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• Hierarchical/Nested Database Structure for Comments

  - by Stephen Melrose

  Hi, I'm trying to figure out the best approach for a database schema for comments. The problem I'm having is that the comments system will need to allow nested/hierarchical comments, and I'm not sure how to design this out properly. My requirements are, Comments can be made on comments, so I need to store the tree hierarchy I need to be able to query the comments in the tree hierarchy order, but efficiently, preferably in a fast single query, but I don't know if this is possible I'd need to make some wierd queries, e.g. pull out the latest 5 root comments, and a maximum of 3 children for each one of those I read an article on the MySQL website on this very subject, http://dev.mysql.com/tech-resources/articles/hierarchical-data.html The "Nested Set Model" in theory sounds like it will do what I need, except I'm worried about querying the thing, and also inserting. If this is the right approach, How would I do my 3rd requirement above? If I have 2000 comments, and I add a new sub-comment on the first comment, that will be a LOT of updating to do. This doesn't seem right to me? Or is there a better approach for the type of data I'm wanting to store and query? Thank you

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• How to get a Class literal from a generically specific Class

  - by h2g2java

  There are methods like these which require Class literals as argument. Collection<EmpInfo> emps = SomeSqlUtil.select( EmpInfo.class, "select * from emps"); or GWT.create(Razmataz.class); The problem presents itself when I need to supply generic specific classes like EmpInfo<String> Razmataz<Integer> The following would be wrong syntax Collection<EmpInfo<String>> emps = SomeSqlUtil.select( EmpInfo<String>.class, "select * from emps"); or GWT.create(Razmataz<Integer>.class); Because you cannot do syntax like Razmataz<Integer>.class So, how would I be able to squeeze a class literal out of EmpInfo<String> Razmataz<Integer> so that I could feed them as arguments to methods requiring Class literals? Further info Okay, I confess that I am asking this primarily for GWT. I have a pair of GWT RPC interface Razmataz. (FYI, GWT RPC interface has to be defined in server-client pairs). I plan to use the same interface pair for communicating whether it be String, Integer, Boolean, etc. GWT.create(Razmataz) for Razmataz<T> complains that, since I did not specify T, GWT compiler treated it as Object. Then GWT compiler would not accept Object class. It needs to be more specific than being an Object. So, it seems there is no way for me to tell GWT.create what T is because a Class literal is a runtime concept while generics is a compile time concept, Right?

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• general learning methodology

  - by momo

  just wanted to hear on the different general learning paths people embark on when learning a new language/framework. the one i currently use, which is how i learned bash and am currently learning python, is: instant hacking tutorial (very short tutorial introducing the basic syntax, variable declaration, loops, data types, etc. and how they are generally used) in depth tutorial with good programming style and slightly topic-specific (e.g. Mark Pilgrim's Dive into Python), important topics for me personally are regex methods, file IO, and ways the different data types are utilized best (i wrote a very primitive bayesian spam filter using python's dictionaries to keep track of word occurrences) spaced-repition of syntax or short recipes (i use anki, with questions like 'create dictionary with filename and filesize metadata, human-readable' or simpler ones like 'match 0 - 3 occurences of the letter M in a string', or 'return/create an iterator from two sequences') the use of spaced-repitition has been invaluable, and i credit it with the ease that i can recall/create python algorithms. however, i've recently started looking into django, and i've found that spaced-repitition, at least in my case, doesn't work very well for learning a framework, it works best with short code recipes (either that or i should start looking into more basic django framework tutorials). the problem i'm encountering is that since framework programming is not only algorithms, but actually learning the API, which can be quite complex since you have to learn all the methods, modules, the places where they are stored, and the sequence of which things have to be done. for ex. in django to start a project that deals with polls (from the django tutorial), one has to create the project, edit the settings.py file, create the polls app, edit the models.py file (which requires knowing the classes that are present in the module models), edit the urls.py file, etc. i found that my spaced-repition method didn't work very well for this type of learning, so i wanted to ask you guys what method(s) you use for learning the different frameworks/APIs.

