This method of returning errors is used only in connection with obsolescent
The <netdb.h> header provides a declaration of h_errno as a
modifiable lvalue of type int.
It is unspecified whether h_errno is a macro or an identifier declared
with external linkage. If a macro definition is suppressed in order to access
an actual object, or a program defines an identifier with the name
h_errno, the behavior is undefined.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html