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Tips for Using Multiple Development Systems

- by Tim Lytle

When I travel, I don't pack up the desktop I use in the office and take it with me. Maybe I should, but I don't. However, since I'm a contract programmer I like to be able to work wherever I am: I'm mostly thinking of web development here. Version Control goes a long way in keeping sane and working on multiple projects on multiple systems (two or three computers); however, there are the issues of: IDE settings - different display sizes mean the IDE settings can't be completely synced, if at all. Database - if the database is 'external' (even if it's running on the same system, it's not in version control), how do you maintain the needed syncs of structure. Development Stack - Some projects need non-standard extensions, libraries, etc installed. Just an overview of some of the hassle involved with developing on multiple systems. I'll probably end up asking some specific questions, but I thought a CW style tips might reveal some things I would even think to ask about. Update: I guess this would also address tips to make upgrading/replacing your development system easier (something I've just done). So, one tip per answer please, so the 'top' tips are easy to find. How do you make it easier to develop on multiple systems, or to transfer work after upgrading/replaceing a development system?

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Do database engines other than SQL Server behave this way?

- by Yishai

I have a stored procedure that goes something like this (pseudo code) storedprocedure param1, param2, param3, param4 begin if (param4 = 'Y') begin select * from SOME_VIEW order by somecolumn end else if (param1 is null) begin select * from SOME_VIEW where (param2 is null or param2 = SOME_VIEW.Somecolumn2) and (param3 is null or param3 = SOME_VIEW.SomeColumn3) order by somecolumn end else select somethingcompletelydifferent end All ran well for a long time. Suddenly, the query started running forever if param4 was 'Y'. Changing the code to this: storedprocedure param1, param2, param3, param4 begin if (param4 = 'Y') begin set param2 = null set param3 = null end if (param1 is null) begin select * from SOME_VIEW where (param2 is null or param2 = SOME_VIEW.Somecolumn2) and (param3 is null or param3 = SOME_VIEW.SomeColumn3) order by somecolumn end else select somethingcompletelydifferent And it runs again within expected parameters (15 seconds or so for 40,000+ records). This is with SQL Server 2005. The gist of my question is this particular "feature" specific to SQL Server, or is this a common feature among RDBMS' in general that: Queries that ran fine for two years just stop working as the data grows. The "new" execution plan destroys the ability of the database server to execute the query even though a logically equivalent alternative runs just fine? This may seem like a rant against SQL Server, and I suppose to some degree it is, but I really do want to know if others experience this kind of reality with Oracle, DB2 or any other RDBMS. Although I have some experience with others, I have only seen this kind of volume and complexity on SQL Server, so I'm curious if others with large complex databases have similar experience in other products.

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Trouble with building up a string in Clojure

- by Aki Iskandar

Hi gang - [this may seem like my problem is with Compojure, but it isn't - it's with Clojure] I've been pulling my hair out on this seemingly simple issue - but am getting nowhere. I am playing with Compojure (a light web framework for Clojure) and I would just like to generate a web page showing showing my list of todos that are in a PostgreSQL database. The code snippets are below (left out the database connection, query, etc - but that part isn't needed because specific issue is that the resulting HTML shows nothing between the <body> and </body> tags). As a test, I tried hard-coding the string in the call to main-layout, like this: (html (main-layout "Aki's Todos" "Haircut<br>Study Clojure<br>Answer a question on Stackoverfolw")) - and it works fine. So the real issue is that I do not believe I know how to build up a string in Clojure. Not the idiomatic way, and not by calling out to Java's StringBuilder either - as I have attempted to do in the code below. A virtual beer, and a big upvote to whoever can solve it! Many thanks! ============================================================= ;The master template (a very simple POC for now, but can expand on it later) (defn main-layout "This is one of the html layouts for the pages assets - just like a master page" [title body] (html [:html [:head [:title title] (include-js "todos.js") (include-css "todos.css")] [:body body]])) (defn show-all-todos "This function will generate the todos HTML table and call the layout function" [] (let [rs (select-all-todos) sbHTML (new StringBuilder)] (for [rec rs] (.append sbHTML (str rec "<br><br>"))) (html (main-layout "Aki's Todos" (.toString sbHTML))))) ============================================================= Again, the result is a web page but with nothing between the body tags. If I replace the code in the for loop with println statements, and direct the code to the repl - forgetting about the web page stuff (ie. the call to main-layout), the resultset gets printed - BUT - the issue is with building up the string. Thanks again. ~Aki

