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• "Can't open display" even after access with xhost

  - by Yann

  I'm trying to run a graphical program remotely, without using ssh. I've set the display variable on the server (let's say server.com, Linux, not ubuntu, and no su rights) to point to my workstation (workstation.com, ubuntu 10.04) setenv DISPLAY workstation.com:0 Then on my workstation I've tried both xhost +server.com and xhost + Then I ssh into the server (to test things): ssh [email protected] and try to run xclock, and get the following error: Error: Can't open display: workstation.com:0 I've looked at /etc/ssh/ssh_config on the workstation and I should be forwarding correctly: X11Forwarding yes. How do I go about troubleshooting this? What logs on the workstation document these failed attempts? To explain why I'm doing this: I want to run a batch job on a server to debug an MPI-based parallel program. I want to run xterm as the batch job executable, per the instructions provided by the system admins. This setup use to work. I reinstalled things on my workstation and since then I frequently get one-time message along the lines The authenticity of host 'hostname (XXX.XXX.XXX.XX)' can't be established. My attempt to fix the above was to move my ~/.ssh/known_hosts file to a back up on both server and host, and then to ssh from each to the other with the flag -o StrictHostKeyChecking=no. I no longer get that message, but I was wondering does this play a part in why X11 forwarding is not working?

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• How to pass one float as four unsigned chars to shader by glVertexPointAttrib?

  - by Kog

  For each vertex I use two floats as position and four unsigned bytes as color. I want to store all of them in one table, so I tried casting those four unsigned bytes to one float, but I am unable to do that correctly... All in all, my tests came to one point: GLfloat vertices[] = { 1.0f, 0.5f, 0, 1.0f, 0, 0 }; glEnableVertexAttribArray(0); glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(float), vertices); // VER1 - draws red triangle // unsigned char colors[] = { 0xff, 0, 0, 0xff, 0xff, 0, 0, 0xff, 0xff, 0, 0, // 0xff }; // glEnableVertexAttribArray(1); // glVertexAttribPointer(1, 4, GL_UNSIGNED_BYTE, GL_TRUE, 4 * sizeof(GLubyte), // colors); // VER2 - draws greenish triangle (not "pure" green) // float f = 255 << 24 | 255; //Hex:0xff0000ff // float colors2[] = { f, f, f }; // glEnableVertexAttribArray(1); // glVertexAttribPointer(1, 4, GL_UNSIGNED_BYTE, GL_TRUE, 4 * sizeof(GLubyte), // colors2); // VER3 - draws red triangle int i = 255 << 24 | 255; //Hex:0xff0000ff int colors3[] = { i, i, i }; glEnableVertexAttribArray(1); glVertexAttribPointer(1, 4, GL_UNSIGNED_BYTE, GL_TRUE, 4 * sizeof(GLubyte), colors3); glDrawArrays(GL_TRIANGLES, 0, 3); Above code is used to draw one simple red triangle. My question is - why do versions 1 and 3 work correctly, while version 2 draws some greenish triangle? Hex values are one I read by marking variable during debug. They are equal for version 2 and 3 - so what causes the difference?

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• ODBC in SSIS 2012

  - by jamiet

  In August 2011 the SQL Server client team published a blog post entitled Microsoft is Aligning with ODBC for Native Relational Data Access in which they basically said "OLE DB is the past, ODBC is the future. Deal with it.". From that blog post:We encourage you to adopt ODBC in the development of your new and future versions of your application. You don’t need to change your existing applications using OLE DB, as they will continue to be supported on Denali throughout its lifecycle. While this gives you a large window of opportunity for changing your applications before the deprecation goes into effect, you may want to consider migrating those applications to ODBC as a part of your future roadmap.I recently undertook a project using SSIS2012 and heeded that advice by opting to use ODBC Connection Managers rather than OLE DB Connection Managers. Unfortunately my finding was that the ODBC Connection Manager is not yet ready for primetime use in SSIS 2012. The main issue I found was that you can't populate an Object variable with a recordset when using an Execute SQL Task connecting to an ODBC data source; any attempt to do so will result in an error:"Disconnected recordsets are not available from ODBC connections." I have filed a bug on Connect at ODBC Connection Manager does not have same funcitonality as OLE DB. For this reason I strongly recommend that you don't make the move to ODBC Connection Managers in SSIS just yet - best to wait for the next version of SSIS before doing that.I found another couple of issues with the ODBC Connection Manager that are worth keeping in mind:It doesn't recognise System Data Source Names (DSNs), only User DSNs (bug filed at ODBC System DSNs are not available in the ODBC Connection Manager)  UPDATE: According to a comment on that Connect item this may only be a problem on 64bit.In the OLE DB Connection Manager parameter ordinals are 0-based, in the ODBC Connection Manager they are 1-based (oh I just can't wait for the upgrade mess that ensues from this one!!!)You have been warned!@jamiet

