% Copyright (c) 1988 Massachusetts Institute of Technology
%	$Source: /mit/zephyr/repository/zephyr/doc/progman/error-handling.tex,v $
%	$Author: jtkohl $
%	$Header: /mit/zephyr/repository/zephyr/doc/progman/error-handling.tex,v 2.0 1989/04/05 15:50:45 jtkohl Exp $
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\subsection{Error Handling}
\label{error-handling}

Almost all routines in the \Zephyr\ library return an error
code of type {\bf Code_t}.  This error code may be a UNIX
error, a Kerberos error (if Kerberos authentication is enabled), or a
\Zephyr\ error.  A {\bf Code_t} may be treated as an integer.  Each
type of error is in a different numeric range (so that
they do not interfere with each other).  This is accomplished using the
{\bf com_err} library.  If a routine succeeds, it will return the
status ZERR_NONE, which is defined to be zero.  A complete list of
\Zephyr\ error codes and their meanings can be found in
\myref{error-codes}, ``Error Codes.''

The following routines provided by the com_err library may be useful.
A full description of the features of the com_err library may be
found in the com_err design document \cite{comerr-paper}.

\nwtemplate{char *}{error_message}{code}
\nwtline{int}{code}
\nwetemplate

Return a string containing the error message associated with error
{\bf code}.

\nwtemplate{void}{com_err}{whoami, code, message}
\nwtline{char}{*whoami}
\nwtline{int}{code}
\nwtline{char}{*message}
\nwetemplate

Print an error message of the form:

{\tt $<$whoami$>$:\ $<$error$>$ $<$message$>$}

\noindent Thus if {\bf whoami} were ``zwrite'', {\bf code} were the
error code for ``Internal error'', and {\bf message} were ``while sending
notice'', the error message printed would be:

{\tt zwrite:\ Internal error while sending notice}