请各位高手帮我写个用户注册，用户名不能重复的例子，在线等

Question

你好，帮我看看这个为什么总是提示说＂使用了未赋值的局部变量“gusername”＂
 protected void save_Click(object sender, EventArgs e)
    {
        string select;
        string str = Context.Server.MapPath(Request.ApplicationPath);
        str = str + "\\" + "App_Data" + "\\" + "wdf.mdb";
        System.Data.OleDb.OleDbConnection oleConn = new System.Data.OleDb.OleDbConnection();
        oleConn.ConnectionString = @"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + str + ";User ID=Admin";
        oleConn.Open();
        System.Data.OleDb.OleDbDataReader Reader;
        select = "SELECT [username] FROM (select [username] FROM ghsb union select [username] FROM [user]) AS regisert where username='" + UserName.Text.Trim() +"'";
        olecomm = new System.Data.OleDb.OleDbCommand(select, oleConn);
        Reader = olecomm.ExecuteReader();
        Reader.Read();
        string gusername;
        
        if (Convert.ToString(Reader.GetValue(0))==UserName.Text.Trim())
        {
           
            Response.Write("<script language='javascript'>alert('对不起'+UserName+'已经有人用了,请换其它的!');</script>");
        }
        else
        {
            gusername = UserName.Text.Trim();
        }
        olecomm.Connection.Close();
        
   　　 string strinsert = "insert into [user] (username)"
                     + " values ('" + gusername + "')";
                    oleConn.Open();
                     oleComm = new System.Data.OleDb.OleDbCommand(strinsert, oleConn);
                     oleComm.ExecuteNonQuery();
                     //Response.Write("<scprit language='javascript'>alert('注册成功,进入首页登录！');</script>");//可修改成在１０秒钟自动进入主页；或是让用户自己选择
                     labelmessage.Text = "注册成功,进入首页登录！";
                     oleComm.Connection.Close();
                     oleConn.Close();                
                    
                  
                       
        
    }

Answer 1

给gusername 赋个初值
string gusername ="";

Answer 2

gusername 在 if (Convert.ToString(Reader.GetValue(0))==UserName.Text.Trim())
        {
           
            Response.Write("<script language='javascript'>alert('对不起'+UserName+'已经有人用了,请换其它的!');</script>");
        }
        else
        {
            gusername = UserName.Text.Trim();
        }
这里只有一种情况赋值，另外一种没有赋值，可以将string gusername;改为string gusername＝null;

Answer 3

string gusername; 
改为全局======================
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======================

Answer 4

我的是这么做的，但是我引用了一个数据库语句类 ，里面的 ttt是这个类的名字
   protected void Button1_Click(object sender, EventArgs e)
    {
        try
        {
            if (password.Text == password1.Text && username.Text != "")
            {
                string strmenoname = "";
                string strmenoid = "";
                string strfgsid = "";
                string strfgsname = "";
                if (quan.SelectedValue.ToString() == "1")
                {
                    strmenoname = menoname.SelectedItem.Text;
                    strmenoid = menoname.SelectedValue.ToString();                }
                
                string strInsert = "select username from admin_tbl where username='" + username.Text + "'";
                if (ttt.ExistDate1(strInsert)==false)//看是否有这个用户名
                {
                    
                    strInsert = "insert into admin_tbl (username,password1,updatetime,quan,menoid) values ('" + username.Text + "','" + password.Text + "','" + DateTime.Now + "','" + quan.SelectedItem.Value.ToString() + "','" + strmenoid + "')";
                    //message.Text = strInsert;
                    ttt.RunProc1(strInsert);
                    Response.Redirect("edituser.aspx");
                }
                else
                {
                    message.Text = "对不起这个用户名已经被占用了，请输入其它的用户名";
                }
            }
            else
            {
                message.Text = message.Text + "用户名不能为空，密码和确认密码要一致！";
            }        }
        catch (Exception ex)
        {
            message.Text = message.Text + "错误" + ex.Message.ToString();
        }
    }

Answer 5

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Answer 6

哥们,你也把数据访问层封装一下啊,何必每次都去写那么多重复代码.
你的错误是:string gusername;
改为string gusername="";