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From: pete@iris49.UUCP (Pete Ware)
Newsgroups: comp.windows.x
Subject: Re: XtAddInput returns; error checking in general
Message-ID: <9102181822.AA09294@iris49.biosym.com>
Date: 18 Feb 91 18:22:15 GMT
References: <65118@brunix.UUCP>
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 27

Reading the documentation, it looks like there is no way to check for
an error return value from XtAddInput().  Seeing that XtInputId is:
	typedef unsigned long	XtInputId;
means zero is the most likely thing that could be an error return
value but no indication that it is an error.

As far as general principles, if a function does not have an error
return value, it _probably_ means the author didn't think there were
any significant errors to return.  It could also mean the
documentation isn't upto date w.r.t. to the source.

A large percentage of the intrinsics are void functions so most do not
need any checking.  The remaining ones usually return useful
information such as Boolean values, the previous error handler, etc,
that you are probably going to use right away and may not have an
error condition (i.e functions returning a Boolean value or function
pointers).  The only exception to this are ones that return Widgets.

I think the toolkit was defined to make it easy to program and not
have to be constantly checking for errors.  Most errors are treated
either as fatal (out of memory) or reported and recovered from
internally.

--pete
Pete Ware / Biosym / San Diego CA / (619) 546-5532
uucp:	  scripps.edu!bioc1!pete
Internet: bioc1!pete@scripps.edu