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• Mutex example / tutorial ?

  - by Nav

  I've noticed that asking questions for the sake of creating a reference list etc. is encouraged in SO. This is one such question, so that anyone Googling for a mutex tutorial will find a good one here. I'm new to multithreading, and was trying to understand how mutexes work. Did a lot of Googling and this is the only decent tutorial I found, but it still left some doubts of how it works because I created my own program and the locking didn't work. One absolutely non-intuitive syntax of the mutex is pthread_mutex_lock( &mutex1 );, where it looks like the mutex is being locked, when what I really want to lock is some other variable. Does this syntax mean that locking a mutex locks a region of code until the mutex is unlocked? Then how do threads know that the region is locked? And isn't such a phenomenon supposed to be called critical section? In short, could you please help with the simplest possible mutex example program and the simplest possible explanation on the logic of how it works? I'm sure this will help plenty of other newbies.

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• document.onclick settimeout function javascript help

  - by Jamex

  Hi, I have a document.onclick function that I would like to have a delay. I can't seem to get the syntax right. my original code is <script type="text/javascript"> document.onclick=check; function check(e){do something} I tried the below, but that code is incorrect, the function did not execute and nothing happened. <script type="text/javascript"> document.onclick=setTimeout("check", 1000); function check(e){do something} I tried the next set, the function got executed, but no delay. <script type="text/javascript"> setTimeout(document.onclick=check, 1000); function check(e){do something} what is the correct syntax for this code. TIA Edit: The solutions were all good, my problem was that I use the function check to obtain the id of the element being clicked on. But after the delay, there is no "memory" of what was being clicked on, so the rest of the function does not get executed. Jimr wrote the short code to preserve clicked event. The code that is working is // Delay execution of event handler function "f" by "time" ms. document.onclick = makeDelayedHandler(check, 250); function makeDelayedHandler( f, time) { return function( e ) {setTimeout(function() {f( e );}, time ); }; } function check(e){ var click = (e && e.target) || (event && event.srcElement); . . . Thank you all.

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• What is the best approach to 2D collision detection on the iPhone?

  - by Magic Bullet Dave

  Been working on this problem of collision detection and there appears to be 3 main approaches I could take: Sprite and mask approach. (AND the overlap of the sprites and check for a non-zero number in the resulting sprite pixel data). Bounding circles, rectangles or polygons. (Create one or more shapes that enclose the sprites and do the basic maths to check for overlaps). Use an existing sprite library. The first approach, even though it would have been the way I would have done it in the old days of 16x16 sprite blocks, it appears that there just isn’t an easy way of getting at the individual image pixel data and/or alpha channel within Quartz (or OPENGL for that matter). Detecting the overlap of the bounding box is easy, but then creating a 3rd image from the overlap and then testing it for pixels is complicated and my gut feel is that even if we could get it to work would be slow. Am I missing something neat here? The second approach involves dividing up our sprites into several polygons and testing them for overlaps. The more polygons the more accurate the collision detection. The benefit is that it is fast, and can be accurate. The downside is it makes the sprite creation more complicated. i.e., we have to create the polygons for each sprite. For speed the best approach is to create a tree of polygons. The 3rd approach I’m not sure about as it involves buying code (or using an open source licence). I am not sure what the best library to use is or whether this would make life easier or give us a problem integrating this into our app. So in short I am favouring the polygon and tree approach and would appreciate you views on this before I go and write lots of code. Best regards Dave

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• find the children in jquery

  - by armin etemadi

  i have a tree structure,there is an unordered list(ul) in that tree.i have li items in it,and in that li items it could be a span or an ul list. this is one part of my codes : <li id="main_li"> <div class="first_division"></div> <span>products</span> <ul style="display: block;"> <li> <div class="division1"></div> <span>products_cat_1</span> <ul style="display: none;"> <li> <span>products_cat_1_milk</span> </li> </ul> </li> <li> <span>products_yoghurt</span> </li> <li> <span>products_butter</span> </li> </ul> </li> i want to access li elements in ul tag where the parent li id is "main_li",i want to get it done by clicking on the span within li. how can i do this with jquery?

