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• virt-install says name is in use, but virsh list --all is empty. Where is virt-install finding this name?

  - by Jay _silly_evarlast_ Wren

  virt-install says name is in use, but virsh list --all says there is nothing. jrwren@delays:{%22}~ $ virt-install -d -n android -r 512 --disk android.qcow2 -s 4 -c /d/cd\ images/android-x86-2.2-generic.iso --vnc --noautoconsole [Thu, 05 Jul 2012 16:57:19 virt-install 23170] DEBUG (cli:220) Launched with command line: /usr/bin/virt-install -d -n android -r 512 --disk android.qcow2 -s 4 -c /d/cd images/android-x86-2.2-generic.iso --vnc --noautoconsole [Thu, 05 Jul 2012 16:57:19 virt-install 23170] DEBUG (cli:326) Requesting libvirt URI default [Thu, 05 Jul 2012 16:57:19 virt-install 23170] DEBUG (cli:328) Received libvirt URI qemu:///session [Thu, 05 Jul 2012 16:57:20 virt-install 23170] DEBUG (virt-install:259) Requesting virt method 'default', hv type 'default'. [Thu, 05 Jul 2012 16:57:20 virt-install 23170] DEBUG (virt-install:469) Received virt method 'hvm' [Thu, 05 Jul 2012 16:57:20 virt-install 23170] DEBUG (virt-install:470) Hypervisor name is 'kvm' [Thu, 05 Jul 2012 16:57:20 virt-install 23170] DEBUG (cli:950) --graphics compat generated: vnc [Thu, 05 Jul 2012 16:57:20 virt-install 23170] ERROR (cli:597) Guest name 'android' is already in use. (venv)jrwren@delays:{%22}~ $ sudo virsh -c qemu:///system list --all Id Name State ---------------------------------- Where is virt-install finding this name? edit: I should mention that LIBVIRT_DEFAULT_URI is not set.

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• Powershell enters foreach loop with null object

  - by SteB

  I'm listing all backups in a given directory: $backups = Get-ChildItem -Path $zipFilepath | Where-Object {($_.lastwritetime -lt (Get-Date).addDays(-7)) -and (-not $_.PSIsContainer) -and ($_.Name -like "backup*")} If I set it to deliberately return no files (.addDays(-600) then the following prints "Empty" (as expected): if (!$backups) { "Empty" } If I try to list the names with an empty $backups variable: foreach ($file in $backups) { $file.FullName; } I get nothing (as expected), if I change this to: "test"+ $file.FullName; then I get a single "test" under the "Empty". How is this possible if $backups is empty?

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• How can I import a CSV file into an SQLite table that doesn't allow null values?

  - by Philip

  I've been using the SQLite Manager extension for Firefox to edit my Chrome web data file in order to restore my keyword searches, and I think I have everything in place except that when I import a CSV file into a table, (a) it won't import into the actual table because the table doesn't allow null values (b) if I import it into a new table that does allow null values, then all the empty strings end up as null and I have to manually edit the row, type and delete a character, and then it's set to empty string and it's fine So: is there either a way to import the CSV so that empty cells are automatically turned into empty strings instead of null, OR is there a way once a table is imported that has null values to convert it into one that doesn't allow null values, where each formerly null value is the empty string? Thanks!

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• How can I make my generic comparer (IComparer) handle nulls? [closed]

  - by Nick G

  Hi, I'm trying to write a generic object comparer for sorting, but I have noticed it does not handle the instance where one of the values it's comparing is null. When an object is null, I want it to treat it the same as the empty string. I've tried setting the null values to String.Empty but then I get an error of "Object must be of type String" when calling CompareTo() on it. public int Compare(T x, T y) { PropertyInfo propertyInfo = typeof(T).GetProperty(sortExpression); IComparable obj1 = (IComparable)propertyInfo.GetValue(x, null); IComparable obj2 = (IComparable)propertyInfo.GetValue(y, null); if (obj1 == null) obj1 = String.Empty; // This doesn't work! if (obj2 == null) obj2 = String.Empty; // This doesn't work! if (SortDirection == SortDirection.Ascending) return obj1.CompareTo(obj2); else return obj2.CompareTo(obj1); } I'm pretty stuck with this now! Any help would be appreciated.

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• If and else condition not working properly in xna [closed]

  - by user1090751

  I am developing chess like game and i wanted to show error message if user try to place any player inside the box which is not empty. For example in certain place if there is empty then the object(2d object) is placed else it should show error message. However in my program it is showing message everytime i.e when i place object on empty place then also it is showing error message. Please see the below code: protected override void Update(GameTime gameTime) { // Allows the game to exit if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed) this.Exit(); // TODO: Add your update logic here for (int i = 0; i < 25; i++) { MouseState mouseState; mouseDiBack = false; mouseState = Mouse.GetState(); if (new Rectangle(mouseState.X, mouseState.Y, 1, 1).Intersects(rect_arr[i])) { background_color_arr[i] = Color.Red; } else { background_color_arr[i] = Color.White; } if (new Rectangle(mouseState.X, mouseState.Y, 1, 1).Intersects(rect_arr[i]) && (mouseState.LeftButton == ButtonState.Pressed)) { if (boxes[i] != "goat" && boxes[i] != "tiger") { place = i; if (turn == "goat") { boxes[i] = "goat"; turn = "tiger"; } else { boxes[i] = "tiger"; turn = "goat"; } } else { errMsg = "This " + i + " block is not empty to place " + turn + ". Please select empty block!!"; } } } base.Update(gameTime); }

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• problem with PHP class function ()

