case insensitive Pos

Question

Is there any comparable function like Pos that is not case-sensitive in D2010 (unicode)?

I know I can use Pos(AnsiUpperCase(FindString), AnsiUpperCase(SourceString)) but

Answer 1

Here's one that I wrote and have been using for years:

function XPos( const cSubStr, cString :string ) :integer;
var
  nLen0, nLen1, nCnt, nCnt2 :integer;
  cFirst :Char;
begin
  nLen0 := Length(cSubStr);
  nLen1 := Length(cString);

  if nLen0 > nLen1 then
    begin
      // the substr is longer than the cString
      result := 0;
    end

  else if nLen0 = 0 then
    begin
      // null substr not allowed
      result := 0;
    end

  else

    begin

      // the outer loop finds the first matching character....
      cFirst := UpCase( cSubStr[1] );
      result := 0;

      for nCnt := 1 to nLen1 - nLen0 + 1 do
        begin

          if UpCase( cString[nCnt] ) = cFirst then
            begin
              // this might be the start of the substring...at least the first
              // character matches....
              result := nCnt;

              for nCnt2 := 2 to nLen0 do
                begin

                  if UpCase( cString[nCnt + nCnt2 - 1] ) <> UpCase( cSubStr[nCnt2] ) then
                    begin
                      // failed
                      result := 0;
                      break;
                    end;

                end;

            end;


          if result > 0 then
            break;
        end;


    end;
end;

Answer 2

The Jedi Code Library has StrIPos and thousands of other useful functions to complement Delphi's RTL. When I still worked a lot in Delphi, JCL and its visual brother JVCL were among the first things I added to a freshly installed Delphi.

Answer 3

On this occasion I couldn't find any approach that was even as good as, let alone better than Pos() + some form of string normalisation (upper/lowercase conversion).

This is not entirely surprising as when benchmarked the Unicode string handling in Delphi 2009 I found that the Pos() RTL routine has improved significantly since Delphi 7, explained in part by the fact that aspects of the FastCode libraries have been incorporated into the RTL for some time now.

The FastStrings library on the other hand has not - iirc - been significantly updated for a long time now. In tests I found that many FastStrings routines have in fact been overtaken by the equivalent RTL functions (with a couple of exceptions, explained by the unavoidable overhead incurred by the additional complications of Unicode).

The "Char-Wise" processing of the solution presented by Steve is the best so far imho.

Any approach that involves normalising the entire strings (both string and sub-string) risks introducing errors in any character-based position in the results due to the fact that with Unicode strings a case conversion may result in a change in the length of the string (some characters convert to more/fewer characters in a case conversion).

These may be rare cases but Steve's routine avoids them and is only about 10% slower than the already quite fast Pos + Uppercase (your benchmarking results don't tally with mine on that score).