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• Raw types and subtyping

  - by Dmitrii

  We have generic class SomeClass<T>{ } We can write the line: SomeClass s= new SomeClass<String>(); It's ok, because raw type is supertype for generic type. But SomeClass<String> s= new SomeClass(); is correct to. Why is it correct? I thought that type erasure was before type checking, but it's wrong. From Hacker's Guide to Javac When the Java compiler is invoked with default compile policy it performs the following passes: parse: Reads a set of *.java source files and maps the resulting token sequence into AST-Nodes. enter: Enters symbols for the definitions into the symbol table. process annotations: If Requested, processes annotations found in the specified compilation units. attribute: Attributes the Syntax trees. This step includes name resolution, type checking and constant folding. flow: Performs data ow analysis on the trees from the previous step. This includes checks for assignments and reachability. desugar: Rewrites the AST and translates away some syntactic sugar. generate: Generates Source Files or Class Files. Generic is syntax sugar, hence type erasure invoked at 6 pass, after type checking, which invoked at 4 pass. I'm confused.

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• Duplicate elements when adding XElement to XDocument

  - by Andy

  I'm writing a program in C# that will go through a bunch of config.xml files and update certain elements, or add them if they don't exist. I have the portion down that updates an element if it exists with this code: XDocument xdoc = XDocument.Parse(ReadFile(_file)); XElement element = xdoc.Elements("project").Elements("logRotator") .Elements("daysToKeep").Single(); element.Value = _DoRevert; But I'm running into issues when I want to add an element that doesn't exist. Most of the time part of the tree is in place and when I use my code it adds another identical tree, and that causes the program reading the xml to blow up. here is how I am attempting to do it xdoc.Element("project").Add(new XElement("logRotator", new XElement("daysToKeep", _day))); and that results in a structure like this(The numToKeep tag was already there): <project> <logRotator> <daysToKeep>10</daysToKeep> </logRotator> <logRotator> <numToKeep>13</numToKeep> </logRotator> </project> but this is what I want <project> <logRotator> <daysToKeep>10</daysToKeep> <numToKeep>13</numToKeep> </logRotator> </project>

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• Doctrine/symfony: getSqlQuery() output in phpMyAdmin/SQL tab

  - by user248959

  Hi, i have created this query that works OK: $q1 = Doctrine_Query::create() ->from('Usuario u') ->leftJoin('u.AmigoUsuario a ON u.id = a.user2_id OR u.id = a.user1_id') ->where("a.user2_id = ? OR a.user1_id = ?", array($id,$id)) ->andWhere("u.id <> ?", $id) ->andWhere("a.estado LIKE ?", 1); echo $q1->getSqlQuery(); The calling to getSqlQuery outputs this clause: SELECT s.id AS s_id, s.username AS s_username, s.algorithm AS s_algorithm, s.salt AS s_salt, s.password AS s__password, s.is_active AS s__is_active, s.is_super_admin AS s__is_super_admin, s.last_login AS s__last_login, s.email_address AS s__email_address, s.nombre_apellidos AS s__nombre_apellidos, s.sexo AS s__sexo, s.fecha_nac AS s__fecha_nac, s.provincia AS s_provincia, s.localidad AS s_localidad, s.fotografia AS s_fotografia, s.avatar AS s_avatar, s.avatar_mensajes AS s__avatar_mensajes, s.created_at AS s__created_at, s.updated_at AS s__updated_at, a.id AS a__id, a.user1_id AS a__user1_id, a.user2_id AS a__user2_id, a.estado AS a__estado FROM sf_guard_user s LEFT JOIN amigo_usuario a ON ((s.id = a.user2_id OR s.id = a.user1_id)) WHERE ((a.user2_id = ? OR a.user1_id = ?) AND s.id < ? AND a.estado LIKE ?) If i take that clause to phpmyadmin SQL tab i get this error 1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '? OR a.user1_id = ?) AND s.id < ? AND a.estado LIKE ?) LIMIT 0, 30' at line 1 Why i'm getting this error? Regards Javi