  - by lusey

  hello this is my first question here and i hope you can help me .. I am trying to find a soloution of the towers of hanoi problem by three search ways (BFS-DFS-IDS) so I use "state" class whitch defined by 5 variables as here : class state { var $tower1 = array(); var $tower2 = array(); var $tower3 = array(); var $depth; var $neighbors = array(); and it also has many function one of them is getneighbors() which supposed to fill the array $neighbors with state neighbors and they are from the type "state" and here is the function : function getneighbors () { $temp=$this->copy(); $neighbor1= $this->copy(); $neighbor2= $this->copy(); $neighbor3= $this->copy(); $neighbor4= $this->copy(); $neighbor5= $this->copy(); $neighbor6= $this->copy(); if(!Empty($temp->tower1)) { if(!Empty($neighbor1->tower2)) { if(end($neighbor1->tower1) < end($neighbor1->tower2)) { array_unshift($neighbor1->tower2,array_pop($neighbor1->tower1)); array_push($neighbors,$neighbor1); }} else { array_unshift($neighbor1->tower2, array_pop($neighbor1->tower1)); array_push($neighbors,$neighbor1); } if(!Empty($neighbor2->tower3)) { if(end($neighbor2->tower1) < end($neighbor2->tower3)) { array_unshift($neighbor2->tower3, array_pop($neighbor2->tower1)); array_push($neighbors,$neighbor2); }} else { array_unshift($neighbor2->tower3,array_shift($neighbor2->tower1)); array_push($neighbors,$neighbor2); } } if(!Empty($temp->tower2)) { if(!Empty($neighbor3->tower1)) { if(end($neighbor3->tower2) < end($neighbor3->tower1)) { array_unshift($neighbor3->tower1,array_shift($neighbor3->tower2)); array_push($neighbors,$neighbor3); } } else { array_unshift($neighbor3->tower1,array_shift($neighbor3->tower2)); array_push($neighbors,$neighbor3); } if(!Empty($neighbor4->tower3)) { if(end($neighbor4->tower2) < end($neighbor4->tower3)) { array_unshift($neighbor4->tower1,array_shift($neighbor4->tower2)); array_push($neighbors,$neighbor4); } } else{ array_unshift($neighbor4->tower3,array_shift($neighbor4->tower2)); array_push($neighbors,$neighbor4); } } if(!Empty($temp->tower3)) { if(!Empty($neighbor5->tower1)) { if(end($neighbor5->tower3) < end($neighbor5->tower1)) {array_unshift($neighbor5->tower1,array_shift($neighbor5->tower3)); array_push($neighbors,$neighbor5); } } else{ array_unshift($neighbor5->tower1,array_shift($neighbor5->tower3)); array_push($neighbors,$neighbor5);} if(!Empty($neighbor6->tower2)) { if(end($neighbor6->tower3) < end($neighbor6->tower2)) { array_unshift($neighbor6->tower2,array_shift($neighbor6->tower3)); array_push($neighbors,$neighbor6); }} else{ array_unshift($neighbor6->tower2,array_shift($neighbor6->tower3)); array_push($neighbors,$neighbor6);} } return $neighbors; } note that toString and equals and copy are defined too now the problem is that when I call getneighbors() it returns an empty $neighbors array can you pleas tell me the problem ?

