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• Designing a peer to peer network

  - by Varun

  I am designing a simple peer to peer network. The basic architecture will be as follows: A central server- that keeps track of all the peers. The job of this server is to keep track of all the peers that join the network. Every peer could do things: a. Download a file from it's peer b. Push a file (send a file) to it's peer. Could anybody please tell me what would be the best design for such a system? What would be the problems that i might run into and so on. I am planning to use Java as the programming language to implement. Would it be a good choice? Also, is it necessary that i would need a Linux box to develop the system? or is it fine if i use a Windows machine? Your help will be much appreciated! Thanks!

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• How to invoke static method in C#4.0 with dynamic type?

  - by Morgan Cheng

  In C#4.0, we have dynamic type, but how to invoke static method of dynamic type object? Below code will generate exception at run time. class Foo { public static int Sum(int x, int y) { return x + y; } } class Program { static void Main(string[] args) { dynamic d = new Foo(); Console.WriteLine(d.Sum(1, 3)); } } IMHO, dynamic is invented to bridge C# and other programming language. There is some other language (e.g. Java) allows to invoke static method through object instead of type. BTW, The introduction of C#4.0 is not so impressive compared to C#3.0.

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• What are good resources for computer graphics basics?

  - by Hanno Fietz

  During Flex programming, I recently ran into several questions (about box models, ways to join lines and misaligning pixels [on doctype]) regarding computer graphics and layout, where I felt that I lacked some basic background on things like concepts like the box model approaches mapping real numbers to a pixel raster (like font anti-aliasing) conventions found across drawing engines, like do you count y coordinates from top or bottom, and why I feel that reading some basic Wikipedia articles, books or tutorials on these subjects might help in phrasing my questions more specifically and debugging my code more systematically. I have repeatedly found myself writing tiny test apps in Flex, just to find out how the APIs do very basic stuff. My assumption would be that if I knew the right vocabulary and some general concepts, I could solve these questions much faster.

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• Default.png images and iPad.

  - by Leg10n

  I'm about to submit my first iPad app, and I have 2 questions regarding to Default.png images. I would prefer a "splash screen" showing some artwork of my app, instead of the UI as if it was loaded, the app is a bit heavy and I've seen the users dispair when the UI is apparently loaded but it's not working. Does anyone know if apple is accepting apps with "splash screens"? I want to provide a Default-X.png for every orientation, I've read the iPad programming guide, my question is, is "Default-LandscapeLeft" a Default image rotated 90 degrees clockwise, and "Default-LandscapeRight" rotated 90 degrees counter clockwise? I'm asking this because I don't have an iPad yet to test this on. Thank you a lot in advance.

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• PHP with SQL Injection

  - by Scott S

  For our first assignment in a System Security class, we have to hack into the professors "cheaply organized" sql database. I know the only user is "admin" and the select statement generated in the php is: select user_id from user where user_username = 'admin' AND user_password = md5('noob') I am having a number of problems attempting to bypass the password part of this statement as the professor has some javascript embedded in the page to sanitize the username and password of any non-alphanumeric values. This can be bypassed by turning off javascript :P but any values sent still get cleaned by the operating system (some build of Debian 32-bit). I've seen the code for the login request and it does not escape any characters. How do I bypass the operating systems escape sequences?

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• Session State Anti-Pattern

  - by Curiosity

  I know the SOLID principles and other design patterns fairly well and have been programming for some time now - seeing many a bit of code throughout the years. Having said that, I'm having trouble coming up with a name to give the pattern, or lack thereof, to bits of code I've been dealing with at a current engagement. The application is an ASP.NET C# WebForms application, backed by a SQL Server/Mainframe backend (more mainframe than backend) and it's riddled with Session State properties being accessed/mutated from multiple pages/classes. Accessing/mutating global variables/application state was usually shunned upon while I was in school. Apparently the creators of this magnificent application didn't think it was such a bad idea. Question: Is there a name for such a pattern/anti-pattern that relies so heavily on Session State? I'd like to call the pig by its name ...

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• How Does Facebook Know What Image To Parse Out of An Article?

