How to check if a String is numeric

{1.}

function IsStrANumber(const S: string): Boolean;
var
  P: PChar;
begin
  P      := PChar(S);
  Result := False;
  while P^ <> #0 do
  begin
    if not (P^ in ['0'..'9']) then Exit;
    Inc(P);
  end;
  Result := True;
end;

{2.}

function IsStrANumber(const S: string): Boolean;
begin
  Result := True;
  try
    StrToInt(S);
  except
    Result := False;
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  if IsStrANumber(edit1.Text) = True then
    ShowMessage('String contains only numbers!');
end;