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• iPhone development - app design patterns

  - by occulus

  There are tons of resources concerning coding on the iPhone. Most of them concern "how do I do X", e.g. "setup a navigation controller", or "download text from a URL". All good and fine. What I'm more interested in now are the questions that follow the simpler stuff - how to best structure your complex UI, or your app, or the common problems that arise. To illustrate: a book like "Beginning iPhone 3 Development" tells you how to set up a multi viewcontroller app with an top 'switcher' viewcontroller that switches between views owned by other view controllers. Fine, but you're only told how to do that, and nothing about the problems that can follow: for example, if I use their paradigm to switch to a UINavigationViewController, the Navigation bar ends up too low on the screen, because UINavigationViewController expects to be the topmost UIViewController (apparently). Also, delegate methods (e.g. relating to orientation changes) go to the top switcher view controller, not the actual controller responsible for the current view. I have fixes for these things but they feel like hacks which makes me unhappy and makes me feel like I'm missing something. One productive thing might be to look at some open source iPhone projects (see this question). But aside from that?

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• How can I use a meter-style progress bar?

  - by Yadyn

  In Vista/7, the Windows Explorer shell window makes use of a special kind of static progress bar to display hard drive space. With default styles, this bar is blue colored and non-animated. It also turns red colored when it gets close to being full (low disk space). Using messaging, I can tell the Windows Forms ProgressBar control to update its state to Paused and Error (yellow and red colored, respectively), which works fine, but these are still specific to progress. In the Windows User Experience Guidelines, it specifically points out this "meter" variant of the Progress Bar: This pattern isn't a progress bar, but it is implemented using the progress bar control. Meters have a distinct look to differentiate them from true progress bars. They say it "is implemented using the progress bar control", so... how? What message could I send to the control to have it behave this way? I've seen that you can send messages for setting the bar color, but the documentation says these calls are ignored when visual styles are enabled. Nothing else in the Windows API documentation for raw ProgressBar controls seemed to suggest a way to do this. Am I just stuck making a custom drawn bar? I'd really like to utilize the OS whenever possible so that the application will appear consistent throughout different OS versions. I realize that pre-Vista versions probably won't support this, though. I'm looking for a Windows Forms solution, but I wonder if it is even exposed at all via Win32 API.

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• ZeroMQ REQ/REP on ipc:// and concurrency

  - by Metiu

  I implemented a JSON-RPC server using a REQ/REP 0MQ ipc:// socket and I'm experiencing strange behavior which I suspect is due to the fact that the ipc:// underlying unix socket is not a real socket, but rather a single pipe. From the documentation, one has to enforce strict zmq_send()/zmq_recv() alternation, otherwise the out-of-order zmq_send() will return an error. However, I expected the enforcement to be per-client, not per-socket. Of course with a Unix socket there is just one pipeline from multiple clients to the server, so the server won't know who it is talking with. Two clients could zmq_send() simultaneously and the server would see this as an alternation violation. The sequence could be: ClientA: zmq_send() ClientB: zmq_send() : will it block until the other send/receive completes? will it return -1? (I suspect it will with ipc:// due to inherent low-level problems, but with TCP it could distinguish the two clients) ClientA: zmq_recv() ClientB: zmq_recv() so what about tcp:// sockets? Will it work concurrently? Should I use some other locking mechanism to work around this?

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• MySQL to SQL Server ODBC Connector?

  - by Scott C.

  My boss wants to have data in MySQL DBs used for our website to be "linked and synced" with a Financial Server that has its DB in SQL Server. Sooooo...even though I have no idea how to accomplish this, this just sounds like an absolute nightmare especially since the MySQL DB is most likely going to be hosted in the cloud and not on a machine next to the Financial Server. Any ideas how to accomplish this? (within reason?) Also, his big thing is he wants to basically pull up the data from any record a user enters and using data pulled from that do all sorts of calculations using ANOTHER program that stores its data (apparently) in SQL Server. Thinking of all the data I might have to convert makes me very uneasy. Please tell a ODBC eliminates complicated junk like this. :/ I'm trying to talk him into just having MySQL do a nightly dump into a CSV file or something and using that (rather than connector) to update the SQL Server DBs. I guess I'm just not that comfortable with a server and/or programming I have no say over being connected DIRECTLY to my MySQL DB for the website. If there's no good answer for this, can anyone offer a suggestion as to what I can say to talk him out of this? (I'm a low-level IT guy w/ a decent grasp on programming...but I'm no expert - should I try to push this off to a seasoned IT pro?) Thanks in advance.