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• Java MySQL Query Problem MySQLSyntaxErrorException When Creating a Table

  - by Aqib Mushtaq

  I fairly new to MySQL with Java, but I have executed a few successful INSERT queries however cannot seem to get the CREATE TABLE query to execute without getting the 'MySQLSyntaxErrorException' exception. My code is as follows: import java.sql.*; Statement stmt; Class.forName("com.mysql.jdbc.Driver"); String url = "jdbc:mysql://localhost:3306/mysql"; Connection con = DriverManager.getConnection(url, "root", "password"); stmt = con.createStatement(); String tblSQL = "CREATE TABLE IF NOT EXISTS \'dev\'.\'testTable\' (\n" + " \'id\' int(11) NOT NULL AUTO_INCREMENT,\n" + " \'date\' smallint(6) NOT NULL\n" + ") ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;"; stmt.executeUpdate(tblSQL); stmt.close(); con.close(); And the error is as follows: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ''dev'.'testTable' ( 'id' int(11) NOT NULL AUTO_INCREMENT, 'date' smallint(6) N' at line 1 I would appreciate it if anyone could spot the mistake in this query, as I've tried executing this within phpMyAdmin and it works as it should. Thanks in advance.

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• Rtti data manipulation and consistency in Delphi 2010

  - by Coco

  Has anyone an idea, how I can make TValue using a reference to the original data? In my serialization project, I use (as suggested in XML-Serialization) a generic serializer which stores TValues in an internal tree-structure (similar to the MemberMap in the example). This member-tree should also be used to create a dynamic setup form and manipulate the data. My idea was to define a property for the Data: TDataModel <T> = class {...} private FData : TValue; function GetData : T; procedure SetData (Value : T); public property Data : T read GetData write SetData; end; The implementation of the GetData, SetData Methods: procedure TDataModel <T>.SetData (Value : T); begin FData := TValue.From <T> (Value); end; procedure TDataModel <T>.GetData : T; begin Result := FData.AsType <T>; end; Unfortunately, the TValue.From method always makes a copy of the original data. So whenever the application makes changes to the data, the DataModel is not updated and vice versa if I change my DataModel in a dynamic form, the original data is not affected. Sure I could always use the Data property before and after changing anything, but as I use lot of Rtti inside my DataModel, I do not realy want to do this anytime. Perhaps someone has a better suggestion?

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• C++ Problems with #import of .NET out-of-proc server.

  - by jm

  In C++ program, I am trying to #import TLB of .NET out of proc server. I get errors like: z:\server.tlh(111) : error C2146: syntax error : missing ';' before identifier 'GetType' z:\server.tlh(111) : error C2501: 'TypePtr' : missing storage-class or type specifiers z:\server.tli(74) : error C2143: syntax error : missing ';' before 'tag::id' z:\server.tli(74) : error C2433: 'TypePtr' : 'inline' not permitted on data declarations z:\server.tli(74) : error C2501: '_TypePtr' : missing storage-class or type specifiers z:\server.tli(74) : fatal error C1004: unexpected end of file found The TLH looks like: ... _bstr_t GetToString ( ); VARIANT_BOOL Equals ( const _variant_t & obj ); long GetHashCode ( ); _TypePtr GetType ( ); long Open ( ); ... I am not really interested in the having the base object .NET object methods like GetType(), Equals(), etc. But GetType() seems to be causing problems. Some google research indicates I could #import MSCORLIB.TLB (or put it in path), but I can't get that to compile either. Any tips?

