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  • Algorithmic trading software safety guards

    - by Adal
    I'm working on an automatic trading system. What sorts of safe-guards should I have in place? The main idea I have is to have multiple pieces checking each other. I will have a second independent little process which will also connect to the same trading account and monitor simple things, like ensuring the total net position does not go over a certain limit, or that there are no more than N orders in 10 minutes for example, or more than M positions open simultaneously. You can also check that the actual open positions correspond to what the strategy process thinks it actually holds. As a bonus I could run this checker process on a different machine/network provider. Besides the checks in the main strategy, this will ensure that whatever weird bug occurs, nothing really bad can happen. Any other things I should monitor and be aware of?

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  • How to Access a Private Variable?

    - by SoulBeaver
    This question isn't meant to sound as blatantly insulting as it probably is right now. This is a homework assignment, and the spec sheet is scarce and poorly designed to say the least. We have a function: double refuel( int liter, GasStation *gs ) { // TODO: Access private variable MaxFuel of gs and decrement. } Sound simple enough? It should be, but the class GasStation comes with no function that accesses the private variable MaxFuel. So how can I access it anyway using the function refuel? I'm not considering creating a function setFuel( int liter ) because the teacher always complains rather energetically if I change his specification. So... I guess I have to do some sort of hack around it, but I'm not sure how to go about this without explicitely changing the only function in GasStation and giving it a parameter so that I can call it here. Any hints perhaps?

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  • How should I change my Graph structure (very slow insertion)?

    - by Nazgulled
    Hi, This program I'm doing is about a social network, which means there are users and their profiles. The profiles structure is UserProfile. Now, there are various possible Graph implementations and I don't think I'm using the best one. I have a Graph structure and inside, there's a pointer to a linked list of type Vertex. Each Vertex element has a value, a pointer to the next Vertex and a pointer to a linked list of type Edge. Each Edge element has a value (so I can define weights and whatever it's needed), a pointer to the next Edge and a pointer to the Vertex owner. I have a 2 sample files with data to process (in CSV style) and insert into the Graph. The first one is the user data (one user per line); the second one is the user relations (for the graph). The first file is quickly inserted into the graph cause I always insert at the head and there's like ~18000 users. The second file takes ages but I still insert the edges at the head. The file has about ~520000 lines of user relations and takes between 13-15mins to insert into the Graph. I made a quick test and reading the data is pretty quickly, instantaneously really. The problem is in the insertion. This problem exists because I have a Graph implemented with linked lists for the vertices. Every time I need to insert a relation, I need to lookup for 2 vertices, so I can link them together. This is the problem... Doing this for ~520000 relations, takes a while. How should I solve this? Solution 1) Some people recommended me to implement the Graph (the vertices part) as an array instead of a linked list. This way I have direct access to every vertex and the insertion is probably going to drop considerably. But, I don't like the idea of allocating an array with [18000] elements. How practically is this? My sample data has ~18000, but what if I need much less or much more? The linked list approach has that flexibility, I can have whatever size I want as long as there's memory for it. But the array doesn't, how am I going to handle such situation? What are your suggestions? Using linked lists is good for space complexity but bad for time complexity. And using an array is good for time complexity but bad for space complexity. Any thoughts about this solution? Solution 2) This project also demands that I have some sort of data structures that allows quick lookup based on a name index and an ID index. For this I decided to use Hash Tables. My tables are implemented with separate chaining as collision resolution and when a load factor of 0.70 is reach, I normally recreate the table. I base the next table size on this http://planetmath.org/encyclopedia/GoodHashTablePrimes.html. Currently, both Hash Tables hold a pointer to the UserProfile instead of duplication the user profile itself. That would be stupid, changing data would require 3 changes and it's really dumb to do it that way. So I just save the pointer to the UserProfile. The same user profile pointer is also saved as value in each Graph Vertex. So, I have 3 data structures, one Graph and two Hash Tables and every single one of them point to the same exact UserProfile. The Graph structure will serve the purpose of finding the shortest path and stuff like that while the Hash Tables serve as quick index by name and ID. What I'm thinking to solve my Graph problem is to, instead of having the Hash Tables value point to the UserProfile, I point it to the corresponding Vertex. It's still a pointer, no more and no less space is used, I just change what I point to. Like this, I can easily and quickly lookup for each Vertex I need and link them together. This will insert the ~520000 relations pretty quickly. I thought of this solution because I already have the Hash Tables and I need to have them, then, why not take advantage of them for indexing the Graph vertices instead of the user profile? It's basically the same thing, I can still access the UserProfile pretty quickly, just go to the Vertex and then to the UserProfile. But, do you see any cons on this second solution against the first one? Or only pros that overpower the pros and cons on the first solution? Other Solution) If you have any other solution, I'm all ears. But please explain the pros and cons of that solution over the previous 2. I really don't have much time to be wasting with this right now, I need to move on with this project, so, if I'm doing to do such a change, I need to understand exactly what to change and if that's really the way to go. Hopefully no one fell asleep reading this and closed the browser, sorry for the big testament. But I really need to decide what to do about this and I really need to make a change. P.S: When answering my proposed solutions, please enumerate them as I did so I know exactly what are you talking about and don't confuse my self more than I already am.

