Op 9/08/2024 om 7:52 schreef Wolfgang Lenerz via Ql-Users:
Hi,
without having looked at the string slicing code in SMSQE, I believe
that the general contract is a$(x to y) where x and y are positive
integers and y is bigger than, or equal to, x. If x is omitted, it is
implied that it should be 1. If y is omitted, it is implied that it
should be the size of the string (this explains j$ and k$).
So the examples where x is bigger than y will either return nothing
(when x=y-1) or an error - as these are non-sensical in regard of the
above contract, that doesn't bother me. This is why the line i$=a$(L
to L-2) fails: x is bigger than y.
By exception, a$(0) returns the length of a$, so in the line d$=a$(0),
d$ isn't 1, but 10. This is also why your line e$=a$(0 to 1) fails.
Notes:
1 - If y is bigger than the size of the string, no error is generated,
and it will be limited to the length of the string: Print a$(1 to 100)
will just print the entire string.
2 - Fun can be had with negative numbers - Norman Dunbar drew my
attention to that.
print a$(1 to -1) will print the entire string. I PRESUME that this is
because both indexes get taken as unsigned integers, so -1 would be
$ffffffff, and thus bigger than the end of the string....
HTH
Wolfgang
100 open#3,con_:window#3,800,600,0,0
105 REMark test done from within QD
110 a$ = "1234567890"
115 L=len(a$)
120 b$ = a$(4 to 3): REMark This works but b$ is empty
125 rem c$ = a$(4 to 2): REMark This fails with an error.
130
135 d$=a$(0) :REMark returns 1 OK WHY?
140 REMark e$=a$(0 to 1) :REMark This fails with an error.
145 f$=a$(1) :REMark This works
150 g$=a$(L) :REMark This works
155 h$=a$(L-1 to l) :REMark This works
160 REMark i$=a$(L to L-2) :REMark This fails with an error.
165 j$=a$( to 2)
170 k$=a$( to )
175 print#3, 'b$= ';b$,len(b$)
180 print#3, 'c$: ';c$ :REMark This fails with an error.
185 print#3, 'd$= ';d$ :REMark This works
190 print#3, 'e$= ';e$ ,len(e$)
195 print#3, 'f$= ';f$
200 print#3, 'g$= ';g$
205 print#3, 'h$= ';h$
210 print#3, 'i$= ';i$
çois
215 print#3, 'j$= ';j$
220 print#3, 'k$= ';k$ ::REMark This works returns a$
225 print#3, 'done'
230 pause
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Hi Wolfgang,
Thank you for reply and explanation.
Have a fine day.
François Van Emelen
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