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• datagrid binding

  - by abcdd007

  using System; using System.Data; using System.Configuration; using System.Collections; using System.Web; using System.Web.Security; using System.Web.UI; using System.Web.UI.WebControls; using System.Web.UI.WebControls.WebParts; using System.Web.UI.HtmlControls; using System.Data.SqlClient; public partial class OrderMaster : System.Web.UI.Page { BLLOrderMaster objMaster = new BLLOrderMaster(); protected void Page_Load(object sender, EventArgs e) { if (!Page.IsPostBack) { SetInitialRow(); string OrderNumber = objMaster.SelectDetails().ToString(); if (OrderNumber != "") { txtOrderNo.Text = OrderNumber.ToString(); txtOrderDate.Focus(); } } } private void InsertEmptyRow() { DataTable dt = new DataTable(); DataRow dr = null; dt.Columns.Add(new DataColumn("ItemCode", typeof(string))); dt.Columns.Add(new DataColumn("Description", typeof(string))); dt.Columns.Add(new DataColumn("Unit", typeof(string))); dt.Columns.Add(new DataColumn("Qty", typeof(string))); dt.Columns.Add(new DataColumn("Rate", typeof(string))); dt.Columns.Add(new DataColumn("Disc", typeof(string))); dt.Columns.Add(new DataColumn("Amount", typeof(string))); for (int i = 0; i < 5; i++) { dr = dt.NewRow(); dr["ItemCode"] = string.Empty; dr["Description"] = string.Empty; dr["Unit"] = string.Empty; dr["Qty"] = string.Empty; dr["Rate"] = string.Empty; dr["Disc"] = string.Empty; dr["Amount"] = string.Empty; dt.Rows.Add(dr); } //GridView1.DataSource = dt; //GridView1.DataBind(); } private void SetInitialRow() { DataTable dt = new DataTable(); DataRow dr = null; dt.Columns.Add(new DataColumn("RowNumber", typeof(string))); dt.Columns.Add(new DataColumn("ItemCode", typeof(string))); dt.Columns.Add(new DataColumn("Description", typeof(string))); dt.Columns.Add(new DataColumn("Unit", typeof(string))); dt.Columns.Add(new DataColumn("Qty", typeof(string))); dt.Columns.Add(new DataColumn("Rate", typeof(string))); dt.Columns.Add(new DataColumn("Disc", typeof(string))); dt.Columns.Add(new DataColumn("Amount", typeof(string))); dr = dt.NewRow(); dr["RowNumber"] = 1; dr["ItemCode"] = string.Empty; dr["Description"] = string.Empty; dr["Unit"] = string.Empty; dr["Qty"] = string.Empty; dr["Rate"] = string.Empty; dr["Disc"] = string.Empty; dr["Amount"] = string.Empty; dt.Rows.Add(dr); //Store DataTable ViewState["OrderDetails"] = dt; Gridview1.DataSource = dt; Gridview1.DataBind(); } protected void AddNewRowToGrid() { int rowIndex = 0; if (ViewState["OrderDetails"] != null) { DataTable dtCurrentTable = (DataTable)ViewState["OrderDetails"]; DataRow drCurrentRow = null; if (dtCurrentTable.Rows.Count > 0) { for (int i = 1; i <= dtCurrentTable.Rows.Count; i++) { //extract the TextBox values TextBox box1 = (TextBox)Gridview1.Rows[rowIndex].Cells[1].FindControl("txtItemCode"); TextBox box2 = (TextBox)Gridview1.Rows[rowIndex].Cells[2].FindControl("txtdescription"); TextBox box3 = (TextBox)Gridview1.Rows[rowIndex].Cells[3].FindControl("txtunit"); TextBox box4 = (TextBox)Gridview1.Rows[rowIndex].Cells[4].FindControl("txtqty"); TextBox box5 = (TextBox)Gridview1.Rows[rowIndex].Cells[5].FindControl("txtRate"); TextBox box6 = (TextBox)Gridview1.Rows[rowIndex].Cells[6].FindControl("txtdisc"); TextBox box7 = (TextBox)Gridview1.Rows[rowIndex].Cells[7].FindControl("txtamount"); drCurrentRow = dtCurrentTable.NewRow(); drCurrentRow["RowNumber"] = i + 1; drCurrentRow["ItemCode"] = box1.Text; drCurrentRow["Description"] = box2.Text; drCurrentRow["Unit"] = box3.Text; drCurrentRow["Qty"] = box4.Text; drCurrentRow["Rate"] = box5.Text; drCurrentRow["Disc"] = box6.Text; drCurrentRow["Amount"] = box7.Text; rowIndex++; } //add new row to DataTable dtCurrentTable.Rows.Add(drCurrentRow); //Store the current data to ViewState ViewState["OrderDetails"] = dtCurrentTable; //Rebind the Grid with the current data Gridview1.DataSource = dtCurrentTable; Gridview1.DataBind(); } } else { // } //Set Previous Data on Postbacks SetPreviousData(); } private void SetPreviousData() { int rowIndex = 0; if (ViewState["OrderDetails"] != null) { DataTable dt = (DataTable)ViewState["OrderDetails"]; if (dt.Rows.Count > 0) { for (int i = 1; i < dt.Rows.Count; i++) { TextBox box1 = (TextBox)Gridview1.Rows[rowIndex].Cells[1].FindControl("txtItemCode"); TextBox box2 = (TextBox)Gridview1.Rows[rowIndex].Cells[2].FindControl("txtdescription"); TextBox box3 = (TextBox)Gridview1.Rows[rowIndex].Cells[3].FindControl("txtunit"); TextBox box4 = (TextBox)Gridview1.Rows[rowIndex].Cells[4].FindControl("txtqty"); TextBox box5 = (TextBox)Gridview1.Rows[rowIndex].Cells[5].FindControl("txtRate"); TextBox box6 = (TextBox)Gridview1.Rows[rowIndex].Cells[6].FindControl("txtdisc"); TextBox box7 = (TextBox)Gridview1.Rows[rowIndex].Cells[7].FindControl("txtamount"); box1.Text = dt.Rows[i]["ItemCode"].ToString(); box2.Text = dt.Rows[i]["Description"].ToString(); box3.Text = dt.Rows[i]["Unit"].ToString(); box4.Text = dt.Rows[i]["Qty"].ToString(); box5.Text = dt.Rows[i]["Rate"].ToString(); box6.Text = dt.Rows[i]["Disc"].ToString(); box7.Text = dt.Rows[i]["Amount"].ToString(); rowIndex++; } dt.AcceptChanges(); } ViewState["OrderDetails"] = dt; } } protected void BindOrderDetails() { DataTable dtOrderDetails = new DataTable(); if (ViewState["OrderDetails"] != null) { dtOrderDetails = (DataTable)ViewState["OrderDetails"]; } else { dtOrderDetails.Columns.Add(""); dtOrderDetails.Columns.Add(""); dtOrderDetails.Columns.Add(""); dtOrderDetails.Columns.Add(""); dtOrderDetails.Columns.Add(""); dtOrderDetails.Columns.Add(""); dtOrderDetails.AcceptChanges(); DataRow dr = dtOrderDetails.NewRow(); dtOrderDetails.Rows.Add(dr); ViewState["OrderDetails"] = dtOrderDetails; } if (dtOrderDetails != null) { Gridview1.DataSource = dtOrderDetails; Gridview1.DataBind(); if (Gridview1.Rows.Count > 0) { ((LinkButton)Gridview1.Rows[Gridview1.Rows.Count - 1].FindControl("btnDelete")).Visible = false; } } } protected void btnSave_Click(object sender, EventArgs e) { if (txtOrderDate.Text != "" && txtOrderNo.Text != "" && txtPartyName.Text != "" && txttotalAmount.Text !="") { BLLOrderMaster bllobj = new BLLOrderMaster(); DataTable dtdetails = new DataTable(); UpdateItemDetailRow(); dtdetails = (DataTable)ViewState["OrderDetails"]; SetValues(bllobj); int k = 0; k = bllobj.Insert_Update_Delete(1, bllobj, dtdetails); if (k > 0) { ScriptManager.RegisterStartupScript(this, this.GetType(), "Login Denied", "<Script>alert('Order Code Alraddy Exist');</Script>", false); } else { ScriptManager.RegisterStartupScript(this, this.GetType(), "Login Denied", "<Script>alert('Record Saved Successfully');</Script>", false); } dtdetails.Clear(); SetInitialRow(); txttotalAmount.Text = ""; txtOrderNo.Text = ""; txtPartyName.Text = ""; txtOrderDate.Text = ""; txttotalQty.Text = ""; string OrderNumber = objMaster.SelectDetails().ToString(); if (OrderNumber != "") { txtOrderNo.Text = OrderNumber.ToString(); txtOrderDate.Focus(); } } else { txtOrderNo.Text = ""; } } public void SetValues(BLLOrderMaster bllobj) { if (txtOrderNo.Text != null && txtOrderNo.Text.ToString() != "") { bllobj.OrNumber = Convert.ToInt16(txtOrderNo.Text); } if (txtOrderDate.Text != null && txtOrderDate.Text.ToString() != "") { bllobj.Date = DateTime.Parse(txtOrderDate.Text.ToString()).ToString("dd/MM/yyyy"); } if (txtPartyName.Text != null && txtPartyName.Text.ToString() != "") { bllobj.PartyName = txtPartyName.Text; } bllobj.TotalBillAmount = txttotalAmount.Text == "" ? 0 : int.Parse(txttotalAmount.Text); bllobj.TotalQty = txttotalQty.Text == "" ? 0 : int.Parse(txttotalQty.Text); } protected void txtdisc_TextChanged(object sender, EventArgs e) { double total = 0; double totalqty = 0; foreach (GridViewRow dgvr in Gridview1.Rows) { TextBox tb = (TextBox)dgvr.Cells[7].FindControl("txtamount"); double sum; if (double.TryParse(tb.Text.Trim(), out sum)) { total += sum; } TextBox tb1 = (TextBox)dgvr.Cells[4].FindControl("txtqty"); double qtysum; if (double.TryParse(tb1.Text.Trim(), out qtysum)) { totalqty += qtysum; } } txttotalAmount.Text = total.ToString(); txttotalQty.Text = totalqty.ToString(); AddNewRowToGrid(); Gridview1.TabIndex = 1; } public void UpdateItemDetailRow() { DataTable dt = new DataTable(); if (ViewState["OrderDetails"] != null) { dt = (DataTable)ViewState["OrderDetails"]; } if (dt.Rows.Count > 0) { for (int i = 0; i < Gridview1.Rows.Count; i++) { dt.Rows[i]["ItemCode"] = (Gridview1.Rows[i].FindControl("txtItemCode") as TextBox).Text.ToString(); if (dt.Rows[i]["ItemCode"].ToString() == "") { dt.Rows[i].Delete(); break; } else { dt.Rows[i]["Description"] = (Gridview1.Rows[i].FindControl("txtdescription") as TextBox).Text.ToString(); dt.Rows[i]["Unit"] = (Gridview1.Rows[i].FindControl("txtunit") as TextBox).Text.ToString(); dt.Rows[i]["Qty"] = (Gridview1.Rows[i].FindControl("txtqty") as TextBox).Text.ToString(); dt.Rows[i]["Rate"] = (Gridview1.Rows[i].FindControl("txtRate") as TextBox).Text.ToString(); dt.Rows[i]["Disc"] = (Gridview1.Rows[i].FindControl("txtdisc") as TextBox).Text.ToString(); dt.Rows[i]["Amount"] = (Gridview1.Rows[i].FindControl("txtamount") as TextBox).Text.ToString(); } } dt.AcceptChanges(); } ViewState["OrderDetails"] = dt; } }

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• Varchar columns: Nullable or not.

