It is only undefined when this file is included by others (like ares) and
in those cases it doesn't matter.

defines are in setup.h.

the external curl include dir.

DEBUG_THREADING_GETHOSTBYNAME is defined

operation as a size_t

it was quite a long time since he experienced that one.

use %zd when outputting size_t

make strtol() returns get stored in long variables
don't mix size_t with int

a curl_off_t type that is larger than 4 bytes