這幾個函式都包含在StrUtils中，所以需要uses StrUtils;

舉例：假設字串是 Dstr := 'Delphi is the BEST'， 那麼
LeftStr(Dstr, 5) := 'Delph'
MidStr(Dstr, 6, 7) := 'i is th'
RightStr(Dstr, 6) := 'e BEST'

但我並不建議在Uses中引入StrUtils的做法，會增加程式體積，要用到其中哪個函式，直接寫個Function就OK了。

function RightStr
(Const Str: String; Size: Word): String;
begin
if Size > Length(Str) then Size := Length(Str) ;
RightStr := Copy(Str, Length(Str)-Size+1, Size)
end;
--------------------------------------
function MidStr
(Const Str: String; From, Size: Word): String;
begin
MidStr := Copy(Str, From, Size)
end;
--------------------------------------
function LeftStr
(Const Str: String; Size: Word): String;
begin
LeftStr := Copy(Str, 1, Size)
end;