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• Why does a sub-class class of a class have to be static in order to initialize the sub-class in the

  - by Alex

  So, the question is more or less as I wrote. I understand that it's probably not clear at all so I'll give an example. I have class Tree and in it there is the class Node, and the empty constructor of Tree is written: public class RBTree { private RBNode head; public RBTree(RBNode head,RBTree leftT,RBTree rightT){ this.head=head; this.head.leftT.head.father = head; this.head.rightT.head.father = head; } public RBTree(RBNode head){ this(head,new RBTree(),new RBTree()); } public RBTree(){ this(new RBNode(),null,null); } public class RBNode{ private int value; private boolean isBlack; private RBNode father; private RBTree leftT; private RBTree rightT; } } Eclipse gives me the error: "No enclosing instance of type RBTree is available due to some intermediate constructor invocation" for the "new RBTree()" in the empty constructor. However, if I change the RBNode to be a static class, there is no problem. So why is it working when the class is static. BTW, I found an easy solution for the cunstructor: public RBTree(){ this.head = new RBNode(); } So, I have no idea what is the problem in the first piece of code.

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• Windows batch - loop over folder string and parse out last folder name

  - by Tim Peel

  Hi, I need to grab the folder name of a currently executing batch file. I have been trying to loop over the current directory using the following syntax (which is wrong at present): set mydir = %~p0 for /F "delims=\" %i IN (%mydir%) DO @echo %i Couple of issues in that I cannot seem to pass the 'mydir' variable value in as the search string. It only seems to work if I pass in commands; I have the syntax wrong and cannot work out why. My thinking was to loop over the folder string with a '\' delimiter but this is causing problems too. If I set a variable on each loop then the last value set will be the current folder name. For example, given the following path: C:\Folder1\Folder2\Folder3\Archive.bat I would expect to parse out the value 'Folder3'. I need to parse that value out as its name will be part of another folder I am going to create further down in the batch file. Many thanks if anyone can help. I may be barking up the wrong tree completely so any other approaches would be greatly received also. Tim

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• MySQL 1064 error, works in command line and phpMyAdmin; not in app

  - by hundleyj

  Here is my query: select * from (select *, 3956 * 2 * ASIN(SQRT(POWER(SIN(RADIANS(45.5200077 - lat)/ 2), 2) + COS(RADIANS(45.5200077)) * COS(RADIANS(lat)) * POWER(SIN(RADIANS(-122.6942014 - lng)/2),2))) AS distance from stops order by distance, route asc) as p group by route, dir order by distance asc limit 10 This works fine at the command line and in PHPMyAdmin. I'm using Dbslayer to connect to MySQL via my JavaScript backend, and the request is returning a 1064 error. Here is the encoded DBSlayer request string: http://localhost:9090/db?{%22SQL%22:%22select%20*%20from%20%28select%20*,%203956%20*%202%20*%20ASIN%28SQRT%28POWER%28SIN%28RADIANS%2845.5200077%20-%20lat%29/%202%29,%202%29%20+%20COS%28RADIANS%2845.5200077%29%29%20*%20COS%28RADIANS%28lat%29%29%20*%20POWER%28SIN%28RADIANS%28-122.6942014%20-%20lng%29/2%29,2%29%29%29%20AS%20distance%20from%20%60stops%60%20order%20by%20%60distance%60,%20%60route%60%20asc%29%20as%20p%20group%20by%20%60route%60,%20%60dir%60%20order%20by%20%60distance%60%20asc%20limit%2010%22} And the response: {"MYSQL_ERRNO" : 1064 , "MYSQL_ERROR" : "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '(RADIANS(45.5200077)) * COS(RADIANS(lat)) * POWER(SIN(RADIANS(-122.6942014 - lng' at line 1" , "SERVER" : "trimet"} Thanks!