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Cannot overload function

- by anio

So I've got a templatized class and I want to overload the behavior of a function when I have specific type, say char. For all other types, let them do their own thing. However, c++ won't let me overload the function. Why can't I overload this function? I really really do not want to do template specialization, because then I've got duplicate the entire class. Here is a toy example demonstrating the problem: http://codepad.org/eTgLG932 The same code posted here for your reading pleasure: #include <iostream> #include <cstdlib> #include <string> struct Bar { std::string blah() { return "blah"; } }; template <typename T> struct Foo { public: std::string doX() { return m_getY(my_t); } private: std::string m_getY(char* p_msg) { return std::string(p_msg); } std::string m_getY(T* p_msg) { return p_msg->blah(); } T my_t; }; int main(int, char**) { Foo<char> x; Foo<Bar> y; std::cout << "x " << x.doX() << std::endl; return EXIT_SUCCESS; } Thank you everyone for your suggestions. Two valid solutions have been presented. I can either specialize the doX method, or specialize m_getY() method. At the end of the day I prefer to keep my specializations private rather than public so I'm accepting Krill's answer.

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Javascript storing properties and functions in variables

- by richard

Hello, I'm having trouble with my programming style and I hope to get some feedback here. I recently bought Javascript: The Good Parts and while I find this a big help, I'm still having trouble designing this application. Especially when it comes to writing function and methods. Example: I have a function that let's the user switches games in my app. This function updates game-specific information in the current view. var games = { active: Titanium.App.Properties.getString('active_game'), gameswitcher_positions: { 'Game 1': 0, 'Game 2': 1, 'Game 3': 2, 'Game 4': 3, 'Game 5': 4 }, change: function(game) { if (active_game !== game) { gameswitcher.children[this.gameswitcher_positions[this.active]].backgroundImage = gameswitcher.children[this.gameswitcher_positions[this.active]].backgroundImage.replace('_selected', ''); gameswitcher.children[this.gameswitcher_positions[game]].backgroundImage = gameswitcher.children[this.gameswitcher_positions[game]].backgroundImage.replace('.png', '_selected.png'); events.update(game); this.active = game; } }, init: function() { gameswitcher.children[this.gameswitcher_positions[this.active]].backgroundImage = gameswitcher.children[this.gameswitcher_positions[this.active]].backgroundImage.replace('.png', '_selected.png'); events.update(this.active); } }; gameswitcher is a container view which contains buttons to switch games. I am not satisfied with this approach but I cannot think of a better one. Should I place the gameswitcher_positions outside of the variable in a seperate variable instead of as a property? And what about the active game? Please give me feedback, what am I doing wrong?

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Why might ASP.NET be putting JavaScript in HTML Comment blocks, not CDATA?

- by d4nt

We have an ASP.NET 2.0 WebForms app that uses MS Ajax 1.0. It's working fine on all our environments (dev, test, IE6 VMs etc.). However, at the customer site the client side validation is not happening. We're currently trying to eliminate all the various factors and along the way we asked them to get their page source and send it to us, and we found something interesting. In our environment, our page has ASP.NET javascript in CDATA blocks: <script type="text/javascript"> //<![CDATA[ . . . //]]> </script> In their environment, the same code looks like this: <script type="text/javascript">  </script> This may be a red herring, but I'd like to eliminate it as the cause of the validation issues. Does anyone know whether specific configurations/patches/versions of ASP.NET will make it do this?

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Special Characters in JS, how to use "/" character

- by user1461222

I've vbulletin 4.2.0 i added an special button to it's editor with this article; http://www.vbulletinguru.com/2012/add-a-new-toolbar-button-to-ckeditor-tutorial/ The thing i want to do is add an syntax highlighter code with this button. When i use below code it's working fine; CKEDITOR.plugins.add( 'YourPluginName', { init: function( editor ) { editor.addCommand( 'SayHello', { exec : function( editor ) { editor.insertHtml( "Hello from my plugin" ); } }); editor.ui.addButton( 'YourPluginName', { label: 'My Button Tooltip', command: 'SayHello', icon: this.path + 'YourPluginImage.png' } ); } } ); so i changed this code to this, because i wannt to add specific text like below; CKEDITOR.plugins.add( 'DKODU', { init: function( editor ) { editor.addCommand( 'SayHello', { exec : function( editor ) { editor.insertHtml( '[kod=delphi][/kod]' ); } }); editor.ui.addButton( 'DKODU', { label: 'My Button Tooltip', command: 'SayHello', icon: this.path + 'star.png' } ); } } ); after update the code when i press the button nothings happen, i checked with google and this site but i couldn't figure it out i think i made mistake with some special characters but i couldn't find what's the problem. If i made some mistakes when i publish this question forgive me and also forgive me for my bad english, thanks.

