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• Why is 'using namespace std;' considered a bad practice in C++?

  - by Mana

  Okay, sorry for the simplistic question, but this has been bugging me ever since I finished high school C++ last year. I've been told by others on numerous occasions that my teacher was wrong in saying that we should have "using namespace std;" in our programs, and that std::cout and std::cin are more proper. However, they would always be vague as to why this is a bad practice. So, I'm asking now: Why is "using namespace std;" considered bad? Is it really that inefficient, or risk declaring ambiguous vars(variables that share the same name as a function in std namespace) that much? Or does this impact program performance noticeably as you get into writing larger applications? I'm sorry if this is something I should have googled to solve; I figured it would be nice to have this question on here regardless in case anyone else was wondering.

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• Handling a binary operation that makes sense only for part of a hierarchy.

  - by usersmarvin_

  I have a hierarchy, which I'll simplify greatly, of implementations of interface Value. Assume that I have two implementations, NumberValue, and StringValue. There is an average operation which only makes sense for NumberValue, with the signature NumberValue average(NumberValue numberValue){ ... } At some point after creating such variables and using them in various collections, I need to average a collection which I know is only of type NumberValue, there are three possible ways of doing this I think: Very complicated generic signatures which preserve the type info in compile time (what I'm doing now, and results in hard to maintain code) Moving the operation to the Value level, and: throwing an unsupportedOperationException for StringValue, and casting for NumberValue. Casting at the point where I know for sure that I have a NumberValue, using slightly less complicated generics to insure this. Does anybody have any better ideas, or a recommendation on oop best practices?

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• Why I should use an N-Tier Approach When using an SqlDatasource is ALOT EASIER ?

  - by The_AlienCoder

  When it comes to web development I have always tried to work SMART not HARD. So for along time My Aproach to interacting with databases in my AspNet projects has been this : 1) Create my stored procedures 2) Drag an SQLDatasource control on my aspx page 3) Bind a DataList Control to my SQLDatasource 4) Insert, Update & Delete by using my Datalist or programmatically using built in SQLDatasource methods e.g MySqlDataSource.InsertParameters["author"].DefaultValue = TextBox1.Text; MySqlDataSource.Insert(); Recently however I got a relatively easy web project. So I decided to employ a 3-tier Model...But I got exhausted halfway and just didnt seem worth it ! It seemed like I was working too HARD for a project that could have been easily accomplished by a couple of SqlDataSource Controls. So Why Is the N-Tier Model better than my Approach? Has it anything to do with performance? What are the advantages of the ObjectDataSource control over the SqlDataSource Control?

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• didSelectRowAtIndexPath being called after viewDidLoad of the called view

  - by Serguei Fedorov

  I am trying to pass variables over to the new view. I have the following code: appDelegate *dataCenter = (AppDelegate*)[[UIApplication sharedApplication] delegate]; dataCenter.myVariable = [array objectAtIndex:indexPath.row]; in the didSelectRowAtIndexPath of the calling view. However, the issue that I have is that this variable is empty in the vewDidLoad function of the next view, simply because it fired off BEFORE the didSelectRowAtIndexPath of the calling view. I am using storyboard to link the views together. Both are UITableView. If I hit back and then reselect the table element it is then set, granted that by the time I hit back and then selected again, the variable got set. Is there any way to for the order of execution? I really don't want to do UI view switching on the back end. Any help is greatly appreciated!

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• I want to get the value of an id from a nested div - jquery

  - by Jean

  Hello I want to obtain the .text() of #inner2 <div class="outer" id="outer"> <div id="inner1" class="inner">test1</div> <div id="inner2" class="inner">test2</div> <div id="inner3" class="inner">test3</div> </div> This is the jquery function I am using $('.outer').bind('click',function() { var one = $('#inner'+x).attr('id'); alert(one); }); The problem is the first #id value is show in the alert. Thanks Jean

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• trying to set a dropdown in MVC

  - by RJ

  I almost have this solved but need a little push. Here's what I have: In the database I have a field called active that is a bit field (True/False) I have placed a dropdownlist on the View form like this: <%= Html.DropDownList("lstActive", new SelectList((IEnumerable)ViewData["ActiveList"])) %> In my controller, I simply have this code to generate the True/False in the dropdown: List<string> activeList = new List<string>(); activeList.Add("True"); activeList.Add("False"); ViewData["ActiveList"] = new SelectList(activeList); I want to bind to the field in the database called active and select it in the dropdown. When I view it like this I get this: So the questions are these: Obviously I am not pointing to the Value and Text property but what is that in this case? And how do I select the value that is in the database? Any help would be appreciated.