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• Semantically linking to code snippets

  - by Tim

  What's the most simple and semantic way of presenting code snippets in HTML? Possible XHTML syntax <a href="code_sample.php" type="text/x-php"> Example of widget creation </a> Example of linked file (code_sample.php): // Create a new widget $widget = new widget(); Pros: Semantically uses title to describe the source code being referenced Up to the client to render snippet Having very many custom server-side implementations tells me it should be standardized Browsers can have plug-ins for copy+paste, download, etc Seems to me this is where it belongs (not in Javascript) Degradation: non-compliant browsers receive a link to the associated content Cons: Not semantic enough? Seems wrong to replace hyperlinks with source code for presentation <object> might be better, but wouldn't degrade as nicely. Background I'm trying to create a "personal" XHTML standard for storing notes (wow, this is probably among the nerdiest things I've said). Since notes are just "scratch" it needs to be very lightweight. SO's markdown is very lightweight but not semantic enough for my needs. Plus, now I'm just curious. What's the most ideal syntax for linking to client-rendered code-snippets?

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• C++ destructos causing crash's

  - by larsonator

  ok, so i got a some what intricate program that simulates the uni systems of students, units, and students enrolling in units. Students are stored in a binary search tree, Units are stored in a standard list. Student has a list of Unit Pointers, to store which units he/she is enrolled in Unit has a list of Student pointers, to store students which are enrolled in that unit. The unit collections (storing units in a list) as made as a static variable where the main function is, as is the Binary search tree of students. when its finaly time to close the program, i call the destructors of each. but at some stage, during the destructors on the unit side, Unhandled exception at 0x002e4200 in ClassAllocation.exe: 0xC0000005: Access violation reading location 0x00000000. UnitCollection destructor: UnitCol::~UnitCol() { list<Unit>::iterator itr; for(itr = UnitCollection.begin(); itr != UnitCollection.end();) { UnitCollection.pop_front(); itr = UnitCollection.begin(); } } Unit Destructor Unit::~Unit() { } now i got the same sorta problem on the student side of things BST destructors void StudentCol::Destructor(const BTreeNode * r) { if(r!= 0) { Destructor(r->getLChild()); Destructor(r->getRChild()); delete r; } } StudentCol::~StudentCol() { Destructor(root); } Student Destructor Student::~Student() { } so yeah any help would be greatly appreciated

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• Dynamic Hierarchical Javascript Object Loop

  - by user1684586

  var treeData = {"name" : "A", "children" : [ {"name" : "B", "children": [ {"name" : "C", "children" :[]} ]} ]}; THE ARRAY BEFORE SHOULD BE EMPTY. THE ARRAY AFTER SHOULD BE POPULATED DEPENDING ON THE NUMBER OF NODES NEEDED THAT WILL BE DEFINED FROM A DYNAMIC VALUE THAT IS PASSED. I would like to build the hierarchy dynamically with each node created as a layer/level in the hierarchy having its own array of nodes. THIS SHOULD FORM A TREE STRUCTURE. This is hierarchy structure is described in the above code. This code has tree level simple for demonstrating the layout of the hierarchy of values. There should be a root node, and an undefined number of nodes and levels to make up the hierarchy size. Nothing should be fixed besides the root node. I do not need to read the hierarchy, I need to construct it. The array should start {"name" : "A", "children" : []} and every new node as levels would be created {"name" : "A", "children" : [HERE-{"name" : "A", "children" : []}]}. In the child array, going deeper and deeper. Basically the array should have no values before the call, except maybe the root node. After the function call, the array should comprise of the required nodes of a number that may vary with every call. Every child array will contain one or more node values. There should be a minimum of 2 node levels, including the root. It should initially be a Blank canvas, that is no predefined array values.

