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• HTML Text writer

  - by user339160

  In my project , i have created a custom control which inherits from label. My aim is to add 2 links in this . I need to use the same label to render these two links.i tried the bellow code only the first link is loading ,not the second .Please help my sample code looks like writer.RenderBeginTag(HtmlTextWriterTag.Link); writer.AddAttribute(HtmlTextWriterAttribute.Href, string.Concat(Path 1)); writer.AddAttribute(HtmlTextWriterAttribute.Type, "text/css"); writer.AddAttribute(HtmlTextWriterAttribute.Rel, "stylesheet"); writer.RenderEndTag(); writer.RenderBeginTag(HtmlTextWriterTag.Link); writer.AddAttribute(HtmlTextWriterAttribute.Href, string.Concat(Path 2 )); writer.AddAttribute(HtmlTextWriterAttribute.Type, "text/css"); writer.AddAttribute(HtmlTextWriterAttribute.Rel, "stylesheet"); writer.RenderEndTag();

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• GoogleMaps API v3 - Need help with two "click" event scenarios. Need similar functionality to v2 AP

  - by Nathan Raley

  In version 2 of the API the map click event returned an Overlay, LatLng, Overlaylatlng. I used this to create a generic map event that would either retrieve the coordinates of the Map click event, or return the coordinates of a Marker or other type of Overlay. Now that API v3 doesn't return the Overlay or Overlaylatlng during the map click event, how can I go about creating a generic "click" event for the map that works if the user clicks on a marker or overlay? I really don't want to create a click event for each marker I have on my page as I am creating anywhere from a handful to a couple thousand markers. Also, I had to create a custom ImageMapType in order to display the StreetViewOverlay like we could do in v2 of the API because I couldn't find anywhere that told me how to add the StreetViewOverlay without the pegman icon. How can I go about retrieving the LatLng coordinates of a click on this overlay type as well?

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• Custom Section Name Crashing NSFetchedResultsController

  - by Mike H.

  I have a managed object with a dueDate attribute. Instead of displaying using some ugly date string as the section headers of my UITableView I created a transient attribute called "category" and defined it like so: - (NSString*)category { [self willAccessValueForKey:@"category"]; NSString* categoryName; if ([self isOverdue]) { categoryName = @"Overdue"; } else if ([self.finishedDate != nil]) { categoryName = @"Done"; } else { categoryName = @"In Progress"; } [self didAccessValueForKey:@"category"]; return categoryName; } Here is the NSFetchedResultsController set up: NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"Task" inManagedObjectContext:managedObjectContext]; [fetchRequest setEntity:entity]; NSMutableArray* descriptors = [[NSMutableArray alloc] init]; NSSortDescriptor *dueDateDescriptor = [[NSSortDescriptor alloc] initWithKey:@"dueDate" ascending:YES]; [descriptors addObject:dueDateDescriptor]; [dueDateDescriptor release]; [fetchRequest setSortDescriptors:descriptors]; fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:@"category" cacheName:@"Root"]; The table initially displays fine, showing the unfinished items whose dueDate has not passed in a section titled "In Progress". Now, the user can tap a row in the table view which pushes a new details view onto the navigation stack. In this new view the user can tap a button to indicate that the item is now "Done". Here is the handler for the button (self.task is the managed object): - (void)taskDoneButtonTapped { self.task.finishedDate = [NSDate date]; } As soon as the value of the "finishedDate" attribute changes I'm hit with this exception: 2010-03-18 23:29:52.476 MyApp[1637:207] Serious application error. Exception was caught during Core Data change processing: no section named 'Done' found with userInfo (null) 2010-03-18 23:29:52.477 MyApp[1637:207] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'no section named 'Done' found' I've managed to figure out that the UITableView that is currently hidden by the new details view is trying to update its rows and sections because the NSFetchedResultsController was notified that something changed in the data set. Here's my table update code (copied from either the Core Data Recipes sample or the CoreBooks sample -- I can't remember which): - (void)controllerWillChangeContent:(NSFetchedResultsController *)controller { [self.tableView beginUpdates]; } - (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath { switch(type) { case NSFetchedResultsChangeInsert: [self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade]; break; case NSFetchedResultsChangeDelete: [self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade]; break; case NSFetchedResultsChangeUpdate: [self configureCell:[self.tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath]; break; case NSFetchedResultsChangeMove: [self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade]; // Reloading the section inserts a new row and ensures that titles are updated appropriately. [self.tableView reloadSections:[NSIndexSet indexSetWithIndex:newIndexPath.section] withRowAnimation:UITableViewRowAnimationFade]; break; } } - (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type { switch(type) { case NSFetchedResultsChangeInsert: [self.tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade]; break; case NSFetchedResultsChangeDelete: [self.tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade]; break; } } - (void)controllerDidChangeContent:(NSFetchedResultsController *)controller { [self.tableView endUpdates]; } I put breakpoints in each of these functions and found that only controllerWillChange is called. The exception is thrown before either controller:didChangeObject:atIndexPath:forChangeType:newIndex or controller:didChangeSection:atIndex:forChangeType are called. At this point I'm stuck. If I change my sectionNameKeyPath to just "dueDate" then everything works fine. I think that's because the dueDate attribute never changes whereas the category will be different when read back after the finishedDate attribute changes. Please help! UPDATE: Here is my UITableViewDataSource code: - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { return [[self.fetchedResultsController sections] count]; } - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section]; return [sectionInfo numberOfObjects]; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; UITableViewCell *cell = [self.tableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease]; } [self configureCell:cell atIndexPath:indexPath]; return cell; } - (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section { id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section]; return [sectionInfo name]; }