  - by NYSystemsAnalyst

  The database development standards in our organization state the varchar fields should not allow null values. They should have a default value of an empty string (""). I know this makes querying and concatenation easier, but today, one of my coworkers questioned me about why that standard only existed for varchar types an not other datatypes (int, datetime, etc). I would like to know if others consider this to be a valid, defensible standard, or if varchar should be treated the same as fields of other data types? I believe this standard is valid for the following reason: I believe that an empty string and null values, though technically different, are conceptually the same. An empty, zero length string is a string that does not exist. It has no value. However, a numeric value of 0 is not the same as NULL. For example, if a field called OutstandingBalance has a value of 0, it means there are $0.00 remaining. However, if the same field is NULL, that means the value is unknown. On the other hand, a field called CustomerName with a value of "" is basically the same as a value of NULL because both represent the non-existence of the name. I read somewhere that an analogy for an empty string vs. NULL is that of a blank CD vs. no CD. However, I believe this to be a false analogy because a blank CD still phyically exists and still has physical data space that does not have any meaningful data written to it. Basically, I believe a blank CD is the equivalent of a string of blank spaces (" "), not an empty string. Therefore, I believe a string of blank spaces to be an actual value separate from NULL, but an empty string to be the absense of value conceptually equivalent to NULL. Please let me know if my beliefs regarding variable length strings are valid, or please enlighten me if they are not. I have read several blogs / arguments regarding this subject, but still do not see a true conceptual difference between NULLs and empty strings.

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• Problems with Database Search Code (asp.net vb)

  - by Phil

  Here is a sample of my database search code: Dim sql As String = "Select * From Table Where " Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load Dim andor As Boolean = AndOr1.SelectedValue 'selection can be AND or OR (0 / 1) 'Code for when the user selects AND If NameSearch.Text.ToString IsNot String.Empty And andor = 0 Then sql += "Surname LIKE '%" & name & "%' AND " End If If EmailSearch.Text.ToString IsNot String.Empty And andor = 0 Then sql += "Email LIKE '%" & email & "%' AND " End If If CitySearchBox.Text.ToString IsNot String.Empty And andor = 0 Then sql += "City LIKE '%" & city & "%' AND " End If 'Code for when the user selects OR If NameSearch.Text.ToString IsNot String.Empty And andor = 1 Then sql += "(Surname LIKE '%" & name & "%' OR " End If If EmailSearch.Text.ToString IsNot String.Empty And andor = 1 Then sql += "Email LIKE '%" & email & "%') OR " End If If CitySearchBox.Text.ToString IsNot String.Empty And andor = 1 Then sql += "(City LIKE '%" & city & "%' OR " End If sql = CleanString(sql) End Sub When the user selects AND (as andor.selectedvalue(0)) then the sql is produced fine like this; Select * From Table Where Surname LIKE '%test%' AND Email LIKE '%test%' AND City LIKE '%test%' But if the user selects OR (as andor.selectedvalue(1)), nothing is outputted except; Select * From Table Where Im sure the controls have values so are not string.empty and when the user selects OR the correct value 1 is being assigned to andor.

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• PHP contact form, am I doing it wrong?

  - by decimal

  I'm learning PHP and I'm trying to write a simple email script. I have a function (checkEmpty) to check if all the forms are filled in and if the email adress is valid (isEmailValid). I'm not sure how to return true checkEmpty funciton. Here's my code: When the submit button is clicked: if (isset($_POST['submit'])) { //INSERT FORM VALUES INTO AN ARRAY $field = array ('name' => $_POST['name'], 'email' => $_POST['email'], 'message' => $_POST['message']); //CONVERT ARRAY KEYS TO VARIABLE NAMES extract ($field); checkEmpty($name, $email, $message); function checkEmpty($name, $email, $message) { global $name_error; global $mail_error; global $message_error; //CHECK IF NAME FIELD IS EMPTY if (isset($name) === true && empty($name) === true) { $name_error = "<span class='error_text'>* Please enter your name</span>"; } //CHECK IF EMAIL IS EMPTY if (isset($email) === true && empty($email) === true) { $mail_error = "<span class='error_text'>* Please enter your email address</span>"; //AND IF IT ISN'T EMPTY CHECK IF IT IS A VALID ONE } elseif (!isValidEmail($email)) { $mail_error = "<span class='error_text'> * Please enter a valid email</span>"; } //CHECK IF MESSAGE IS EMPTY if (isset($message) === true && empty($message) === true) { $message_error = "<span class='error_text'>* Please enter your message</span>"; } } // This function tests whether the email address is valid function isValidEmail($email){ $pattern = "^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})$"; if (eregi($pattern, $email)) { return true; } else { return false; } } I know I shouldn't be using globals in the function, I don't know an alternative. The error messages are display beside each form element.

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• update/validate embedded forms before saving in symfony

  - by Stanislav Palatnik

  I would like to validate an embedded form field before it gets saved in the database. Currently it will save an empty value into the database if the form field is empty. I'm allowing empty fields, but I want nothing inserted if the form field is empty. Also quick question, how to alter field values before validating/saving an embedded form field? $this-form-getObject works in the action, but $this-embeddedForm-getObject says object not found

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• Designing a database file format

  - by RoliSoft

  I would like to design my own database engine for educational purposes, for the time being. Designing a binary file format is not hard nor the question, I've done it in the past, but while designing a database file format, I have come across a very important question: How to handle the deletion of an item? So far, I've thought of the following two options: Each item will have a "deleted" bit which is set to 1 upon deletion. Pro: relatively fast. Con: potentially sensitive data will remain in the file. 0x00 out the whole item upon deletion. Pro: potentially sensitive data will be removed from the file. Con: relatively slow. Recreating the whole database. Pro: no empty blocks which makes the follow-up question void. Con: it's a really good idea to overwrite the whole 4 GB database file because a user corrected a typo. I will sell this method to Twitter ASAP! Now let's say you already have a few empty blocks in your database (deleted items). The follow-up question is how to handle the insertion of a new item? Append the item to the end of the file. Pro: fastest possible. Con: file will get huge because of all the empty blocks that remain because deleted items aren't actually deleted. Search for an empty block exactly the size of the one you're inserting. Pro: may get rid of some blocks. Con: you may end up scanning the whole file at each insert only to find out it's very unlikely to come across a perfectly fitting empty block. Find the first empty block which is equal or larger than the item you're inserting. Pro: you probably won't end up scanning the whole file, as you will find an empty block somewhere mid-way; this will keep the file size relatively low. Con: there will still be lots of leftover 0x00 bytes at the end of items which were inserted into bigger empty blocks than they are. Rigth now, I think the first deletion method and the last insertion method are probably the "best" mix, but they would still have their own small issues. Alternatively, the first insertion method and scheduled full database recreation. (Probably not a good idea when working with really large databases. Also, each small update in that method will clone the whole item to the end of the file, thus accelerating file growth at a potentially insane rate.) Unless there is a way of deleting/inserting blocks from/to the middle of the file in a file-system approved way, what's the best way to do this? More importantly, how do databases currently used in production usually handle this?

