offset returns bizarre artefacts

[pderks]

Hi,

I took Peter Brigham's 'offsets' routine, found in his 'TextLib' stack

Code: Select all

function offsets str,tContainer,includeOverlaps
   -- returns a comma-delimited list of all the offsets of str in tContainer
   -- returns 0 if not found
   -- third param is optional:
   --     offsets("xx","xxxxxx") returns "1,3,5" not "1,2,3,4,5"
   --     ie, by default, overlapping offsets are not counted
   --     if you want overlapping offsets then pass "true" in 3rd param
   -- note: to get the last occurrence of a string in a container (often useful)
   --     use "item -1 of offsets(...)"
   
   if str is not in tContainer then return 0
   if includeOverlaps = empty then put false into includeOverlaps
   put empty into offsetList
   put 0 into startPoint
   repeat
      put offset(str,tContainer,startPoint) into thisOffset
      if thisOffset = 0 then exit repeat
      add thisOffset to startPoint
      put startPoint & comma after offsetList
      if not includeOverlaps then
         add length(str)-1 to startPoint
      end if
   end repeat
   return item 1 to -1 of offsetList -- delete trailing comma
end offsets

to find certain strings in a large file list.

Very often but not always I got an endless loop.
I modified Peter's function:

Code: Select all

function offsets str,tContainer,includeOverlaps
   put "" into msg
   put "" into XX
   put length(tContainer) into charCount
   put length(str)-1 into LS
   --
   if str is not in tContainer then return 0
   if includeOverlaps = empty then put false into includeOverlaps
   put empty into offsetList
   put 0 into startPoint
   repeat
      put offset(str,tContainer,startPoint) into thisOffset
      if thisOffset = 0 \
            or startPoint > charCount \
            then exit repeat
      add thisOffset to startPoint
      put startPoint & comma after offsetList
      if not includeOverlaps then
         put thisOffset && "•" && startPoint & cr after msg
         add LS to startPoint
      end if
   end repeat
   return item 1 to -1 of offsetList -- delete trailing comma
end offsets

Due to line 'or startPoint > charCount \' the message box now shows results like
1283 • 1283
151109 • 152400
86061 • 238469
4294967288 • 4295205765,
although my source list contains only 263067 (= charCount) characters.

Regards

Peter

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MacPro 2012 • OS X El Capitan 10.11.6 • LiveCode Community 8.1.3