I'm trying to discover the possible cause for an oddity when using the
'offset' parameter as
in the 'substr' funtion in the small script below. This sample exercise is
a miniaturization
of the same phenomenon which I noticed when creating a much larger
'series' item by reading
fixed-length records from a file one at a time and valuing
some variables with pieces of those records.
The notes at the right of the 2nd (uncommented) 'for' loop below indicate
that I get the
same results and values in the 'print' results when using 'different'
starting positions
in the series call to 'substr' which uses 'starting position' and 'length'
as its parameters.
The commented 'for' loop which appears first, delivers the correct
results.....but I really need
to understnd why the 2nd loop can use different position 'starting
values' in the call .......
and output the same results.....it doesn't seem 'right and proper'.
(There are (3) instances of a simulated record in the variable 'sample'
below, each is (38) characters long).
Thanks............ John D.
********************************************************************
Rebol[Title: "Sample copy/part script"]
substr: func [record offset len] [
copy/part at record offset len
]
sample: "0015342HORNBECK EDNA A0024667BADGER DONALD
R0035457ECONOMOU THOMAS S"
;for i 1 114 38 [
;
; recnbr: substr sample i + 0 3
; regnbr: substr sample i + 3 4
; lname: substr sample i + 7 15 ;This version using the 'i'
varibale plus what I consider the 'correct' adjustment
; fname: substr sample i + 22 15 ; produces the expected result
presuming 'series' start at offset '1'
; minit: substr sample i + 37 1
; print [recnbr regnbr lname fname minit]
;
;]
; should
be able to use 'fixed' offset values and get correct result also
; doesn't seem as though more
than one 'starting position' could possibly
; deliver the same results ........and
yet.....it seems to.
for i 1 114 38 [
rec1: substr sample i 38
recnbr: substr rec1 0 3 ; zero or 1 offset gives same
result
regnbr: substr rec1 4 4 ; 3 or 4 offset does NOT give
same result
lname: substr rec1 8 15 ; 7 or 8 offset does NOT give
same result
fname: substr rec1 22 15 ; 22 or 23 offset gives same
result
minit: substr rec1 38 1 ; 37 or 38 offset does NOT
give same result
print [recnbr regnbr lname fname minit]
]
halt
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