Subject: [FreeVMS] Re: Null Termination & Optional Arguments
From: Andrew Allison (andrew.allison@sympatico.ca)
Date: Sun Dec 28 2003 - 00:49:14 CET
Hello:
Yes. As far as my memory goes, I believe all VMS optional arguments are at
the end and if you need to skip one argument to get to the other then a Null
or something is required. Now you've got me thinking...
Would it be a null pushed on the stack since that indicated the end of
variable list or is it something else?
On the stack is pushed an argument count, but is that incorporated into C's
variable arguments
i.e. Can you skip over an argument to get to the next one?
Or was VMS designed such that there would not be a need to skip arguments to
get to the next one?
If yes what is in it's place?
OK I'm stumped :-)
Well, I guess I'll worry about that one when I run into it.
Andrew
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From: "Geoffrey Pratt" <geoff@genna.demon.co.uk>
To: <freevms@ml.free.fr>
References: <001b01c3ccd1$3b1d1a20$4600000a@allison.com>
Subject: [FreeVMS] Re: Null Termination & Optional Arguments
Date: Sat, 27 Dec 2003 18:37:43 -0500
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Yo,
If the optional arguments are not at the end, then something has to
pushed onto the stack - it does not matter what language one is using -
The syntax may differ between languages, but at the machine code level, I
believe, there will be a 32-bit zero pushed onto the stack. In C, that
would be a NULL pointer (or an integer of zero, depending on the context
[data-type])
Geoff.
>>>>>>>>>>>>>>>>>> Original Message <<<<<<<<<<<<<<<<<<
On 27/12/03, 23:29:10, "Andrew Allison" <freevms@sympatico.ca> wrote
regarding [FreeVMS] Null Termination & Optional Arguments:
> Hello:
> Just to let you know, I using the C style variable arguments in the
run
> time libraries I'm writing. The parameter may or may NOT be there. I not
> assuming that there will be null filled parameter lists. For example I
just
> finished str$find_first_substring which can have any number of trailing
> arguments. i.e there is no finite number specified. I think the NULL
place
> holder is a requirement determined by the programming language used.
> source, index, subindex, substring, [...substring]
> ( Just don't ask me if that was correct BNF syntax)
> Survey time
> Language Null filled
> ------------------------------
> DCL Yes / Comma's
> Cobol Comma's
> C No
> Fortran Can't remember
> Assembly No
> As a foot note I had some bizarre behavior in the operation of va_arg
where
> null was not passed onto the stack correctly.
> Now, to spice things up somewhat with null terminated strings.
> I've combine the descriptor / counted string VMS concept with the Null
> terminated string concept.
> I'm presuming that a little re-writing will be required when FreeVMS
> progresses a little further.
> A: Since we are writing in C under Linux, strings are null terminated
and
> I haven't written / or seen a printf scanf routine that handles string
> descriptors.
> B: I been a little concerned about the use of the linux C string
function
> calls since they all expect null termination, but I hope when we write
the C
> compiler these little problems will go away :-)
> Andrew
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