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  • C# .net framework- border on only one side of the form

    - by user161179
    I am an inexperienced programmer , completely new to programming for windows . I am writing a little program that I always wanted . Its being written using C# using .net framework. atleast thats what I think I am doing. All the talk about framework and .nets , windows forms , and win32 api has all got me really confused.. :( anyways I have simple Form object. Form f = new Form() ; f.Text = "" ; f.ControlBox =false ; Now How to remove the all the borders on the form except one sides? As in, the side borders should go , but the top border should stay FormBorderStyle doesn't have anything for this Also how do you people solve such problems yourself , without asking ? look at others code ? read a a book ? any particular website ? I have googled , but it didn't turn up nothing.

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  • Security precautions and techniques for a User-submitted Code Demo Area

    - by Jack W-H
    Hey folks Maybe this isn't really feasible. But basically, I've been developing a snippet-sharing website and I would like it to have a 'live demo area'. For example, you're browsing some snippets and click the Demo button. A new window pops up which executes the web code. I understand there are a gazillion security risks involved in doing this - XSS, tags, nasty malware/drive by downloads, pr0n, etc. etc. etc. The community would be able to flag submissions that are blatantly naughty but obviously some would go undetected (and, in many cases, someone would have to fall victim to discover whatever nasty thing was submitted). So I need to know: What should I do - security wise - to make sure that users can submit code, but that nothing malicious can be run - or executed offsite, etc? For your information my site is powered by PHP using CodeIgniter. Jack

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  • C++: set of C-strings

    - by Nicholas
    I want to create one so that I could check whether a certain word is in the set using set::find However, C-strings are pointers, so the set would compare them by the pointer values by default. To function correctly, it would have to dereference them and compare the strings. I could just pass the constructor a pointer to the strcmp() function as a comparator, but this is not exactly how I want it to work. The word I might want to check could be part of a longer string, and I don't want to create a new string due to performance concerns. If there weren't for the set, I would use strncmp(a1, a2, 3) to check the first 3 letters. In fact, 3 is probably the longest it could go, so I'm fine with having the third argument constant. Is there a way to construct a set that would compare its elements by calling strncmp()? Code samples would be greatly appreciated.

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  • What should I consider when deploying a new web farm?

    - by tsilb
    My web app has been chugging along just great in Production for years with one App server and one Web server. Now we're moving to a multi-server environment with 2 App and 3 Web servers. I have enough time to make changes before the go-live. As a Developer, what considerations should I take into account from coding, deployment, and architectural/ecosystem management perspectives? Already on my list: Remove tight-coupling between servers Applicable files (i.e. downloadables) stored in IMAGE fields in SQL instead of files on app server Deployment: Take out node out of the farm at a time

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  • change extension obfuscate XML file contents

    - by FFish
    I have SlideShowPro, a Flash photo app that loads an XML file with the paths to the images. Now I don't want people to go sniff in the XML file to get to the images. I tried changing the file images.xml to spacer.gif and it seems to work fine. But I would like to know if I would run into any problems changing the extension. btw already used a few techniques to make the images not so accessible, I know there is no bulletproof solution. Obfuscating the XML file is just another trick..