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• Simplifying a four-dimensional rule table in Matlab: addressing rows and columns of each dimension

  - by Cate

  Hi all. I'm currently trying to automatically generate a set of fuzzy rules for a set of observations which contain four values for each observation, where each observation will correspond to a state (a good example is with Fisher's Iris Data). In Matlab I am creating a four dimensional rule table where a single cell (a,b,c,d) will contain the corresponding state. To reduce the table I am following the Hong and Lee method of row and column similarity checking but I am having difficulty understanding how to address the third and fourth dimensions' rows and columns. From the method it is my understanding that each dimension is addressed individually and if the rule is true, the table is simplified. The rules for merging are as follows: If all cells in adjacent columns or rows are the same. If two cells are the same or if either of them is empty in adjacent columns or rows and at least one cell in both is not empty. If all cells in a column or row are empty and if cells in its two adjacent columns or rows are the same, merge the three. If all cells in a column or row are empty and if cells in its two adjacent columns or rows are the same or either of them is empty, merge the three. If all cells in a column or row are empty and if all the non-empty cells in the column or row to its left have the same region, and all the non-empty cells in the column or row to its right have the same region, but one different from the previously mentioned region, merge these three columns into two parts. Now for the confusing bit. Simply checking if the entire row/column is the same as the adjacent (rule 1) seems simple enough: if (a,:,:,:) == (a+1,:,:,:) (:,b,:,:) == (:,b+1,:,:) (:,:,c,:) == (:,:,c+1,:) (:,:,:,d) == (:,:,:,d+1) is this correct? but to check if the elements in the row/column match, or either is zero (rules 2 and 4), I am a bit lost. Would it be something along these lines: for a = 1:20 for i = 1:length(b) if (a+1,i,:,:) == (a,i,:,:) ... else if (a+1,i,:,:) == 0 ... else if (a,i,:,:) == 0 etc. and for the third and fourth dimensions: for c = 1:20 for i = 1:length(a) if (i,:,c,:) == (i,:,c+1,:) ... else if (i,:,c+1,:) == 0 ... else if (i,:,c,:) == 0 etc. for d = 1:20 for i = 1:length(a) if (i,:,:,d) == (i,:,:,d+1) ... else if (i,:,:,d+1) == 0 ... else if (i,:,:,d) == 0 etc. even any help with four dimensional arrays would be useful as I'm so confused by the thought of more than three! I would advise you look at the paper to understand my meaning - they themselves have used the Iris data but only given an example with a 2D table. Thanks in advance, hopefully!

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• CSS: How to make a Div of text underneath another Div selectable?

  - by jesse

  Hi, I have a few empty Divs on a page that are basically empty boxes to help me position some stuff to make a "liquid" website. Now I've got content underneath these Divs but I can't highlight/click on the links because these empty Divs are blocking it. I've got a reason I need to have the empty Divs to be on the top layer so I need a way to "click through" these Divs. What can I do? Thanks.

