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• Advanced SQL query with lots of joins

  - by lund.mikkel

  Hey fellow programmers Okay, first let me say that this is a hard one. I know the presentation may be a little long. But I how you'll bare with me and help me through anyway :D So I'm developing on an advanced search for bicycles. I've got a lot of tables I need to join to find all, let's say, red and brown bikes. One bike may come in more then one color! I've made this query for now: SELECT DISTINCT p.products_id, #simple product id products_name, #product name products_attributes_id, #color id pov.products_options_values_name #color name FROM products p LEFT JOIN products_description pd ON p.products_id = pd.products_id INNER JOIN products_attributes pa ON pa.products_id = p.products_id LEFT JOIN products_options_values pov ON pov.products_options_values_id = pa.options_values_id LEFT JOIN products_options_search pos ON pov.products_options_values_id = pos.products_options_values_id WHERE pos.products_options_search_id = 4 #code for red OR pos.products_options_search_id = 5 #code for brown My first concern is the many joins. The Products table mainly holds product id and it's image and the Products Description table holds more descriptive info such as name (and product ID of course). I then have the Products Options Values table which holds all the colors and their IDs. Products Options Search is containing the color IDs along with a color group ID (products_options_search_id). Red has the color group code 4 (brown is 5). The products and colors have a many-to-many relationship managed inside Products Attributes. So my question is first of all: Is it okay to make so many joins? Is i hurting the performance? Second: If a bike comes in both red and brown, it'll show up twice even though I use SELECT DISTINCT. Think this is because of the INNER JOIN. Is this possible to avoid and do I have to remove the doubles in my PHP code? Third: Bikes can be double colored (i.e. black and blue). This means that there are two rows for that bike. One where it says the color is black and one where is says its blue. (See second question). But if I replace the OR in the WHERE clause it removes both rows, because none of them fulfill the conditions - only the product. What is the workaround for that? I really hope you will and can help me. I'm a little desperate right now :D Regards Mikkel Lund

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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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• log4net initialisation

  - by Ruben Bartelink

  I've looked hard for duplicates but have to ask the following, no matter how basic it may seem, to get it clear once and for all! In a fresh Console app using log4net version 1.2.10.0 on VS28KSP1 on 64 bit W7, I have the following code:- using log4net; using log4net.Config; namespace ConsoleApplication1 { class Program { static readonly ILog _log = LogManager.GetLogger(typeof(Program)); static void Main(string[] args) { _log.Info("Ran"); } } } In my app.config, I have: <?xml version="1.0" encoding="utf-8" ?> <configuration> <configSections> <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net" /> </configSections> <log4net> <appender name="RollingFileAppender" type="log4net.Appender.RollingFileAppender"> <file value="Program.log" /> <lockingModel type="log4net.Appender.FileAppender+MinimalLock" /> <appendToFile value="true" /> <rollingStyle value="Size" /> <maxSizeRollBackups value="10" /> <maximumFileSize value="1MB" /> <staticLogFileName value="true" /> <layout type="log4net.Layout.PatternLayout"> <conversionPattern value="[%username] %date [%thread] %-5level %logger [%property{NDC}] - %message%newline" /> </layout> </appender> <root> <level value="DEBUG" /> <appender-ref ref="RollingFileAppender" /> </root> </log4net> </configuration> This doesnt write anything, unless I either add an attribute: [ assembly:XmlConfigurator ] Or explicitly initialise it in Main(): _log.Info("This will not go to the log"); XmlConfigurator.Configure(); _log.Info("Ran"); This raises the following questions: I'm almost certain I've seen it working somewhere on some version of log4net without the addition of the assembly attribute or call in Main. Can someone assure me I'm not imagining that? Can someone please point me to where in the doc it explicitly states that both the config section and the initialisation hook are required - hopefully with an explanation of when this changed, if it did? I can easily imagine why this might be the policy -- having the initialisation step explicit to avoid surprises etc., it's just that I seem to recall this not always being the case... (And normally I have the config in a separate file, which generally takes configsections out of the picture)

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• Windows 7 - pydoc from cmd

  - by Random_Person

  Okay, I'm having one of those moments that makes me question my ability to use a computer. This is not the sort of question I imagined asking as my first SO post, but here goes. Started on Zed's new "Learn Python the Hard Way" since I've been looking to get back into programming after a 10 year hiatus and python was always what I wanted. This book has really spoken to me. That being said, I'm having a serious issue with pydoc from the command. I've got all the directories in c:/python26 in my system path and I can execute pydoc from the command line just fine regardless of pwd - but it accepts no arguments. Doesn't matter what I type, I just get the standard pydoc output telling me the acceptable arguments. Any ideas? For what it's worth, I installed ActivePython as per Zed's suggestion. C:\Users\Chevee>pydoc file pydoc - the Python documentation tool pydoc.py <name> ... Show text documentation on something. <name> may be the name of a Python keyword, topic, function, module, or package, or a dotted reference to a class or function within a module or module in a package. If <name> contains a '\', it is used as the path to a Python source file to document. If name is 'keywords', 'topics', or 'modules', a listing of these things is displayed. pydoc.py -k <keyword> Search for a keyword in the synopsis lines of all available modules. pydoc.py -p <port> Start an HTTP server on the given port on the local machine. pydoc.py -g Pop up a graphical interface for finding and serving documentation. pydoc.py -w <name> ... Write out the HTML documentation for a module to a file in the current directory. If <name> contains a '\', it is treated as a filename; if it names a directory, documentation is written for all the contents. C:\Users\Chevee> EDIT: New information, pydoc works just fine in PowerShell. As a linux user, I have no idea why I'm trying to use cmd anyways--but I'd still love to figure out what's up with pydoc and cmd. EDIT 2: More new information. In cmd... c:\>python c:/python26/lib/pydoc.py file ...works just fine. Everything works just fine with just pydoc in PowerShell without me worrying about pwd, or extensions or paths.

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• SVN: Branches for Every Little Change?

