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From: jeh@crash.cts.com (Jamie Hanrahan)
Newsgroups: comp.os.vms
Subject: Re: QIO Question
Summary: What you pass is what you get!
Message-ID: <3036@crash.cts.com>
Date: 28 May 88 19:07:06 GMT
References: <8805280702.AA03906@ucbvax.Berkeley.EDU>
Reply-To: jeh@crash.CTS.COM (Jamie Hanrahan)
Organization: CMKRNL Press, San Diego, CA
Lines: 16

In article <8805280702.AA03906@ucbvax.Berkeley.EDU> EPRF@SNYCENVM.BITNET (Peter Flass) writes:
>
>  When you issue a $QIO with the "astprm" argument, how is the parameter
>passed to the completion AST?  

It's passed exactly as you passed it.  That is, the longword that you put
in the ASTPRM position in the argument list for the $QIO call is copied
verbatim into the second longword of the argument list that's passed to your
AST procedure (making it the first argument, the first longword being
the number-of-arguments longword).  So, for instance, if you pass
something by value, your AST procedure can pick it up by value, and etc. 
$QIO does not check the argument in any way, so if you intend to pass
something by reference or by descriptor, but get it wrong somehow, 
your AST procedure (and not the $QIO call) will incur an access violation.

Does that help?