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• Application wide messaging... without singletons?

  - by StormianRootSolver

  So, I want to go for a more Singleton - less design in the future. However, there seem to be a lot of tasks in an application that can't be done in meaningful way without singletons. I call them "application wide services", but they also fall into the same category as the cross cutting concerns, which I usually fix via AOP. Lets take an example: I want an application wide message queue that dispatches messages to components, every component can subscribe and publish there, it's a very nice multicast thing. The message queue and dispatching system are usually a (rather short) singleton class, which is very easy to implement in, say, C#. You can even use double dispatching and utilize message type metadata and the like, it's all so easy to do, it's almost trivial. However, having singletons is not really "object oriented design" (it introduces global variables) and it makes testing harder. Do you have any ideas? I'm asking this question because I'm willing to learn more about this topic, a LOT more. :-)

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• The case of the mysterious MySQL caching across restarts

  - by shanusmagnus

  I found a very slow MySQL query in my web app. The weird thing is that the query is only slow the first time it's executed, despite the fact that the query_cache is set to its default (query_cache_size 0) like so: mysql> show variables like 'query%'; +------------------------------+---------+ | Variable_name | Value | +------------------------------+---------+ | query_alloc_block_size | 8192 | | query_cache_limit | 1048576 | | query_cache_min_res_unit | 4096 | | query_cache_size | 0 | | query_cache_type | ON | | query_cache_wlock_invalidate | OFF | | query_prealloc_size | 8192 | +------------------------------+---------+ The even weirder thing is that this speedup persists even after the MySQL server has been stopped and restarted (I'm using OSX, and perform this restart using the system preferences pane.) The only way I can re-create the poor performance of the initial query is by rebooting the system. So my question is: how is this happening? Obviously some sort of caching at work, but where? And how does it persist across database restarts? This query is mediated through our web app, which comes via PHP/Apache, but there are no extra bells and whistles, and the curious caching also persists across Apache restarts. Help?

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• Javascript: Taking the highest 2 numerical values out of a series of 4 possible values.

  - by Bodhi

  What I'm trying to do is to take the highest two values out of 4 possible variables and add them together, while ignoring the lesser two values. My values will be anywhere between 1 and 5. So, for example, if I have Trait1, Trait2, Trait3 and Trait4 with the following assigned values: 3, 3, 2, 1, the script will pick up the 3 and the 3, but not the 2 and the 1. If I change the values around so that I have 4, 3, 1, 5, the script will pick up the 4 and the 5, but not the 3 and the 1. How would I go about doing this? Thank you in advance.

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• jquery "this" binding issue on event handler

  - by clyfe

  In jquery an event hadler's binding is the event generating DOM element (this points to the dom element). In prototype to change the binding of an event handler one can use the bindAsEventListener function; How can I access both the instance and the DOM element from a event handler? Similar to http://stackoverflow.com/questions/117361/how-can-i-bind-an-event-handler-to-an-instance-in-jquery function Car(){ this.km = 0; $("#sprint").click(this.drive); //setup event handler } // event handler // in it I need to access both the clicked element // and the binding object (instance of car) Car.prototype.drive = function(){ this.km += 10; // i'd like to access the binding (but jq changes it) this.css({ left: this.km }); // also the element // NOTE that is inside this function I want to access them not elsewhere } var car = new Car();

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• When to save a variable in viewstate?