  - by Travis

  First off I want to say that I wasn't really sure where to post this but it is very much programming related. If it is in the wrong spot I apologize and please let me know where I should post it instead. When sharing an article on a friends wall, facebook will grab a thumbnail of the article. How do they always get the right thumbnail from articles? It doesn't grab the logo img element of of http://www.nytimes.com/2010/06/07/world/asia/07convoys.html?hp for example but rather grabs the correct image element that corresponds with the article. I'm looking to do something similar and was wondering of a good way to parse the html to find the image given this example. Thanks.

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• Determining if and where a photon will collide with a polygon in 3D space.

  - by Peter

  The problem is straight forward: 1) We have a photon traveling from Point 1 (x,y,z) to Point 2 (x,y,z), both of which could be located anywhere in 3D space. 2) We have a polygon that is both rotated randomly on the x-axis and/or y-axis and also located anywhere in 3D space. 3) We want to find: a) if the photon will collide with the polygon at all and b) if it does where will that be (x,y,z)? An image of the problem: http://dl.dropbox.com/u/3150177/Programming/3D/Math/Photon%20Path/Photon%20Path.png The aim of this is to calculate how the photon's path should be altered from an interaction(s) with the polygon(s). I am reading up on this subject now but I was wondering if anyone could give me a head start. Thanks in advance.

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• Does anyone know of a way to easily convert a PDF to a docx format programmatically

  - by Rob

  We have a couple 3rd party systems that give us PDFs. We would like to convert those PDFs for display on the web without using an Adobe product. Ideally we would like to use Silverlight to render the PDFs but are having trouble converting from a PDF to Xaml or using docx format as a middle man. There are lots of libraries that give PDFs but that is not what we need. If there is a library out there that does this, a .net lib would be preferable but we can run the conversion using the command line as well if that is an option.

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• How do I choose a database?

  - by liamzebedee

  I need a comparison table of some sort for database varieties (MySQL, SQLite etc.). I can't find one. My use case is, I am implementing storage of objects in a distributed hash table. I need a database solution that is: Fast for sorting Simplistic (no users, preferably no additional structures like multiple tables etc.) Concurrent (if possible) Multi-platform File based (not stored in memory primarily) Centralized I will be programming in Go. As I understand, I believe I need what is called a Document Orientated Database, because I am storing objects, identified by keys. EDIT: While I am implementing a DHT, I will also be storing metadata about the objects, such as access counts etc. It would also be preferable to have TLL (time to live)

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• iPhone simple commercial barcode reader via camera

  - by user347635

  Hey all, I've done some iPhone programming (safely midlevel) and now a requirement has come up for us to write a barcode reader that uses the iPhone camera. This is not for shopping or the general public but will be for internal use. My first thought was to simply programatically take a picture, upload it to server, and have a web service or something similar handle the heavy lifting of extracting the numbers out of the bar code. However I recently installed some apps already available on the iPhone that read bar codes, refer you to shopping sites, etc. and they seem to use the video camera to identify barcodes and extract the numbers. Does anyone know how this is being done or could point me to some open source or sample code?

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• What is the best way to learn VB/VBA?

  - by Noah

  I have wanted to learn VB and VBA for a long time. My school offers a coarse, but it doesn't fit with the rest of my schedule. It will be my first programing language. I was considering using the textbook my school uses (An introduction to programing using visual basic 2008, but I wold get the 2010 version), but I was wondering if there were better resources I could use. I mainly want to lean to learn VBA so I cam create macros and other tools for MS Word. Please understand that this is the fist time I will be programming and I am teaching myself (with the books/online resources).

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• Touch event missing when pushing new view

  - by Milu

  Hello, I am new in iPhone programming. At the moment I am trying to recognize a constant touch. For example I want the user to leave his finger on the screen for the whole application. I use a navigationcontroller which holds the different views. If the user now touches the screen in view1 and then the view is changed to view2 by pushing it on the stack (with pushviewcontroller) with still touching the screen then there are no touch events recognized by view2. If the user then releases his finger (no touch event) and touches the screen again then all events are recognized. Is this a bug or am I doing something totally wrong? I haven't found any answer on this. Could someone help me?