  - by yar

  Hi. We have a client (who has a client, who has a client) who is driving us mad with change requests to a code base (in PHP). Our first response was to just work in a main trunk in SVN, but the client often comes back and requests that a certain change needs to get pushed to the live servers ASAP. On the other hand, other changes get reduced in priority suddenly, which originally came grouped with other changes (seemingly). We are thinking of using a branch for every change request. Is this mad? What other solutions might work? Thanks! Edit: This is a really hard question to choose the correct answer for. Thanks to everybody for your great answers. Edit: I know that the best answer I chose was not particularly popular. I too wanted to find a technical solution to this problem. But now I think that if the client wants software with features that can be deployed in a modular fashion... this problem should not be solved in our use of the version control system. It would have to be designed into the software. Edit: Now it's almost a month later and my coworker/client has convinced me that multiple branches is the way to go. This is not just due to the client's insanity, but also based on our need to be able to determine if a feature is "ready to go" or "needs more work" or whatever. I don't have the SVN with me, but we merge using the advice from the SVN Cookbook: you merge the branch from the revision it was branched to the head revision. Also, using this system, we merge all branches at some point and that becomes the new QA and then live build. Then we branch from that. Last Edit (Perhaps): Months later, this system is still working out for us. We create branches for every ticket and rarely have problems. On the other hand, we do try to keep things separate as far as what people are working on... Two Years Later: We use GIT now, and now this system is actually quite reasonable.

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• HTML5 <audio> Safari live broadcast vs not

  - by Peter Parente

  I'm attempting to embed an HTML5 audio element pointing to MP3 or OGG data served by a PHP file . When I view the page in Safari, the controls appear, but the UI says "Live Broadcast." When I click play, the audio starts as expected. Once it ends, however, I can't start it playing again by clicking play. Even using the JS API on the audio element and setting currentTime to 0 fails with an index error exception. I suspected the headers from the PHP script were the problem, particularly missing a content length. But that's not the case. The response headers include a proper Content- Length to indicate the audio has finite size. Furthermore, everything works as expected in Firefox 3.5+. I can click play on the audio element multiple times to hear the sound replay. If I remove the PHP script from the equation and serve up a static copy of the MP3 file, everything works fine in Safari. Does this mean Safari is treating audio src URLs with query parameters differently than URLs that don't have them? Anyone have any luck getting this to work? My simple example page is: <!DOCTYPE html> <html> <head></head> <body> <audio controls autobuffer> <source src="say.php?text=this%20is%20a%20test&format=.ogg" /> <source src="say.php?text=this%20is%20a%20test&format=.mp3" /> </audio> </body> </html> HTTP Headers from PHP script: HTTP/1.x 200 OK Date: Sun, 03 Jan 2010 15:39:34 GMT Server: Apache X-Powered-By: PHP/5.2.10 Content-Length: 8993 Keep-Alive: timeout=2, max=98 Connection: Keep-Alive Content-Type: audio/mpeg HTTP Headers from direct file access: HTTP/1.x 200 OK Date: Sun, 03 Jan 2010 20:06:59 GMT Server: Apache Last-Modified: Sun, 03 Jan 2010 03:20:02 GMT Etag: "a404b-c3f-47c3a14937c80" Accept-Ranges: bytes Content-Length: 8993 Keep-Alive: timeout=2, max=100 Connection: Keep-Alive Content-Type: audio/mpeg I tried hard-coding the Accept-Ranges header into the script too, but no luck.

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• show-hide image onmouseover

  - by butters

  I have 3 images on top of each other. The first one is a normal .jpg image, the second a greyscale version and the 3rd is some kind of effect i add with a transparent .png Now what i want is that, if i move the mouse over those images, the greyscale image is hidden or replaced by another image and afterwards visible again. The problem here is that i am a js noob, so it's kind of hard for me to find a solution ^^ my code looks something like this: <html> <head> <style type="text/css"> <!-- ul li{ display: inline-table; } .frame{ position: relative; height: 110px; width: 110px; } .frame div{ position: absolute; top:0px; left:0px; } .effect{ background:url(images/effect.png) no-repeat; height:110px; width: 110px; } .image{ height:100px; width:100px; border: 1px solid red; margin:4px; } .greyscale{ height:100px; width:100px; border: 1px solid red; margin:4px; } --> </style> </head> <body> <ul> <li> <div class="frame"> <div class="image"><img src="images/pic1.jpg" height="100" width="100"></div> <div class="greyscale"><img src="images/grey1.jpg" height="100" width="100"></div> <div class="effect">qwert</div> </div> </li> <li> <div class="frame"> <div class="image"><img src="images/pic2.jpg" height="100" width="100"></div> <div class="greyscale"><img src="images/grey2.jpg" height="100" width="100"></div> <div class="effect">qewrt</div> </div> </li> </ul> </body> </html> </code></pre> would be super-awesome if someone can help me out :)

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• Move options between multiple lists

  - by Martha

  We currently have a form with the standard multi-select functionality of "here are the available options, here are the selected options, here are some buttons to move stuff back and forth." However, the client now wants the ability to not just select certain items, but to also categorize them. For example, given a list of books, they want to not just select the ones they own, but also the ones they've read, the ones they would like to read, and the ones they've heard about. (All examples fictional.) Thankfully, a selected item can only be in one category at a time. I can find many examples of moving items between listboxes, but not a single one for moving items between multiple listboxes. To add to the complication, the form needs to have two sets of list+categories, e.g. a list of movies that need to be categorized in addition to the aforementioned books. EDIT: Having now actually sat down to try to code the non-javascripty bits, I need to revise my question, because I realized that multiple select lists won't really work from the "how do I inform the server about all this lovely new information" standpoint. So the html code is now a pseudo-listbox, i.e. an unordered list (ul) displayed in a box with a scrollbar, and each list item (<li>) has a set of five radio buttons (unselected/own/read/like/heard). My task is still roughly the same: how to take this one list and make it easy to categorize the items, in such a way that the user can tell at a glance what is in what category. (The pseudo-listbox has some of the same disadvantages as a multi-select listbox, namely it's hard to tell what's selected if the list is long enough to scroll.) The dream solution would be a drag-and-drop type thing, but at this point even buttons would be OK. Another modification (a good one) is that the client has revised the lists, so the longest is now "only" 62 items long (instead of the many hundreds they had before). The categories will still mostly contain zero, one, or two selected items, possibly a couple more if the user was overzealous. As far as OS and stuff, the site is in classic asp (quit snickering!), the server-side code is VBScript, and so far we've avoided the various Javascript libraries by the simple expedient of almost never using client-side scripting. This one form for this one client is currently the big exception. Give 'em an inch and they want a mile... Oh, and I have to add: I suck at Javascript, or really at any C-descendant language. Curly braces give me hives. I'd really, really like something I can just copy & paste into my page, maybe tweak some variable names, and never look at it again. A girl can dream, can't she? :) [existing code deleted because it's largely irrelevant.]

