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Date: 16 Sep 93 14:28:00 GMT
From: emery@mitre-bedford.arpa  (David Emery)
Subject: Re: Comparison of Ada and C++ exceptions?
Message-ID: <EMERY.93Sep16092800@goldfinger.mitre.org>
List-Id: <comp.lang.ada>

One version of the POSIX/Ada binding used separate exceptions for each
POSIX error condition.  However, for the reasons Mats mentioned, this
was changed to a single exception (POSIX_ERROR) and a set of
operations to get the error code,  
	type ERROR_CODE is <implementation defined integer>;
	function GET_ERROR_CODE return ERROR_CODE;
	function IS_POSIX_ERROR (ERROR : ERROR_CODE) return BOOLEAN;
	function IMAGE (ERROR : ERROR_CODE) return STRING;
	
	NO_ERROR : constant ERROR_CODE := 0;
	ARGUMENT_LIST_TOO_LONG : constant ERROR_CODE
			       := <implementation defined static expression>;
	BAD_FILE_DESCRIPTOR    : constant ERROR_CODE
			       := <implementation defined static expression>;
	--- etc.
There is an additional requirement that the error code value be kept
on a per-task basis.  See IEEE Std. 1003.5-1992 for more information,
particularly for a discussion on why the type ERROR_CODE is an integer
type rather than a private type or enumeration type.

Now, if we had 'execption parameters' or a similar mechanism, then we
could have attached the error code to the POSIX_ERROR exception.  I
would have liked that very much, and that was a feature I was hoping
to get with 9X.

				dave