delphi的字符截取函数LeftStr, MidStr, RightStr

这几个函数都包含在StrUtils中，所以需要uses StrUtils; 
假设字符串是 Dstr := ’Delphi is the BEST’, 那么 
LeftStr(Dstr, 5) := ’Delph’ 
MidStr(Dstr, 6, 7) := ’i is th’ 
RightStr(Dstr, 6) := ’e BEST’ 

~~~~~~~~~~~~~~~~~~~~~~~~~ 
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; 

这几个函数经常结合Pos, Length, Copy使用