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• getting another website data to manipulate it's value in perl

  - by aun ali

  use CGI qw(:standard); use CGI::Carp qw(fatalsToBrowser warningsToBrowser); our @a=param(src="http://fxrates.forexpros.com/index.php?pairs_ids=1525=last_update"); print header(),start_html('results.pl'); $a=http://fxrates.forexpros.com/index.php?pairs_ids=1525=last_update; '<iframe frameborder="0" scrolling="no" height="95" width="213" allowtransparency="true" marginwidth="0" marginheight="0" src="http://fxrates.forexpros.com/index.php?pairs_ids=1525;&header-text-color=%23FFFFFF&curr-name-color=%230059b0&inner-text-color=%23000000&green-text-color=%232A8215&green-background=%23B7F4C2&red-text-color=%23DC0001&red-background=%23FFE2E2&inner-border-color=%23CBCBCB&border-color=%23cbcbcb&bg1=%23F6F6F6&bg2=%23ffffff&bid=hide&ask=hide&last=hide&high=hide&low=hide&change=hide&change_in_percents=hide&last_update=show"></iframe><br /><div style="width:213"><span style="float:left"><span style="font-size: 11px;color: #333333;text-decoration: none;">The <a href="http://www.forexpros.com/quotes" target="_blank" style="font-size: 11px;color: #06529D; font-weight: bold;" class="underline_link">Forex Quotes</a> are Powered by Forexpros - The Leading Financial Portal.</span></span></div>'; print '<br/>'; print "$a"; print end_html();' getting error: Can't modify constant item in scalar assignment at livedata.pl line 4, near ""http://fxrates.forexpros.com/index.php?pairs_ids=1525=last_update")" syntax error at livedata.pl line 6, near "http:" Execution of livedata.pl aborted due to compilation errors.

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• In SVG is there a way to grab a shape anywhere when it has fill = "none"

  - by Shaunwithanau

  I have a series of shapes that I want the user to be able click anywhere on the shape to pick up as part of a drag and drop feature. All of these shapes are bounded by a rectangle. For example: <g id="shape1" fill="none" stroke="black"> <rect x="0" y="0" width="100" height="100"/> <circle cx="50" cy="50" r="50"/> </g> <g id="shape2" fill="none" stroke="black"> <rect x="0" y="0" width="100" height="100"/> <line x1="0" y1="0" x2="50" y2="100"/> <line x1="100" y1="0" x2="50" y2="100"/> </g> I already have all of the drag and drop parts working, the problem is all of these shapes have to have fill="none" so you can see anything that may be underneath of them. This means that even though they are bounded by the rectangle, at the moment users have to physically click on one of the lines in order to pick it up instead of being able to click anywhere on the shape like I want. My original idea was to use fill="white" and then set opacity="0" or some really low value but this applies to the stroke as well so this didn't work out. Any ideas on how I can get this working?

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• How to easily Generate Synth Chords Sounds in Android?

  - by barata7

  How to easily Generate Synth Chords Sounds in Android? I wanna be able to generate dynamically an in game Music using 8bit. Tried with AudioTrack, but did not get good results of nice sounds yet. Any examples out there? I have tried the following code without success: public class BitLoose { private final int duration = 1; // seconds private final int sampleRate = 4200; private final int numSamples = duration * sampleRate; private final double sample[] = new double[numSamples]; final AudioTrack audioTrack; public BitLoose() { audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC, sampleRate, AudioFormat.CHANNEL_CONFIGURATION_MONO, AudioFormat.ENCODING_PCM_8BIT, numSamples, AudioTrack.MODE_STREAM); audioTrack.play(); } public void addTone(final int freqOfTone) { // fill out the array for (int i = 0; i < numSamples; ++i) { sample[i] = Math.sin(2 * Math.PI * i / (sampleRate / freqOfTone)); } // convert to 16 bit pcm sound array // assumes the sample buffer is normalised. final byte generatedSnd[] = new byte[numSamples]; int idx = 0; for (final double dVal : sample) { // scale to maximum amplitude final short val = (short) ((((dVal * 255))) % 255); // in 16 bit wav PCM, first byte is the low order byte generatedSnd[idx++] = (byte) (val); } audioTrack.write(generatedSnd, 0, sampleRate); } public void stop() { audioTrack.stop(); }

