[Info-vax] Notable VMS "feature"

[Johnny Billquist]

On 2016-01-28 03:18, VAXman- at SendSpamHere.ORG wrote:
> In article <n8bj49$u3u$1 at Iltempo.Update.UU.SE>, Johnny Billquist <bqt at softjar.se> writes:
>> On 2016-01-27 12:54, VAXman- at SendSpamHere.ORG wrote:
>>> In article <n89ec2$1bpl$1 at gioia.aioe.org>, George Cornelius <cornelius at charter.NOWHERE.net> writes:
>>>> On 01/26/2016 06:31 AM, Jess Goodman wrote:
>>>>> On Sunday, January 24, 2016 at 3:40:18 PM UTC-5, gcorn... at charter.net wrote:
>>>>>> gcornelius at charter.net wrote:
>>>>>>> gcornelius at charter.net wrote:
>>>>>>>> The rest is of course stolen from you.
>>>>>>
>>>>>> Except the part where I forgot the parentheses
>>>>>> about istat.and.1 in the if statement.
>>>>>>
>>>>>> I believe the simplified form
>>>>>>
>>>>>> 	if (istat.and.1)  ! no .eq.1
>>>>>>
>>>>>> would work, though, so no need to have compared
>>>>>> the results of the .and. to 1.
>>>>>>
>>>>>> George
>>>>
>>>>> Actually in VMS Fortran (and in DCL) only the low-order bit of a
>>>>> logical value determines if it is TRUE or FALSE.  I remember this
>>>>> as "truth is odd".  And since for VMS status values "success is
>>>>> odd" you can code this way:
>>>>
>>>> And I code that way in DCL. In Fortran, which is
>>>> a standards-based language, I have begun to think
>>>> that even if it is low bit only it is best to make
>>>> it explicit.
>>>
>>> Then wouldn't be be more "explicit) with...
>>>
>>>           INCLUDE '($STSDEF)'
>>>
>>>           if (istat.and.STS$M_SUCCESS)
>>
>> Isn't there a mask that contains all the bits that should be checked for
>> status? And then you should really mask istat with that, and check if
>> the masked value equals success?
>
> "M" ;)

I was wondering about that, but is STS$M_SUCCESS is a mask, your code 
don't make sense, as errors would also result in a non-zero value. Or is 
STS$M_SUCCESS a mask that only includes the bits that indicates 
success/no success?

Hmm, I bet it is. So I would guess that it's a mask with just one bit?

Oh well. In which case I agree with other comments still, it's better to 
still check that the result value actually equals success, than just 
assuming that the success value is actually when it is non-zero, and 
that any non-zero value from an expression is interpreted as .TRUE.


Making up names, I would prefer something like:

IF ((istat .AND. STS$M_STATUS) .EQ. STS$C_SUCCESS)

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
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