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• c++ queue template

  - by Dalton Conley

  ALright, pardon my messy code please. Below is my queue class. #include <iostream> using namespace std; #ifndef QUEUE #define QUEUE /*---------------------------------------------------------------------------- Student Class # Methods # Student() // default constructor Student(string, int) // constructor display() // out puts a student # Data Members # Name // string name Id // int id ----------------------------------------------------------------------------*/ class Student { public: Student() { } Student(string iname, int iid) { name = iname; id = iid; } void display(ostream &out) const { out << "Student Name: " << name << "\tStudent Id: " << id << "\tAddress: " << this << endl; } private: string name; int id; }; // define a typedef of a pointer to a student. typedef Student * StudentPointer; template <typename T> class Queue { public: /*------------------------------------------------------------------------ Queue Default Constructor Preconditions: none Postconditions: assigns default values for front and back to 0 description: constructs a default empty Queue. ------------------------------------------------------------------------*/ Queue() : myFront(0), myBack(0) {} /*------------------------------------------------------------------------ Copy Constructor Preconditions: requres a reference to a value for which you are copying Postconditions: assigns a copy to the parent Queue. description: Copys a queue and assigns it to the parent Queue. ------------------------------------------------------------------------*/ Queue(const T & q) { myFront = myBack = 0; if(!q.empty()) { // copy the first node myFront = myBack = new Node(q.front()); NodePointer qPtr = q.myFront->next; while(qPtr != NULL) { myBack->next = new Node(qPtr->data); myBack = myBack->next; qPtr = qPtr->next; } } } /*------------------------------------------------------------------------ Destructor Preconditions: none Postconditions: deallocates the dynamic memory for the Queue description: deletes the memory stored for a Queue. ------------------------------------------------------------------------*/ ~Queue() { NodePointer prev = myFront, ptr; while(prev != NULL) { ptr = prev->next; delete prev; prev = ptr; } } /*------------------------------------------------------------------------ Empty() Preconditions: none Postconditions: returns a boolean value. description: returns true/false based on if the queue is empty or full. ------------------------------------------------------------------------*/ bool empty() const { return (myFront == NULL); } /*------------------------------------------------------------------------ Enqueue Preconditions: requires a constant reference Postconditions: allocates memory and appends a value at the end of a queue description: ------------------------------------------------------------------------*/ void enqueue(const T & value) { NodePointer newNodePtr = new Node(value); if(empty()) { myFront = myBack = newNodePtr; newNodePtr->next = NULL; } else { myBack->next = newNodePtr; myBack = newNodePtr; newNodePtr->next = NULL; } } /*------------------------------------------------------------------------ Display Preconditions: requires a reference of type ostream Postconditions: returns the ostream value (for chaining) description: outputs the contents of a queue. ------------------------------------------------------------------------*/ void display(ostream & out) const { NodePointer ptr; ptr = myFront; while(ptr != NULL) { out << ptr->data << " "; ptr = ptr->next; } out << endl; } /*------------------------------------------------------------------------ Front Preconditions: none Postconditions: returns a value of type T description: returns the first value in the parent Queue. ------------------------------------------------------------------------*/ T front() const { if ( !empty() ) return (myFront->data); else { cerr << "*** Queue is empty -- returning garbage value ***\n"; T * temp = new(T); T garbage = * temp; delete temp; return garbage; } } /*------------------------------------------------------------------------ Dequeue Preconditions: none Postconditions: removes the first value in a queue ------------------------------------------------------------------------*/ void dequeue() { if ( !empty() ) { NodePointer ptr = myFront; myFront = myFront->next; delete ptr; if(myFront == NULL) myBack = NULL; } else { cerr << "*** Queue is empty -- " "can't remove a value ***\n"; exit(1); } } /*------------------------------------------------------------------------ pverloaded = operator Preconditions: requires a constant reference Postconditions: returns a const type T description: this allows assigning of queues to queues ------------------------------------------------------------------------*/ Queue<T> & operator=(const T &q) { // make sure we arent reassigning ourself // e.g. thisQueue = thisQueue. if(this != &q) { this->~Queue(); if(q.empty()) { myFront = myBack = NULL; } else { myFront = myBack = new Node(q.front()); NodePointer qPtr = q.myFront->next; while(qPtr != NULL) { myBack->next = new Node(qPtr->data); myBack = myBack->next; qPtr = qPtr->next; } } } return *this; } private: class Node { public: T data; Node * next; Node(T value, Node * first = 0) : data(value), next(first) {} }; typedef Node * NodePointer; NodePointer myFront, myBack, queueSize; }; /*------------------------------------------------------------------------ join Preconditions: requires 2 queue values Postconditions: appends queue2 to the end of queue1 description: this function joins 2 queues into 1. ------------------------------------------------------------------------*/ template <typename T> Queue<T> join(Queue<T> q1, Queue<T> q2) { Queue<T> q1Copy(q1), q2Copy(q2); Queue<T> jQueue; while(!q1Copy.empty()) { jQueue.enqueue(q1Copy.front()); q1Copy.dequeue(); } while(!q2Copy.empty()) { jQueue.enqueue(q2Copy.front()); q2Copy.dequeue(); } cout << jQueue << endl; return jQueue; } /*---------------------------------------------------------------------------- Overloaded << operator Preconditions: requires a constant reference and a Queue of type T Postconditions: returns the ostream (for chaining) description: this function is overloaded for outputing a queue with << ----------------------------------------------------------------------------*/ template <typename T> ostream & operator<<(ostream &out, Queue<T> &s) { s.display(out); return out; } /*---------------------------------------------------------------------------- Overloaded << operator Preconditions: requires a constant reference and a reference of type Student Postconditions: none description: this function is overloaded for outputing an object of type Student. ----------------------------------------------------------------------------*/ ostream & operator<<(ostream &out, Student &s) { s.display(out); } /*---------------------------------------------------------------------------- Overloaded << operator Preconditions: requires a constant reference and a reference of a pointer to a Student object. Postconditions: none description: this function is overloaded for outputing pointers to Students ----------------------------------------------------------------------------*/ ostream & operator<<(ostream &out, StudentPointer &s) { s->display(out); } #endif Now I'm having some issues with it. For one, when I add 0 to a queue and then I output the queue like so.. Queue<double> qdub; qdub.enqueue(0); cout << qdub << endl; That works, it will output 0. But for example, if I modify that queue in any way.. like.. assign it to a different queue.. Queue<double> qdub1; Queue<double> qdub2; qdub1.enqueue(0; qdub2 = qdub1; cout << qdub2 << endl; It will give me weird values for 0 like.. 7.86914e-316. Help on this would be much appreciated!

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• How to write Haskell function to verify parentheses matching?

  - by Rizo

  I need to write a function par :: String -> Bool to verify if a given string with parentheses is matching using stack module. Ex: par "(((()[()])))" = True par "((]())" = False Here's my stack module implementation: module Stack (Stack, push, pop, top, empty, isEmpty) where data Stack a = Stk [a] deriving (Show) push :: a -> Stack a -> Stack a push x (Stk xs) = Stk (x:xs) pop :: Stack a -> Stack a pop (Stk (_:xs)) = Stk xs pop _ = error "Stack.pop: empty stack" top :: Stack a -> a top (Stk (x:_)) = x top _ = error "Stack.top: empty stack" empty :: Stack a empty = Stk [] isEmpty :: Stack a -> Bool isEmpty (Stk [])= True isEmpty (Stk _) = False So I need to implement a 'par' function that would test a string of parentheses and say if parentheses in it matches or not. How can I do that using a stack?

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• IWebBrowser2.Navigate opens second window

  - by Sam Barham

  The following code, on Vista with Internet Explorer 7, opens two windows (the one I create, and then a second one when Navigate is called, which is the one that the file appears in). This doesn't happen in Internet Explorer 8, or on XP as far as I know. Any idea how I can stop it doing that? SHDocVw.InternetExplorerClass ieObject = (SHDocVw.InternetExplorerClass)this.ieObject; if (this.ieObject == null) { ieObject = new SHDocVw.InternetExplorerClass(); this.ieObject = ieObject; } SHDocVw.IWebBrowser2 browserApp = (SHDocVw.IWebBrowser2)this.ieObject; object empty = System.Reflection.Missing.Value; browserApp.Visible = true; User32.SetForegroundWindow(new IntPtr(browserApp.HWND)); browserApp.Navigate(filePath, ref empty, ref empty, ref empty, ref empty);

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• Problem with Variable Scoping in Rebol's Object

