procedure TForm1.DBGrid1DrawColumnCell(Sender: TObject; const Rect: TRect;
  DataCol: Integer; Column: TColumn; State: TGridDrawState);
var
  s:String;
begin
  TDBGrid(Sender).DefaultDrawColumnCell(Rect,DataCol,Column,State);
  s:=Column.Field.DisplayText;
  if (Column.FieldName='FAX') and (Length(s)<10) then
  begin
    with TDBGrid(Sender).Canvas do
    begin
      Pen.Color :=clRed;
      Arc(Rect.Left,Rect.Top,Rect.Right,Rect.Bottom,Rect.Left,Rect.Top,Rect.Left,Rect.Top);
    end;
  end;
end;
直接画圆弧就可以了，后面的这种方法只是提供一种参考：
procedure TForm1.DBGrid1DrawColumnCell(Sender: TObject; const Rect: TRect;
  DataCol: Integer; Column: TColumn; State: TGridDrawState);
const
  Flags:array [TAlignment] of DWORD=(DT_LEFT,DT_RIGHT,DT_CENTER);
var
  s:String;
  R:TRect;
begin
  TDBGrid(Sender).DefaultDrawColumnCell(Rect,DataCol,Column,State);
  s:=Column.Field.DisplayText;
  r:=Rect;
  if (Column.FieldName='FAX') and (Length(s)<10) then
  begin
    with TDBGrid(Sender).Canvas do
    begin
      Pen.Color :=clRed;
      RoundRect(Rect.Left,Rect.Top,Rect.Right,Rect.Bottom,Rect.Left,Rect.Top);
      DrawText(Handle,pchar(s),length(s),R,Flags[Column.Alignment] or DT_VCENTER);
    end;
  end;
end;

bytetype,用于判断某个 Char 是单个字母，还是双字节的前一位或后一位。
mbSingleByte 单字母
mbLeadByte 双字节第一位
mbTrailByte 双字节第二位

ExtractStrings,分割字符串

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