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• how to deal with the position in a c# stream

  - by CapsicumDreams

  The (entire) documentation for the position property on a stream says: When overridden in a derived class, gets or sets the position within the current stream. The Position property does not keep track of the number of bytes from the stream that have been consumed, skipped, or both. That's it. OK, so we're fairly clear on what it doesn't tell us, but I'd really like to know what it in fact does stand for. What is 'the position' for? Why would we want to alter or read it? If we change it - what happens? In a pratical example, I have a a stream that periodically gets written to, and I have a thread that attempts to read from it (ideally ASAP). From reading many SO issues, I reset the position field to zero to start my reading. Once this is done: Does this affect where the writer to this stream is going to attempt to put the data? Do I need to keep track of the last write position myself? (ie if I set the position to zero to read, does the writer begin to overwrite everything from the first byte?) If so, do I need a semaphore/lock around this 'position' field (subclassing, perhaps?) due to my two threads accessing it? If I don't handle this property, does the writer just overflow the buffer? Perhaps I don't understand the Stream itself - I'm regarding it as a FIFO pipe: shove data in at one end, and suck it out at the other. If it's not like this, then do I have to keep copying the data past my last read (ie from position 0x84 on) back to the start of my buffer? I've seriously tried to research all of this for quite some time - but I'm new to .NET. Perhaps the Streams have a long, proud (undocumented) history that everyone else implicitly understands. But for a newcomer, it's like reading the manual to your car, and finding out: The accelerator pedal affects the volume of fuel and air sent to the fuel injectors. It does not affect the volume of the entertainment system, or the air pressure in any of the tires, if fitted. Technically true, but seriously, what we want to know is that if we mash it to the floor you go faster..

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• Optimize slow ranking query

  - by Juan Pablo Califano

  I need to optimize a query for a ranking that is taking forever (the query itself works, but I know it's awful and I've just tried it with a good number of records and it gives a timeout). I'll briefly explain the model. I have 3 tables: player, team and player_team. I have players, that can belong to a team. Obvious as it sounds, players are stored in the player table and teams in team. In my app, each player can switch teams at any time, and a log has to be mantained. However, a player is considered to belong to only one team at a given time. The current team of a player is the last one he's joined. The structure of player and team is not relevant, I think. I have an id column PK in each. In player_team I have: id (PK) player_id (FK -> player.id) team_id (FK -> team.id) Now, each team is assigned a point for each player that has joined. So, now, I want to get a ranking of the first N teams with the biggest number of players. My first idea was to get first the current players from player_team (that is one record top for each player; this record must be the player's current team). I failed to find a simple way to do it (tried GROUP BY player_team.player_id HAVING player_team.id = MAX(player_team.id), but that didn't cut it. I tried a number of querys that didn't work, but managed to get this working. SELECT COUNT(*) AS total, pt.team_id, p.facebook_uid AS owner_uid, t.color FROM player_team pt JOIN player p ON (p.id = pt.player_id) JOIN team t ON (t.id = pt.team_id) WHERE pt.id IN ( SELECT max(J.id) FROM player_team J GROUP BY J.player_id ) GROUP BY pt.team_id ORDER BY total DESC LIMIT 50 As I said, it works but looks very bad and performs worse, so I'm sure there must be a better way to go. Anyone has any ideas for optimizing this? I'm using mysql, by the way. Thanks in advance Adding the explain. (Sorry, not sure how to format it properly) id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY t ALL PRIMARY NULL NULL NULL 5000 Using temporary; Using filesort 1 PRIMARY pt ref FKplayer_pt77082,FKplayer_pt265938,new_index FKplayer_pt77082 4 t.id 30 Using where 1 PRIMARY p eq_ref PRIMARY PRIMARY 4 pt.player_id 1 2 DEPENDENT SUBQUERY J index NULL new_index 8 NULL 150000 Using index

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• Moving from Windows to Ubuntu.

  - by djzmo

  Hello there, I used to program in Windows with Microsoft Visual C++ and I need to make some of my portable programs (written in portable C++) to be cross-platform, or at least I can release a working version of my program for both Linux and Windows. I am total newcomer in Linux application development (and rarely use the OS itself). So, today, I installed Ubuntu 10.04 LTS (through Wubi) and equipped Code::Blocks with the g++ compiler as my main weapon. Then I compiled my very first Hello World linux program, and I confused about the output program. I can run my program through the "Build and Run" menu option in Code::Blocks, but when I tried to launch the compiled application externally through a File Browser (in /media/MyNTFSPartition/MyProject/bin/Release; yes, I saved it in my NTFS partition), the program didn't show up. Why? I ran out of idea. I need to change my Windows and Microsoft Visual Studio mindset to Linux and Code::Blocks mindset. So I came up with these questions: How can I execute my compiled linux programs externally (outside IDE)? In Windows, I simply run the generated executable (.exe) file How can I distribute my linux application? In Windows, I simply distribute the executable files with the corresponding DLL files (if any) What is the equivalent of LIBs (static library) and DLLs (dynamic library) in linux and how to use them? In Windows/Visual Studio, I simply add the required libraries to the Additional Dependencies in the Project Settings, and my program will automatically link with the required static library(-ies)/DLLs. Is it possible to use the "binary form" of a C++ library (if provided) so that I wouldn't need to recompile the entire library source code? In Windows, yes. Sometimes precompiled *.lib files are provided. If I want to create a wxWidgets application in Linux, which package should I pick for Ubuntu? wxGTK or wxX11? Can I run wxGTK program under X11? In Windows, I use wxMSW, Of course. If question no. 4 is answered possible, are precompiled wxX11/wxGTK library exists out there? Haven't tried deep google search. In Windows, there is a project called "wxPack" (http://wxpack.sourceforge.net/) that saves a lot of my time. Sorry for asking many questions, but I am really confused on these linux development fundamentals. Any kind of help would be appreciated =) Thanks.