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• template static classes across dynamic linked libraries

  - by user322274

  Hello, I have a templated class with a static value, like this: template <class TYPE> class A{ static TYPE value; }; in the code of a dll I assign the static value: code of DLL_1 A<float>::value = 2.0; I wish the value to be shared by all the dlls I'm using, i.e. I want that: code of DLL_2 printf("value on DLL_2 %f",A<float>::value); print out "2.0" any clues? thx

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• Maven giving error Missing artifact

  - by newbie

  I'm adding Google App Engine, Spring and Tiles2 to same project, for some reason Apache Maven gives this error. Missing artifact org.apache.commons:com.springsource.org.apache.commons.collections:jar:3.2.1:compile here is my pom.xml where i include dependency: <dependency> <groupId>org.apache.commons</groupId> <artifactId>com.springsource.org.apache.commons.collections</artifactId> <version>3.2.1</version> <type>pom</type> </dependency>

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• how can we change the value by using radio buttons

  - by magna

  I am making a website in Adobe Dreamweaver with php. In the site there’s a 3 buttons for selecting payment method that will act as the continue button. What I want is when the user checks a radio buttons (I agree button), it will be add with that amount and display with previous amount.. there is three buttons which has the corresponding values(amount in pounds).. plz check my website http://www.spsmobile.co.uk in this linkgo to mobile phone unlocking and after add the cart click make payment it will go to next page there is a delivery mail details.. for that delivery mail details only am asking.. here i mentioned code: <input id="radio-1" type="radio" name="rmr" value="1"> <label for="radio-1">£3</label> <input id="radio-2" type="radio" name="rmr" value="2"> <label for="radio-2">£5.5</label> <input id="radio-3" type="radio" name="rmr" value="4"> <label for="radio-3">£10</label> <div class="total-text" style="font-size:36px">£10</div> var total = parseInt($("div.total-text").text().substring(1), 10); $("input[name='rmr']").bind('change', function() { var amount = 0; switch (this.value) { case "1": amount = 3; break; case "2": amount = 5.5; break; case "4": amount = 10; break; } $("div.total-text").text("£" + (total + amount)); }); but there is no change , my previous amount did not add with that. while am clicking previous amount only displayed on browser.. i need when i cliks radio button the value should change correspondingly.. where i did that mistake...plz give me some idea and what should i do..is there any need for storing db.. thanks in adv

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• installing a package with xml based configuration in python

