how to print data from gridview control using asp.net with c#

<script language="javascript" type="text/javascript">
function Print(str)
{
var prntData=document.getElementById(str);
var prntWindow=window.open("","Print","width=20,height=20,left=0,top=0,toolbar=0,scrollbar=0,status=0");
prntWindow.document.write(prntData.InnerHTML);
prntWindow.document.close();
prntWindow.focus();
prntWindow.print();
prntWindow.close();
}

</script>

<div id="grid">
<asp:gridview runat="server" .......="" xmlns:asp="#unknown">
......
</asp:gridview>
</div>

 <asp:Button ID="btnPrint" runat="server" Text="Print" OnClientClick="Print('grid');" />