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• Views : ViewControllers, many to one, or one to one?

  - by conor

  I have developed an Android application where, typically, each view (layout.xml) displayed on the screen has it's own corresponding fragment (for the purpose of this question I may refer to this as a ViewController). These views and Fragments/ViewControllers are appropriately named to reflect what they display. So this has the effect of allowing the programmer to easily pinpoint the files associated with what they see on any given screen. The above refers to the one to one part of my question. Please note that with the above there are a few exceptions where very similar is displayed on two views so the ViewController is used for two views. (Using a simple switch (type) to determine what layout.xml file to load) On the flip side. I am currently working on the iOS version of the same app, which I didn't develop. It seems that they are adopting more of a one-to-many (ViewController:View) approach. There appears to be one ViewController that handles the display logic for many different types of views. In the ViewController are an assortment of boolean flags and arrays of data (to be displayed) that are used to determine what view to load and how to display it. This seems very cumbersome to me and coupled with no comments/ambiguous variable names I am finding it very difficult to implement changes into the project. What do you guys think of the two approaches? Which one would you prefer? I'm really considering putting in some extra time at work to refactor the iOS into a more 1:1 oriented approach. My reasoning for 1:1 over M:1 is that of modularity and legibility. After all, don't some people measure the quality of code based on how easy it is for another developer to pick up the reigns or how easy it is to pull a piece of code and use it somewhere else?

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• TXPAUSE : polite waiting for hardware transactional memory

  - by Dave

  Classic locks are an appropriate tool to prevent potentially conflicting operations A and B, invoked by different threads, from running at the same time. In a sense the locks cause either A to run before B or vice-versa. Similarly, we can replace the locks with hardware transactional memory, or use transactional lock elision to leverage potential disjoint access parallelism between A and B. But often we want A to wait until B has run. In a Pthreads environment we'd usually use locks in conjunction with condition variables to implement our "wait until" constraint. MONITOR-MWAIT is another way to wait for a memory location to change, but it only allows us to track one cache line and it's only available on x86. There's no similar "wait until" construct for hardware transactions. At the instruction-set level a simple way to express "wait until" in transactions would be to add a new TXPAUSE instruction that could be used within an active hardware transaction. TXPAUSE would politely stall the invoking thread, possibly surrendering or yielding compute resources, while at the same time continuing to track the transaction's address-set. Once a transaction has executed TXPAUSE it can only abort. Ideally that'd happen when some other thread modifies a variable that's in the transaction's read-set or write-set. And since we're aborting all writes would be discarded. In a sense this gives us multi-location MWAIT but with much more flexibility. We could also augment the TXPAUSE with a cycle-count bound to cap the time spent stalled. I should note that we can already enter a tight spin loop in a transaction to wait for updates to address-set to cause an abort. Assuming that the implementation monitors the address-set via cache-coherence probes, by waiting in this fashion we actually communicate via the probes, and not via memory values. That is the updating thread signals the waiter via probes instead of by traditional memory values. But TXPAUSE gives us a polite way to spin.

