试了以下代码，提示 OleDbDataReader reader = cmd.ExecuteReader();
这一句错误：
“标准表达式中数据类型不匹配。 ”
请大侠帮忙！！！
 
                    string strPath = Application.StartupPath + "\\gk.mdb";
                    string strconn = "provider=microsoft.jet.oledb.4.0;data source='" + strPath + "'";
                    OleDbConnection oleconn = new OleDbConnection(strconn);
                    
                    string strcmd = "select * from tb_user where username='" + txtuser.Text.Trim() + "'and userpwd='" + txtpwd.Text.Trim() + "' ";
                    OleDbCommand cmd = new OleDbCommand(strcmd, oleconn);
                    oleconn.Open();
                    OleDbDataReader reader =cmd.ExecuteReader();
                    try
                    {
                        reader.Read();
                        if (reader.HasRows)
                        {
                            string pp = txtuser.Text;

                            // Frm_Main newfrm = new Frm_Main(pp);
                            frm_main main = new frm_main();
                            main.Show();
                            this.Hide();
                        }
                        else
                        {
                            MessageBox.Show("用户名或密码错误！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
                            txtuser.Text = "";
                            txtpwd.Text = "";
                            txtuser.Focus();
                        }
                    }

                    finally
                    {
                        if (reader != null)
                            oleconn.Close();
                    }


[ 本帖最后由 zjdjh 于 2012-3-12 21:46 编辑 ]

看起来好像没错！

access数据库的后缀名似乎是accdb吧，mdb的是否可以，没有尝试过，楼主看看是否是这个原因

你试一下下面这一段！


string strPath = Application.StartupPath + "\\gk.mdb";
                    string strconn = "provider=microsoft.jet.oledb.4.0;data source='" + strPath + "'";
                    OleDbConnection oleconn = new OleDbConnection(strconn);
                    string strcmd = "select * from tb_user where username='" + txtuser.Text.Trim() + "'and  userpwd='" + txtpwd.Text.Trim() + "' ";
                    OleDbCommand cmd = new OleDbCommand();
                      = strcmd;
                    try
                    {
                        
                        if (null == cmd.ExecuteScalar())
                        {
                            string pp = txtuser.Text;

                            // Frm_Main newfrm = new Frm_Main(pp);
                            frm_main main = new frm_main();
                            main.Show();
                            this.Hide();
                        }
                        else
                        {
                            MessageBox.Show("用户名或密码错误！", "提示", MessageBoxButtons.OK,  
MessageBoxIcon.Information);
                            txtuser.Text = "";
                            txtpwd.Text = "";
                            txtuser.Focus();
                        }
                    }