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How to implement string pattern matching with wildcards (Views: 100)


Problem/Question/Abstract:

How to implement string pattern matching with wildcards

Answer:

There are many times when you need to compare two strings, but want to use wild cards in the match - all last names that begin with 'St', etc.

This function takes two strings and compares them. The first string can be anything, but should not contain pattern characters (* or ?). The pattern string can have as many of these pattern characters as you want. For example: MatchStrings('David Stidolph','*St*') would return True.}

function MatchStrings(source, pattern: string): Boolean;
var
  pSource: array[0..255] of Char;
  pPattern: array[0..255] of Char;

  function MatchPattern(element, pattern: PChar): Boolean;

    function IsPatternWild(pattern: PChar): Boolean;
    var
      t: Integer;
    begin
      Result := StrScan(pattern, ' * ') <> nil;
      if not Result then
        Result := StrScan(pattern, ' ? ') <> nil;
    end;

  begin
    if 0 = StrComp(pattern, ' * ') then
      Result := True
    else if (element^ = Chr(0)) and (pattern^ <> Chr(0)) then
      Result := False
    else if element^ = Chr(0) then
      Result := True
    else
    begin
      case pattern^ of
        ' * ':
          if MatchPattern(element, @pattern[1]) then
            Result := True
          else
            Result := MatchPattern(@element[1], pattern);
        ' ? ':
          Result := MatchPattern(@element[1], @pattern[1]);
      else
        if element^ = pattern^ then
          Result := MatchPattern(@element[1], @pattern[1])
        else
          Result := False;
      end;
    end;
  end;

begin
  StrPCopy(pSource, source);
  StrPCopy(pPattern, pattern);
  Result := MatchPattern(pSource, pPattern);
end;

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