  - by Rebol Tutorial

  I have modified the rebodex app so that it can be called from rebol's console any time by typing rebodex. To show the title of the app, I need to store it in app-title: system/script/header/title so tha it could be used later in view/new/title dex reform [self/app-title version] That works but as you can see I have named the var name "app-title", but if I use "title" instead, the window caption would show weird stuff (vid code). Why ? REBOL [ Title: "Rebodex" Date: 23-May-2010 Version: 2.1.1 File: %rebodex.r Author: "Carl Sassenrath" Modification: "Rebtut" Purpose: "A simple but useful address book contact database." Email: %carl--rebol--com library: [ level: 'intermediate platform: none type: 'tool domain: [file-handling DB GUI] tested-under: none support: none license: none see-also: none ] ] rebodex.context: context [ app-title: system/script/header/title version: system/script/header/version set 'rebodex func[][ names-path: %names.r ;data file name-list: none fields: [name company title work cell home car fax web email smail notes updat] names: either exists? names-path [load names-path][ [[name "Carl Sassenrath" title "Founder" company "REBOL Technologies" email "%carl--rebol--com" web "http://www.rebol.com"]] ] brws: [ if not empty? web/text [ if not find web/text "http://" [insert web/text "http://"] error? try [browse web/text] ] ] dial: [request [rejoin ["Dial number for " name/text "? (Not implemented.)"] "Dial" "Cancel"]] dex-styles: stylize [ lab: label 60x20 right bold middle font-size 11 btn: button 64x20 font-size 11 edge [size: 1x1] fld: field 200x20 font-size 11 middle edge [size: 1x1] inf: info font-size 11 middle edge [size: 1x1] ari: field wrap font-size 11 edge [size: 1x1] with [flags: [field tabbed]] ] dex-pane1: layout/offset [ origin 0 space 2x0 across styles dex-styles lab "Name" name: fld bold return lab "Title" title: fld return lab "Company" company: fld return lab "Email" email: fld return lab "Web" brws web: fld return lab "Address" smail: ari 200x72 return lab "Updated" updat: inf 200x20 return ] 0x0 updat/flags: none dex-pane2: layout/offset [ origin 0 space 2x0 across styles dex-styles lab "Work #" dial work: fld 140 return lab "Home #" dial home: fld 140 return lab "Cell #" dial cell: fld 140 return lab "Alt #" dial car: fld 140 return lab "Fax #" fax: fld 140 return lab "Notes" notes: ari 140x72 return pad 136x1 btn "Close" #"^q" [store-entry save-file unview] ] 0x0 dex: layout [ origin 8x8 space 0x1 styles dex-styles srch: fld 196x20 bold across rslt: list 180x150 [ nt: txt 178x15 middle font-size 11 [ store-entry curr: cnt find-name nt/text update-entry unfocus show dex ] ] supply [ cnt: count + scroll-off face/text: "" face/color: snow if not n: pick name-list cnt [exit] face/text: select n 'name face/font/color: black if curr = cnt [face/color: system/view/vid/vid-colors/field-select] ] sl: slider 16x150 [scroll-list] return return btn "New" #"^n" [new-name] btn "Del" #"^d" [delete-name unfocus update-entry search-all show dex] btn "Sort" [sort names sort name-list show rslt] return at srch/offset + (srch/size * 1x0) bx1: box dex-pane1/size bx2: box dex-pane2/size return ] bx1/pane: dex-pane1/pane bx2/pane: dex-pane2/pane rslt/data: [] this-name: first names name-list: copy names curr: none search-text: "" scroll-off: 0 srch/feel: make srch/feel [ redraw: func [face act pos][ face/color: pick face/colors face system/view/focal-face if all [face = system/view/focal-face face/text search-text] [ search-text: copy face/text search-all if 1 = length? name-list [this-name: first name-list update-entry show dex] ] ] ] update-file: func [data] [ set [path file] split-path names-path if not exists? path [make-dir/deep path] write names-path data ] save-file: has [buf] [ buf: reform [{REBOL [Title: "Name Database" Date:} now "]^/[^/"] foreach n names [repend buf [mold n newline]] update-file append buf "]" ] delete-name: does [ remove find/only names this-name if empty? names [append-empty] save-file new-name ] clean-names: function [][n][ forall names [ if any [empty? first names none? n: select first names 'name empty? n][ remove names ] ] names: head names ] search-all: function [] [ent flds] [ clean-names clear name-list flds: [name] either empty? search-text [insert name-list names][ foreach nam names [ foreach word flds [ if all [ent: select nam word find ent search-text][ append/only name-list nam break ] ] ] ] scroll-off: 0 sl/data: 0 resize-drag scroll-list curr: none show [rslt sl] ] new-name: does [ store-entry clear-entry search-all append-empty focus name ; update-entry ] append-empty: does [append/only names this-name: copy []] find-name: function [str][] [ foreach nam names [ if str = select nam 'name [ this-name: nam break ] ] ] store-entry: has [val ent flag] [ flag: 0 if not empty? trim name/text [ foreach word fields [ val: trim get in get word 'text either ent: select this-name word [ if ent val [insert clear ent val flag: flag + 1] ][ if not empty? val [repend this-name [word copy val] flag: flag + 1] ] if flag = 1 [flag: 2 updat/text: form now] ] if not zero? flag [save-file] ] ] update-entry: does [ foreach word fields [ insert clear get in get word 'text any [select this-name word ""] ] show rslt ] clear-entry: does [ clear-fields bx1 clear-fields bx2 updat/text: form now unfocus show dex ] show-names: does [ clear rslt/data foreach n name-list [ if n/name [append rslt/data n/name] ] show rslt ] scroll-list: does [ scroll-off: max 0 to-integer 1 + (length? name-list) - (100 / 16) * sl/data show rslt ] do resize-drag: does [sl/redrag 100 / max 1 (16 * length? name-list)] center-face dex new-name focus srch show-names view/new/title dex reform [app-title version] insert-event-func [ either all [event/type = 'close event/face = dex][ store-entry unview ][event] ] do-events ] ]

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• jQuery to PHP: no input... kinda

  - by Seva Alekseyev

  Hi all, I'm using jQuery to post HTTP requests to my PHP page (Apache/Linux, if that matters). I carefully validate on the client so that empty requests are not sent. However on occasions, I'd get an empty request like this: - $_POST collection empty ($_GET collection also empty); - Content-Length is nonzero (a number below 100, consistent with a valid POST from my script) - Content-Type properly application/x-www-form-urlencoded - reading from php://input yields an empty string It's as if $_POST is somehow eaten on the way. I checked the code very carefully - I don't do anything to the contents of $_POST. Any ideas, please?

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• Binary Search Tree node removal

  - by doc

  I've been trying to implement a delete function for a Binary Search Tree but haven't been able to get it to work in all cases. This is my latest attempt: if(t->get_left() == empty) *t = *t->get_left(); else if(t->get_right() == empty) *t = *t->get_right(); else if((t->get_left() != empty) && (t->get_right() != empty)) { Node* node = new Node(t->get_data(), t->get_parent(), t->get_colour(), t->get_left(), t->get_right()); *t = *node; } t is a node and empty is just a node with nothing in it. I'm just trying to swap the values but I'm getting a runtime error. Any ideas? Thanks

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• velocity: join optional fields with a separator/prefix

  - by SlowStrider

  What would be the most concise/readable way in a velocity template to join multiple fields with a separator while leaving out empty or null Strings without adding excess separators? As an example we have a tooltip or appointments that goes like: Appointment ($number) [with $employee] [-] [$remarks] [-] [$roomToVisit] Where I used brackets to indicate optional data. When filled in it would normally show as Appointment (3) with John - ballroom - serve Java coffee When $remarks is empty but $roomToVisit is not, this becomes: Appointment (3) with John - ballroom When $remarks is "serve Java coffee" but $roomToVisit is empty we get: Appointment (3) with John - serve Java coffee When both are empty: Appointment (3) with John Bonus: also make the field prefix optional. When only $employee is empty we should get: Appointment (2) serve Java coffee - ballroom Ideally I would like the velocity template to look very similar to the first code box. If this is not possible, how would you achieve this with a minimum of distracting code tags? Similar ideas (first is much more verbose): Join with intelligent separators velocity: do something except in last loop iteration