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How Would a Newborn Baby Learn Web Programming?

- by Mugatu

Hello all, I chose that title because I equate my knowledge of web programming and web development with that of a newborn. Here's the shortest version of my story and what I'm looking to do: A friend and I have been coming up with website ideas for a couple years, mostly just jotting them down whenever we come up with a good, useful idea when browsing the web. For the past 6 months we've hired a couple different programmers to make a couple of the sites for us, but have been disappointed with how it's gone. Been too slow and too many miscommunications for our liking. So like the saying goes if you want something done right do it yourself, we're going to do it ourselves. I know nothing about programming, I've never written a line of code in my life. I consider myself very good with math and about as logical as you can get, but I have zero real-life programming knowledge. The sites we want to make are all pretty 'Web 2.0'ish', meaning user-generated content, commenting on posts, pages that change on the fly, etc. So here are some of my questions for anyone who's been there before: Is there a language you'd recommend learning first? Something that is a good indicator how most other languages work? What web programming languages do you recommend learning first based on popularity both now and the future. I don't want to learn a language that's going to be outdated by the time I'm an expert at it. Any specific books you'd recommend? Any general advice you'd give to someone literally starting at square zero for coding who plans on being in it for the long haul? Thanks in advance for the help

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how would I call/use Subsonic from within a WinForms app being deployed over clickonce (with Sqlite

- by Greg

Hi, Background - I need a framework/approach to managed database updates for a .NET Winforms app being deployed on users PC's via clickonce deploy. The app uses a sqlite database. Q1. What mechanism does Subsonic use to run such migrations on the local PC? e.g. would it be MSBuild Q2. If it does need a tool like how can my application robustly kick off MsBuild? i.e. how can it be sure what path it is installed, what if it is not installed, should I be including the MSBuild.exe in the clickonce package so that I know it is there for sure myself? Q3. Any other suggestions on how to use Subsonic in this specific use case? Q4. Any comments on whether MigratorDotNet would be a better fit? (if someone has had experience with both) Q5. Could I use subsonic's bare migration framework and just have a set of SQL files to do the upgrade/downgrade? i.e. just use the framework to check database version and which scripts to run etc?

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Why am I getting "Message sent to deallocated instance" in Objective-C?

- by Dave C

I have several buttons on my app that are being created dynamically. They are all pointed at the button click event when pressed. When the button pressed method is called, the sender's tag (int value) is parsed into the controller's house ID. It works with one of the buttons — the first one created, to be specific — but the others throw the following error: -[CFNumber intValue]: message sent to deallocated instance 0xc4bb0ff0 I am not releasing these buttons anywhere in my code. I haven't set them to autorelease or anything like that. I'm just wondering why they are doing this on the click. The button click event: - (IBAction) ButtonClick: (id) sender { HouseholdViewController *controller = [[HouseholdViewController alloc] initWithNibName:@"HouseholdViewController" bundle:nil]; controller.delegate = self; controller.HouseID = [(NSInteger)[(UIButton *)sender tag] intValue]; //this line throws an error controller.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal; [self presentModalViewController:controller animated:YES]; [controller release]; } Where I am creating the buttons: UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom]; button.frame = CGRectMake(MyLongInScreenCoords, MyLatInScreenCoords, 50, 50); UIImage *buttonImageNormal = [UIImage imageNamed:@"blue_pin.png"]; UIImage *strechableButtonImageNormal = [buttonImageNormal stretchableImageWithLeftCapWidth:50 topCapHeight:50]; [button setBackgroundImage:strechableButtonImageNormal forState:UIControlStateNormal]; [self.view addSubview:button]; button.tag = [NSNumber numberWithInt:[[words objectAtIndex: i] intValue]]; ButtonPoints[CurrentHouseCount][0] = button; ButtonPoints[CurrentHouseCount][1] = [NSValue valueWithCGPoint:CGPointMake(MyActualLat, MyActualLong)]; [button addTarget:self action:@selector(ButtonClick:) forControlEvents:UIControlEventTouchUpInside]; CurrentHouseCount++;

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Which is faster for large "for" loop: function call or inline coding?