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• Configuring a html page from an original demo page

  - by Wold

  I forked into rainyday.js through github, an awesome javascript program made by maroslaw at this link: https://github.com/maroslaw/rainyday.js. Basically I tried taking his demo page and my own photo city.jpg and changed the applicable fields so that I could run it on my own site, but only the picture loads and the script itself doesn't start to run. I'm pretty new to html and javascript so I'm probably omitting something very simple, but here is the script for the demo code: <script src="rainyday.js"></script> <script> function getURLParameter(name) { return decodeURIComponent((new RegExp('[?|&]' + name + '=' + '([^&;]+?)(&|#|;|$)').exec(location.search)||[,''])[1].replace(/\+/g, '%20'))||null; } function demo() { var image = document.getElementById('background'); image.onload = function () { var engine = null; var preset = getURLParameter('preset') || '1'; if (preset === '1') { engine = new RainyDay({ element: 'background', blur: 10, opacity: 1, fps: 30, speed: 30 }); engine.rain([ [1, 2, 8000] ]); engine.rain([ [3, 3, 0.88], [5, 5, 0.9], [6, 2, 1] ], 100); } else if (preset === '2') { engine = new RainyDay({ element: 'background', blur: 10, opacity: 1, fps: 30, speed: 30 }); engine.VARIABLE_GRAVITY_ANGLE = Math.PI / 8; engine.rain([ [0, 2, 0.5], [4, 4, 1] ], 50); } else if (preset === '3') { engine = new RainyDay({ element: 'background', blur: 10, opacity: 1, fps: 30, speed: 30 }); engine.trail = engine.TRAIL_SMUDGE; engine.rain([ [0, 2, 0.5], [4, 4, 1] ], 100); } }; image.crossOrigin = 'anonymous'; if (getURLParameter('imgur')) { image.src = 'http://i.imgur.com/' + getURLParameter('imgur') + '.jpg'; } else if (getURLParameter('img')) { image.src = getURLParameter('img') + '.jpg'; } var youtube = getURLParameter('youtube'); if (youtube) { var div = document.getElementById('sound'); var player = document.createElement('iframe'); player.frameborder = '0'; player.height = '1'; player.width = '1'; player.src = 'https://youtube.com/embed/' + youtube + '?autoplay=1&controls=0&showinfo=0&autohide=1&loop=1'; div.appendChild(player); } } </script> This is where I am naming my background and specifying the photo from within the directory. <body onload="demo();"> <div id="sound" style="z-index: -1;"></div> <div id="parent"> <img id='background' alt="background" src="city.jpg" /> </div> </body> The actual code for the whole entire rainyday.js script can be found here: https://github.com/maroslaw/rainyday.js/blob/master/rainyday.js Thanks in advance for any help and advice!

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• .NET Windows Service with timer stops responding

  - by Biri

  I have a windows service written in c#. It has a timer inside, which fires some functions on a regular basis. So the skeleton of my service: public partial class ArchiveService : ServiceBase { Timer tickTack; int interval = 10; ... protected override void OnStart(string[] args) { tickTack = new Timer(1000 * interval); tickTack.Elapsed += new ElapsedEventHandler(tickTack_Elapsed); tickTack.Start(); } protected override void OnStop() { tickTack.Stop(); } private void tickTack_Elapsed(object sender, ElapsedEventArgs e) { ... } } It works for some time (like 10-15 days) then it stops. I mean the service shows as running, but it does not do anything. I make some logging and the problem can be the timer, because after the interval it does not call the tickTack_Elapsed function. I was thinking about rewrite it without a timer, using an endless loop, which stops the processing for the amount of time I set up. This is also not an elegant solution and I think it can have some side effects regarding memory. The Timer is used from the System.Timers namespace, the environment is Windows 2003. I used this approach in two different services on different servers, but both is producing this behavior (this is why I thought that it is somehow connected to my code or the framework itself). Does somebody experienced this behavior? What can be wrong? Edit: I edited both services. One got a nice try-catch everywhere and more logging. The second got a timer-recreation on a regular basis. None of them stopped since them, so if this situation remains for another week, I will close this question. Thank you for everyone so far. Edit: I close this question because nothing happened. I mean I made some changes, but those changes are not really relevant in this matter and both services are running without any problem since then. Please mark it as "Closed for not relevant anymore".

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• MVC EditorFor bind to type in array

  - by BradBrening

  I have a ViewModel that, among other properties, contains an array of 'EmailAddress' objects. EmailAddress itself has properties such as "Address", and "IsPrimary". My view model breakdown is: public class UserDetailsViewModel { public BUser User { get; set; } public string[] Roles { get; set; } public EmailAddress[] EmailAddresses { get; set; } } I am showing a "User Details" page that is pretty standard. For example, I'm displaying data using @Html.DisplayFor(model => model.User.UserName) and @Html.DisplayFor(model => model.User.Comment) I also have a section on the page that lists all of the EmailAddress objects associated with the user: @if(Model.EmailAddresses.Length > 0) { foreach (var address in Model.EmailAddresses) { <div> @Html.DisplayFor(model => address.Address) </div> } } else { <div class="center">User does not have any email addresses.</div> } My problem is that I would like to show an "Add Email Address" form above the list of email addresses. I thought I would take the "normal" approach thusly: @using(Html.BeginForm(new { id=Model.User.UserName, action="AddUserEmailAddress" })) { <text>Address:</text> @Html.EditorFor(model => ** HERE I AM STUCK **) <input type="submit" value="Add Email" class="button" /> } As you may be able to tell, I am stuck here. I've tried model => Model.EmailAddresses[0] and model => Model.EmailAddresses.FirstOrDefault(). Both of these have failed horribly. I am sure that I am going about this all wrong. I've even thought of adding a "dummy" property to my ViewModel of type EmailAddress just so that I can bind to that in my EditorFor - but that seems to be a really bad hack. There has to be something simple that I'm overlooking! I would appreciate any help anyone can offer with this matter. Thank you in advance!