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• Continuous build infrastructure recommendations for primarily C++; GreenHills Integrity

  - by andersoj

  I need your recommendations for continuous build products for a large (1-2MLOC) software development project. Characteristics: ClearCase revision control Approx 80% C++; 15% Java; 5% script or low-level Compiles for Green Hills Integrity OS, but also some windows and JVM chunks Mostly an embedded system; also includes some UI pieces and some development support (simulation tools, config tools, etc...) Each notional "version" of the deliverable includes deployment images for a number of boards, UI machines, etc... (~10 separate images; 5 distinct operating systems) Need to maintain/track many simultaneous versions which, notably, are built for a variety of different board support packages Build cycle time is a major issue on the project, need support for whatever features help address this (mostly need to manage a large farm of build machines, I guess..) Operates in a secure environment (this is a gov't program) (Edited to add: This is a classified program; outsourcing the build infrastructure is a non-starter.) Interested in any best practices or peripheral guidance you might offer. The build automation issues is one of several overlapping best practices that appear to be missing on the program, but try to keep your answers focused on build infrastructure piece and observations directly related. Cost is not an object. Scalability and ease of retrofitting onto an existing infrastructure are key. JA

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• A generic C++ library that provides QtConcurrent functionality?

  - by Lucas

  QtConcurrent is awesome. I'll let the Qt docs speak for themselves: QtConcurrent includes functional programming style APIs for parallel list processing, including a MapReduce and FilterReduce implementation for shared-memory (non-distributed) systems, and classes for managing asynchronous computations in GUI applications. For instance, you give QtConcurrent::map() an iterable sequence and a function that accepts items of the type stored in the sequence, and that function is applied to all the items in the collection. This is done in a multi-threaded manner, with a thread pool equal to the number of logical CPU's on the system. There are plenty of other function in QtConcurrent, like filter(), filteredReduced() etc. The standard CompSci map/reduce functions and the like. I'm totally in love with this, but I'm starting work on an OSS project that will not be using the Qt framework. It's a library, and I don't want to force others to depend on such a large framework like Qt. I'm trying to keep external dependencies to a minimum (it's the decent thing to do). I'm looking for a generic C++ framework that provides me with the same/similar high-level primitives that QtConcurrent does. AFAIK boost has nothing like this (I may be wrong though). boost::thread is very low-level compared to what I'm looking for. I know C# has something very similar with their Parallel Extensions so I know this isn't a Qt-only idea. What do you suggest I use?

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• How do I compare two PropertyInfos or methods reliably?

  - by Rob Ashton

  Same for methods too: I am given two instances of PropertyInfo or methods which have been extracted from the class they sit on via GetProperty or GetMember etc, (or from a MemberExpression maybe). I want to determine if they are in fact referring to the same Property or the same Method so (propertyOne == propertyTwo) or (methodOne == methodTwo) Clearly that isn't going to actually work, you might be looking at the same property, but it might have been extracted from different levels of the class hierarchy (in which case generally, propertyOne != propertyTwo) Of course, I could look at DeclaringType, and re-request the property, but this starts getting a bit confusing when you start thinking about Properties/Methods declared on interfaces and implemented on classes Properties/Methods declared on a base class (virtually) and overridden on derived classes Properties/Methods declared on a base class, overridden with 'new' (in IL world this is nothing special iirc) At the end of the day, I just want to be able to do an intelligent equality check between two properties or two methods, I'm 80% sure that the above bullet points don't cover all of the edge cases, and while I could just sit down, write a bunch of tests and start playing about, I'm well aware that my low level knowledge of how these concepts are actually implemented is not excellent, and I'm hoping this is an already answered topic and I just suck at searching. The best answer would give me a couple of methods that achieve the above, explaining what edge cases have been taken care of and why :-)

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• gcc compilations (sometimes) result in cpu underload