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• key-words highlight in <textarea> (again)

  - by Halst

  Wait, I know! I know that this "syntax highlight in textarea"-question was raised like a million times on stackoverflow! But, please, listen. offtopic: I'm not a web-developer, and technically I'm not a programmer at all. I study mechatronics and deal mostly with control-engineering and digital-hardware. And I'm so pissed off that whenever I want to share some application (that would be helpful in my field) and embed it into the web, I need to know such a crazy amount of technologies, like html, css, javascript, flash, etc.. that takes time, which I could have been spending for the benefit of my own field. Right now I'm playing with hardware-description-languages and I'm writing some Python-libraries to convert one HDL into another. And I wanted to embed such feature on the web: http://xhdl2vhdl.appspot.com/ I wanted to implement some basic syntax highlighting (only keywords highlighting will be enough) so that the code could be readable. But the whole idea highlighting something in textarea is not trivial at all. The other difficulty is that the languages I work with are rare, and there are no out-of-box solutions for them. I tried to dig into these solutions, but they are very complicated for me: http://www.nicolarizzo.com/gamesroom/experimental/CodeEditor.html http://marijn.haverbeke.nl/codemirror/jstest.html and there is no clear descriptions how to use them (for my level of knowledge of web-development). So, is there a simple solution, just to highlight a bunch of key-words in textarea or perform something equivalent? Thank you.

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• How do I use a custom cookie session serializer in Rack?

  - by Damien Wilson

  Hello SO. I'm currently integrating Warden into a new Rack application I'm building. I'd like to implement a recent patch to Rack that allows me to specify how sessions are serialized; specifically, I'd like to use Rack::Session::Cookie::Identity as the session processor. Unfortunately, the documentation is a little unclear as to what syntax I should use to configure Rack::Session::Cookie in my rackup file, can anyone here tell me what I'm doing wrong? config.ru require 'my_sinatra_app' app = self use Rack::Session::Cookie.new(app, Rack::Session::Cookie::Identity.new), {:key => "auth_token"} use Warden::Manager do |warden| # Must come AFTER Rack::Session warden.default_strategies :password warden.failure_app Jelli::Auth.run! end run MySinatraApp error message from thin !! Unexpected error while processing request: undefined method `new' for #<Rack::Session::Cookie:0x00000110124128> PS: I'm using bundler to manage my gem dependencies and I've likewise included rack's master branch as the desired version. Update: As suggested in the comments below, I have read the documentation; sadly the suggested syntax in the docs is not working. Update: Still no luck on my end; offering up a bounty to whoever can help me figure this out.

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• How do I interact with a Perl object that has a hash attribute?

  - by brydgesk

  I have a class with several variables, one of which is a hash (_runs): sub new { my ($class, $name) = @_; my $self = { _name => $name, ... _runs => (), _times => [], ... }; bless ($self, $class); return $self; } Now, all I'm trying to do is create an accessor/mutator, as well as another subroutine that pushes new data into the hash. But I'm having a hell of a time getting all the referencing/dereferencing/$self calls working together. I've about burned my eyes out with "Can't use string ("blah") as a HASH ref etc etc" errors. For the accessor, what is 'best practice' for returning hashes? Which one of these options should I be using (if any)?: return $self->{_runs}; return %{ $self->{_runs} }; return \$self->{_runs}; Further, when I'm using the hash within other subroutines in the class, what syntax do I use to copy it? my @runs = $self->{_runs}; my @runs = %{ $self->{_runs} }; my @runs = $%{ $self->{_runs} }; my @runs = $$self->{_runs}; Same goes for iterating over the keys: foreach my $dt (keys $self->{_runs}) foreach my $dt (keys %{ $self->{_runs} }) And how about actually adding the data? $self->{_runs}{$dt} = $duration; %{ $self->{_runs} }{$dt} = $duration; $$self->{_runs}{$dt} = $duration; You get the point. I've been reading articles about using classes, and articles about referencing and dereferencing, but I can't seem to get my brain to combine the knowledge and use both at the same time. I got my _times array working finally, but mimicking my array syntax over to hashes didn't work.