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  • CakePHP Bake association problem

    - by Apu
    I have only two tables in my database with a one-to-many relationship between them (user hasMany messages) and am trying to get basic CRUD functionality going. Bake detects the associations correctly and specifies them correctly inside the model classes, but in controllers and views it looks like Cake doesn't know anything about those associations -- I don't even get a select tag for user_id when I go add a new message. Has anyone come across this problem before? What can I be doing wrong? Table structure appears to be fine: CREATE TABLE users ( id int(11) NOT NULL AUTO_INCREMENT, username varchar(255) NOT NULL, `password` varchar(255) NOT NULL, email varchar(255) NOT NULL, created datetime NOT NULL, modified datetime NOT NULL, PRIMARY KEY (id) ) ENGINE=MyISAM DEFAULT CHARSET=utf8; CREATE TABLE IF NOT EXISTS `messages` ( `id` int(11) NOT NULL AUTO_INCREMENT, `user_id` int(11) NOT NULL, `content` varchar(255) NOT NULL, `created` datetime NOT NULL, `modified` datetime NOT NULL, PRIMARY KEY (`id`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ;

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  • View Animation (Resizing a Ball)

    - by user270811
    hi, i am trying to do this: 1) user long touches the screen, 2) a circle/ball pops up (centered around the user's finger) and grows in size as long as the user is touching the screen 3) once the user lets go of the finger, the ball (now in its final size) will bounce around. i think i have the bouncing around figure out from the DivideAndConquer example, but i am not sure how to animate the ball's growth. i looked at various view flipper examples such as this: http://www.inter-fuser.com/2009/08/android-animations-3d-flip.html but it seems like view flipper is best for swapping two static pictures. i wasn't able to find a good view animator example other than the flippers. also, i would prefer to use images as opposed to just a circle. can someone point me in the right direction? thanks.

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  • How would one use Cocos2d to create a game like this.

    - by John Stewart
    http://itunes.apple.com/us/app/angry-birds/id343200656?mt=8&ign-mpt=uo%3D6 So I am getting started with this all game dev thing on iphone and I decided that I will start playing with Cocos2d as my starting engine. Now just so i have a goal in mind, I picked angry birds as my initial target of what sort of game play would I like to learn to build. This is not going to be a market release game. This is totally going to be learning purposes only. So to start off my question is: Would something like this be achievable using Cocos2d? How would I go about building the physics for this? How can one do a screen scroll like the way they do in cocos2d? (any example code would be great) This is just to start off. If you have any particular questions please do add to this question.

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  • Rules Engine vs Expert System

    - by User1
    What is the difference between a rules engine and an expert system? Example1: Let's say that I have a program that determines the expiration date of a new driver's license. It takes inputs like visa expiration date, passport number, birthday, etc. It determines the expiration date of the driver's license from this input. It can even give an error if the input did not have enough valid identifications to allow a new driver's license. Example2: Let's say I am making an online version of the game Monopoly. I want the ability to change the rules of the game (say $400 for passing go or no one can buy properties until they land on the same property twice, etc). I have a module in the code to handle these rules. Are these both rules engines or are they expert systems? They both seem so similar. Is it just a synonym?

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  • Recursive FTP directory listing in shell/bash with a single session (using cURL or ftp)

    - by Timo
    I am writing a little shellscript that needs to go through all folders and files on an ftp server (recursively). So far everything works fine using cURL - but it's pretty slow, becuase cURL starts a new session for every command. So for 500 directories, cURL preforms 500 logins. Does anybody know, whether I can stay logged in using cURL (this would be my favourite solution) or how I can use ftp with only one session in a shell script? I know how to execute a set of ftp commands and retrieve the response, but for the recursive listing, it has to be a little more dynamic... Thanks for your help!

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  • algorithm to find overlaps

    - by Gary
    Hey, Basically I've got some structs of type Ship which are going to go on a board which can have a variable width and height. The information about the ships is read in from a file, and I just need to know the best way to make sure that none of the ships overlap. Here is the structure of Ship: int x // x position of first part of ship int y // y position of first part of ship char dir // direction of the ship, either 'N','S','E' or 'W' int length // length of the ship Also, what would be a good way to handle the directions. Something cleaner than using a switch statement and using a different condition for each direction. Any help would be greatly appreciated!

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  • Android HelloWorld Build Path error

    - by BahaiResearch.com
    On my Mac I installed Eclipse, the SDK and created a new project, then hit build expecting to see my first helloworld app. I got the error "the project cannot be built until build path errors are fixed". After going thru all the path-like options in Preferences, I noticed that on the tab "Java Build Path" the "Google APIs [Android 2.2]" option did not have its check box checked. Checking it made the problem go away. It works now and I can see the app in the Emulator Have I not set up my environment correctly? I used all the defaults in Eclipse and the Android SDK.