  - by Umut

  Hi, I have searched the web for the answer and saw that mostly variables are saved in viewstate on page.prerender event. However, when I save a variable in viewstate on prerender or load events, how can it store the changed value of the variable? Let's say, after page load, user clicked a button and the value of the variable was changed in onClick event of the button. Then the postback event raised since the button was clicked. According to me, the new value should have been lost and cannot be saved in the viewstate if I save the variable in the viewstate only in prerender event. Shouldn't I save the variable in the viewstate just before the postback event rises? Am I wrong? If so, how can viewstate store the new value of the variable? Thanks for the answer in advance..

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• WPF Creating an instance of a class in xaml

  - by Cloverness

  Hi, I have a problem with creating the instance of a class in xaml file. I thought you can do it like this: in the resource part of the user control and then use it in the xaml file (for example bind to it). But even tough the class I created is located in the same namespace it says that: "The type was not found. Verfiy that all assemblies were built, etc". How to get it right? is there another method? Thanks for suggestions.

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• How can I implement a login wall for expired or inappropriate pages?

  - by Redandwhite

  I am writing a website that very explicitly requires a login wall. Visitors should be required to log in before they are allowed to view a page. The page being built depends very much on the user's "ID". I am not sure how or where to store the user's login. I am not sure whether I should use a session variable (e.g. Session["userId"]), or some other method. The problem I see with session variables is that it's difficult to time out sessions. Note: I'm using C# 3.5 with ASP.NET in Visual Studio 2008.

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• Hiding dropdown list when list is empty

  - by Amina

  I currently have a dropdown list that is populated on page load and sometimes the dropdown list doesn't contain anything and is empty. I would like the hide the dropdown list whenever there aren't any items in the list. I thought i could do this via javascript but i am not sure what i could be doing wrong because after adding the javascript it stills appear on the page. dropdown select: <select data-bind="options: endReason() ? endReason().SubReasons : [], value: subReasonId, optionsText: 'Text', optionsValue: 'Value', visible: isChecked" name="subReasons"> </select> This is my Javascript: <script type="text/javascript"> function OnClientDropDownOpening(sender, eventArgs) { var combo = $find("<%= subReasons %>"); items = combo.get_items(); if(items.get_count()==0) { eventArgs.set_cancel(true); } } </script>

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• Annotation based data structure visualization - are there similar tools out there?

  - by Helper Method

  For a project at university I plan to build an annotation based tool to visualize/play around with data structures. Here's my idea: Students which want to try out their self-written data structures need to: mark the type of their data structures using some sort of marker annotation e.g. @List public class MyList { ... } so that I know how to represent the data structure need to provide an iterator so that I can retrieve the elements in the right order need to annotate methods for insertion and removal, e.g. @add public boolean insert(E e) { ... } so that I can "bind" that method to some button. Do similar applications exist? I googled a little bit around but didn't find anything like that.

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• Insert date and time into Mysql

  - by Jerry

  Hi..guys I am trying to insert date and time into mysql datetime field. When a user select a date and time, it will generate two POST variables. I have searched internet but still not sure how to do it. My code. //date value is 05/25/2010 //time value is 10:00 $date=$_POST['date']; $time=$_POST['time']; $datetime=$date.$time If I insert $datetime into mysql, the date appears to be 0000-00-00:00:00:00 I appreciate it if anyone could help me about this. Thanks.

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• What should I name instances of a twisted.internet.defer.Deferred?

  - by slacy

  I'm writing code using Twisted, and having trouble coming up with a sensible variable name for my twisted internet deferred's. Here are my candidates: d : Too generic, too short, violates pylint rule C0103. def : Conflicts with function defintion builtin. defer : Conflicts with module twisted.internet.defer deferred : OK but pretty long cb : Still too short, violates pylint C0103, conflicts with many callback method names. cback : Too Weird? callback : Conflicts with method Deferred.callback() I'm looking for other suggestions. It seems like most of the Twisted example code uses "d" which is fine for simple invocations, but when you're passing Deferred's around to methods and storing them as member variables, it's really far too descriptive.

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• C++ Memory allocation question involving vectors

  - by TheFuzz

  vector< int > vect; int *int_ptr = new int(10); vect.push_back( *int_ptr ); I under stand that every "new" needs to be followed by a "delete" at some point but does the clear() method clean this memory? What about this method of doing the same thing: vector< int > vect; int int_var = 10; vect.push_back( int_var ); From what I understand, clear() calls the variables destructors, but both vect.push_back() methods in this example push an object on the vector, not a pointer. so does the first example using an int pointer need something other than clear() to clean up memory?