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• C++ destructors causing crash's

  - by larsonator

  ok, so i got a some what intricate program that simulates the uni systems of students, units, and students enrolling in units. Students are stored in a binary search tree, Units are stored in a standard list. Student has a list of Unit Pointers, to store which units he/she is enrolled in Unit has a list of Student pointers, to store students which are enrolled in that unit. The unit collections (storing units in a list) as made as a static variable where the main function is, as is the Binary search tree of students. when its finaly time to close the program, i call the destructors of each. but at some stage, during the destructors on the unit side, Unhandled exception at 0x002e4200 in ClassAllocation.exe: 0xC0000005: Access violation reading location 0x00000000. UnitCollection destructor: UnitCol::~UnitCol() { list<Unit>::iterator itr; for(itr = UnitCollection.begin(); itr != UnitCollection.end();) { UnitCollection.pop_front(); itr = UnitCollection.begin(); } } Unit Destructor Unit::~Unit() { } now i got the same sorta problem on the student side of things BST destructors void StudentCol::Destructor(const BTreeNode * r) { if(r!= 0) { Destructor(r->getLChild()); Destructor(r->getRChild()); delete r; } } StudentCol::~StudentCol() { Destructor(root); } Student Destructor Student::~Student() { } so yeah any help would be greatly appreciated

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• Checking if any of a list of values falls within a table of ranges

  - by Conspicuous Compiler

  I'm looking to check whether any of a list of integers fall in a list of ranges. The ranges are defined in a table defined something like: # Extra Type Field Default Null Key 0 int(11) rangeid 0 NO PRI 1 int(11) max 0 NO MUL 2 int(11) min 0 NO MUL Using MySQL 5.1 and Perl 5.10. I can check whether a single value, say 7, is in any of the ranges with a statement like SELECT 1 FROM range WHERE 7 BETWEEN min AND max If 7 is in any of those ranges, I get a single row back. If it isn't, no rows are returned. Now I have a list of, say, 50 of these values, not stored in a table at present. I assemble them using map: my $value_list = '(' . ( join ', ', map { int $_ } @values ) . ')' ; I want to see if any of the items in the list fall inside of any of the ranges, but am not particularly concerned with which number nor which range. I'd like to use a syntax such as: SELECT 1 FROM range WHERE (1, 2, 3, 4, 5, 6, 7, 42, 309, 10000) BETWEEN min AND max MySQL kindly chastises me for such syntax: Operand should contain 1 column(s) I pinged #mysql who were quite helpful. However, having already written this up by the time they responded and thinking it'd be helpful to fix the answer in a more permanent medium, I figured I'd post the question anyhow. Maybe SO will provide a different solution?

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• TicTacToe strategic reduction

  - by NickLarsen

  I decided to write a small program that solves TicTacToe in order to try out the effect of some pruning techniques on a trivial game. The full game tree using minimax to solve it only ends up with 549,946 possible games. With alpha-beta pruning, the number of states required to evaluate was reduced to 18,297. Then I applied a transposition table that brings the number down to 2,592. Now I want to see how low that number can go. The next enhancement I want to apply is a strategic reduction. The basic idea is to combine states that have equivalent strategic value. For instance, on the first move, if X plays first, there is nothing strategically different (assuming your opponent plays optimally) about choosing one corner instead of another. In the same situation, the same is true of the center of the walls of the board, and the center is also significant. By reducing to significant states only, you end up with only 3 states for evaluation on the first move instead of 9. This technique should be very useful since it prunes states near the top of the game tree. This idea came from the GameShrink method created by a group at CMU, only I am trying to avoid writing the general form, and just doing what is needed to apply the technique to TicTacToe. In order to achieve this, I modified my hash function (for the transposition table) to enumerate all strategically equivalent positions (using rotation and flipping functions), and to only return the lowest of the values for each board. Unfortunately now my program thinks X can force a win in 5 moves from an empty board when going first. After a long debugging session, it became apparent to me the program was always returning the move for the lowest strategically significant move (I store the last move in the transposition table as part of my state). Is there a better way I can go about adding this feature, or a simple method for determining the correct move applicable to the current situation with what I have already done?

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