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• Symfony2 Entity to array

  - by Adriano Pedro

  I'm trying to migrate my flat php project to Symfony2, but its coming to be very hard. For instance, I have a table of Products specification that have several specifications and are distinguishables by its "cat" attribute in that Extraspecs DB table. Therefore I've created a Entity for that table and want to make an array of just the specifications with "cat" = 0... I supose the code is this one.. right? $typeavailable = $this->getDoctrine() ->getRepository('LabsCatalogBundle:ProductExtraspecsSpecs') ->findBy(array('cat' => '0')); Now how can i put this in an array to work with a form like this?: form = $this ->createFormBuilder($product) ->add('specs', 'choice', array('choices' => $typeavailableArray), 'multiple' => true) Thank you in advance :) # Thank you all.. But now I've came across with another problem.. In fact i'm building a form from an existing object: $form = $this ->createFormBuilder($product) ->add('name', 'text') ->add('genspec', 'choice', array('choices' => array('0' => 'None', '1' => 'General', '2' => 'Specific'))) ->add('isReg', 'choice', array('choices' => array('0' => 'Material', '1' => 'Reagent', '2' => 'Antibody', '3' => 'Growth Factors', '4' => 'Rodents', '5' => 'Lagomorphs'))) So.. in that case my current value is named "extraspecs", so i've added this like: ->add('extraspecs', 'entity', array( 'label' => 'desc', 'empty_value' => ' --- ', 'class' => 'LabsCatalogBundle:ProductExtraspecsSpecs', 'property' => 'specsid', 'query_builder' => function(EntityRepository $er) { return $er ->createQueryBuilder('e'); But "extraspecs" come from a relationship of oneToMany where every product has several extraspecs... Here is the ORM: Labs\CatalogBundle\Entity\Product: type: entity table: orders__regmat id: id: type: integer generator: { strategy: AUTO } fields: name: type: string length: 100 catnumber: type: string scale: 100 brand: type: integer scale: 10 company: type: integer scale: 10 size: type: decimal scale: 10 units: type: integer scale: 10 price: type: decimal scale: 10 reqcert: type: integer scale: 1 isReg: type: integer scale: 1 genspec: type: integer scale: 1 oneToMany: extraspecs: targetEntity: ProductExtraspecs mappedBy: product Labs\CatalogBundle\Entity\ProductExtraspecs: type: entity table: orders__regmat__extraspecs fields: extraspecid: id: true type: integer unsigned: false nullable: false generator: strategy: IDENTITY regmatid: type: integer scale: 11 spec: type: integer scale: 11 attrib: type: string length: 20 value: type: string length: 200 lifecycleCallbacks: { } manyToOne: product: targetEntity: Product inversedBy: extraspecs joinColumn: name: regmatid referencedColumnName: id HOw should I do this? Thank you!!!

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• How to get started with testing(jMock)

  - by London

  Hello, I'm trying to learn how to write tests. I'm also learning Java, I was told I should learn/use/practice jMock, I've found some articles online that help to certain extend like : http://www.theserverside.com/news/1365050/Using-JMock-in-Test-Driven-Development http://jeantessier.com/SoftwareEngineering/Mocking.html#jMock And most articles I found was about test driven development, write tests first then write code to make the test pass. I'm not looking for that at the moment, I'm trying to write tests for already existing code with jMock. The official documentation is vague to say the least and just too hard for me. Does anybody have better way to learn this. Good books/links/tutorials would help me a lot. thank you EDIT - more concrete question : http://jeantessier.com/SoftwareEngineering/Mocking.html#jMock - from this article Tried this to mock this simple class : import java.util.Map; public class Cache { private Map<Integer, String> underlyingStorage; public Cache(Map<Integer, String> underlyingStorage) { this.underlyingStorage = underlyingStorage; } public String get(int key) { return underlyingStorage.get(key); } public void add(int key, String value) { underlyingStorage.put(key, value); } public void remove(int key) { underlyingStorage.remove(key); } public int size() { return underlyingStorage.size(); } public void clear() { underlyingStorage.clear(); } } Here is how I tried to create a test/mock : public class CacheTest extends TestCase { private Mockery context; private Map mockMap; private Cache cache; @Override @Before public void setUp() { context = new Mockery() { { setImposteriser(ClassImposteriser.INSTANCE); } }; mockMap = context.mock(Map.class); cache = new Cache(mockMap); } public void testCache() { context.checking(new Expectations() {{ atLeast(1).of(mockMap).size(); will(returnValue(int.class)); }}); } } It passes the test and basically does nothing, what I wanted is to create a map and check its size, and you know work some variations try to get a grip on this. Understand better trough examples, what else could I test here or any other exercises would help me a lot. tnx

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• Reading and writing C++ vector to a file

