private void ExportToExcel(DataGridView dgv)
        {
            if (dgv_report.Rows.Count > 0)
            {

                Microsoft.Office.Interop.Excel.Application xcelApp = new Microsoft.Office.Interop.Excel.Application();
                xcelApp.Application.Workbooks.Add(Type.Missing);

                for (int i = 1; i < dgv_report.Columns.Count + 1; i++)
                {
                    xcelApp.Cells[1, i] = dgv_report.Columns[i - 1].HeaderText;
                }

                for (int i = 0; i < dgv_report.Rows.Count; i++)
                {
                    for (int j = 0; j < dgv_report.Columns.Count; j++)
                    {
                        xcelApp.Cells[i + 2, j + 1] = dgv_report.Rows[i].Cells[j].Value.ToString();
                    }
                }
                xcelApp.Columns.AutoFit();
                xcelApp.Visible = true;
            }
        }