- by zaplec

Hi, I have programmed an embedded software (using C of course) and now I'm considering ways to improve the running time of the system. The most important single module in my system is one very large nested for loop module. That module consists of two nested for loops that loops max 122500 times. That's not very much yet, but the problem is that inside that nested for loop I have a function call to a function that is in another source file. That specific function consists mostly of two another nested for loops which loops always 22500 times. So now I have to make a function call 122500 times. I have made that function that is to be called a lot lighter and shorter (yet still works as it should) and now I started to think that would it be faster to rip off that function call and write that process directly inside those first two for loops? The processor in that system is ARM7TDMI and its frequency is 55MHz. The system itself isn't very time critical so it doesn't have to be real time capable. However the faster it can process its duties the better. Also would it be also faster to use while loops instead of fors? And any piece of advice about how to improve the running time is appreciated. -zaplec

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PHP package manager

- by Mathias

Hey, does anyone know a package manager library for PHP (as e.g. apt or yum for linux distros) apart from PEAR? I'm working on a system which should include a package management system for module management. I managed to get a working solution using PEAR, but using the PEAR client for anything else than managing a PEAR installation is not really the optimal solution as it's not designed for that. I would have to modify/extend it (e.g. to implement actions on installation/upgrade or to move PEAR specific files like lockfiles away from the system root) and especially the CLI client code is quite messy and PHP4. So maybe someone has some suggestions for an alternative PEAR client library which is easy to use and extend (the server side has some nice implementations like Pirum and pearhub) for completely different package management systems written in PHP (ideally including dependency tracking and different channels) for some general ideas how to implement such a PM system (yes, I'm still tinkering with the idea of implementing such a system from scratch) I know that big systems like Magento and symfony use PEAR for their PM. Magento uses a hacked version of the original PEAR client (which I'd like to avoid), symfony's implementation seems quite integrated with the framework, but would be a good starting point to at least write the client from scratch. Anyway, if anybody has suggestions: please :)

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Getting the first of a GROUP BY clause in SQL

- by Michael Bleigh

I'm trying to implement single-column regionalization for a Rails application and I'm running into some major headaches with a complex SQL need. For this system, a region can be represented by a country code (e.g. us) a continent code that is uppercase (e.g. NA) or it can be NULL indicating the "default" information. I need to group these items by some relevant information such as a foreign key (we'll call it external_id). Given a country and its continent, I need to be able to select only the most specific region available. So if records exist with the country code, I select them. If, not I want a records with the continent code. If not that, I want records with a NULL code so I can receive the default values. So far I've figured that I may be able to use a generated CASE statement to get an arbitrary sort order. Something like this: SELECT *, CASE region WHEN 'us' THEN 1 WHEN 'NA' THEN 2 ELSE 3 END AS region_sort FROM my_table WHERE region IN ('us','NA') OR region IS NULL GROUP BY external_id ORDER BY region_sort The problem is that without an aggregate function the actual data returned by the GROUP BY for a given row seems to be untameable. How can I massage this query to make it return only the first record of the region_sort ordered groups?

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Maven3 Issues with building a multi-module enterprise project

- by Sujit K

I just migrated from Maven2 to Maven3 and I'm able to build each module individually or all the modules in one shot by calling mvn clean install. However, in Maven2, since we have multi-module enterprise project, we build multiple ear's and each ear is built as its own module with its own child pom. To build an individual ear with its dependents, the below command works fine in Maven2 but not in Maven3. Let me explain the issue in Maven3 a bit later. mvn -pl ear_module -rf first_dependent_module -am clean install In Maven2 when the reactor lists the build order, I see first_dependent_module second_dependent_module ear_module End of the day I have my ear module also part of the reactor which is how it should be. The reason we call -rf is we don't want to delete the target folder at the main ${project.basedir} (so not to delete the output created in target from building the other ear modules). With Maven3, however, this is all I see when the reactor lists the build order: first_dependent_module second_dependent_module Maven3 totally ignores the argument (ear_module) set to -pl flag to be also built after its dependents have been. Not sure what I'm missing here. Any help/tips would be greatly appreciated. P.S: The build I'm making is similar to the one below.... Build specific module in multi-module project Thanks, SK

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How to start with entity framework and service oriented architecture?