  - by JB

  For some graphics work I need to read in a large amount of data as quickly as possible and would ideally like to directly read and write the data structures to disk. Basically I have a load of 3d models in various file formats which take too long to load so I want to write them out in their "prepared" format as a cache that will load much faster on subsequent runs of the program. Is it safe to do it like this? My worries are around directly reading into the data of the vector? I've removed error checking, hard coded 4 as the size of the int and so on so that i can give a short working example, I know it's bad code, my question really is if it is safe in c++ to read a whole array of structures directly into a vector like this? I believe it to be so, but c++ has so many traps and undefined behavour when you start going low level and dealing directly with raw memory like this. I realise that number formats and sizes may change across platforms and compilers but this will only even be read and written by the same compiler program to cache data that may be needed on a later run of the same program. #include <fstream> #include <vector> using namespace std; struct Vertex { float x, y, z; }; typedef vector<Vertex> VertexList; int main() { // Create a list for testing VertexList list; Vertex v1 = {1.0f, 2.0f, 3.0f}; list.push_back(v1); Vertex v2 = {2.0f, 100.0f, 3.0f}; list.push_back(v2); Vertex v3 = {3.0f, 200.0f, 3.0f}; list.push_back(v3); Vertex v4 = {4.0f, 300.0f, 3.0f}; list.push_back(v4); // Write out a list to a disk file ofstream os ("data.dat", ios::binary); int size1 = list.size(); os.write((const char*)&size1, 4); os.write((const char*)&list[0], size1 * sizeof(Vertex)); os.close(); // Read it back in VertexList list2; ifstream is("data.dat", ios::binary); int size2; is.read((char*)&size2, 4); list2.resize(size2); // Is it safe to read a whole array of structures directly into the vector? is.read((char*)&list2[0], size2 * sizeof(Vertex)); }

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• Dealing with personal failure

  - by codeelegance

  A while ago I was given the task of updating and extending the functionality of a software project. I was given a year to make the needed changes working solo. A month into development I came to the conclusion that it would take longer to change the existing product than to rewrite it from the ground up. I'd never attempted a complete rewrite so I talked with my boss about it and he was thrilled with the idea. I'm a fan of agile development but had never had the opportunity to take advantage of all of the prescribed practices so when I set to work I tried to incorporate as many as I could. I didn't have direct access to the customer and my coworkers (non-programmers) knew the business domain but were already so busy they didn't really have time to participate in design meetings so I resigned to working in the dark and occasionally calling one of them over to my desk to get feedback on my progress. I used TDD and refactored mercilessly and even tried taking a domain driven design approach. Things went well for a while. As the deadline came closer and the complexity of the project grew my productivity start slipping. I found myself cutting corners and ignoring the practices I had established as the pressure increased to meet the deadline. I also started working late nights and weekends to keep up with the load. In the end it made little difference how hard I worked. The project missed its deadline and what was completed wasn't enough to give to the customer. I had failed. Not only had I not finished on time but the previous version had sat untouched for almost a year so it wouldn't be of any help. Luckily we had another product that offered some of the same functionality. My boss decided to cancel the project entirely and moved all our orphaned customers to the other product. I spent weeks (along with everyone else at the company) manning the phones providing technical support for those customers. After it was all over, my boss was gracious enough not to fire me for nearly ruining the company. I was moved to the other product and have been trying to redeem myself ever since. Where did I go wrong? Has anyone else had to deal with this kind of defeat? How did you recover?

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• PDF Report generation

  - by IniTech

  EDIT : I completed this project using ABCpdf. For anyone interested, I love this product and their support is A+. Everything I listed as a 'Con' for the HTML - PDF solution was easily doable in ABCpdf. I've been charged with creating a data driven pdf report. After reviewing the plethora of options, I have narrowed it down to 2. I need you all to to help me decide, or offer alternatives I haven't considered. Here are the requirements: 100% Data driven Eventually PDF (a stop in HTML is fine, so long as it is converted) Can be run with multiple sets of data (the layout is always the same, the data is variable) Contains normal analysis-style copy (saved in DB with html markup) Contains tables (data for tables is generated at run-time) Header/Page # on each page Table of Contents .NET (VB or C#) Done quickly Now, because of the fact that the report is going to be generated with multiple sets of data, I don't think a stamped pdf template will work since I won't know how long or how many pages a certain piece of the report could require. So, I think my best options are: Programmatic creation using an iText-like solution. Generate in HTML and convert to PDF using a third-party application (ABCPdf is the tool I have played with so far) Both solutions have their pro's and con's. Programmatic solution: Pros: Flexible Easy page numbering/page header/table of contents Free Cons: Time consuming (to write a layer on top of iText to do what I need and keep maintainable) Since the copy is already stored in the db with html markup, I would have to parse through the data before I place it into the pdf, ensuring I don't have to break the paragraph into chunks so I can apply bold, italic, underline, etc. to specific phrases. This seems like a huge PITA, and I hope I am wrong about that assumption. HTML - PDF Pros: Easy to generate from db (no parsing necessary) Many tools for conversion Uses technology I am already familiar with Built-in "Print Preview" - not a req, but nice Cons: (Edited after project completion. All of my assumptions were incorrect and ABCpdf is awesome) 1. Almost impossible to generate page headers - Not True 2. Very difficult to generate page numbers Not True 3. Nearly impossible to generate table of contents Not True 4. (Cross-browser support isn't a con; Since its internal, I can dictate what browser to use) 5. Conversion tool quirks - may not convert exactly as rendered in browser Not True 6. Overall, I think it would be very hard to format the HTML exactly as I would want it to appear/convert to PDF. Not True That's it - I need the communitys help in deciding which way I should go. I might be wrong about some of my Pro/Con assumptions. If I am, please tell me. All thoughts and suggestions are welcome and appreciated. Thanks

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• Dependency Injection: I don't get where to start!