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• Design pattern for extending Android's activities?

  - by Carl

  While programming on Android, I end up writing a parent activity which is extended by several others. A bit like ListActivity. My parent activity extends Activity. if I intend to use a Map or a List, I can't use my parent activity as superclass - the child activity can only extend one activity obviously. As such I end up writing my parent activities with the same logic for Activity, ListActivity, MapActivity and so forth. What am I looking for is some sort of trait functionality/design pattern which would help in this case. Any suggestions?

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• Custom nib UITableViewCell height

  - by Chuck

  I've created a custom UITableViewCell in IB, linked it to the root view controller's property for it, and set it up in CellForRowAtIndexPath. But the height of my drawn cells doesn't match what I setup in IB, advice? Here's some screenshots and the code. - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *AddressCellIdentifier = @"AddressCellIdent"; UITableViewCell *thisCell = [tableView dequeueReusableCellWithIdentifier:AddressCellIdentifier]; if (thisCell == nil) { [[NSBundle mainBundle] loadNibNamed:@"AddressCell" owner:self options:nil]; thisCell = addressCell; self.addressCell = nil; } return thisCell ; } addressCell is a @property (nonatomic, assign) IBOutlet UITableViewCell *addressCell;, and is linked up in IB to the file's owner (the table view controller). I'm using the example from Apple's table view programming guide.

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• In a virtual machine monitor such as VMware's ESXi Server, how are shadow page tables implemented?

  - by ali01

  My understanding is that VMMs such as VMware's ESXi Server maintain shadow page tables to map virtual page addresses of guest operating systems directly to machine (hardware) addresses. I've been told that shadow page tables are then used directly by the processor's paging hardware to allow memory access in the VM to execute without translation overhead. I would like to understand a bit more about how the shadow page table mechanism works in a VMM. Is my high level understanding above correct? What kind of data structures are used in the implementation of shadow page tables? What is the flow of control from the guest operating system all the way to the hardware? How are memory access translations made for a guest operating system before its shadow page table is populated? How is page sharing supported? Short of straight up reading the source code of an open source VMM, what resources can I look into to learn more about hardware virtualization?

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• JS Variable inside another variable

  - by Tusk

  I have a function that would use other variables, depending on what has been passed. Like this = ActionBar(slot) slot contains "one". and I would like to create a call inside that like object.slot.name but it should convert it before hand to make the command look like object.one.name. Is there a way to do this in javascript/jquery? I remember vaguely that some other language does this as {slot} or something like that. Sorry if this question was already asked, I've checked google and stackoverflow too, but didn't find an answer. Also I'd like to know what's the proper programming term for this kind of variable passing? Edited it cause of misunderstandings. I'm looking into OOP js, so object is an object, one is an object, and name is an attribute, but when passing I'm passing "one" as a string to the function. Tried eval, it doesn't work while dotted with an object.

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• How to pass PHP array parameter to Javascript Function???

  - by Son of Man

  index.php <script type="text/javascript" src="javascript.js"> </script> <?php $movies = array("Bloodsport", "Kickboxer", "Cyborg", "Timecop", "Universal Soldier", "In Hell", "The Quest"); ?> <input type="submit" value="Test Javascript" onclick="showMovies(<?php echo $movies; ?>);" /> javascript.js function showMovies(movies) { alert(movies.length); return false; } I am new to programming so Im having hard time fixing this one which is obviously simple for you guys. When I hit the submit button it says the that the array size is 1 which I think should be 7. How could this be??? Pls tell me what to do... Thanks in Advance...

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• Suggestions for a C++ IDE?