  - by confusedCoder

  I have a larger C++ program which starts out by reading thousands of small text files into memory and storing data in stl containers. This takes about a minute. Periodically, a compilation will exhibit behavior where that initial part of the program will run at about 22-23% CPU load. Once that step is over, it goes back to ~100% CPU. It is more likely to happen with O2 flag turned on but not consistently. It happens even less often with the -p flag which makes it almost impossible to profile. I did capture it once but the gprof output wasn't helpful - everything runs with the same relative speed just at low cpu usage. I am quite certain that this has nothing to do with multiple cores. I do have a quad-core cpu, and most of the code is multi-threaded, but I tested this issue running a single thread. Also, when I run the problematic step in multiple threads, each thread only runs at ~20% CPU. I apologize ahead of time for the vagueness of the question but I have run out of ideas as to how to troubleshoot it further, so any hints might be helpful. UPDATE: Just to make sure it's clear, the problematic part of the code does sometimes (~30-40% of the compilations) run at 100% CPU, so it's hard to buy the (otherwise reasonable) argument that I/O is the bottleneck

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• CSS - Why is this invisible margin being applied to my <a> tag css-button?

  - by Kenny Bones

  I was having trouble with two types of buttons. It was a form button and a css button basically. And I was advised that the css button whould use display:inline-block; This made the whole a href tag actually look like a button. But this invisible margin seems to be screwing up something. I tried separating them into separate css classes, but oddly, applying a real margin to the css button gives an additional margin as well. What's causing this? You can easily see it here (low graphics): www.matkalenderen.no Basically, code looks like this: <input type="submit" value="Logg inn" class="button_blue" alt="ready to login"> <a class="button_css_red" href="access.php">Glemt passord</a> CSS .button_red, .button_blue, .button_css_red, .button_css_blue { background-image:url("../img/sprite_buttons.png"); background-repeat:no-repeat; border: none; color:#FFFFFF; display:inline-block; display:inline-block; font-size:12px; height:27px; width:98px; } .button_css_red, .button_css_blue { margin-top:20px; }

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• Building a survey to put in a WordPress website using Python/Django

  - by chiurox

  So I've been given a task to build a survey to get data regarding time slot preferences of prospective students for a particular course. I know there are really quick solutions to this like Google Forms, SurveyMonkey, but since it's not unusually hard, I want to implement the survey myself in a totally new language as an opportunity to get started with it and also be able to customize and provide dynamic info to the users who are voting. Although I have done some stuff in PHP, C++, javascript, etc, I'm pretty new to Python+Django framework but it's something I've been meaning to get into since a long time ago. Initially, what I want is to make a grid with the days of the week as columns and time-durations as rows. In each cell I want to provide users a way to choose how strong (high/medium/low) their preference for this particular day+time is. I also want to show how many "votes" have already been cast for this particular preference because this will influence a lot in their decisions and as a result make this process easier when we are going to define the classes. I'll probably store the data in MySQL. Could anyone point me to some really good Python+Django tutorials for my particular purpose? Does anyone think I'm wasting my time with this trivial task by choosing new tools and that I should just use something I already know (like PHP) or a free service or plugin for Wordpress? Thanks!

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• Deterministic floating point and .NET

  - by code2code

  How can I guarantee that floating point calculations in a .NET application (say in C#) always produce the same bit-exact result? Especially when using different versions of .NET and running on different platforms (x86 vs x86_64). Inaccuracies of floating point operations do not matter. In Java I'd use strictfp. In C/C++ and other low level languages this problem is essentially solved by accessing the FPU / SSE control registers but that's probably not possible in .NET. Even with control of the FPU control register the JIT of .NET will generate different code on different platforms. Something like HotSpot would be even worse in this case... Why do I need it? I'm thinking about writing a real-time strategy (RTS) game which heavily depends on fast floating point math together with a lock stepped simulation. Essentially I will only transmit user input across the network. This also applies to other games which implement replays by storing the user input. Not an option are: decimals (too slow) fixed point values (too slow and cumbersome when using sqrt, sin, cos, tan, atan...) update state across the network like an FPS: Sending position information for hundreds or a few thousand units is not an option Any ideas?

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• Suggestions for opening the Rails toolbox to design a challenge game?