  - by Andy

  I have several articles about Dependency Injection, and I can see the benefits, especially when it comes to unit testing. The units can me loosely coupled, and mocking of dependencies can be made. The trouble is - I just don't get where to start. Consider this snippet below of (much edited for the purpose of this post) code that I have. I am instantiating a Plc object from the main form, and passing in a communications mode via the Connect method. In it's present form it becomes hard to test, because I can't isolate the Plc from the CommsChannel to unit test it. (Can I?) The class depends on using a CommsChannel object, but I am only passing in a mode that is used to create this channel within the Plc itself. To use dependancy injection, I should really pass in an already created CommsChannel (via an 'ICommsChannel' interface perhaps) to the Connect method, or maybe via the Plc constructor. Is that right? But then that would mean creating the CommsChannel in my main form first, and this doesn't seem right either, because it feels like everything will come back to the base layer of the main form, where everything begins. Somehow it feels like I am missing a crucial piece of the puzzle. Where do you start? You have to create an instance of something somewhere, but I'm struggling to understand where that should be. public class Plc() { public bool Connect(CommsMode commsMode) { bool success = false; // Create new comms channel. this._commsChannel = this.GetCommsChannel(commsMode); // Attempt connection success = this._commsChannel.Connect(); return this._connected; } private CommsChannel GetCommsChannel(CommsMode mode) { CommsChannel channel; switch (mode) { case CommsMode.RS232: channel = new SerialCommsChannel( SerialCommsSettings.Default.ComPort, SerialCommsSettings.Default.BaudRate, SerialCommsSettings.Default.DataBits, SerialCommsSettings.Default.Parity, SerialCommsSettings.Default.StopBits); break; case CommsMode.Tcp: channel = new TcpCommsChannel( TCPCommsSettings.Default.IP_Address, TCPCommsSettings.Default.Port); break; default: // Throw unknown comms channel exception. } return channel; } }

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• Ajax problem after deleting a div, then creating a new one

  - by Matt Nathanson

  I'm building a custom CMS where you can add and delete clients using ajax and jquery 1.4.2. My problem lies after I delete a div. The ajax is used to complete this and refresh automatically.. But when I go to create a new div (without a hard refresh) it puts it back in the slot of the div I just deleted. How can I get this to completely forget about the div i just deleted and place the new div in the next database table? link for reference: http://staging.sneakattackmedia.com/cms/ //Add New client // function AddNewClient() { dataToLoad = 'addClient=yes'; $.ajax({ type: 'post', url: '/clients/controller.php', datatype: 'html', data: dataToLoad, target: ('#clientssidebar'), async: false, success: function(html){ $(this).click(function() {reInitialize()}); //$('#clientssidebar').html(html); $('div#' + clientID).slideDown(800); $(this).click(function() { ExpandSidebar()});}, error: function() { alert('An error occured! 222');} });}; //Delete Client // function DeleteClient(){ var yes = confirm("Whoa there chief! Do you really want to DELETE this client?"); if (yes == 1) { dataToLoad = 'clientID=' + clientID + '&deleteClient=yes', $.ajax({ type: 'post', url: '/clients/controller.php', datatype: 'html', data: dataToLoad, success: function(html) { alert('Client' + clientID + ' should have been deleted from the database.'); $(this).click(function() {reInitialize()}); $('div#' +clientID).slideUp(800); }, error: function() { alert('error'); }});};}; //Re Initialize // function reInitialize() { $('#addnew').click(function() {AddNewClient()}); $('.deletebutton').click(function() {clientID = $(this).parent().attr('id'); DeleteClient()}) $('.clientblock').click(function() {clientID = $(this).attr('id'); ExpandSidebar()});}; //Document Ready // $(document).ready(function(){ if ($('isCMS')){ editCMS = 1; $('.deletebutton').click(function() {clientID = $(this).parent().attr('id'); DeleteClient()}); $('#addnew').click(function() {AddNewClient()}); $('.clientblock').click(function() {clientID = $(this).attr('id'); ExpandSidebar()}); $('.clientblock').click(function() {if (clickClient ==true) { $(this).css('background-image', 'url(/images/highlightclient.png)'); $(this).css('margin-left' , '30px'); }; $(this).click(function(){ $(this).css('background-image', ''); }); $('.uploadbutton').click(function(){UploadThings()}); }); } else ($('#clientscontainer')) { $('#editbutton').css('display', 'none'); }; }); Please help!!!

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• approximating log10[x^k0 + k1]

  - by Yale Zhang

  Greetings. I'm trying to approximate the function Log10[x^k0 + k1], where .21 < k0 < 21, 0 < k1 < ~2000, and x is integer < 2^14. k0 & k1 are constant. For practical purposes, you can assume k0 = 2.12, k1 = 2660. The desired accuracy is 5*10^-4 relative error. This function is virtually identical to Log[x], except near 0, where it differs a lot. I already have came up with a SIMD implementation that is ~1.15x faster than a simple lookup table, but would like to improve it if possible, which I think is very hard due to lack of efficient instructions. My SIMD implementation uses 16bit fixed point arithmetic to evaluate a 3rd degree polynomial (I use least squares fit). The polynomial uses different coefficients for different input ranges. There are 8 ranges, and range i spans (64)2^i to (64)2^(i + 1). The rational behind this is the derivatives of Log[x] drop rapidly with x, meaning a polynomial will fit it more accurately since polynomials are an exact fit for functions that have a derivative of 0 beyond a certain order. SIMD table lookups are done very efficiently with a single _mm_shuffle_epi8(). I use SSE's float to int conversion to get the exponent and significand used for the fixed point approximation. I also software pipelined the loop to get ~1.25x speedup, so further code optimizations are probably unlikely. What I'm asking is if there's a more efficient approximation at a higher level? For example: Can this function be decomposed into functions with a limited domain like log2((2^x) * significand) = x + log2(significand) hence eliminating the need to deal with different ranges (table lookups). The main problem I think is adding the k1 term kills all those nice log properties that we know and love, making it not possible. Or is it? Iterative method? don't think so because the Newton method for log[x] is already a complicated expression Exploiting locality of neighboring pixels? - if the range of the 8 inputs fall in the same approximation range, then I can look up a single coefficient, instead of looking up separate coefficients for each element. Thus, I can use this as a fast common case, and use a slower, general code path when it isn't. But for my data, the range needs to be ~2000 before this property hold 70% of the time, which doesn't seem to make this method competitive. Please, give me some opinion, especially if you're an applied mathematician, even if you say it can't be done. Thanks.

