带输出参数的存储过程

调用带输出参数的存储过程,在程序中除了声明该参数的值类型外,还必须指明返回值的大小,否则会出现错误.
正确例子:public void getpwd()
            {
                conn.Open();
                SqlCommand comm = new SqlCommand();
                comm.CommandText = "Stest";
                comm.CommandType = CommandType.StoredProcedure;
                comm.Connection = conn;
                SqlParameter[] prams ={ new SqlParameter("@username", SqlDbType.NChar), new SqlParameter("@userpwd", SqlDbType.NChar,20) };//@userpwd 是output 大小 20,在次必须指明
                prams[0].Value = this._username;
                prams[1].Direction = ParameterDirection.Output ;
                comm.Parameters.AddRange(prams);
                try
                {
                    comm.ExecuteNonQuery();
                }
                catch (Exception e)
                {
                    throw e;
                }
                finally
                {
                    this._UserPwd = comm.Parameters[1].Value.ToString ();
                    conn.Close();
                }
            }