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  • .NET Database Apps: Your Preferred Setup

    - by mdvaldosta
    I'm struggling to settle into a pattern for developing typical database driven apps in C# and Visual Studio. There are so many ways to set them up, using drag/drop datasets and adapters or writing the queries manually in ADO.NET or Linq to SQL, Linq to Entities, to bind or not to data bind etc etc. Where to store the connection string, in app.config or in a method or both etc etc. So many tutorials and all of them are different. Everytime I write something I start hating the way it looks and works, so I scrap it and start over. It's getting a bit tedious. Maybe it's alittle of the OCD in me. Would any of you professional developers out there share your method of setting up and structuring your database logic and maybe some sample code? It's really how to go about organizing the code and the method(s) of interacting with SQL that I'm trying to get into a routine with, one that works and won't get me laughed at by someone reviewing it.

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  • DataGridView and Binding List Event.

    - by bearrito
    I have a datagridview with a datasource of type binding list. I understand that when the datagridview changed this will update the items in the binding list. I also know that if the objects in the bindinglist implement Inotifypropertychanged then if the obects are changed outside the grid then the objects will notify the bindlist which will then notify the datagrid My question is: If the datagrid view changing an object, I want the bindinglist or changed object to fire an event that allows me to pass the object to a WCF service that will persist the object on the data access layer side e.g. Service.Save(ChangedObject) How would I go about doing this?

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  • VoiceXML Prompt & SSML <mark> element. How to read prompt from the specified position?

    - by EugeneP
    <mark> element informs that reading went on to some point. But is there a way we could read the prompt again from the specified position returned by mark (name) id? It could be useful in such a scenario: we are reading a long text. Then the user commands: PAUSE. We stop. Then the user would say "Go on". And we continue to read the prompt from the last position. IS that possible at all? And I would ask yet another question. No matter with the usage of SSML or not: How to make it work - pause the prompt reading and then continue from the position where we stopped? Pause means "take full control over that pause", so that we could continue whenever we wanted. Dynamically.

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  • Passing parameters thru Ruby's OAuth

    - by JP
    I'm using Mirven's Twitter OAuth Sinatra example and trying to figure out how I can send a 'next page' parameter with the Oauth request: ie. The user attempts to visit /edit/profile which requires a login so I redirect to /request which deals with login via twitter - I now want to be able to redirect the user to the address they were originally looking for if they log in successfully. I thought I could do this in the .get_request_token line with this code: @request_token = @consumer.get_request_token({:oauth_callback => "http://#{request.host}/auth"},{:next => params['next'] || '/'}) But params has no additional items in the /auth handler. I'm new to OAuth, how would I go about doing this?

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  • Displaying custom error message for a blank field in a simple JSF application

    - by 29b5k
    Hi all, I was trying out a simple JSF application, in which I need to check if the "name" field is blank, then display an error message. The code which takes the field's value is: <h:outputLabel value="Name"></h:outputLabel> <h:inputText value="#{greeting.name}" required = "true"> <f:validator validatorId="NumValidator"></f:validator> </h:inputText> The control of the program does not go into the validator class, if the field is submitted without entering anything, and it displays the default error message: j_id_jsp_869892673_1:j_id_jsp_869892673_4: Validation Error: Value is required. How do i display a custom message for this ?

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  • Rails: Need a helping hand to finish this Jquery/Ajax problem.

