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Groups > comp.sys.acorn.programmer > #5526

Re: how to use a sysvar in Basic

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In message <pn0ke8$1n2o$1@gioia.aioe.org>
          Steve Drain <steve@kappa.me.uk> wrote:

> On 08/09/2018 10:32, Matthew Phillips wrote:
>> on 6 Sep 2018 Steve Drain  wrote:
>>> I would be interested to find the flaws here.
>> 
>> I think the only doubt in my mind is the state of the memory at END, because
>> if the variable does not exist, XOS_ReadVarVal does not alter the
>> contents of
>> the buffer at all.  So v$ would get the string that happened to be at
>> END (if
>> there was one) when the call was entered.

> Without following through, I think BASIC is initialising the return
> string variable to null), but on the error it does not copy it.

>> Perhaps the SWI documentation is unnecessarily cautious.  We can not inspect
>> the source to see what the OS really does.

> Well, we can, but that might spoil the fun of speculation. ;-)

I see from volume 5A of the PRM (the one containg corrections, 
additions) that using OS_ReadVarVal to check for the existence of a 
variable Bit 31 of R2 set) corrupts R0 on exit. Just one to watch out 
for.

-- 
Alan Adams, from Northamptonshire
alan@adamshome.org.uk
http://www.nckc.org.uk/

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how to use a sysvar in Basic Jim Nagel <jimnewsm13c@abbeypress.co.uk> - 2018-09-04 16:20 +0100
  Re: how to use a sysvar in Basic Steve Drain <steve@kappa.me.uk> - 2018-09-04 18:00 +0100
    Re: how to use a sysvar in Basic Jim Nagel <jimnewsm13c@abbeypress.co.uk> - 2018-09-04 18:54 +0100
      Re: how to use a sysvar in Basic Julian Fry <julianfry@orpheusmail.co.uk> - 2018-09-08 21:03 +0100
    Re: how to use a sysvar in Basic Jim Nagel <jimnewsm13c@abbeypress.co.uk> - 2018-09-05 17:13 +0100
      Re: how to use a sysvar in Basic Matthew Phillips <spam2011m@yahoo.co.uk> - 2018-09-05 20:19 +0100
        Re: how to use a sysvar in Basic Steve Drain <steve@kappa.me.uk> - 2018-09-06 11:19 +0100
          Re: how to use a sysvar in Basic Matthew Phillips <spam2011m@yahoo.co.uk> - 2018-09-08 10:32 +0100
            Re: how to use a sysvar in Basic Steve Drain <steve@kappa.me.uk> - 2018-09-08 14:56 +0100
              Re: how to use a sysvar in Basic Alan Adams <alan@adamshome.org.uk> - 2018-09-08 19:39 +0100
              Re: how to use a sysvar in Basic Matthew Phillips <spam2011m@yahoo.co.uk> - 2018-09-10 07:27 +0100
                Re: /  not  (OT) Jim Nagel <jnews18c@abbeypress.co.uk> - 2018-09-10 11:37 +0100
                Re: /  not  (OT) News <chrisjohnson@spamcop.net> - 2018-09-10 14:34 +0100
    Re: how to use a sysvar in Basic Alan Adams <alan@adamshome.org.uk> - 2018-09-08 11:20 +0100
      Re: how to use a sysvar in Basic Steve Drain <steve@kappa.me.uk> - 2018-09-08 14:40 +0100
  Re: how to use a sysvar in Basic "John Williams (News)" <UCEbin@tiscali.co.uk> - 2018-09-04 18:16 +0100
    Re: how to use a sysvar in Basic Alan Adams <alan@adamshome.org.uk> - 2018-09-04 22:04 +0100
      Re: how to use a sysvar in Basic Matthew Phillips <spam2011m@yahoo.co.uk> - 2018-09-05 08:03 +0100
        Re: how to use a sysvar in Basic Martin Wuerthner <spamtrap@mw-software.com> - 2018-09-05 14:39 +0200
          Re: how to use a sysvar in Basic Matthew Phillips <spam2011m@yahoo.co.uk> - 2018-09-05 19:45 +0100
            Re: how to use a sysvar in Basic Steve Drain <steve@kappa.me.uk> - 2018-09-06 11:24 +0100
    Re: how to use a sysvar in Basic "John Williams (News)" <UCEbin@tiscali.co.uk> - 2018-09-05 20:56 +0100
      Re: how to use a sysvar in Basic svrsig <chris@svrsig.org> - 2018-09-05 20:13 -0700
        Re: how to use a sysvar in Basic Matthew Phillips <spam2011m@yahoo.co.uk> - 2018-09-06 07:21 +0100
  Re: how to use a sysvar in Basic A. N. Other <ANOther@argonet.co.uk> - 2018-09-04 18:11 +0100
    Re: how to use a sysvar in Basic Jim Nagel <jimnewsm13c@abbeypress.co.uk> - 2018-09-04 18:42 +0100
      Re: how to use a sysvar in Basic Matthew Phillips <spam2011m@yahoo.co.uk> - 2018-09-05 08:08 +0100
  Re: how to use a sysvar in Basic jgh@mdfs.net - 2018-09-06 17:12 -0700

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