On 08/01/2024 18:46, pjw via Ql-Users wrote:
> 100 a$ = "1234567890"
> 105 b$ = a$(4 to 3): REMark This works
> 110 REMark c$ = a$(4 to 2): REMark This fails with an error.
> 115 c$ = a$( to 0) : REMark no error returned
> 120 c$ = a$(0): : REMark no error returned BUT ERROR IF QLIBERATED
> 125 pause:stop
Line 105: The construct a$(n to n - 1) represents the empty string (even
when n = 1). Since it is replicated in JS, Minerva and SMSQ/E Im
assuming it is by design.
If it's by design, it it actually documented anywhere? I do not recall
it being in the QL Manual, as supplied with new QLs back in the day, and
I don't recall Jan Jones mentioning it either.
My QL Manual is packed away ready for a house move---which fell
through---Just checked with Jan Jones (the QUANTA version), she doesn't
mention how this works (or doesn't!)
It also makes sense as there would be no other
way to represent a string slice of null.
I'm wondering though, why you would need to get a "string slice of
null"? If I want to obtain a an empty string, just assigne on A$="" for
example.
To get a slice that is null, I need to determine that this is exactly
what I need, and then make sure that my slicing parameters are specified
with the end being exactly one less than the start? Too much faffing
around, just assign an empty string (as above!)
Line 115: I guess a$( to 0) is read as a$(1 to 0) which fits the
criteria above.
I agree with your observation. Jan Jones states that when slicing a
string variable, the zeroth elephant cannot be accessed. (Page 28.)
Line 120: a$(0) should be fine also. It represents the string length.
Assignment to this location is also acceptable:
Jan Jones documents this in her QL SuperBASIC Handbook, page 23.
I still think that returning "" for a specific string slice from (a to
a-1) is a bug! Bite me!!! ;-)
Cheers,
Norm.
--
Norman Dunbar.
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