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I'm trying to create a function that is similar to Delphi's pos function, but that i could pass different strings to be searched, instead of only one. So i could call the function like this :

multipos('word1#word2#word3','this is a sample text with word2',false); // will return 'word2'

The function would return which string was found.

The code i did is below and it's working but it's too slow. How could i improve the speed of this code ?

function multipos(needles,key: string; requireAll: boolean): string; var k: array [1 .. 50] of string; i, j: integer; r, aux: string; flag: boolean; begin if trim(key) = '' then Result := '' else try r := ''; Result := ''; j := 1; for i := 1 to 50 do k[i] := ''; for i := 1 to length(needles) do begin if needles[i] <> '#' then aux := aux + needles[i] else begin k[j] := aux; Inc(j); aux := ''; end; if j >= 50 then break; end; if aux <> '' then k[j] := aux; for i := 1 to j do begin if k[i] = '' then break else if pos(lowercase(k[i]), lowercase(key)) > 0 then begin if not requireAll then begin Result := k[i]; break; end else begin r := r + k[i] + ','; flag := i = j; if not flag then flag := k[i + 1] = ''; if flag then begin Result := r; end; end; end else if requireAll then begin break; end; end; except on e: exception do begin Result := ''; end; end; end;
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    Your sample call and the working code have mismatching signatures. What is needle? Why are you limiting the array k to 50? What exactly is your multipos supposed to return on that example call? Commented Apr 26, 2022 at 14:20
  • @Sherlock70 I fixed the signature and edited the question to clarify. I'm limiting to 50 due to performance issues Commented Apr 26, 2022 at 14:23
  • I am still unsure what the requireAll option actually means. My interpretation is: return all needles that are present in key. Commented Apr 26, 2022 at 15:22

3 Answers 3

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Consider to pass the items as an array, like:

function Multipos(const A: array of string; const S: string): string; begin for var E in A do if Pos(E, S) > 0 then Exit(E); Result := ''; // Nothing found end; // sample calls Multipos(['word1', 'word2', 'word3'], 'sample text with word2'); Multipos('word1#word2#word3'.Split(['#']), 'sample text with word2');

To implement RequireAll functionality, stop on first failure. Just check what to return in that case.

Also, TStrings/TStringList could work for your needs. Check it's Delimiter and DelimitedText properties.

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As you didn't specify a Delphi version, I simply assume the latest:

function multipos(const needles,key: string; requireAll: boolean): string; var lst: TStringList; begin lst := TStringList.Create; try var lowerkey := key.ToLower; // do this only once for var needle in needles.Split(['#']) do begin if lowerkey.Contains(needle.ToLower) then begin if not requireAll then Exit(needle); lst.Add(needle); end; end; Result := lst.CommaText; finally lst.Free; end; end;
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The fact it will need to create and free a stringlist every time the function is called, won't make this version slower ?
Usually object creation and destruction is pretty fast in Delphi. So unless you have measured a significant performance drop I wouldn't bother. Always the first goal is to make it work - then make it fast only if necessary.
Why did you chose to not inline declare lst, too?
@AmigoJack, because in MMX the try-finally wizard doesn't support it (yet).
@UweRaabe, why to add one by one all needles in the list as anyway at the end, if reached, it will contain all input items.. best to simply replace # with a comma
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The array solution by Marcodor is good. Here is a TStringList alternative:

function multipos(SubStrs: TStringList; Str: string; RequireAll: Boolean): string; var i: Integer; begin if (not Str.IsEmpty) and (not SubStrs.Count < 1) then begin Result := ''; for i := 0 to SubStrs.Count - 1 do if Pos(SubStrs[i], Str) > 0 then Result := Result + Copy(Str, Pos(SubStrs[i], Str), SubStrs[i].Length) else if RequireAll then Result := ''; end; end; var myList: TStringList; begin myList := TStringList.Create; myList.Delimiter := '#'; myList.DelimitedText := 'word1#word2#word3'; Writeln(multipos(myList, 'this word1is a sample word3 text with word2', False)); end.

Obviously you'll need system.classes for the StringList. And perhaps some better checking if everything is in order before accessing the parameters, but it works for RequireAll True and False.

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