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• Dynamically loading modules in Python (+ threading question)

  - by morpheous

  I am writing a Python package which reads the list of modules (along with ancillary data) from a configuration file. I then want to iterate through each of the dynamically loaded modules and invoke a do_work() function in it which will spawn a new thread, so that the code runs in a separate thread. At the moment, I am importing the list of all known modules at the beginning of my main script - this is a nasty hack I feel, and is not very flexible, as well as being a maintenance pain. This is the function that spawns the threads. I will like to modify it to dynamically load the module when it is encountered. The key in the dictionary is the name of the module containing the code: def do_work(work_info): for (worker, dataset) in work_info.items(): #import the module defined by variable worker here... t = threading.Thread(target=worker.do_work, args=[dataset]) # I'll NOT dameonize since spawned children need to clean up on shutdown # Since the threads will be holding resources #t.daemon = True t.start() Question 1 When I call the function in my script (as written above), I get the following error: AttributeError: 'str' object has no attribute 'do_work' Which makes sense, since the dictionary key is a string (name of the module to be imported). When I add the statement: import worker before spawning the thread, I get the error: ImportError: No module named worker This is strange, since the variable name rather than the value it holds are being used - when I print the variable, I get the value (as I expect) whats going on? Question 2 As I mentioned in the comments section, I realize that the do_work() function written in the spawned children needs to cleanup after itself. My understanding is to write a clean_up function that is called when do_work() has completed successfully, or an unhandled exception is caught - is there anything more I need to do to ensure resources don't leak or leave the OS in an unstable state? Question 3 If I comment out the t.daemon flag statement, will the code stil run ASYNCHRONOUSLY?. The work carried out by the spawned children are pretty intensive, and I don't want to have to be waiting for one child to finish before spawning another child. BTW, I am aware that threading in Python is in reality, a kind of time sharing/slicing - thats ok Lastly is there a better (more Pythonic) way of doing what I'm trying to do?

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• are C functions declared in <c____> headers guaranteed to be in the global namespace as well as std?

  - by Evan Teran

  So this is something that I've always wondered but was never quite sure about. So it is strictly a matter of curiosity, not a real problem. As far as I understand, what you do something like #include <cstdlib> everything (except macros of course) are declared in the std:: namespace. Every implementation that I've ever seen does this by doing something like the following: #include <stdlib.h> namespace std { using ::abort; // etc.... } Which of course has the effect of things being in both the global namespace and std. Is this behavior guaranteed? Or is it possible that an implementation could put these things in std but not in the global namespace? The only way I can think of to do that would be to have your libstdc++ implement every c function itself placing them in std directly instead of just including the existing libc headers (because there is no mechanism to remove something from a namespace). Which is of course a lot of effort with little to no benefit. The essence of my question is, is the following program strictly conforming and guaranteed to work? #include <cstdio> int main() { ::printf("hello world\n"); } EDIT: The closest I've found is this (17.4.1.2p4): Except as noted in clauses 18 through 27, the contents of each header cname shall be the same as that of the corresponding header name.h, as specified in ISO/IEC 9899:1990 Programming Languages C (Clause 7), or ISO/IEC:1990 Programming Languages—C AMENDMENT 1: C Integrity, (Clause 7), as appropriate, as if by inclusion. In the C + + Standard Library, however, the declarations and definitions (except for names which are defined as macros in C) are within namespace scope (3.3.5) of the namespace std. which to be honest I could interpret either way. "the contents of each header cname shall be the same as that of the corresponding header name.h, as specified in ISO/IEC 9899:1990 Programming Languages C" tells me that they may be required in the global namespace, but "In the C + + Standard Library, however, the declarations and definitions (except for names which are defined as macros in C) are within namespace scope (3.3.5) of the namespace std." says they are in std (but doesn't specify any other scoped they are in).

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• Why does Rails with Passenger/nginx only works in development mode? No logs available

  - by Michael W.

  Hey folks, I have a serious problem with one of our webservers... after having an internal alpha-testing with a mongrel/haproxy-cluster that worked well, we wanted to use nginx with passenger for our first production server (customers will access this server). However, I can only run the rails app via development mode with passenger/nginx. The app itself runs perfect with mongrel or webrick in production mode. My biggest problem with this case is that I don't find ANY information in the nginx or rails-logs (only when I use mongrel or webrick). Permissions are correct. Passenger-status shows that the app is running, but I always get the static 500.html-error page... It would be so nice if you guys could give me a hint and help me solve the problem. I put the config at the bottom of the post... This exact config works with rails_env development;but I'd like to use the production mode ;-) Thank you very much for your help! Version: Ubuntu 8.04.2 64bit / nginx-0.7.64 (compiled and installed via passenger-2.2.11) cat /opt/nginx/conf/nginx.conf user www-data; worker_processes 4; error_log logs/error.log; #pid logs/nginx.pid; events { worker_connections 1024; } http { passenger_root /usr/lib/ruby/gems/1.8/gems/passenger-2.2.11; passenger_ruby /usr/bin/ruby1.8; passenger_log_level 3; include mime.types; default_type application/octet-stream; #log_format main '$remote_addr - $remote_user [$time_local] "$request" ' # '$status $body_bytes_sent "$http_referer" ' # '"$http_user_agent" "$http_x_forwarded_for"'; access_log logs/access.log; sendfile on; #tcp_nopush on; #keepalive_timeout 0; keepalive_timeout 65; #gzip on; server { listen 80; server_name <<servername>>; root /srv/app01/public; passenger_enabled on; }

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• How do I use Ruby metaprogramming to refactor this common code?