- by citronas

At work I need to create a new web application, that will connection to an MySql Database. (So far I only have expercience with Linq-To-Sql classes and MSSQL Servers.) My superior tells me to use the entity framework (he probably refers to Linq-To-Entity) and provide everything as a service based architecture. Unfortunatly nobody at work has experience with that framework and with a real nice server oriented architecture. (till now no customer wanted to pay for architecture that he can't see. This speficic project I'm leading will be long-term, meaning multiple years, so it would be best to design it the way, that multiple targetting plattforms like asp.net, c# wpf, ... could use it) For now, the main target plattform is ASP.net So I do have the following questions: 1) Where can I read best what's really behind service oriented architecture (but for now beginner tutorials work fine as well) and how to do it in best practise? 2) So far I can't seem a real difference between Linq-To-Sql classes and the information I've google so far on the 'entity framework'. So, whats the difference? Where do I find nice tutorials for it. 3) Is there any difference in the entity framework regarding the database server (MSSQL or MySQL). If not, does that mean that code snipperts I will stumble across will word database independent? 4) I do you Visual Studio 2010. Do I have to regard something specific?

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Problem convert column values from VARCHAR(n) to DECIMAL

- by Kevin Babcock

I have a SQL Server 2000 database with a column of type VARCHAR(255). All the data is either NULL, or numeric data with up to two points of precision (e.g. '11.85'). I tried to run the following T-SQL query but received the error 'Error converting data type varchar to numeric' SELECT CAST([MyColumn] AS DECIMAL) FROM [MyTable]; I tried a more specific cast, which also failed. SELECT CAST([MyColumn] AS DECIMAL(6,2)) FROM [MyTable]; I also tried the following to see if any data is non-numeric, and the only values returned were NULL. SELECT ISNUMERIC([MyColumn]), [MyColumn] FROM [MyTable] WHERE ISNUMERIC([MyColumn]) = 0; I tried to convert to other data types, such as FLOAT and MONEY, but only MONEY was successful. So I tried the following: SELECT CAST(CAST([MyColumn] AS MONEY) AS DECIMAL) FROM [MyTable]; ...which worked just fine. Any ideas why the original query failed? Will there be a problem if I first convert to MONEY and then to DECIMAL? Thanks!

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Personalized UIView created with Interface Builder

- by Malox

I need to project a personalized UIView with a UIImageView and 3 UILabel. I need to allocate more of this view because I want put it into a UIScrollView. I would avoid to generate the view programatically because it's difficult and boring design it. My idea is to create a new class that extends UIView and design it with interface builder. For example my Personalized View code is like that: #import <UIKit/UIKit.h> @interface PersonalizedPreview : UIView { IBOutlet UIImageView *image; IBOutlet UILabel *first_label; IBOutlet UILabel *second_label; IBOutlet UILabel *third_label; } -(void) setImage:(UIImage *)image; @property (nonatomic, retain) IBOutlet UIImageView *image; @property (nonatomic, retain) IBOutlet UILabel *label; .... @end I would create an associated xib file for this view and initialize it simply specifing the xib file. Note that I don't want create a specific ViewController for this view and PersonalizedView is instantiate at runtime not when the app runs, moreover I don't know how many PersonalizedView I will instantiate, it depends on runtime execution. Anyone can help me? Thank you very much.

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How to avoid hard-coded credentials in Sharepoint webpart?

- by Bryan

I am building a Sharepoint web part that will be used by all users, but can only be modified by admins. The web part connects to a web service which needs credentials. I hard coded credentials in the web part's code. query.Credentials = new System.Net.NetworkCredential("username", "password", "domain"); query is an instance of the web service class This may not be a good approach. In regard with security, the source code of the web apart is available to people who are not allowed to see the credentials. In normal ASP.net applications, credentials can be written into web.config and encrypted. A web part doesn't have a .config file associated. There is a application-level .config file for the whole sharepoint site, but I don't want to modify it for a single webpart. I wonder if there is a webpart-specific way to solve the credential problem? Say we provide a WebBrowsable property of that web part so that privileged users can modify credentials. If this is desirable, how should I make the property displayed in a password ("*") rather than in plain text? Thanks.