  - by saminny

  Hi, I am planning to write a generic python module for installing a package. This script should retrieve the module from a remote machine or locally and install it on a given host and user. However, there needs to be changes made to the package files based on the host, user and given environment. My approach is to use XML to describe changes to be made to package files based on environment. It will first extract the package to the user directory and then using an xml configuration file, it should replace the file values in the package directory. The xml would look something like this: <package version="1.3.3"> <environment type="prod"> <file dir="d1/d2" name="f1"> <var id="RECV_HOST" value="santo"> <var id="RECV_PORT" value="RECV_PORT_SERVICE" type="service"> <var id="JEPL_SERVICE_NAME" value="val_omgact"> </file> <var dir="d4/d3/s2" name="f2"> <var id="PRECISION" value="true"> <var id="SEND_STATUS_CODE" value="323"> <var id="JEPL_SERVICE_NAME" value="val_omgact"> </file> </environment> <environment type="qa"> <file dir="d1/d2" name="f1"> <var id="RECV_HOST" value="test"> <var id="RECV_PORT" value="1444"> <var id="JEPL_SERVICE_NAME" value="val_tsdd"> </file> <file dir="d4/d3/s2" name="f2"> <var id="PRECISION" value="false"> <var id="SEND_STATUS_CODE" value="323"> <var id="JEPL_SERVICE_NAME" value="val_dsd"> </file> </environment> </package> What are your thoughts on this approach? Is there an existing python module, package or script that I could use for this purpose since this seems fairly generic and can be used for any installation. Thanks! Sam

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• C++ template nontype parameter arithmetic

  - by aaa

  hello I am trying to specialize template the following way: 132 template<size_t _1,size_t _2> 131 struct integral_index_ {}; ... 141 template<size_t _1> 142 struct integral_index_<_1, _1 + 1> { ... 148 }; however I get compiler message error the template argument list of the partial specialization includes a non -type argument whose type depends on a template parameter. what do my doing wrong? thanks

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• posting data to a site in C#

  - by Michel

  i'm flabbergasted, i've looked at almost every example, but it just doesn't work (the other party says they don't receive my data in the request parameter) I want to do this in code (send some xml data (without the xml declaration) to a uri): <form method="post" action="http://http://100.100.100.100:11111/getinfo"> <input type="text" value="<ps:Balance>100</ps:Balance>" name="request" id="request"> <br><br> <input type="submit" value="go"> </form>

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• Django ORM dealing with MySQL BIT(1) field

  - by Carles Barrobés

  In a Django application, I'm trying to access an existing MySQL database created with Hibernate (a Java ORM). I reverse engineered the model using: $ manage.py inspectdb > models.py This created a nice models file from the Database and many things were quite fine. But I can't find how to properly access boolean fields, which were mapped by Hibernate as columns of type BIT(1). The inspectdb script by default creates these fields in the model as TextField and adds a comment saying that it couldn't reliably obtain the field type. I changed these to BooleanField but it doesn't work (the model objects always fetch a value of true for these fields). Using IntegerField won't work as well (e.g. in the admin these fields show strange non-ascii characters). Any hints of doing this without changing the database? (I need the existing Hibernate mappings and Java application to still work with the database).

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• IE - hidden radio button not checked when the corresponding label is clicked

  - by ScottE

  I just noticed a strange behaviour in IE7. I have radio buttons with associated labels as follows: <input type="radio" name="filter" id="filter_1" value="Activities" checked="checked" /> <label for="filter_1">Activities</label> <input type="radio" name="filter" id="filter_2" value="Services" /> <label for="filter_2">Services</label> The radio button is hidden via css with display:none or visibility: hidden (don't ask) The problem is - when I click the label in IE7 (haven't looked at other IE versions yet) the associated radio button is not actually checked. I confirmed this with jquery - the label click event is fired, but the radio button click event is not. A form post also confirms that the checked radio button does not change. This works correctly in firefox, and also works correctly if I remove the CSS that hides the radio buttons. Is this an IE bug or am I missing something?

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• How to correctly bind an object to a WPF DataGrid?

  - by mbadawi23

  I'm trying to get a WPF DataGrid to work from a user control I'm building. Things seems to work fine. But I noticed this message in the Output window in the IDE: System.Windows.Data Error: 39 : BindingExpression path error: 'Name' property not found on 'object' ''Object' (HashCode=18165668)'. BindingExpression:Path=Name; DataItem='Object' (HashCode=18165668); target element is 'TextBlock' (Name=''); target property is 'Text' (type 'String') System.Windows.Data Error: 39 : BindingExpression path error: 'Department' property not found on 'object' ''Object' (HashCode=18165668)'. BindingExpression:Path=Name; DataItem='Object' (HashCode=18165668); target element is 'TextBlock' (Name=''); target property is 'Text' (type 'String')

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• Why my combobox count is 0?

