SharePoint Update All Item In Library Not Update Version And Modified Date SSOM

protected void UpdateName()
{
    DateTime issueDate = new DateTime();
    if (SPContext.Current != null)
    {
        try
        {
            SPSecurity.RunWithElevatedPrivileges(delegate()
                {
                    writeFile = new StreamWriter("c:\\<foldrname>\\" + "test.txt");
                    textlogwirte(Sb.AppendLine("Update Strarted" + System.DateTime.Now.ToLongTimeString()));
                    using(SPSite elevatedSite = new SPSite(SPContext.Current.Web.Url))
                    {
                        using(SPWeb oWebsite = elevatedSite.OpenWeb())
                        {
                            SPQuery oQuery = new SPQuery();
                            string where = "<Where><IsNotNull><FieldRef Name='fieldName'></FieldRef></IsNotNull></Where>";
                            oQuery.Query = where;
                            if (txtSPQuery.Text.Length > 0)
                            {
                                oQuery.Query = txtSPQuery.Text;
                            }
                            int numItms = 0;
                            string listname = "Library Display Name";
                            //foreach (string listname in libraryName)
                            //{
                            Sb.Clear();
                            Sb.AppendLine("List Name :" + listname.ToString());
                            oWebsite.AllowUnsafeUpdates = true;
                            try
                            {
                                SPList oList = oWebsite.Lists.TryGetList(listname);
                                if (oList != null)
                                {
                                    // if we update single or coupld of fileds you can use
                                    // if (oList.Fields.ContainsField("filedinternalname")) this comments before after the loop start.
                                    oQuery.ViewFields = "<FieldRef Name=\"FileRef\" />";
                                    oQuery.ViewFields += @ "<FieldRef Name='field1' Nullable='TRUE' />";
                                    oQuery.ViewFields += @ "<FieldRef Name='field1' Nullable='TRUE' />";
                                    oQuery.ViewAttributes = "Scope=\"Recursive\"";
                                    oQuery.RowLimit = 50;
                                    int intIndex = 1;
                                    do {
                                        SPListItemCollection collListItems = oList.GetItems(oQuery);
                                        foreach(SPListItem curItm in collListItems)
                                        {
                                            if (curItm.File.CheckOutType == Microsoft.SharePoint.SPFile.SPCheckOutType.None)
                                            {
                                                if (curItm["IssueDate"] != null)
                                                {
                                                    Dateupdate = DateTime.Parse(curItm["fiedlsname"].ToString(), null, DateTimeStyles.None);
                                                    curItm["fieldname"] = Dateupdate;
                                                }
                                                curItm["fieldname"] = "XXXXXXXX";
                                                curItm["fieldname"] = "xxx";
                                                try
                                                {
                                                    curItm.SystemUpdate(false);
                                                    numItms++;
                                                }
                                                catch (Exception ex)
                                                {}
                                            }
                                        }
                                        oQuery.ListItemCollectionPosition = collListItems.ListItemCollectionPosition;
                                        intIndex++;
                                    }
                                    while (oQuery.ListItemCollectionPosition != null);
                                    oWebsite.AllowUnsafeUpdates = false;
                                    Sb.AppendLine("List Name :" + listname.ToString() + intIndex);
                                }
                                //list object null check
                                else
                                {
                                    //log error msg                                        }
                                }
                                catch (Exception ex)
                                {
                                    Sb.AppendLine(ex.Message.ToString());
                                    textlogwirte(Sb);
                                    Sb.Clear();
                                }
                                //if list is not available.. try catch end
                                Sb.AppendLine("List Name :" + listname.ToString() + "-- update end ---");
                                textlogwirte(Sb);
                                Sb.Clear();
                                //} //for loop
                                Sb.AppendLine("Update process completed" + System.DateTime.Now.ToLongTimeString());
                                textlogwirte(Sb);
                                writeFile.Close();
                                writeFile = null;
                                lblMsg.Text = "There were " + numItms.ToString() + " item(s) updated";
                            }
                            //spweb
                        }
                    });
            }
            catch (Exception ex)
            {
                Sb.AppendLine(ex.Message.ToString());
                textlogwirte(Sb);
                Sb.Clear();
            }
        }
        else
        {
            Sb.AppendLine("SP context Null");
            textlogwirte(Sb);
            Sb.Clear();
        }
    }
}