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• Poor man's "lexer" for C#

  - by Paul Hollingsworth

  I'm trying to write a very simple parser in C#. I need a lexer -- something that lets me associate regular expressions with tokens, so it reads in regexs and gives me back symbols. It seems like I ought to be able to use Regex to do the actual heavy lifting, but I can't see an easy way to do it. For one thing, Regex only seems to work on strings, not streams (why is that!?!?). Basically, I want an implementation of the following interface: interface ILexer : IDisposable { /// <summary> /// Return true if there are more tokens to read /// </summary> bool HasMoreTokens { get; } /// <summary> /// The actual contents that matched the token /// </summary> string TokenContents { get; } /// <summary> /// The particular token in "tokenDefinitions" that was matched (e.g. "STRING", "NUMBER", "OPEN PARENS", "CLOSE PARENS" /// </summary> object Token { get; } /// <summary> /// Move to the next token /// </summary> void Next(); } interface ILexerFactory { /// <summary> /// Create a Lexer for converting a stream of characters into tokens /// </summary> /// <param name="reader">TextReader that supplies the underlying stream</param> /// <param name="tokenDefinitions">A dictionary from regular expressions to their "token identifers"</param> /// <returns>The lexer</returns> ILexer CreateLexer(TextReader reader, IDictionary<string, object> tokenDefinitions); } So, pluz send the codz... No, seriously, I am about to start writing an implementation of the above interface yet I find it hard to believe that there isn't some simple way of doing this in .NET (2.0) already. So, any suggestions for a simple way to do the above? (Also, I don't want any "code generators". Performance is not important for this thing and I don't want to introduce any complexity into the build process.)

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• how to develop a program to minimize errors in human transcription of hand written surveys

  - by Alex. S.

  I need to develop custom software to do surveys. Questions may be of multiple choice, or free text in a very few cases. I was asked to design a subsystem to check if there is any error in the manual data entry for the multiple choices part. We're trying to speed up the user data entry process and to minimize human input differences between digital forms and the original questionnaires. The surveys are filled with handwritten marks and text by human interviewers, so it's possible to find hard to read marks, or also the user could accidentally select a different value in some question, and we would like to avoid that. The software must include some automatic control to detect possible typing differences. Each answer of the multiple choice questions has the same probability of being selected. This question has two parts: The GUI. The most simple thing I have in mind is to implement the most usable design of the questions display: use of large and readable fonts and space generously the choices. Is there something else? For faster input, I would like to use drop down lists (favoring keyboard over mouse). Given the questions are grouped in sections, I would like to show the answers selected for the questions of that section, but this could slow down the process. Any other ideas? The error checking subsystem. What else can I do to minimize or to check human typos in the multiple choice questions? Is this a solvable problem? is there some statistical methodology to check values that were entered by the users are the same from the hand filled forms? For example, let's suppose the survey has 5 questions, and each has 4 options. Let's say I have n survey forms filled in paper by interviewers, and they're ready to be entered in the software, then how to minimize the accidental differences that can have the manual transcription of the n surveys, without having to double check everything in the 5 questions of the n surveys? My first suggestion is that at the end of the processing of all the hand filled forms, the software could choose some forms randomly to make a double check of the responses in a few instances, but on what criteria can I make this selection? This validation would be enough to cover everything in a significant way? The actual survey is nation level and it has 56 pages with over 200 questions in total, so it will be a lot of hand written pages by many people, and the intention is to reduce the likelihood of errors and to optimize speed in the data entry process. The surveys must filled in paper first, given the complications of taking laptops or handhelds with the interviewers.

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• Gotchas INSERTing into SQLite on Android?

  - by paul.meier

  Hi friends, I'm trying to set up a simple SQLite database in Android, handling the schema via a subclass of SQLiteOpenHelper. However, when I query my tables, the columns I think I've inserted are never present. Namely, in SQLiteOpenHelper's onCreate(SQLiteDatabase db) method, I use db.execSQL() to run CREATE TABLE commands, then have tried both db.execSQL and db.insert() to run INSERT commands on the tables I've just created. This appears to run fine, but when I try to query them I always get 0 rows returned (for debugging, the queries I'm running are simple SELECT * FROM table and checking the Cursor's getCount()). Anybody run into anything like this before? These commands seem to run on command-line sqlite3. Are they're gotchas that I'm missing (e.g. INSERTS must/must not be semicolon terminated, or some issue involving multiple tables)? I've attached some of the code below. Thanks for your time, and let me know if I can clarify further. @Override public void onCreate(SQLiteDatabase db) { db.execSQL("CREATE TABLE "+ LEVEL_TABLE +" (" + " "+ _ID +" INTEGER PRIMARY KEY AUTOINCREMENT," + " level TEXT NOT NULL,"+ " rows INTEGER NOT NULL,"+ " cols INTEGER NOT NULL);"); db.execSQL("CREATE TABLE "+ DYNAMICS_TABLE +" (" + " level_id INTEGER NOT NULL," + " row INTEGER NOT NULL,"+ " col INTEGER NOT NULL,"+ " type INTEGER NOT NULL);"); db.execSQL("CREATE TABLE "+ SCORE_TABLE +" (" + " level_id INTEGER NOT NULL," + " score INTEGER NOT NULL,"+ " date_achieved DATE NOT NULL,"+ " name TEXT NOT NULL);"); this.enterFirstLevel(db); } And a sample of the insert code I'm currently using, which gets called in enterFirstLevel() (some values hard-coded just to get it running...): private void insertDynamic(SQLiteDatabase db, int row, int col, int type) { ContentValues values = new ContentValues(); values.put("level_id", "1"); values.put("row", Integer.toString(row)); values.put("col", Integer.toString(col)); values.put("type", Integer.toString(type)); db.insertOrThrow(DYNAMICS_TABLE, "col", values); } Finally, query code looks like this: private Cursor fetchLevelDynamics(int id) { SQLiteDatabase db = this.leveldata.getReadableDatabase(); try { String fetchQuery = "SELECT * FROM " + DYNAMICS_TABLE; String[] queryArgs = new String[0]; Cursor cursor = db.rawQuery(fetchQuery, queryArgs); Activity activity = (Activity) this.context; activity.startManagingCursor(cursor); return cursor; } finally { db.close(); } }

