C#导出Excel动态列

 string _sPath = GenerateSalaryMonthlyReport(dgvSalarySum);
 System.Diagnostics.Process.Start(_sPath);

 public String GenerateSalaryMonthlyReport(DataGridView dgvData)
        {
            String _sPath = String.Format(@".\{0}.txt", BaseClass.getGUID());
            String _sGoal = String.Format(@"{0}{1}.xls", System.Configuration.ConfigurationManager.AppSettings["Statistic"],
                                                         BaseClass.ExcelFileName("员工每月薪酬表"));

            System.IO.StreamWriter _sw = new System.IO.StreamWriter(_sPath, false, Encoding.Default);

            //表头
            _sw.WriteLine("人力宝人力资源管理系统V2.0");
            _sw.WriteLine("薪酬管理模块 <<员工每月薪酬表>>");
            _sw.WriteLine();

            _sw.Write(String.Format("{0}\t", "序号"));
            foreach (DataGridViewColumn dgvc in dgvData.Columns)
            {
                if (dgvc.Visible)
                {
                    _sw.Write(String.Format("{0}\t", dgvc.HeaderText));
                }
            }
            _sw.Write(String.Format("{0}\t{1}\t{2}", "员工签字", "日期", "备注"));
            _sw.WriteLine();

            int i = 1;
            foreach (DataGridViewRow dgvr in dgvData.Rows)
            {
                _sw.Write(String.Format("{0}", i));
                for (int j = 0; j < dgvData.Columns.Count - 1; j++)
                {
                    if (dgvData.Columns[j].Visible)
                    {
                        if (j == 3)
                        {
                            _sw.Write(String.Format("\t'{0}", dgvr.Cells[j].Value));
                        }
                        else 
                        {
                         _sw.Write(String.Format("\t{0}", dgvr.Cells[j].Value));
                        }
                    }
                }

                i++;
                _sw.WriteLine();
            }
            _sw.WriteLine();
            _sw.WriteLine(String.Format("{0}\t\t{1}\t\t\t\t{2}\t\t{3}", "制表人", "制表日期", "审核人", "审核日期"));
            _sw.Close();
            System.IO.File.Move(_sPath, _sGoal);
            return _sGoal;
        }