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delphidelphi-7

How to effectively check if a string contains one of a few sub strings?

How can I effectively check if a string contains one of a few sub strings? Suppose I have a string:

`Hi there, <B>my</B> name is Joe <DIV>.</DIV> Hello world. &nbsp;`

How can I check if the string contains either <B> OR <DIV> OR &nbsp;?

I could do a simple:

Result := (Pos('<B>', S) > 0) or 
          (Pos('<DIV>', S) > 0) or 
          (Pos('&nbsp;', S) > 0);

But this seems to be very inefficient since it make N (at worst) passes and my strings are considerably large.

Solution

  • Slightly better version:

    function StringContainsAny(const S: string; const AnyOf: array of string): Boolean;
var
  CurrChr, C: PChar;
  i, j, Ln: Integer;
begin
  for i := 1 to Length(S) do
  begin
    CurrChr := @S[i];
    for j := 0 to High(AnyOf) do
    begin
      C := @AnyOf[j][1]; // assume that no empty strings
      if C^ <> CurrChr^ then
        Continue;

      Ln := Length(AnyOf[j]);
      if (Length(S) + 1 - i) < Ln then // check bounds
        Continue;

      if CompareMem(C, CurrChr, Ln * SizeOf(C^)) then
        Exit(True);
    end;
  end;

  Exit(False);
end;

    You can also build some table of stop-symbols and improve speed. It's kinda complex topic, so I can just suggest you to read, for example, book Bill Smyth "Computing Patterns in Strings".