How to Export Gridview in CSV

Response.Clear();
   Response.Buffer = true;
   Response.AddHeader("content-disposition",
    "attachment;filename=GridViewExport.csv");
   Response.Charset = "";
   Response.ContentType = "application/text";

   GridView1.AllowPaging = false;
   GridView1.DataBind();

   StringBuilder sb = new StringBuilder();
   for (int k = 0; k < GridView1.Columns.Count; k++)
   {
       //add separator
       sb.Append(GridView1.Columns[k].HeaderText + ',');
   }
   //append new line
   sb.Append("\r\n");
   for (int i = 0; i < GridView1.Rows.Count; i++)
   {
       for (int k = 0; k < GridView1.Columns.Count; k++)
       {
           //add separator
           sb.Append(GridView1.Rows[i].Cells[k].Text + ',');
       }
       //append new line
       sb.Append("\r\n");
   }
   Response.Output.Write(sb.ToString());
   Response.Flush();
   Response.End();