusing error message in a network-related app, it's likely that the programmer used perror() instead of the h_errno-related stuff.
Anyone have any idea why they didn't just use
errno? I don't.
1: A word to the uninitiated: the functions are BSD-derived, though they exist in just about every modern UNIX-like operating system, including those without BSD code.