判断IP地址是否非法！

判断IP地址是否非法的代码：

function   TForm1.IsIPString(IPStr:   string):   Boolean;
  var
      i,DotNum:integer;
      Tmpstr:string;
  begin
      Result:=true;
      DotNum:=0;
      for   i:=1   to   Length(IPStr)   do
          Case   IPStr[i]   of
              '0'..'9','.':
                  begin
                  if   IPStr[i]<>'.'   then
                      begin
                          Tmpstr:=Tmpstr+IPStr[i];
                          if   StrtoInt(tmpstr)>255     then
                          begin
                              Result:=False;
                              exit;
                          end;
                      end
                  else
                      begin
                          if   (TmpStr='')and(DotNum>0)   then     //如果连续2个点的情况
                          begin
                              Result:=False;
                              Exit;
                          end;
                          Tmpstr:='';
                          DotNum:=DotNum+1;
                      end;
                  end;
              else
                  begin   Result:=false;   exit;   end;
          end;
      if   DotNum<>3   then   Result:=False;
  end;