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Is there a JavaScript event that fires when a tab index switch is triggered? (TABINDEX does not work for inputs in IFRAME)

- by treeface

My specific use case is that I have a WYSIWYG editor which is basically an editable iframe. To the user, however, it looks like a standard-issue textarea. My problem is that I have inputs that sit before and after this editor in the (perceived) tab index and I'd like the user to be able to press tab (or the equivalent on his platform of choice) to get to the WYSIWYG editor when he's in the previous element and shift-tab to get to it when he's in the latter element. I know this can be faked using the key events and checking whether or not the tab key was pressed, but I'm curious if there's a better way. UPDATE. treeface clarified the actual problem in the comments. PROBLEM: In normal case, you can use "TABINDEX" attribute of the <input> element to control that, when tabbing out of "Subject" input field (in an email form), the focus lands on "Body" input field in the e-mail. This is done simply by assigning correctly ordered values to "TABINDEX" attribute of both input fields. The problem is that TABINDEX attribute only orders elements within the same frame. So, if "Body" input field is actually in an internal IFRAME, you can't tab out of "Subject" in the parent frame straight into "Body" in the IFRAME using TABINDEX order.

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How do I use .htaccess to redirect to a URL containing HTTP_HOST?

- by Jon Cram

Problem I need to redirect some short convenience URLs to longer actual URLs. The site in question uses a set of subdomains to identify a set of development or live versions. I would like the URL to which certain requests are redirected to include the HTTP_HOST such that I don't have to create a custom .htaccess file for each host. Host-specific Example (snipped from .htaccess file) Redirect /terms http://support.dev01.example.com/articles/terms/ This example works fine for the development version running at dev01.example.com. If I use the same line in the main .htaccess file for the development version running under dev02.example.com I'd end up being redirected to the wrong place. Ideal rule (not sure of the correct syntax) Redirect /terms http://support.{HTTP_HOST}/articles/terms/ This rule does not work and merely serves as an example of what I'd like to achieve. I could then use the exact same rule under many different hosts and get the correct result. Answers? Can this be done with mod_alias or does it require the more complex mod_rewrite? How can this be achieved using mod_alias or mod_rewrite? I'd prefer a mod_alias solution if possible. Clarifications I'm not staying on the same server. I'd like: http://example.com/terms/ - http://support.example.com/articles/terms/ https://secure.example.com/terms/ - http://support.example.com/articles/terms/ http://dev.example.com/terms/ - http://support.dev.example.com/articles/terms/ https://secure.dev.example.com/terms/ - http://support.dev.example.com/articles/terms/ I'd like to be able to use the same rule in the .htaccess file on both example.com and dev.example.com. In this situation I'd need to be able to refer to the HTTP_HOST as a variable rather than specifying it literally in the URL to which requests are redirected. I'll investigate the HTTP_HOST parameter as suggested but was hoping for a working example.

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Change css when tab has active class

- by Yunowork

I'm trying to change the background colour of the <body> depending on what tab specific is active. When a tab is active, a class called 'st_view_active' is added onto the tab content. In the tab content I add a hidden div with the hex code of what my body background colour should be when that tab is active, my jQuery code looks like this: $(document).ready(function() { $(function(){ $('body').css('backgroundColor',$('.st_view_active').find('.background').text()); }); }); And my html code when the tab is active is following: <div class="tab-6 st_view st_view_active" > <div style="display:none" class="background">yellow</div> <div class="st_view_inner"> tab 6 </div> </div> So when tab6 is active the background of the body should be yellow. However, this is not working, the background colour is not changing, what am I doing wrong here? DEMO and JSfiddle Thanks PS: The red and blue square is the next and previous tab handler..

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Sequential access to asynchronous sockets

- by Lars A. Brekken

I have a server that has several clients C1...Cn to each of which there is a TCP connection established. There are less than 10,000 clients. The message protocol is request/response based, where the server sends a request to a client and then the client sends a response. The server has several threads, T1...Tm, and each of these may send requests to any of the clients. I want to make sure that only one of these threads can send a request to a specific client at any one time, while the other threads wanting to send a request to the same client will have to wait. I do not want to block threads from sending requests to different clients at the same time. E.g. If T1 is sending a request to C3, another thread T2 should not be able to send anything to C3 until T1 has received its response. I was thinking of using a simple lock statement on the socket: lock (c3Socket) { // Send request to C3 // Get response from C3 } I am using asynchronous sockets, so I may have to use Monitor instead: Monitor.Enter(c3Socket); // Before calling .BeginReceive() And Monitor.Exit(c3Socket); // In .EndReceive I am worried about stuff going wrong and not letting go of the monitor and therefore blocking all access to a client. I'm thinking that my heartbeat thread could use Monitor.TryEnter() with a timeout and throw out sockets that it cannot get the monitor for. Would it make sense for me to make the Begin and End calls synchronous in order to be able to use the lock() statement? I know that I would be sacrificing concurrency for simplicity in this case, but it may be worth it. Am I overlooking anything here? Any input appreciated.