  - by James Wenton

  I inherited a project with a lot of badly-written Rake tasks that I need to clean up a bit. Because the Rakefiles are enormous and often prone to bizarre nonsensical dependencies, I'm simplifying and isolating things a bit by refactoring everything to classes. Specifically, that pattern is the following: namespace :foobar do desc "Frozz the foobar." task :frozzify do unless Rake.application.lookup('_frozzify') require 'tasks/foobar' Foobar.new.frozzify end Rake.application['_frozzify'].invoke end # Above pattern repeats many times. end # Several namespaces, each with tasks that follow this pattern. In tasks/foobar.rb, I have something that looks like this: class Foobar def frozzify() # The real work happens here. end # ... Other tasks also in the :foobar namespace. end For me, this is great, because it allows me to separate the task dependencies from each other and to move them to another location entirely, and I've been able to drastically simplify things and isolate the dependencies. The Rakefile doesn't hit a require until you actually try to run a task. Previously this was causing serious issues because you couldn't even list the tasks without it blowing up. My problem is that I'm repeating this idiom very frequently. Notice the following patterns: For every namespace :xyz_abc, there is a corresponding class in tasks/... in the file tasks/[namespace].rb, with a class name that looks like XyzAbc. For every task in a particular namespace, there is an identically named method in the associated namespace class. For example, if namespace :foo_bar has a task :apples, you would expect to see def apples() ... inside the FooBar class, which itself is in tasks/foo_bar.rb. Every task :t defines a "meta-task" _t (that is, the task name prefixed with an underscore) which is used to do the actual work. I still want to be able to specify a desc-description for the tasks I define, and that will be different for each task. And, of course, I have a small number of tasks that don't follow the above pattern at all, so I'll be specifying those manually in my Rakefile. I'm sure that this can be refactored in some way so that I don't have to keep repeating the same idiom over and over, but I lack the experience to see how it could be done. Can someone give me an assist?

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• fancybox image sometimes renders outside box

  - by Colleen

  I have the following django template: <script type="text/javascript" src="{{ STATIC_URL }}js/ jquery.fancybox-1.3.4.pack.js"></script> <link rel="stylesheet" href="{{ STATIC_URL }}css/ jquery.fancybox-1.3.4.css" type="text/css" media="screen" /> {% include "submission-form.html" with section="photos" %} <div class="commentables"> {% load thumbnail %} {% for story in objects %} <div class="image {% if forloop.counter|add:"-1"| divisibleby:picsinrow %}left{% else %}{% if forloop.counter| divisibleby:picsinrow %}right{% else %}middle{% endif %}{% endif %}"> {% if story.image %} {% thumbnail story.image size crop="center" as full_im %} <a rel="gallery" href="{% url post slug=story.slug %}"> <img class="preview" {% if story.title %} alt="{{ story.title }}" {% endif %} src="{{ full_im.url }}" full- image="{% if story.image_url %}{{ story.image_url }}{% else %} {{ story.image.url }}{% endif %}"> </a> {% endthumbnail %} {% else %} {% if story.image_url %} {% thumbnail story.image_url size crop="center" as full_im %} <a rel="gallery" href="{% url post slug=story.slug %}"> <img class="preview" {% if story.title %} alt="{{ story.title }}" {% endif %} src="{{ full_im.url }}" full- image="{{ story.image_url }}"> </a> {% endthumbnail %} {% endif %} {% endif %} </div> {% endfor %} {% if rowid != "last" %} <br style="clear: both" /> {% endif %} {% if not no_more_button %} <p style="text-align: right;" class="more-results"><a href="{% url images school_slug tag_slug %}">more...</a></p> {% endif %} </div> <script> $(document).ready(function(){ function changeattr(e){ var f = $(e.clone()); $(f.children()[0]).attr('src', $(f.children() [0]).attr("full-image")); $(f.children()[0]).attr('height', '500px'); return f[0].outerHTML; } $('.image a').each(function(idx, elem) { var e = $(elem); e.fancybox({ title: $(e.children()[0]).attr('alt'), content: changeattr(e) }); }); }); </script> and I'm occasionally getting weird display errors where the box will either not render anything at all (so it will show up as just a thin white bar, basically) or it will render only about 30 px wide, and position itself halfway down the page. In both cases, if I inspect element, I can see the "shadow" of the full picture, at the right size, with the right url. Image source doesnt' seem to make a difference, I'm getting no errors, and this is happening in both chrome and firefox. Does anyone have any ideas?

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• emacs: how do I use edebug on code that is defined in a macro?

  - by Cheeso

  I don't even know the proper terminology for this lisp syntax, so I don't know if the words I'm using to ask the question, make sense. But the question makes sense, I'm sure. So let me just show you. cc-mode (cc-fonts.el) has things called "matchers" which are bits of code that run to decide how to fontify a region of code. That sounds simple enough, but the matcher code is in a form I don't completely understand, with babckticks and comma-atsign and just comma and so on, and furthermore it is embedded in a c-lang-defcost, which itself is a macro. And I want to run edebug on that code. Look: (c-lang-defconst c-basic-matchers-after "Font lock matchers for various things that should be fontified after generic casts and declarations are fontified. Used on level 2 and higher." t `(;; Fontify the identifiers inside enum lists. (The enum type ;; name is handled by `c-simple-decl-matchers' or ;; `c-complex-decl-matchers' below. ,@(when (c-lang-const c-brace-id-list-kwds) `((,(c-make-font-lock-search-function (concat "\\<\\(" (c-make-keywords-re nil (c-lang-const c-brace-id-list-kwds)) "\\)\\>" ;; Disallow various common punctuation chars that can't come ;; before the '{' of the enum list, to avoid searching too far. "[^\]\[{}();,/#=]*" "{") '((c-font-lock-declarators limit t nil) (save-match-data (goto-char (match-end 0)) (c-put-char-property (1- (point)) 'c-type 'c-decl-id-start) (c-forward-syntactic-ws)) (goto-char (match-end 0))))))) I am reading up on lisp syntax to figure out what those things are and what to call them, but aside from that, how can I run edebug on the code that follows the comment that reads ;; Fontify the identifiers inside enum lists. ? I know how to run edebug on a defun - just invoke edebug-defun within the function's definition, and off I go. Is there a corresponding thing I need to do to edebug the cc-mode matcher code forms?

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• jquery ui is not scaling text properly!