  - by just_name

  Why the count of items in my ComboBox is always 0 although the datasource of this combobox has data !! <div align="right" dir="rtl"> <asp:Label ID="lbl_contactListName" runat="server" Text="Menu Name :" CssClass="span"></asp:Label> <telerik:RadComboBox ID="ddl_contactList" runat="server" AutoPostBack="True" CausesValidation="False" CollapseDelay="0" Culture="ar-EG" ExpandDelay="0" Filter="StartsWith" ItemsPerRequest="10" MarkFirstMatch="true" Skin="Outlook" EnableAutomaticLoadOnDemand="True" EmptyMessage="-New Menu-" ShowMoreResultsBox="True" OnSelectedIndexChanged="ddl_contactList_SelectedIndexChanged" EnableVirtualScrolling="True" DataTextField="list_desc" DataValueField="list_code" DataSourceID="ObjectDataSource1" EnableViewState="true" Width="300px"> </telerik:RadComboBox> </div> <asp:ObjectDataSource ID="ObjectDataSource1" runat="server" SelectMethod="GetContactListsByDep" TypeName="SendSMS_EmailModule.ContactList"> <SelectParameters> <asp:SessionParameter Name="year" SessionField="year" Type="Int32" /> <asp:SessionParameter Name="main_code" SessionField="main_code" Type="Int32" /> </SelectParameters> </asp:ObjectDataSource>

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• jquery background image fade

  - by Nick

  I am using jQuery to load ina background image that fills the page width / height. I have the following in the Head: $(document).ready(function() { $('body').css({ 'background-image' : 'url({HTML_BASE}images/backgrounds/randoms/{BACK_IMG})', 'background-repeat' : 'no-repeat', 'background-position' : 'center top', 'background-attachment': 'fixed', 'background-size': '100% 100%', }); $('#home-promo').innerfade({ speed: 'slow', timeout: 5000, type: 'sequence', containerheight: 'auto' }); $('.model-search').innerfade({ speed: 'slow', timeout: 5000, type: 'sequence', containerheight: '393' }); }); This works fine and can be seen at http://projects.snowshtechnologies.com/golden_dragon/home/ I want the BG image to fade in from the black background colour. I have looked at a few other threads on Stack that suggest its not possible as a body element defined in css, but in this scenario the BG image is being loaded in by jQuery. How would I go about adding a fade in to this code to bring the image in with a nice fadein?

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• jQuery UI problem: why do the elements go flying around the screen?

  - by George Edison

  Yes, I know the title sounds a little suspicious. I will try to explain this the best I can... The code below is supposed to have the blue div slide down beside the red div. The first time you hit the Show the div button, it works. Also, the Hide the div works. Then when I click to show the div again, it appears to the right of where it is supposed to be! Why is this?!? Note: You can find a live example of the code here <html> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> <title>Demo</title> <style type='text/css'> #red { background-color: red; width: 200px; height: 150px; position: absolute; } #blue { background-color: blue; width: 150px; height: 200px; position: absolute; display: none; } #tester_1 { top: 300px; left: 300px; position: absolute; } #tester_2 { top: 350px; left: 300px; position: absolute; } </style> </head> <script type="text/javascript" src="jquery.js"></script> <script type='text/javascript'> function Show() { $('#blue').position({ of: $('#red'), my: 'left top', at: 'right top'}).slideDown(); } function Hide() { $('#blue').hide(); } </script> <body> <div id='red'></div> <div id='blue'></div> <button id='tester_1' onclick='Show()'>Show the <kbd>div</kbd></button> <button id='tester_2' onclick='Hide()'>Hide the <kbd>div</kbd></button> </body> </html>

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• Image input onclick event being fired when enter button Pressed

  - by Anthony

  I have a strange problem where an onclick event on an input image is being fired when i hit enter in input text box <form id="MyForm" action="/someaction"> <input type="image" src="someimage.jpg" onclick="doStuff();$('#MyForm').submit();" /> <input type="text" name="textInput"/> </form> When the cursor is in the text box and i hit enter, rather than the form being submitted it calls the onclick event on the image input. Any ideas whats going on ?