  - by keruilin

  How would you suggest designing a challenge system as part of a food-eating game so that it's automated as possible? All RoR tools, design patterns and logic are at your disposal (e.g., admin consoles, crontab, arch, etc.). Prize goes to whoever can suggest the simplest and most-automated design! Here are the requirements: User has many challenges. Badge has many challenges. (A unique badge is awarded for each challenge won.) Only one challenge can run at a time. Each challenge has a limited number of days that it runs. For example, one challenge can run 3 days, while another runs 7 days. Challenges can be seasonal. For example, "Eat 13 Pumpkins" only runs during the Fall. New challenges are added to the game on an ongoing basis. For example, a new challenge every week. Each challenge has a certain probability of being selected to run. For example, "Eat 10 Pies" challenge has 10% chance of being selected to run. As each new challenge is added to the database, I want the probabilities of running to change dynamically. I want to avoid the scenario where I'm manually updating a database field just to change the probability from 10% to 5%, for example. Challenges act like Easter eggs. Challenge icons pop-up at different places on the webpage. User is awarded a badge for successfully completing a challenge, but only when it's active. There is some wait time between each challenge. Between 1 and 7 days. Which wait time is random, but the probability of the wait time being short is high and the probability of it being a long wait time is low.

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• Get Highest Res Favicon

  - by Jeremy

  I'm making a website that needs to dynamically obtain the favicon of sites upon request. I've found a few api's that can accomplish this fairly well, and so far I'm liking http://www.fvicon.com/. The final image for my website will be 64x64px, and some websites such as Google and Wordpress have nice images of this size that are easily retrieved via this api. Though, of course, most websites only have a 16x16 favicon image and scaling that image to 64x64 has very bad quality loss. Examples: (high res) http://a.fvicon.com/wordpress.com?format=png&width=64&height=64 (low res) http://a.fvicon.com/yahoo.com?format=png&width=64&height=64 Keeping this in mind, I'm planning on somehow determining whether a high-res image is available and, if so, the website will use this image. If not, I want to use a pre-made 64x64 icon with the smaller icon layered over it. What I'm having trouble with is determining if there is a high res favicon available or not. Also, I'm curious if there's a better approach to this situation. I'd rather not use smaller images (64x64 works out really well for this project). The lowest res I'm willing to drop to is 48x48 but even then there will be a significant quality loss for scaling up 16x16 favicons. Any ideas? If you need any more information I will gladly provide it. Thank you!

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• Creating a network adapter - how hard is it?

  - by Vilx-

  I'm interested in building a little (commercial) device on top of Arduino. I want it to be able to interface with network. Network as in standard Ethernet, Cat5, RJ-45, etc. I know that there is an Ethernet Shield, but it costs even more than the Arduino itself, and it's pretty big. Naturally, I want my device to be as small and as cheap as possible. So I'm thinking about recreating an Ethernet module myself. The problem is - I haven't got any experience with Ethernet, nor do I have a good idea where to start looking. Thus I can't even say if my ideas are feasible. Ultimately I would like the device to have three ports - one for incoming signal, two for outgoing, so the device is essentially a little switch where it is plugged in itself as well. The switching capabilities need not be very fast - the volume of data will be low. 10Mbit is more than enough, can be even slower. If that is not possible, a single port for controlling the device itself will also do. Another possibility I'm considering is power line communications - sending information through power lines. That's another area I've no experience with. What hardware should I be looking at, and where can I find information about the necessary software? So - can anyone tell me if these ideas are feasible, and if yes - where should I start looking?

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• File upload fails when user is authenticated. Using IIS7 Integrated mode.

  - by Nikkelmann

  These are the user identities my website tells me that it uses: Logged on: NT AUTHORITY\NETWORK SERVICE (Can not write any files at all) and Not logged on: WSW32\IUSR_77 (Can write files to any folder) I have a ASP.NET 4.0 website on a shared hosting IIS7 web server running in Integrated mode with 32-bit applications support enabled and MSSQL 2008. Using classic mode is not an option since I need to secure some static files and I use Routing. In my web.config file I have set the following: <system.webServer> <modules runAllManagedModulesForAllRequests="true" /> </system.webServer> My hosting company says that Impersonation is enabled by default on machine level, so this is not something I can change. I asked their support and they referred me to this article: http://www.codinghub.net/2010/08/differences-between-integrated-mode-and.html Citing this part: Different windows identity in Forms authentication When Forms Authentication is used by an application and anonymous access is allowed, the Integrated mode identity differs from the Classic mode identity in the following ways: * ServerVariables["LOGON_USER"] is filled. * Request.LogognUserIdentity uses the credentials of the [NT AUTHORITY\NETWORK SERVICE] account instead of the [NT AUTHORITY\INTERNET USER] account. This behavior occurs because authentication is performed in a single stage in Integrated mode. Conversely, in Classic mode, authentication occurs first with IIS 7.0 using anonymous access, and then with ASP.NET using Forms authentication. Thus, the result of the authentication is always a single user-- the Forms authentication user. AUTH_USER/LOGON_USER returns this same user because the Forms authentication user credentials are synchronized between IIS 7.0 and ASP.NET. A side effect is that LOGON_USER, HttpRequest.LogonUserIdentity, and impersonation no longer can access the Anonymous user credentials that IIS 7.0 would have authenticated by using Classic mode. How do I set up my website so that it can use the proper identity with the proper permissions? I've looked high and low for any answers regarding this specific problem, but found nil so far... I hope you can help!