  - by Stephen Belanger

  I'm trying use jquery ui to scale a div that I'm dragging around to make it easier to see what's behind it, but any text inside it is scaling strangely. The text itself becomes smaller, but it seems to have a bunch of padding around it and is floating now. The text extends past the bottom of the div even though it should be contained properly by the div. I put a red border around the lines of text and the borders are the same size as the original text. I'm not really sure what to do to get this to work... HTML: <div class="item draggable" id="item-1'"> <div class="image-block"> <a class="delete-button" title="delete me!" href="/remove/1" onclick="return $(this).confirm(\'Really remove this image?\');">X</a> <a class="image" href="/edit/1"><img src="/someimage.jpg" /></a> <div class="clear-block"></div> </div> <h3>Some title</h3> </div> CSS: div.image-list div.item { float:left; background:#fff; width:150px; padding:5px; margin:4px; border:1px solid #d3d5d6; } div.image-list div.item h3 { margin:0; padding:0; border:solid 1px #F00; } div.image-list div.item div.image-block a.delete-button { float:right; position:relative; background:#fff; display:none; top:0.8em; margin-bottom:-20.0em; width:3em; height:1.8em; padding:0.2em 1em; } div.image-list div.item div.image-block a.image { float:left; display:block; } .clear-block { clear:both; } jquery: $(".draggable").draggable({ helper: 'clone', start: function(ev, ui) { $(ui.helper).effect( "scale", { percent: 50 }, 200 ); } });

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• MATLAB arbitrary code execution

  - by aristotle2600

  I am writing an automatic grader program under linux. There are several graders written in MATLAB, so I want to tie them all together and let students run a program to do an assignment, and have them choose the assignment. I am using a C++ main program, which then has mcc-compiled MATLAB libraries linked to it. Specifically, my program reads a config file for the names of the various matlab programs, and other information. It then uses that information to present choices to the student. So, If an assignment changes, is added or removed, then all you have to do is change the config file. The idea is that next, the program invokes the correct matlab library that has been compiled with mcc. But, that means that the libraries have to be recompiled if a grader gets changed. Worse, the whole program must be recompiled if a grader is added or removed. So, I would like one, simple, unchanging matlab library function to call the grader m-files directly. I currently have such a library, that uses eval on a string passed to it from the main program. The problem is that when I do this, apparently, mcc absorbs the grader m-code into itself; changing the grader m code after compilation has no effect. I would like for this not to happen. It was brought to my attention that Mathworks may not want me to be able to do this, since it could bypass matlab entirely. That is not my intention, and I would be happy with a solution that requires a full matlab install. My possible solutions are to use a mex file for the main program, or have the main program call a mcc library, which then calls a mex file, which then calls the proper grader. The reason I am hesitant about the first solution is that I'm not sure how many changes I would have to make to my code to make it work; my code is C++, not C, which I think makes things more complicated. The 2nd solution, though, may just be more complicated and ultimately have the same problem. So, any thoughts on this situation? How should I do this?

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• Basic data alignment question

  - by Broken Logic

  I've been playing around to see how my computer works under the hood. What I'm interested in is seeing is what happens on the stack inside a function. To do this I've written the following toy program: #include <stdio.h> void __cdecl Test1(char a, unsigned long long b, char c) { char c1; unsigned long long b1; char a1; c1 = 'b'; b1 = 4; a1 = 'r'; printf("%d %d - %d - %d %d Total: %d\n", (long)&b1 - (long)&a1, (long)&c1 - (long)&b1, (long)&a - (long)&c1, (long)&b - (long)&a, (long)&c - (long)&b, (long)&c - (long)&a1 ); }; struct TestStruct { char a; unsigned long long b; char c; }; void __cdecl Test2(char a, unsigned long long b, char c) { TestStruct locals; locals.a = 'b'; locals.b = 4; locals.c = 'r'; printf("%d %d - %d - %d %d Total: %d\n", (long)&locals.b - (long)&locals.a, (long)&locals.c - (long)&locals.b, (long)&a - (long)&locals.c, (long)&b - (long)&a, (long)&c - (long)&b, (long)&c - (long)&locals.a ); }; int main() { Test1('f', 0, 'o'); Test2('f', 0, 'o'); return 0; } And this spits out the following: 9 19 - 13 - 4 8 Total: 53 8 8 - 24 - 4 8 Total: 52 The function args are well behaved but as the calling convention is specified, I'd expect this. But the local variables are a bit wonky. My question is, why wouldn't these be the same? The second call seems to produce a more compact and better aligned stack. Looking at the ASM is unenlightening (at least to me), as the variable addresses are still aliased there. So I guess this is really a question about the assembler itself allocates the stack to local variables. I realise that any specific answer is likely to be platform specific. I'm more interested in a general explanation unless this quirk really is platform specific. For the record though, I'm compiling with VS2010 on a 64bit Intel machine.

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• Best practices for displaying large number of images as thumbnails in c#

  - by andySF

  I got to a point where it's very difficult to get answers by debugging and tracing object, so i need some help. What I'm trying to do: A history form for my screen capture pet project. The history must list all images as thumbnails (ex: picasa). What I've done: I created a HistoryItem:UserControl. This history item has a few buttons, a check box, a label and a picture box. The buttons are for delete/edit/copy image. The check box is used for selecting one or more images and the label is for some info text. The picture box is getting the image from a public property that is a path and a method creates a proportional thumbnail to display it when the control has been loaded. This user control has two public events. One for deleting the image and one for bubbling the events for mouse enter and mouse leave trough all controls. For this I use EventBroadcastProvider. The bubbling is useful because wherever I move the mouse over the control, the buttons appear. The dispose method has been extended and I manually remove the events. All images are loaded by looping a xml file that contains the path of all images. For each image in this XML I create a new HitoryItem that is added (after a little coding to sort and limit the amount of images loaded) to a flow layout panel. The problem: When I lunch the history form, and the flow layout panel is populated with my HistoryItem custom control, my memory usage increases drastically.From 14Mb to around 100MB with 100 images loaded. By closing the history form and disposing whatever I could dispose and even trying to call GC.Collect() the memory increase remain. I search for any object that could not be disposed properly like an image or event but wherever I used them they are disposed. The problem seams to be from multiple sources. One is that the events for bubbling are not disposing properly, and the other is from the picture box itself. All of this i could see by commenting all the code to a limited version when only the custom control without any image processing and even events is loaded. Without the events the memory consumption is reduced by axiomatically 20%. So my real question is if this logic, flow layout panels and custom controls with picture boxes, is the best solution for displaying large amounts of images as thumbnails. Thank you!