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• Calling cdecl Functions That Have Different Number of Arguments

  - by KlaxSmashing

  I have functions that I wish to call based on some input. Each function has different number of arguments. In other words, if (strcmp(str, "funcA") == 0) funcA(a, b, c); else if (strcmp(str, "funcB") == 0) funcB(d); else if (strcmp(str, "funcC") == 0) funcC(f, g); This is a bit bulky and hard to maintain. Ideally, these are variadic functions (e.g., printf-style) and can use varargs. But they are not. So exploiting the cdecl calling convention, I am stuffing the stack via a struct full of parameters. I'm wondering if there's a better way to do it. Note that this is strictly for in-house (e.g., simple tools, unit tests, etc.) and will not be used for any production code that might be subjected to malicious attacks. Example: #include <stdio.h> typedef struct __params { unsigned char* a; unsigned char* b; unsigned char* c; } params; int funcA(int a, int b) { printf("a = %d, b = %d\n", a, b); return a; } int funcB(int a, int b, const char* c) { printf("a = %d, b = %d, c = %s\n", a, b, c); return b; } int funcC(int* a) { printf("a = %d\n", *a); *a *= 2; return 0; } typedef int (*f)(params); int main(int argc, char**argv) { int val; int tmp; params myParams; f myFuncA = (f)funcA; f myFuncB = (f)funcB; f myFuncC = (f)funcC; myParams.a = (unsigned char*)100; myParams.b = (unsigned char*)200; val = myFuncA(myParams); printf("val = %d\n", val); myParams.c = (unsigned char*)"This is a test"; val = myFuncB(myParams); printf("val = %d\n", val); tmp = 300; myParams.a = (unsigned char*)&tmp; val = myFuncC(myParams); printf("a = %d, val = %d\n", tmp, val); return 0; } Output: gcc -o func func.c ./func a = 100, b = 200 val = 100 a = 100, b = 200, c = This is a test val = 200 a = 300 a = 600, val = 0

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• Is this a legitimate implementation of a 'remember me' function for my web app?

  - by user246114

  Hi, I'm trying to add a "remember me" feature to my web app to let a user stay logged in between browser restarts. I think I got the bulk of it. I'm using google app engine for the backend which lets me use java servlets. Here is some pseudo-code to demo: public class MyServlet { public void handleRequest() { if (getThreadLocalRequest().getSession().getAttribute("user") != null) { // User already has session running for them. } else { // No session, but check if they chose 'remember me' during // their initial login, if so we can have them 'auto log in' // now. Cookie[] cookies = getThreadLocalRequest().getCookies(); if (cookies.find("rememberMePlz").exists()) { // The value of this cookie is the cookie id, which is a // unique string that is in no way based upon the user's // name/email/id, and is hard to randomly generate. String cookieid = cookies.find("rememberMePlz").value(); // Get the user object associated with this cookie id from // the data store, would probably be a two-step process like: // // select * from cookies where cookieid = 'cookieid'; // select * from users where userid = 'userid fetched from above select'; User user = DataStore.getUserByCookieId(cookieid); if (user != null) { // Start session for them. getThreadLocalRequest().getSession() .setAttribute("user", user); } else { // Either couldn't find a matching cookie with the // supplied id, or maybe we expired the cookie on // our side or blocked it. } } } } } // On first login, if user wanted us to remember them, we'd generate // an instance of this object for them in the data store. We send the // cookieid value down to the client and they persist it on their side // in the "rememberMePlz" cookie. public class CookieLong { private String mCookieId; private String mUserId; private long mExpirationDate; } Alright, this all makes sense. The only frightening thing is what happens if someone finds out the value of the cookie? A malicious individual could set that cookie in their browser and access my site, and essentially be logged in as the user associated with it! On the same note, I guess this is why the cookie ids must be difficult to randomly generate, because a malicious user doesn't have to steal someone's cookie - they could just randomly assign cookie values and start logging in as whichever user happens to be associated with that cookie, if any, right? Scary stuff, I feel like I should at least include the username in the client cookie such that when it presents itself to the server, I won't auto-login unless the username+cookieid match in the DataStore. Any comments would be great, I'm new to this and trying to figure out a best practice. I'm not writing a site which contains any sensitive personal information, but I'd like to minimize any potential for abuse all the same, Thanks

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• Learn C# now or finish up with Java and then learn C#?

  - by Sahat

  Ok here is my situation. I've studied Java in my college for 2 semesters. But you know they teach you jack in there, just the basics. We skipped half of our textbook and even then our professors don't teach from section to section of each chapter. I don't blame them. It's hard as it is for new students to understand even the basic concepts of programming. Now this is a community college we are talking about and not Stanford, MIT or Berkeley. So like I said I've done 2 semester of Java. I really like our textbook because it has some challenging projects to do at the end of each chapter. This textbook is pretty clear and i have no problem understanding it (although 2-D and 3-D Arrays have given me some trouble). I have tried reading a few C# books such as Pro C# 2008 and .NET 3.5 and C# 4.0 in a Nutshell. I found these books to be dry and overloaded with information that put me to sleep (No offense to the authors of those 2 wonderful, according to amazon ratings, books). Would you suggest I finish my Java textbook, brush up my knowledge of Arrays, Polymorphism, and etc that are universal to most programming languages. And then switch to C#, plus the syntax is very similar so it should be easy to switch. Or should I just start learning C# right now from the very beginning? If it's the latter then could you recommend some free online resources that will keep me engaged and at the same time teach me everything I need to know about C#. Someone has recommended me to learn .NET first, but I found it to be not the brightest idea. .NET is just a big monster full of libraries. How am I going to apply it if I don't even know the C# or VB!? Anyway back to my question: Master Java and switch to C# or just go with C#? DISCLAIMER: I don't want to start .NET vs J2EE or C# vs Java flame war. I am going with C#. I've decided that I want to work in a Microsoft shop in the future. .NET is what I want to learn. Thanks! Will be waiting for the answers.