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Trying to make a plugin system in C++/Qt

- by Pirate for Profit

I'm making a task-based program that needs to have plugins. Tasks need to have properties which can be easily edited, I think this can be done with Qt's Meta-Object Compiler reflection capabilities (I could be wrong, but I should be able to stick this in a QtPropertyBrowser?) So here's the base: class Task : public QObject { Q_OBJECT public: explicit Task(QObject *parent = 0) : QObject(parent){} virtual void run() = 0; signals: void taskFinished(bool success = true); } Then a plugin might have this task: class PrinterTask : public Task { Q_OBJECT public: explicit PrinterTask(QObject *parent = 0) : Task(parent) {} void run() { Printer::getInstance()->Print(this->getData()); // fictional emit taskFinished(true); } inline const QString &getData() const; inline void setData(QString data); Q_PROPERTY(QString data READ getData WRITE setData) // for reflection } In a nutshell, here's what I want to do: // load plugin // find all the Tasks interface implementations in it // have user able to choose a Task and edit its specific Q_PROPERTY's // run the TASK It's important that one .dll has multiple tasks, because I want them to be associated by their module. For instance, "FileTasks.dll" could have tasks for deleting files, making files, etc. The only problem with Qt's plugin setup is I want to store X amount of Tasks in one .dll module. As far as I can tell, you can only load one interface per plugin (I could be wrong?). If so, the only possible way to do accomplish what I want is to create a FactoryInterface with string based keys which return the objects (as in Qt's Plug-And-Paint example), which is a terrible boilerplate that I would like to avoid. Anyone know a cleaner C++ plugin architecture than Qt's to do what I want? Also, am I safely assuming Qt's reflection capabilities will do what I want (i.e. able to edit an unknown dynamically loaded tasks' properties with the QtPropertyBrowser before dispatching)?

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How can I help fellow students struggling in programming classes?

- by David Barry

I'm a computer science student finishing up my second semester of programming classes. I've enjoyed them quite a bit, and learned a lot, but it seems other students are struggling with the concepts and assignments more than I am. When an assignment is due, the inevitable group email comes out the day or two before with people needing some help either with a specific part of the problem, or sometimes people just seem to have a hard time knowing where to start. I'd really like to be able to help out, but I have a hard time thinking of the right way to give them help without giving them the answer. When I'm having trouble understanding a concept, a code snippet can go along way to helping me, but at the same time if it makes a lot of sense, it can be difficult to think of another way to go about it. Plus the Academic Integrity section of each assignment is always looming overhead warning against sharing code with others. I've tried using pseudo code to help give others an idea on program flow, leaving them to figure out how to implement certain aspects of it, but I didn't get too much feedback and don't know how much it actually helped them out, or if it just confused them further. So I'm basically looking to see if anyone has experience with this, or good ways that I can help out other students to nudge them in the right direction or help them think about the problem in the right way.

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What about race condition in multithreaded reading?

- by themoob

Hi, According to an article on IBM.com, "a race condition is a situation in which two or more threads or processes are reading or writing some shared data, and the final result depends on the timing of how the threads are scheduled. Race conditions can lead to unpredictable results and subtle program bugs." . Although the article concerns Java, I have in general been taught the same definition. As far as I know, simple operation of reading from RAM is composed of setting the states of specific input lines (address, read etc.) and reading the states of output lines. This is an operation that obviously cannot be executed simultaneously by two devices and has to be serialized. Now let's suppose we have a situation when a couple of threads access an object in memory. In theory, this access should be serialized in order to prevent race conditions. But e.g. the readers/writers algorithm assumes that an arbitrary number of readers can use the shared memory at the same time. So, the question is: does one have to implement an exclusive lock for read when using multithreading (in WinAPI e.g.)? If not, why? Where is this control implemented - OS, hardware? Best regards, Kuba

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