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• how to send 2d barcode sms

  - by Puneet Patel

  any one know how to send 2d barcode on sms or which type of sms format require to send barcode image on sms?

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• Go - Concurrent method

  - by nevalu

  How to get a concurrent method? In my case, the library would be called from a program to get a value to each argument str --in method Get()--. When it's used Get() then it assigns a variable from type bytes.Buffer which it will have the value to return. The returned values --when it been concurrently called-- will be stored into a database or a file and it doesn't matter that its output been of FIFO way (from method). type test struct { foo uint8 bar uint8 } func NewTest(arg1 string) (*test, os.Error) {...} func (self *test) Get(str string) ([]byte, os.Error) { var format bytes.Buffer ... } I think that all code inner of method Get() should be put inner of go func() {...}(), and then to use a channel. Would there be a problem if it's called another method from Get()? Or would it also has to be concurrent?

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• MSMQ empty object on message body

  - by Owen

  Ok, so I'm very VERY new to MSMQ and I'm already confused. I have created a private queue and added a few messages to it, all good so far. BUT when I retrieve the messages back from the queue the message body contains a empty object of the type I added. By this I don't mean that the body is null, it does have a reference to a type of the object that I added, but it's not instantiated so all the properties are in their null or default state. This is the code I use to add to the queue: using (var mQueue = new MessageQueue(QueueName)) { var msg = new Message(observation) { Priority = MessagePriority.Normal, UseJournalQueue = true, AcknowledgeType = AcknowledgeTypes.FullReceive, }; mQueue.Send(msg); } And this is the code that dequeues the messages: using (var mQueue = new MessageQueue(QueueName)) { mQueue.MessageReadPropertyFilter.SetAll(); ((XmlMessageFormatter)mQueue.Formatter).TargetTypes = new[] { typeof(Observation) }; var msg = mQueue.Receive(new TimeSpan(0, 0, 5)); var observation = (Observation)msg.Body; return observation; }

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• Why can't iterate over a listProerty an appengine?

  - by Juanjo Conti

  I've just got this error from Google App Engine: TypeError: argument of type 'ListProperty' is not iterable why?

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• Can't move li elements from one unorderted list to another

  - by Roland

  I have two un-ordered list <ul id="#list1"> <li>one</li> <li>two</li> </ul> <ul id="#list2"></ul> and two buttons <input id="add" name="yt1" type="button" value="<<" /><br /> <input id="remove" name="yt2" type="button" value=">>" /> If the button with the id add is pressed all elements from #list1 should be move to #list2. How do I move elements from one list to another using JQuery I though of something like the below, but not sure how to do the actual moving $("#add").click(function(){ $("#list1 li").each(function(){ //Do not know what to put in here } })

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• photo and video sharing on facebook in asp.net

  - by IphoneDeveloper

  i have to share the photo on facebook for which i have written the following code try { labelSteps_1_2.Text = "<a name=\"fb_share\" type=\"button\"></a>" + "<script " + "src=\"http://static.ak.fbcdn.net/connect.php/js/FB.Share\" " + "type=\"text/javascript\"></script>"; HtmlMeta tag = new HtmlMeta(); tag.Name = "title"; tag.Content = "This is the Title"; Page.Header.Controls.Add(tag); HtmlLink link = new HtmlLink(); link.Href = "http://admin.bizofair.com/UploadOffers/O_O11090004_14032012053503_183_183.jpeg"; link.Attributes["rel"] = "image_src"; link.Style.Add("color", "red"); Page.Header.Controls.Add(link); } catch (Exception ex) { // Handle the exception } on page load but it is not showing the image and when i have paste url of my image in facebook debugger on facebook developer it is giving error Errors That Must Be Fixed Can't Download: Could not retrieve data from URL.

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• PHP & MySQL - saving and looping problems.