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• Migrating from hand-written persistence layer to ORM

  - by Sergey Mikhanov

  Hi community, We are currently evaluating options for migrating from hand-written persistence layer to ORM. We have a bunch of legacy persistent objects (~200), that implement simple interface like this: interface JDBC { public long getId(); public void setId(long id); public void retrieve(); public void setDataSource(DataSource ds); } When retrieve() is called, object populates itself by issuing handwritten SQL queries to the connection provided using the ID it received in the setter (this usually is the only parameter to the query). It manages its statements, result sets, etc itself. Some of the objects have special flavors of retrive() method, like retrieveByName(), in this case a different SQL is issued. Queries could be quite complex, we often join several tables to populate the sets representing relations to other objects, sometimes join queries are issued on-demand in the specific getter (lazy loading). So basically, we have implemented most of the ORM's functionality manually. The reason for that was performance. We have very strong requirements for speed, and back in 2005 (when this code was written) performance tests has shown that none of mainstream ORMs were that fast as hand-written SQL. The problems we are facing now that make us think of ORM are: Most of the paths in this code are well-tested and are stable. However, some rarely-used code is prone to result set and connection leaks that are very hard to detect We are currently squeezing some additional performance by adding caching to our persistence layer and it's a huge pain to maintain the cached objects manually in this setup Support of this code when DB schema changes is a big problem. I am looking for an advice on what could be the best alternative for us. As far as I know, ORMs has advanced in last 5 years, so it might be that now there's one that offers an acceptable performance. As I see this issue, we need to address those points: Find some way to reuse at least some of the written SQL to express mappings Have the possibility to issue native SQL queries without the necessity to manually decompose their results (i.e. avoid manual rs.getInt(42) as they are very sensitive to schema changes) Add a non-intrusive caching layer Keep the performance figures. Is there any ORM framework you could recommend with regards to that?

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• Ruby: Parse, replace, and evaluate a string formula

  - by Swartz

  I'm creating a simple Ruby on Rails survey application for a friend's psychological survey project. So we have surveys, each survey has a bunch of questions, and each question has one of the options participants can choose from. Nothing exciting. One of the interesting aspects is that each answer option has a score value associated with it. And so for each survey a total score needs to be calculated based on these values. Now my idea is instead of hard-coding calculations is to allow user add a formula by which the total survey score will be calculated. Example formulas: "Q1 + Q2 + Q3" "(Q1 + Q2 + Q3) / 3" "(10 - Q1) + Q2 + (Q3 * 2)" So just basic math (with some extra parenthesis for clarity). The idea is to keep the formulas very simple such that anyone with basic math can enter them without resolving to some fancy syntax. My idea is to take any given formula and replace placeholders such as Q1, Q2, etc with the score values based on what the participant chooses. And then eval() the newly formed string. Something like this: f = "(Q1 + Q2 + Q3) / 2" # some crazy formula for this survey values = {:Q1 => 1, :Q2 => 2, :Q3 => 2} # values for substitution result = f.gsub(/(Q\d+)/) {|m| values[$1.to_sym] } # string to be eval()-ed eval(result) So my questions are: Is there a better way to do this? I'm open to any suggestions. How to handle formulas where not all placeholders were successfully replaced (e.g. one question wasn't answered)? Ex: {:Q3 = 2} wasn't in values hash? My idea is to rescue eval()... any thoughts? How to get proper result? Should be 2.5, but due to integer arithmetic, it will truncate to 2. I can't expect people who provide the correct formula (e.g. / 2.0 ) to understand this nuance. I do not expect this, but how to best protect eval() from abuse (e.g. bad formula, manipulated values coming in)? Thank you!

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• IEnumerable<T> ToArray usage, is it a copy or a pointer?

  - by Daniel

  I am parsing an arbitrary length byte array that is going to be passed around to a few different layers of parsing. Each parser creates a Header and a Packet payload just like any ordinary encapsulation. And my problem lies in how the encapsulation holds its packet byte array payload. Say i have a 100 byte array, and it has 3 levels of encapsulation. 3 packet objects will be created and i want to set the payload of these packets to the corresponding position in the byte array of the packet. For example lets say the payload size is 20 for all levels, then imagine it has a public byte[] Payload on each object. However the problem is that this byte[] Payload is a copy of the original 100 bytes. So i'm going to end up with 160 bytes in memory instead of 100. If it were in c++ i could just easily use a pointer however i'm writing this in c#. So i created the following class: public class PayloadSegment<T> : IEnumerable<T> { public readonly T[] Array; public readonly int Offset; public readonly int Count; public PayloadSegment(T[] array, int offset, int count) { this.Array = array; this.Offset = offset; this.Count = count; } public T this[int index] { get { if (index < 0 || index >= this.Count) throw new IndexOutOfRangeException(); else return Array[Offset + index]; } set { if (index < 0 || index >= this.Count) throw new IndexOutOfRangeException(); else Array[Offset + index] = value; } } public IEnumerator<T> GetEnumerator() { for (int i = Offset; i < Offset + Count; i++) yield return Array[i]; } System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { IEnumerator<T> enumerator = this.GetEnumerator(); while (enumerator.MoveNext()) { yield return enumerator.Current; } } } This way i can simply reference a position inside the original byte array but use positional indexing. However if i do something like: PayloadSegment<byte> something = new PayloadSegment<byte>(someArray, 5, 10); byte[] somethingArray = something.ToArray(); Will the somethingArray be a copy of the bytes, or a reference to the original PayloadSegment which in turn is a reference to the original byte array? Sorry it was hard to word this lol _<

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