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• Why did File::Find finish short of completely traversing a large directory?

  - by Stan

  A directory exists with a total of 2,153,425 items (according to Windows folder Properties). It contains .jpg and .gif image files located within a few subdirectories. The task was to move the images into a different location while querying each file's name to retrieve some relevant info and store it elsewhere. The script that used File::Find finished at 20462 files. Out of curiosity I wrote a tiny recursive function to count the items which returned a count of 1,734,802. I suppose the difference can be accounted for by the fact that it didn't count folders, only files that passed the -f test. The problem itself can be solved differently by querying for file names first instead of traversing the directory. I'm just wondering what could've caused File::Find to finish at a small fraction of all files. The data is stored on an NTFS file system. Here is the meat of the script; I don't think including DBI stuff would be relevant since I reran the script with nothing but a counter in process_img() which returned the same number. find(\&process_img, $path_from); sub process_img { eval { return if ($_ eq "." or $_ eq ".."); ## Omitted querying and composing new paths for brevity. make_path("$path_to\\img\\$dir_area\\$dir_address\\$type"); copy($File::Find::name, "$path_to\\img\\$dir_area\\$dir_address\\$type\\$new_name"); }; if ($@) { print STDERR "eval barks: $@\n"; return } } And here is another method I used to count files: count_images($path_from); sub count_images { my $path = shift; opendir my $images, $path or die "died opening $path"; while (my $item = readdir $images) { next if $item eq '.' or $item eq '..'; $img_counter++ && next if -f "$path/$item"; count_images("$path/$item") if -d "$path/$item"; } closedir $images or die "died closing $path"; } print $img_counter;

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• Objective-C memory management issue

  - by Toby Wilson

  I've created a graphing application that calls a web service. The user can zoom & move around the graph, and the program occasionally makes a decision to call the web service for more data accordingly. This is achieved by the following process: The graph has a render loop which constantly renders the graph, and some decision logic which adds web service call information to a stack. A seperate thread takes the most recent web service call information from the stack, and uses it to make the web service call. The other objects on the stack get binned. The idea of this is to reduce the number of web service calls to only those appropriate, and only one at a time. Right, with the long story out of the way (for which I apologise), here is my memory management problem: The graph has persistant (and suitably locked) NSDate* objects for the currently displayed start & end times of the graph. These are passed into the initialisers for my web service request objects. The web service call objects then retain the dates. After the web service calls have been made (or binned if they were out of date), they release the NSDate*. The graph itself releases and reallocates new NSDates* on the 'touches ended' event. If there is only one web service call object on the stack when removeAllObjects is called, EXC_BAD_ACCESS occurs in the web service call object's deallocation method when it attempts to release the date objects (even though they appear to exist and are in scope in the debugger). If, however, I comment out the release messages from the destructor, no memory leak occurs for one object on the stack being released, but memory leaks occur if there are more than one object on the stack. I have absolutely no idea what is going wrong. It doesn't make a difference what storage symantics I use for the web service call objects dates as they are assigned in the initialiser and then only read (so for correctness' sake are set to readonly). It also doesn't seem to make a difference if I retain or copy the dates in the initialiser (though anything else obviously falls out of scope or is unwantedly released elsewhere and causes a crash). I'm sorry this explanation is long winded, I hope it's sufficiently clear but I'm not gambling on that either I'm afraid. Major big thanks to anyone that can help, even suggest anything I may have missed?

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• Deleting a node in a family tree

  - by user559142

  Hi, I'm trying to calclulate the best way to delete a node in a family tree. First, a little description of how the app works. My app makes the following assumption: Any node can only have one partner. That means that any child a single node has, it will also be the partner nodes child too. Therefore, step relations, divorces etc aren't compensated for. A node always has two parents - A mother and father cannot be added seperately. If the user doesn't know the details - the nodes attributes are set to a default value. Also any node can add parents, siblings, children to itself. Therefore in law relationships can be added. I have the following classes: FamilyMember String fName; String lName; String dob; String gender; FamilyMember mother, father, partner; ArrayListchildren; int index; int generation; void linkParents(); void linkPartner(); void addChild(); //gets & sets for fields Family ArrayListfamily; void addMember(); void removeMember(); FamilyMember getFamilyMember(index); ArrayListgetFamilyMembers(); FamilyTree Family family; void removeMember(); //need help void displayFamilyMembers(); void addFamilyMember(); void enterDetails(); void displayAncestors(); void displayDescendants(); void printDescendants(); FamilyMember findRootNode(); void sortGenerations(); void getRootGeneration(); I am having trouble with identifying the logic for removing a member. All other functions work fine. Has anyone developed a family tree app before who knows how to deal with removing various different nodes in the family "tree"? e.g. removing a leaf removing a leaf with partner (what if partner has parents etc) removing a parent It seems to be another recursive property but my head is swelling from over thought.