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• AsyncTask never finishes when other tasks are running

  - by rebeccamaher

  In my app, I show a menu screen immediately to the user and then use an AsyncTask to load some data from disk. Loading takes about 3 seconds if that's all the app had to do. When the user hits a menu option and the data hasn't loaded yet, a "Please wait, loading" screen appears. I have two problems: I recently added ads to my app and have found this is making my app hang sometimes because the AsyncTask never finishes loading. What seems to be happening is that the ad banner (I'm using admob and this happens when adsense ads are shown which admob do occasionally) is using resources by playing a simple animation and the AsyncTask never gets a chance to finish. I want to play a simple looping animation (e.g. making a view rotate) on my menu screen and this makes the AsyncTask take about 5 times longer to finish which renders the background loading pointless. How can I avoid situations where my background data never finishes loading or has such a low priority it takes a long time? I can't seem to find a way to increase the priority of an AsyncTask.

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• c++ and visual studio 08, how to develop the following web extracting application. folloow up of las

  - by user287745

  the purpose is to use c++ in a useful way. i have just started programming and have made a few small applications in c and c#. my understanding is that programming for web and thing related to web is now a days a very easy task. please note this is for personnel learning not for rent a coder or any money making. an application which can run on any windows platform even win98. the application should start automatically at a scheduled time and do the following. connect to a site which displays stock prices summary (high low current open ). captures the data (excluding the other things in the site) and saves it to disk ( a sql database) please note:- internet connection is assumed to be there always. do not want to know how to make database schema or database. the stock exchange has no law prohibiting the use of the data provided on its site, but i do not want to mention the name in case i am wrong, but its for personnel private use only. the data of summary of pricing is arranged in a table such that when copied pasted to ms excel it automatically forms a table. guidance needed thank u.

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• CakePHP dropping session between pages

  - by DavidYell

  Hi, I have an application with multiple regions and various incoming links. The premise, well it worked before, is that in the app_controller, I break out these incoming links and set them in the session. So I have a huge beforeFilter() in my *app_controller* which catches these and sets two variables in the session. Viewing.region and Search.engine, no problem. The problem arises that the session does not seem to be persistant across page requests. So for example, going to /reviews/write (userReviews/add) should have a session available which was set when the user arrived at the site. Although it seems to have vanished! It would appear that unless $this-params is caught explicitly in the *app_controller* and a session variable written, it does not exist on other pages. So far I have tried, swapping between storing session in 'cake' and 'php' both seem to exhibit the same behaviour. I use 'php' as a default. My Session.timeout is '120', Session.checkAgent is False and Security.level is 'low'. All of which should give enough leniency to the framework to allow sessions the most room to live! I'm a bit stumped as to why the session seems to be either recreated or blanked when a new page is being requested. I have commented out the requestAction() calls to make sure that isn't confusing the session request object also, which doesn't seem to make a difference. Any help would be great, as I don't have to have to recode the site to pass all the various variables via parameters in the url, as that would suck, and it's worked before, thus switching on $this-Session-read('Viewing.region') in all my code!

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• Type-safe generic data structures in plain-old C?