    - by DJTripleThreat
    Here's my problem: I have a combo box that when its index changes I want a div tag with the id="services" to repopulate with checkboxes based on that comboboxes value. I want this to be done using ajax. This is my first time working with ajax for rails so I need a helping hand. Here is what I have so far: My application.js file. Something that Ryan uses in one of his railscasts. This is supposed to be a helper method for handling ajax requests. Is this useful? Should I be using this?: //<![CDATA[ $.ajaxSetup({ 'beforeSend': function(xhr) {xhr.setRequestHeader("Accept","text/javascript")} }); // This function doesn't return any results. How might I change that? Or // should I have another function to do that? $.fn.submitWithAjax = function() { this.submit(function() { $.post($(this).attr("action"), $(this).serialize(), null, "script"); return true; }); }; //]]> An external javascript file for this template (/public/javascripts/combo_box.js): //<![CDATA[ $(document).ready(function(){ $('#event_service_time_allotment').change(function () { // maybe I should be using submitWithAjax(); ?? $(this).parent().submit(); }); }); //]]> My ???.js.erb file. I'm not sure where this file should go. Should I make an ajax controller?? Someone help me out with that part please. I can write this code no problem, I just need to know where it should go and what the file name should be called (best practices etc): // new.js.erb: dynamic choices... expecting a time_allotment alert('test'); // TODO: Return a json object or something with a result set of services // I should be expecting something like: // params[:event_service][:time_allotment] i think which I should use // to return a json object (??) to be parsed or rendered html // for the div#services. Here is my controller's new action. Am I supposed to respond to javascript here? Should I make an ajax controller instead? What's the best way to do this?: # /app/controllers/event_services_controller.rb def new @event_service = EventService.new respond_to do |format| format.html # new.html.erb format.xml { render :xml => @event_service } format.js # should I have a javascript handler here? i'm lost! end end My /app/views/event_service/new.html.erb. My ajax call I think should be a different action then the form: <% content_for :head do %> <%= javascript_include_tag '/javascripts/combo_box.js' %> <% end %> <% form_for @event_service, :url => admin_events_path, :html => {:method => :post} do |f| %> <!-- TimeAllotment is a tabless model which is why this is done like so... --> <!-- This select produces an id of: "event_service_time_allotment" and a name of: "event_service[time_allotment]" --> <%= select("event_service", "time_allotment", TimeAllotment.all.collect {|ta| [ta.title, ta.value]}, {:prompt => true}) %> Services: <!-- this div right here needs to be repopulated when the above select changes. --> <div id="services"> <% for service_type in ServiceType.all %> <div> <%= check_box_tag "event_service[service_type_ids][]", service_type.id, false %> <%=h service_type.title %> </div> <% end %> </div> <% end %> ok so right now ALL of the services are there to be chosen from. I want them to change based on what is selected in the combobox event_service_time_allotment. Thanks, I know this is super complicated so any helpful answers will get an upvote.

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  • How to calculate real-time stats?

    - by Diego Jancic
    I have a site with millions of users (well, actually it doesn't have any yet, but let's imagine), and I want to calculate some stats like "log-ins in the past hour". The problem is similar to the one described here: http://highscalability.com/blog/2008/4/19/how-to-build-a-real-time-analytics-system.html The simplest approach would be to do a select like this: select count(distinct user_id) from logs where date>='20120601 1200' and date <='20120601 1300' (of course other conditions could apply for the stats, like log-ins per country) Of course this would be really slow, mainly if it has millions (or even thousands) of rows, and I want to query this every time a page is displayed. How would you summarize the data? What should go to the (mem)cache? EDIT: I'm looking for a way to de-normalize the data, or to keep the cache up-to-date. For example I could increment an in-memory variable every time someone logs in, but that would help to know the total amount of logins, not the "logins in the last hour". Hope it's more clear now.

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  • What would you like to see in an beginner's ASP.NET security book

    - by blowdart
    This is a shameless information gathering exercise for my own book. One of the talks I give in the community is an introduction to web site vulnerabilities. Usually during the talk I can see at least two members of the audience go very pale; and this is basic stuff, Cross Site Scripting, SQL Injection, Information Leakage, Cross Site Form Requests and so on. So, if you can think back to being one, as a beginning web developer (be it ASP.NET or not) what do you feel would be useful information about web security and how to develop securely? I will already be covering the OWASP Top Ten (And yes this means stackoverflow will be in the acknowledgements list if someone comes up with something I haven't thought of yet!) It's all done now, and published, thank you all for your responses

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  • Creating an image from webcam every x miliseconds

    - by Rita
    Hello everyone, I am using c# to integrate with a web cam. I need to generate a snapshot image every x miliseconds and save it to file. I already have the code up and running to save to file on a button click event, however I wonder what am I supposed to do when taking snapshots in the background - Should this be multi threaded? I'm honestly not sure. I could just block the UI thread, put Thread.Sleep and then just take the snapshot, but I don't know if this is right. I thought of using a background worker, but I am now experiencing cross threaded difficulties with SendMessage... So I wonder if I should even go and bother to multi-thread or just block the UI. Help greatly appertained, thanks in advance.

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  • C# Silverlight Progamming Technology in general?

    - by Rico
    I Strive to Keep up but I always feel 3 steps behind. How do the people here who answer all my stupid questions keep up with everything? Litterally What websites do you subscribe to? What Blogs do you read? How often? How much time in your day do you spend doing it? What release notes do you care about? what conferences do you go to I can't sit idly by any more and expect to keep up.

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