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• Why my register form don't accept spry validation in dw? [migrated]

  - by shaghayeh

  Why my register form don't accept spry validation in dw? Here is my code: <?php if(isset($_POST['go_register'])) { $last_login=jdate('Y/n/j ,H:i:s'); $firstname=trim($_POST['firstname']); $lastname=trim($_POST['lastname']); $email=trim($_POST['username']); $password=sha1($_POST['password']); $register_date=$_POST['register_date']; if(!empty($firstname)&& !empty($lastname)&& !empty($email)&& !empty($password)&& !empty($register_date)){ $reg_query="insert into users(firstname,lastname,email,password,register_date,last_login)values('$firstname','$lastname','$email','$password','$register_date','$last_login')"; $reg_result=mysqli_query($connection,$reg_query); if($reg_result){ echo "ok"; } }//end of not empty }//end of isset ?> <div class="sectionclass"> <script src="../SpryAssets/SpryValidationTextField.js" type="text/javascript"></script> <link href="../SpryAssets/SpryValidationTextField.css" rel="stylesheet" type="text/css"> <h2>??? ??? ???</h2> <form method="post" action="<?php echo $_SERVER['PHP_SELF']."?catid=2"; ?>"> <div> <span style="color:#F00">*</span> <label>??? </label> <span id="sprytextfield1"> <input type="text" name="firstname" /> <span class="textfieldRequiredMsg">A value is required.</span></span></div> <div> <span style="color:#F00">*</span> <label>??? ????????</label><input type="text" name="lastname" /> </div> <div> <span style="color:#F00">*</span> <label>??? ??????(?????)</label><input dir="ltr" type="text" name="username" /> </div> <div> <span style="color:#F00">*</span> <label>??? ????</label><input type="password" name="password" /> </div> <input type="hidden" name="register_date" value="<?php echo jdate('Y/n/j'); ?>"> <div> <input type="submit" name="go_register" value="??? ???"/> </div> </form> </div> <script type="text/javascript"> var sprytextfield1 = new Spry.Widget.ValidationTextField("sprytextfield1"); </script>

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• (1 2 3 . #<void>)- heapsort

  - by superguay

  Hello everybody: I tried to implement a "pairing heap" with all the regular operations (merge, delete-min etc.), then I've been requested to write a function that would sort a list using my newly constructed heap implementation. Unfortunately it seems that someting goes wrong... Here's the relevant code: (define (heap-merge h1 h2) (cond ((heap-empty? h1) h2) ((heap-empty? h2) h1) (else (let ((min1 (heap-get-min h1)) (min2 (heap-get-min h2))) (if ((heap-get-less h1) min1 min2) (make-pairing-heap (heap-get-less h1) min1 (cons h2 (heap-get-subheaps h1))) (make-pairing-heap (heap-get-less h1) min2 (cons h1 (heap-get-subheaps h2)))))))) (define (heap-insert element h) (heap-merge (make-pairing-heap (heap-get-less h) element '()) h)) (define (heap-delete-min h) (define (merge-in-pairs less? subheaps) (cond ((null? subheaps) (make-heap less?)) ((null? (cdr subheaps)) (car subheaps)) (else (heap-merge (heap-merge (car subheaps) (cadr subheaps)) (merge-in-pairs less? (cddr subheaps)))))) (if (heap-empty? h) (error "expected pairing-heap for first argument, got an empty heap ") (merge-in-pairs (heap-get-less h) (heap-get-subheaps h)))) (define (heapsort l less?) (let aux ((h (accumulate heap-insert (make-heap less?) l))) (if (not (heap-empty? h)) (cons (heap-get-min h) (aux (heap-delete-min h)))))) And these are some selectors that may help you to understand the code: (define (make-pairing-heap less? min subheaps) (cons less? (cons min subheaps))) (define (make-heap less?) (cons less? '())) (define (heap-get-less h) (car h)) (define (heap-empty? h) (if (null? (cdr h)) #t #f)) Now lets get to the problem: When i run 'heapsort' it returns the sorted list with "void", as you can see: (heapsort (list 1 2 3) <) (1 2 3 . #)..HOW CAN I FIX IT? Regards, Superguay

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• ADT-like polymorphism in Java (without altering class)

  - by ffriend

  In Haskell I can define following data type: data Tree = Empty | Leaf Int | Node Tree Tree and then write polymorphic function like this: depth :: Tree -> Int depth Empty = 0 depth (Leaf n) = 1 depth (Node l r) = 1 + max (depth l) (depth r) In Java I can emulate algebraic data types with interfaces: interface Tree {} class Empty implements Tree {} class Leaf implements Tree { int n; } class Node implements Tree { Tree l; Tree r; } But if I try to use Haskell-like polymorphism, I get an error: int depth(Empty node) { return 0; } int depth(Leaf node) { return 1; } int depth(Node node) { return 1 + Math.max(depth(node.l), depth(node.r)); // ERROR: Cannot resolve method 'depth(Tree)' } Correct way to overcome this is to put method depth() to each class. But what if I don't want to put it there? For example, method depth() may be not directly related to Tree and adding it to class would break business logic. Or, even worse, Tree may be written in 3rd party library that I don't have access to. In this case, what is the simplest way to implement ADT-like polymorpism? Just in case, for the moment I'm using following syntax, which is obviously ill-favored: int depth(Tree tree) { if (tree instanceof Empty) depth((Empty)tree) if (tree instanceof Leaf) depth((Leaf)tree); if (tree instanceof Node) depth((Node)tree); else throw new RuntimeException("Don't know how to find depth of " + tree.getClass()); }

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• Adding string items to a list of type Person C#

  - by user1862808

  Im makeing a simple registration application and I have an assignment to learn more about lists. I have an assignment that says that i am to create a class called Persons and in that class set the values from the text fields in variables and add this to a list of type Person. So far: in the Person class: string strSocialSecurityNumber = string.Empty;//---( This will not be used now.) string strFirstName = string.Empty; string strLastName = string.Empty; string strFullName = string.Empty; string strAge = string.Empty; string strAll = string.Empty; int intAge = 0; List<Person> lstPerson = new List<Person>(); public void SetValues(string FirstName, string LastName, int Age) { strFirstName = FirstName; strLastName = LastName; strFullName = strFirstName + " " + strLastName; intAge = Age; strAge = Convert.ToString(intAge); strAll = strAge + " " + strFullName; } public List<Person> Person() { lstPerson.Add(strAll); return lstPerson; } Error message: "can not convert from string to Person" The assignment says that the list is to be of the type Person so i am suppose to add strings to it and ive looked how to do this but I dont know how. I have seen that there are options like "ConvertAll" But im not sure if I am allowed to use it since the list should be of type Person. Thank you!

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