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• Approaches for Content-based Item Recommendations

  - by PartlyCloudy

  Hello, I'm currently developing an application where I want to group similar items. Items (like videos) can be created by users and also their attributes can be altered or extended later (like new tags). Instead of relying on users' preferences as most collaborative filtering mechanisms do, I want to compare item similarity based on the items' attributes (like similar length, similar colors, similar set of tags, etc.). The computation is necessary for two main purposes: Suggesting x similar items for a given item and for clustering into groups of similar items. My application so far is follows an asynchronous design and I want to decouple this clustering component as far as possible. The creation of new items or the addition of new attributes for an existing item will be advertised by publishing events the component can then consume. Computations can be provided best-effort and "snapshotted", which means that I'm okay with the best result possible at a given point in time, although result quality will eventually increase. So I am now searching for appropriate algorithms to compute both similar items and clusters. At important constraint is scalability. Initially the application has to handle a few thousand items, but later million items might be possible as well. Of course, computations will then be executed on additional nodes, but the algorithm itself should scale. It would also be nice if the algorithm supports some kind of incremental mode on partial changes of the data. My initial thought of comparing each item with each other and storing the numerical similarity sounds a little bit crude. Also, it requires n*(n-1)/2 entries for storing all similarities and any change or new item will eventually cause n similarity computations. Thanks in advance! UPDATE tl;dr To clarify what I want, here is my targeted scenario: User generate entries (think of documents) User edit entry meta data (think of tags) And here is what my system should provide: List of similar entries to a given item as recommendation Clusters of similar entries Both calculations should be based on: The meta data/attributes of entries (i.e. usage of similar tags) Thus, the distance of two entries using appropriate metrics NOT based on user votings, preferences or actions (unlike collaborative filtering). Although users may create entries and change attributes, the computation should only take into account the items and their attributes, and not the users associated with (just like a system where only items and no users exist). Ideally, the algorithm should support: permanent changes of attributes of an entry incrementally compute similar entries/clusters on changes scale something better than a simple distance table, if possible (because of the O(n²) space complexity)

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• Create a Color Picker, similar to Photoshop's, using Javascript and HTML Canvas

  - by André Alçada Padez

  I am not at all versed in Computer Graphics and am in need of creating a color picker as a javascript tool to embed in an HTML page. First, and looking at Photoshop's one, i thought of the RGB palette as a three-dimensional matrix. My first attempt envolved: <script type="text/javascript"> var rgCanvas = document.createElement('canvas'); rgCanvas.width = 256; rgCanvas.height = 256; rgCanvas.style.border = '3px solid black'; for (g = 0; g < 256; g++){ for (r = 0; r < 256; r++){ var context = rgCanvas.getContext('2d'); context.beginPath(); context.moveTo(r,g); context.strokeStyle = 'rgb(' + r + ', ' + g + ', 0)'; context.lineTo(r+1,g+1); context.stroke(); context.closePath(); } } var bCanvas = document.createElement('canvas'); bCanvas.width = 20; bCanvas.height = 256; bCanvas.style.border = '3px solid black'; for (b = 0; b < 256; b++){ var context = bCanvas.getContext('2d'); context.beginPath(); context.moveTo(0,b); context.strokeStyle = 'rgb(' + 0 + ', ' + 0 + ', ' + b + ')'; context.lineTo(20, b); context.stroke(); context.closePath(); } document.body.appendChild(rgCanvas); document.body.appendChild(bCanvas); </script> this results in something like My thought is this is too linear, comparing to the ones i see in Photoshop and on the web. I would like to know the logic behind the color mapping in a picker like this: I don't really need the algorythms itself, i'm mainly trying to understand the logic. Thanks

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• Best approach for using Scanner Objects in Java?

  - by devjeetroy

  Although I'm more of a C++/ASM guy, I have to work with java as a part of my undergrad course at college. Our teacher taught us input using Scanner(System.in), and told us that if multiple functions are were taking user input, it would be advisable that a single Scanner object is passed around so as to reduce chances of the input stream getting screwed up. Now using this approach has gotten me into a situation where I'm trying to use a Scanner.nextLine(), and this statement does not wait for user input. It just moves on to the following statement. I figured there may be some residual cr/lf or other characters in the Scanner that might not have been retrieved are causing the problem. Here is the code. while(lineScanner.hasNext()) { if(isPlaceHolder(temp = lineScanner.next())) { temp = temp.replace("<",""); temp = temp.replace(">", ""); System.out.print("Enter "+aOrA(temp.charAt(0)) +" " +temp + " : "); temp = consoleInput.nextLine(); } outputFileStream.print(temp + " "); } All of the code is inside a function which receives a Scanner object consoleInput. Ok, so what happens when i run it is that when the program enters the if() the first time, It carries out theSystem.out.print, does not wait for user input, and moves on to the second time that it enters the 'if' block. This time, it takes the input and the rest of the program operates normally. What is even more surprising is that when i check the output file created by the program, it is perfect, just as i want to be. Almost as if the first time input using the scanner is correct. I have solved this problem by creating a new system.in Scanner in the function itself, instead of receiving the Scanner object as a parameter. But I am still very curious to know what the hell is happening and why it couldn't be solved using a simple Scanner.reset(). Would it be better to just simply create a Scanner Object for each function? Thanks, Devjeet PS. Although I know how to take input using fileinputstreams and the like, we are not supposed to use it with the homework.

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• Is a Multi-DAL Approach the way to go here?

  - by Krisc

  Working on the data access / model layer in this little MVC2 project and trying to think things out to future projects. I have a database with some basic tables and I have classes in the model layer that represent them. I obviously need something to connect the two. The easiest is to provide some sort of 'provider' that can run operations on the database and return objects. But this is for a website that would potentially be used "a lot" (I know, very general) so I want to cache results from the data layer and keep the cache updated as new data is generated. This question deals with how best to approach this problem of dual DALS. One that returns cached data when possible and goes to the data layer when there is a cache miss. But more importantly, how to integrate the core provider (thing that goes into database) with the caching layer so that it too can rely on cached objects rather than creating new ones. Right now I have the following interfaces: IDataProvider is used to reach the database. It doesn't concern itself with the meaning of the objects it produces, but simply the way to produce them. interface IDataProvider{ // Select, Update, Create, et cetera access IEnumerable<Entry> GetEntries(); Entry GetEntryById(int id); } IDataManager is a layer that sits on top of the IDataProvider layer and manages the cache interface IDataManager : IDataProvider{ void ClearCache(); } Note that in practice the IDataManager implementation will have useful helper functions to add objects to their related cache stores. (In the future I may define other functions on the interface) I guess what I am looking for is the best way to approach a loop back from the IDataProvider implementations so that they can access the cache. Or a different approach entirely may be in order? I am not very interested in 3rd party products at the moment as I am interested in the design of these things much more than this specific implementation. Edit: I realize the title may be a bit misleading. I apologize for that... not sure what to call this question.