  - by R.I.P.coalMINERS

  I'm new to PHP and MySQL I want a user to be able to store multiple names and there meanings in a MySQL database tables named names using PHP I will dynamically create form fields with JQuery every time a user clicks on a link so a user can enter 1 to 1,000,000 different names and there meanings which will be stored in a table called names. Since I asked my last question I figured out how to store my values from my form using the for loop but every time I loop my values when I add one or more dynamic fields the second form field named meaning will not save the value entered also my dynamic form fields keep looping doubling, tripling and so on the entered values into the database it all depends on how many form fields are added dynamically. I was wondering how can I fix these problems? On a side note I replaced the query with echo's to see the values that are being entered. Here is the PHP code. <?php if(isset($_POST['submit'])) { $mysqli = mysqli_connect("localhost", "root", "", "site"); $dbc = mysqli_query($mysqli,"SELECT * FROM names WHERE userID='$userID'"); $name = $_POST['name']; $meaning = $_POST['meaning']; if(isset($name['0']) && mysqli_num_rows($dbc) == 0 && trim($name['0'])!=='' && trim($meaning['0'])!=='') { for($n = 0; $n < count($name); $n++) { for($m = 0; $m < count($meaning); $m++) { echo $name[$n] . '<br />'; echo $meaning[$m] . '<br /><br />'; break; } } } } ?> And here is the HTML code. <form method="post" action="index.php"> <ul> <li><label for="name">Name: </label><input type="text" name="name[]" id="name" /></li> <li><label for="meaning">Meaning: </label><input type="text" name="meaning[]" id="meaning" /></li> <li><input type="submit" name="submit" value="Save" /></li> </ul> </form> If needed I will place the JQuery code.

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• How can I document and automate a system's configuration?

  - by Diomidis Spinellis

  Having a system's configuration represented by its current state is risky, inefficient, and opaque. At some point you may be left with an unsupported system and no upgrade path. Then configuring a new system compatible with the old is a process or trial and error. Furthermore, if at some point the system is damaged the only option is to go back to the most recent full backup, and try to remember what changes followed from that point. Also, the only way to create a system compatible with the original is through a complete dump/restore. Finally, in such a setup there's no way to know how you solved a particular problem; the only thing you can do is to look at the corresponding configuration files and try to guess what you changed to achieve the desired effect. Currently for each system I maintain, I keep a log file where I record all system administration activity, starting from the installation: installation options, added packages, changes in configuration files, updates, problem fixes etc. In theory this allows me to (manually) replay all changes to arrive at the current state, or to unroll an erroneous change by executing the reverse commands. However, this process is also inefficient, error-prone, and relies on human judgment. Another thing I've tried is to put /etc configuration files under version control with git. This helps me document the changes automatically and also apply them on a clean setup. But it's not without problems: git has to run under sudo, passwords and private keys may be stored in the repository, installed packages can't be meaningfully tracked, and git will have a fit if I try to extend this approach to all the system's directories. I've also thought about performing all changes through shell scripts or makefiles, but I think this process will require a lot of effort and will be fragile. Are there some better methods or tools that I'm missing?

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• This code appears to achieve the return of a null reference in C++

  - by Chuck

  Hi folks, My C++ knowledge is somewhat piecemeal. I was reworking some code at work. I changed a function to return a reference to a type. Inside, I look up an object based on an identifier passed in, then return a reference to the object if found. Of course I ran into the issue of what to return if I don't find the object, and in looking around the web, many people claim that returning a "null reference" in C++ is impossible. Based on this advice, I tried the trick of returning a success/fail boolean, and making the object reference an out parameter. However, I ran into the roadblock of needing to initialize the references I would pass as actual parameters, and of course there is no way to do this. I retreated to the usual approach of just returning a pointer. I asked a colleague about it. He uses the following trick quite often, which is accepted by both a recent version of the Sun compiler and by gcc: MyType& someFunc(int id) { // successful case here: // ... // fail case: return *static_cast<MyType*>(0); } // Use: ... MyType& mt = somefunc(myIdNum); if (&mt) // test for "null reference" { // whatever } ... I have been maintaining this code base for a while, but I find that I don't have as much time to look up the small details about the language as I would like. I've been digging through my reference book but the answer to this one eludes me. Now, I had a C++ course a few years ago, and therein we emphasized that in C++ everything is types, so I try to keep that in mind when thinking things through. Deconstructing the expression: "*static_cast(0);", it indeed seems to me that we take a literal zero, cast it to a pointer to MyType (which makes it a null pointer), and then apply the dereferencing operator in the context of assigning to a reference type (the return type), which should give me a reference to the same object pointed to by the pointer. This sure looks like returning a null reference to me. Any advice in explaining why this works (or why it shouldn't) would be greatly appreciated. Thanks, Chuck

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