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• Perl array and hash manipulation using map

  - by somebody

  I have the following test code use Data::Dumper; my $hash = { foo => 'bar', os => 'linux' }; my @keys = qw (foo os); my $extra = 'test'; my @final_array = (map {$hash->{$_}} @keys,$extra); print Dumper \@final_array; The output is $VAR1 = [ 'bar', 'linux', undef ]; Shouldn't the elements be "bar, linux, test"? Why is the last element undefined and how do I insert an element into @final_array? I know I can use the push function but is there a way to insert it on the same line as using the map command? Basically the manipulated array is meant to be used in an SQL command in the actual script and I want to avoid using extra variables before that and instead do something like: $sql->execute(map {$hash->{$_}} @keys,$extra);

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• Is it bad practice to use Reflection in Unit testing?

  - by Sebi

  During the last years I always thought that in Java, Reflection is widely used during Unit testing. Since some of the variables/methods which have to be checked are private, it is somehow necessary to read the values of them. I always thought that the Reflection API is also used for this purpose. Last week i had to test some packages and therefore write some JUnit tests. As always i used Reflection to access private fields and methods. But my supervisor who checked the code wasn't really happy with that and told me that the Reflection API wasn't meant to use for such "hacking". Instead he suggested to modifiy the visibility in the production code. Is it really bad practice to use Reflection? I can't really believe that

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• jQuery - Using .one() with hover

  - by Jared

  Is there any way to get a hover function to only execute once? This is what I'm currently trying: $('#ask').live('hover', function() { $('#homesearch-after').hide(300); $.doTimeout( 300, function() { hideClosedSearchLink(); showHomeSearch(); }); }); But that's not working. How can I only get this hover to activate once? I've tried changing .live with .one and .bind... resulting in nothingness.

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• reload a form with the same parameter of the previous

  - by kawtousse

  Hi every one, I have really a problem that I don't know how to deal with it. I am using JSP and Servlet with the Eclipse IDE. First of all, the user fill an html table with the values that he has selected and written in the form. after that he will find his parameters displayed in the html table. the problem now is : the table contains in each row an edit button when clicking on it; the user should have the form automatically filled with values"previously selected" of the row. so it's how to reload the form with variables from html table. Note : I construct the table with a servlet. Please help.

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• How to set ItemsSource?

  - by Mark

  This dialog makes no sense to me And I'm having trouble finding good tutorials on it. Most of the examples aren't detailed enough, or do stuff via code, but I'd like to take advantage of the IDE as much as possible. Whats the difference between ItemsSource and DataContext? I'd like to bind it to just a List for starters. I don't need SQL or databases or anything fancy. Where would I declare my list? In MainWindow.xaml.cs? How do I get it to appear in that dialog?

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• Possible to exclude or reorder a column from `*` ?

  - by Earlz

  Is it possible to exclude a column from a select * from table statement with SQL Server? I have a need for this and this is my only option other than parsing a raw SQL string to get out the required field names (I really don't want to do that). Just to be bold. When the query is made I do not have access to the list of fields needed from the table but I do know which field I do not need. This is part of a complex multi-part query. Surely there must be some way even if it's "hackish" such as using table variables or views My other option is to reorder the columns. My problem is with ExecuteScalar SQL functions which get the first row and first column.

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• bash tools for parsing arguments

  - by BCS

  I have a bash script that uses a few variables (call them $foo and $bar). Right now the script defines them at the top with hard coded values like this: foo=fooDefault bar=barDefault .... # use $foo and $bar What I want is to be able to use the script like any of these: myscript # use all defaults myscript -foo=altFoo # use default bar myscript -bar=altBar # use default foo myscript -bar=altBar -foo=altFoo An ideal solution would allow me to just list the variable that I want to check for flags for. Is there a reasonably nice way to do this? I've seen getopt and I think it might do about 70% of what I'm looking for but I'm wondering if there is a tool or indium that builds on it or the like that gets the rest.

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