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• Java: Switch statements with methods involving arrays

  - by Shane

  Hi guys I'm currently creating a program that allows the user to create an array, search an array and delete an element from an array. Looking at the LibraryMenu Method, the first case where you create an array in the switch statement works fine, however the other ones create a "cannot find symbol error" when I try to compile. My question is I want the search and delete functions to refer to the first switch case - the create Library array. Any help is appreciated, even if its likely from a simple mistake. import java.util.*; public class EnterLibrary { public static void LibraryMenu() { java.util.Scanner scannerObject =new java.util.Scanner(System.in); LibraryMenu Menu = new LibraryMenu(); Menu.displayMenu(); switch (scannerObject.nextInt() ) { case '1': { System.out.println ("1 - Add Videos"); Library[] newLibrary; newLibrary = createLibrary(); } break; case '2': System.out.println ("2 - Search Videos"); searchLibrary(newLibrary); break; case '3': { System.out.println ("3 - Change Videos"); //Change video method TBA } break; case '4': System.out.println ("4 - Delete Videos"); deleteVideo(newLibrary); break; default: System.out.println ("Unrecognized option - please select options 1-3 "); break; } } public static Library[] createLibrary() { Library[] videos = new Library[4]; java.util.Scanner scannerObject =new java.util.Scanner(System.in); for (int i = 0; i < videos.length; i++) { //User enters values into set methods in Library class System.out.print("Enter video number: " + (i+1) + "\n"); String number = scannerObject.nextLine(); System.out.print("Enter video title: " + (i+1) + "\n"); String title = scannerObject.nextLine(); System.out.print("Enter video publisher: " + (i+1) + "\n"); String publisher = scannerObject.nextLine(); System.out.print("Enter video duration: " + (i+1) + "\n"); String duration = scannerObject.nextLine(); System.out.print("Enter video date: " + (i+1) + "\n"); String date= scannerObject.nextLine(); System.out.print("VIDEO " + (i+1) + " ENTRY ADDED " + "\n \n"); //Initialize arrays videos[i] = new Library (); videos[i].setVideo( number, title, publisher, duration, date ); } return videos; } public static void printVidLibrary( Library[] videos) { //Get methods to print results System.out.print("\n======VIDEO CATALOGUE====== \n"); for (int i = 0; i < videos.length; i++) { System.out.print("Video number " + (i+1) + ": \n" + videos[i].getNumber() + "\n "); System.out.print("Video title " + (i+1) + ": \n" + videos[i].getTitle() + "\n "); System.out.print("Video publisher " + (i+1) + ": \n" + videos[i].getPublisher() + "\n "); System.out.print("Video duration " + (i+1) + ": \n" + videos[i].getDuration() + "\n "); System.out.print("Video date " + (i+1) + ": \n" + videos[i].getDate() + "\n "); } } public static Library searchLibrary( Library[] videos) { //User enters values to setSearch Library titleResult = new Library(); java.util.Scanner scannerObject =new java.util.Scanner(System.in); for (int n = 0; n < videos.length; n++) { System.out.println("Search for video number:\n"); String newSearch = scannerObject.nextLine(); titleResult.getSearch( videos, newSearch); if (!titleResult.equals(-1)) { System.out.print("Match found!\n" + newSearch + "\n"); } else if (titleResult.equals(-1)) { System.out.print("Sorry, no matches found!\n"); } } return titleResult; } public static void deleteVideo( Library[] videos) { Library titleResult = new Library(); java.util.Scanner scannerObject =new java.util.Scanner(System.in); for (int n = 0; n < videos.length; n++) { System.out.println("Search for video number:\n"); String deleteSearch = scannerObject.nextLine(); titleResult.deleteVideo(videos, deleteSearch); System.out.print("Video deleted\n"); } } public static void main(String[] args) { Library[] newLibrary; new LibraryMenu(); } }

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• how to set footer image in this video screen?

  - by bala

  hi my problem is how to create footer image in this video screen while playing.... how to create this format. now i am give my description: • 1) Header image, a stretched background image. The location of this external image comes from the application xml; • 2) Footer image, a stretched background image. The location of this external image comes from the application xml; 2.a) the copyright, disclaimer and buy block, this block contains links to popup windows that contain a copyright and or disclaimer. And an option to buy the application for the advertisement less version. The content of this block is fed trough the application XML feed. The color of the text is fed by the application xml plus the popup links and texts itself; • 3) Carousel image, a stretched background image. The location of this external image comes from the application xml; 3.a) the carousel contains objects that can flow from right to left, possibly trough a animation (a soft break of the slide). The first object is centered in the middle of the carousel. This is the first element in the video feed. All the subsequent video object are added to the right of the centered object; 4) Total Video object, this object links to window two with the corresponding video of this object. This object is visually build out of the following sub parts:o 4.a) Thumb object (possible playing video thumb); 4.b) Reflection of the Thumb; 4.c) Textual Explanation of Thumb. 1) Video stream, this is the video stream coming from a external server streamed to the television (maybe up scaled) as 720p stream; 2) Advertisement, the type of advertisement shown overlaid on the video is based on previous settings in the video feed. This could mean that Admob, Adsense or a third party image plus URL could be shown. When the advertisement is selected trough navigation (it will highlight in a different color as a border around the advertisement. The color an thickness can be managed trough the application xml), when clicked a browser will open with the associated site (the application will be pushed to the background process, when the user is finished it will return to the app); 3) A back button, an image and navigational element. The location of the image comes from the application xml. The button is only shown when a cursor is moved (a button is pressed on the remote) it will highlight when selected and when pressed will forward the screen to the main window. When the main window is opened the video will be removed from cache and memory and cannot be start from the point it was exited. please give me your idea....

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