procedure TForm1.Button4Click(Sender: TObject);
var
  myString:PChar;
Begin
  //SetLength (S1, 100);
  //GetWindowText (Handle, PChar (S1), Length (S1));
  //Button1.Caption := S1;

  GetMem(myString,1024);//开辟1024个字节

  GetWindowText (Handle, myString, 100);
  Button4.Caption :=format('%s:%d',[myString,strlen(myString)]);
  
  FreeMem(myString,1024);//释放
end;