The fastest way to compare a partial string?

Question

Hello,

I have to compare a partial string "SKILL_______EU_______WAND_______CLERIC_______BASE_____01" with "SKILL".It's meant to check if the first four characters are "SKILL".or the first character only,optimization is needed here!

My problems:

1. I don't know how to do an optimized comparison.
2. It has to be repeated 35 000 times so it must be something very fast.

Thanks!

Answer 1

35000 repetitions really isn't that much these days, it probably doesn't matter what you do.

Answer 2

I think the Delphi routines are quite optimized and fast, so just use them.

var
  position : Integer;

begin
  // AnsiPos
  //   returns the position of a substring in a string
  //   or 0 if the substring isn't found
  position := AnsiPos('SKILL', 'SKILL_______EU_______WAND_______CLERIC_______BASE_____01');
end;

Answer 3

I don't know much about Delphi, but I think (in any language / framework / platform) Regex is the fastest way for string scanning ...

You didn't exactly specify all the conditions you are searching for...

Answer 4

In case you want to check just the 1st character, you can do it like this:

if 'S' = 'SKILL_______EU_______WAND_______CLERIC_______BASE_____01'[1] then
begin
    showmessage('SKILL');
end

Answer 5

Why not do:

function StartsWith( const AMatchStr, ATestStr : string ) : boolean;
begin
  Result := SameText( AMatchStr, copy( ATestStr, 1, Length( AMatchStr ));
end;

This will not process any part of ATestStr beyond your starting text. Bri

Answer 6

If you just what to check the first 4/5 characters you could do

i:= Length('SKILL');

LeftStr('SKILL_______EU_______WAND_______CLERIC_______BASE_____01',i) = 'SKILL'

Answer 7

No matter which solution you choose please keep in mind to actually test and benchmark it against your current implementation.

Otherwise you are just guessing, not optimizing.

And be aware that premature optimization is the root of all evil.

Good luck!

Answer 8

Use StrUtils.AnsiStartsStr for case-sensitive, StrUtils.AnsiStartsText for case-insensitive (add StrUtils to your uses clause)