  - by AedonEtLIRA

  I know this is is a shifty question and really isn't easy to answer, but bare with me. For a while now I have been using Eclipse and doing Java programming. Now that I reach a point where I'm comfortable in Java, I wish to move on back into C++ and actually make something more than a single class that prints to terminal; and work in OpenGL :). So I wonder if anybody has a recomendation of IDE's that resemble or are as fluid as Eclipse? I am aware that Eclipse has a C++ plugin, but it really doesn't feel user friendly (at least to a pampered java programmer!). I have (I think I still have it?) a copy of Visual Studio 2005, but want to see if anyone has any better ideas. Thanks ~Aedon

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• learning and "singing" Ruby with Sinatra

  - by microspino

  Hello I'm trying to improve my ruby knowledge by reading The Ruby Programming Language book. Reading Coders at work I saw that lot of the interviewees suggest to dive into a project source code to learn best practices to be aware of bad habits and of course to take new inspirations for how to do things. I decided to pick a project as more self contained as I could find. My choice was Sinatra since It's 1000 LOC. Is It a good project to learn? Do you suggest another one more simple (i.e. less LOCs)? I've tried to see rails machinery before but I came out scared from It.

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• Why does it not allowed to use try-catch statement without {} ?

  - by alex

  Why can't I use code like this ? 1 int i = 0; try i = int.Parse("qwerty"); catch throw; 2 try i = int.Parse("qwerty"); catch; finally Log.Write("error"); And should write like this 1 int i = 0; try { i = int.Parse("qwerty"); } catch { throw; } 2 try { i = int.Parse("qwerty");} catch {} finally {Log.Write("error");} PS: I can use if-else statement without {}. Why should I use them with try-catch(-finally) statement ? Is there any meaningful reason ? Is it only because that some people think that code is hard to read ? Several months ago I asked that question on russian programming forum but I got no satisfactory answer ...

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• Design interoperable web services

  - by Zyd

  Hi everyone, I'm designing a set of web services to allow our clients to connect from their apps to one of our systems. Our clients have their apps developed in all varieties of frameworks (.NET, Java, PHP, Python and even the occasional all JS app), so obviously WS is the way to go. Investigating a little about truly interop WS I've found that the way to go is to design first the WSDL and XSD and derive the implementations from there. What i'm really looking for is guidance if this is really the way to go. I've read that WCF creates interoperable WS but i'm not a fan of MS creating something standard. Should i use WCF or there is a good set of tools for designing WSDL and XSD without the pain i'm expecting. Thanks in advance

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• MonoDevelop in Linux -- Terminal Commands

  - by Sandeep Bansal

  Hi everyone, I want to make a C# app in Mono as it's the only programming language I'm mostly comfortable with. Anyway, ATI Drivers on Linux do not have a Fan control feature and therefore the cards to tend to heat up. For me I prefer to have a cooler card. What I want to do is run a command such as: aticonfig --pplib-cmd 'set fanspeed 0 70' In a application but I the thing is..How can I run that code so it works, I am currently running Ubuntu 10.04, and it does work in the terminal, but I want to implement it into an application. Thanks

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• Linux, C++ audio capturing (just microphone) library

  - by TheOm3ga

  I'm developing a musical game, it's like a singstar but instead of singing, you have to play the recorder. It's called oFlute, and it's still in early development stage. In the game, I capture the microphone input, then run a simple FFT analysis and compare the results to typical recorder's frequencies, thus getting the played note. At the beginning, the audio library I was using was RtAudio, but I don't remember why I switched to PortAudio, which is what I'm currently using. The problem is that, from time to time, either it crashes randomly or stops capturing, like if there were no sound coming from the microphone. My question is, what's the best option to capture microphone input on Linux? I just need to open, read, and close a flow of bytes from the microphone. I've been reading this guide, and (un)surprisingly it says: I don't think that PortAudio is very good API for Unix-like operating systems. So, what do you recommend me?

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• n00b: receive input over TCP/IP and use it to update HTML

  - by mawg

  This has got to be a FAQ, so can someone please just direct me to a "network programming for dummies" URL? The server wants to push information to a client or broadcast to all, when an event happens - as opposed to the clients constantly polling the server "just in case". The client then updates a browser page display. How do I do that? (toldya it was a n00b question) Should I have a thread which receives info on a socket and then writes it to a database which the browser display (PHP) can process with an HTML refresh tag, or what? Sorry to sound so dumb.

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