  - by Bradford Larsen

  I have done far more C++ programming than "plain old C" programming. One thing I sorely miss when programming in plain C is type-safe generic data structures, which are provided in C++ via templates. For sake of concreteness, consider a generic singly linked list. In C++, it is a simple matter to define your own template class, and then instantiate it for the types you need. In C, I can think of a few ways of implementing a generic singly linked list: Write the linked list type(s) and supporting procedures once, using void pointers to go around the type system. Write preprocessor macros taking the necessary type names, etc, to generate a type-specific version of the data structure and supporting procedures. Use a more sophisticated, stand-alone tool to generate the code for the types you need. I don't like option 1, as it is subverts the type system, and would likely have worse performance than a specialized type-specific implementation. Using a uniform representation of the data structure for all types, and casting to/from void pointers, so far as I can see, necessitates an indirection that would be avoided by an implementation specialized for the element type. Option 2 doesn't require any extra tools, but it feels somewhat clunky, and could give bad compiler errors when used improperly. Option 3 could give better compiler error messages than option 2, as the specialized data structure code would reside in expanded form that could be opened in an editor and inspected by the programmer (as opposed to code generated by preprocessor macros). However, this option is the most heavyweight, a sort of "poor-man's templates". I have used this approach before, using a simple sed script to specialize a "templated" version of some C code. I would like to program my future "low-level" projects in C rather than C++, but have been frightened by the thought of rewriting common data structures for each specific type. What experience do people have with this issue? Are there good libraries of generic data structures and algorithms in C that do not go with Option 1 (i.e. casting to and from void pointers, which sacrifices type safety and adds a level of indirection)?

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• Fastest reliable way for Clojure (Java) and Ruby apps to communicate

  - by jkndrkn

  Hi There, We have cloud-hosted (RackSpace cloud) Ruby and Java apps that will interact as follows: Ruby app sends a request to Java app. Request consists of map structure containing strings, integers, other maps, and lists (analogous to JSON). Java app analyzes data and sends reply to Ruby App. We are interested in evaluating both messaging formats (JSON, Buffer Protocols, Thrift, etc.) as well as message transmission channels/techniques (sockets, message queues, RPC, REST, SOAP, etc.) Our criteria: Short round-trip time. Low round-trip-time standard deviation. (We understand that garbage collection pauses and network usage spikes can affect this value). High availability. Scalability (we may want to have multiple instances of Ruby and Java app exchanging point-to-point messages in the future). Ease of debugging and profiling. Good documentation and community support. Bonus points for Clojure support. What combination of message format and transmission method would you recommend? Why? I've gathered here some materials we have already collected for review: Comparison of various java serialization options Comparison of Thrift and Protocol Buffers (old) Comparison of various data interchange formats Comparison of Thrift and Protocol Buffers Fallacies of Protocol Buffers RPC features Discussion of RPC in the context of AMQP (Message-Queueing) Comparison of RPC and message-passing in distributed systems (pdf) Criticism of RPC from perspective of message-passing fan Overview of Avro from Ruby programmer perspective

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• How can multiple variables be passed to a function cleanly in C?

  - by aquanar

  I am working on an embedded system that has different output capabilities (digital out, serial, analog, etc). I am trying to figure out a clean way to pass many of the variables that will control those functions. I don't need to pass ALL of them too often, but I was hoping to have a function that would read the input data (in this case from a TCP network), and then parse the data (IE, the 3rd byte contains the states of 8 of the digital outputs (according to which bit in that byte is high or low)), and put that into a variable where I can then use elsewhere in the program. I wanted that function to be separate from the main() function, but to do so would require passing pointers to some 20 or so variables that it would be writing to. I know I could make the variables global, but I am trying to make it easier to debug by making it obvious when a function is allowed to edit that variable, by passing it to the function. My best idea was a struct, and just pass a pointer to it, but wasn't sure if there was a more efficient way, especially since there is only really 1 function that would need to access all of them at once, while most others only require parts of the information that will be stored in this bunch of state variables. So anyway, is there a clean way to send many variables between functions at once that need to be edited?

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• Hashing 11 byte unique ID to 32 bits or less

  - by MoJo

  I am looking for a way to reduce a 11 byte unique ID to 32 bits or fewer. I am using an Atmel AVR microcontroller that has the ID number burned in at the factory, but because it has to be transmitted very often in a very low power system I want to reduce the length down to 4 bytes or fewer. The ID is guaranteed unique for every microcontroller. It is made up of data from the manufacturing process, basically the coordinates of the silicone on the wafer and the production line that was used. They look like this: 304A34393334-16-11001000 314832383431-0F-09000C00 Obviously the main danger is that by reducing these IDs they become non-unique. Unfortunately I don't have a large enough sample size to test how unique these numbers are. Having said that because there will only be tens of thousands of devices in use and there is secondary information that can be used to help identify them (such as their approximate location, known at the time of communication) collisions might not be too much of an issue if they are few and far between. Is something like MD5 suitable for this? My concern is that the data being hashed is very short, just 11 bytes. Do hash functions work reliably on such short data?

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