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• Dreaded SQLs

  - by lavanyadeepak

  Dreaded SQLs We used to think that a SQL statement without a where clause is only dangerous right since running that on a server TSQL is just going to impact the entire table like waving the magic wand. For that reason we should cultivate the habit first to write the statement as select and then to modify the select portion as update. Within the T-SQL Window, I would normally prefer the following first: select * from employee where empid in (4,5) and then once I am satisfied with the results, I would go ahead with the following change: --select * delete from employee where empid in (4,5) Today I just discovered another coding horror. This would typically be applicable in a stored procedure and with respect to variable nomenclature. It is always desirable to have a suitable nomenclature for parameters distinct from the column names and internal variables. This would help quicker debugging of the stored procedures besides enhancing the readability. Else in a quick bout of enthusiasm a statement like   if (@CustomerID = @CustomerID) [when the latter is intended to denote the column name and there is a superflous @ prepended], zeroing in on the problem would be little tricky. Had there been a still powerful nomenclature rules then debugging would have been more straight-forward and simpler right?

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• Would form keys reduce the amount of spam we receive?

  - by David Wilkins

  I work for a company that has an online store, and we constantly have to deal with a lot of spam product reviews, and bogus customer accounts. These are all created by automated systems and are more of a nuisance than anything. What I am thinking of (in lieu of captcha, which can be broken) is adding a sort of form key solution to all relevant forms. I know for certain some of the spammers are using XRumer, and I know they seldom request a page before sending us the form data (Is this the definition of CSRF?) so I would think that tying a key to each requested form would at least stem the tide. I also know the spammers are lazy and don't check their work, or they would see that we have never posted a spam review, and they have never gained any revenue from our site. Would this succeed in significantly reducing the volume of spam product reviews and customer account creations we are seeing? EDIT: To clarify what I mean by "Form Keys": I am referring to creating a unique identifier (or "key") that will be used as an invisible, static form field. This key will also be stored either in the database (relative to the user session) or in a cookie variable. When the form's target gets a request, the key must be validated for the form's data to be processed. Those pesky bots won't have the key because they don't load the javascript that generates the form (they just send a blind request to the target) and even if they did load the javascript once, they'd only have one valid key, and I'm not sure they even use cookies.

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• Strategies for managing use of types in Python

  - by dave

  I'm a long time programmer in C# but have been coding in Python for the past year. One of the big hurdles for me was the lack of type definitions for variables and parameters. Whereas I totally get the idea of duck typing, I do find it frustrating that I can't tell the type of a variable just by looking at it. This is an issue when you look at someone else's code where they've used ambiguous names for method parameters (see edit below). In a few cases, I've added asserts to ensure parameters comply with an expected type but this goes against the whole duck typing thing. On some methods, I'll document the expected type of parameters (eg: list of user objects), but even this seems to go against the idea of just using an object and let the runtime deal with exceptions. What strategies do you use to avoid typing problems in Python? Edit: Example of the parameter naming issues: If our code base we have a task object (ORM object) and a task_obj object (higher level object that embeds a task). Needless to say, many methods accept a parameter named 'task'. The method might expect a task or a task_obj or some other construct such as a dictionary of task properties - it is not clear. It is them up to be to look at how that parameter is used in order to work out what the method expects.

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• Algorithm for rating books: Relative perception

  - by suneet

  So I am developing this application for rating books (think like IMDB for books) using relational database. Problem statement : Let's say book "A" deserves 8.5 in absolute sense. In case if A is the best book I have ever seen, I'll most probably rate it 9.5 whereas for someone else, it might be just an average book, so he/they will rate it less (say around 8). Let's assume 4 such guys rate it 8. If there are 10 guys who are like me (who haven't ever read great literature) and they all rate it 9.5-10. This will effectively make it's cumulative rating greater than 9 (9.5*10 + 8*4) / 14 = 9.1 whereas we needed the result to be 8.5 ... How can I take care of(normalize) this bias due to incorrect perception of individuals. MyProposedSolution : Here's one of the ways how I think it could be solved. We can have a variable Lit_coefficient which tells us how much knowledge a user has about literature. If I rate "A"(the book) 9.5 and person "X" rates it 8, then he must have read books much better than "A" and thus his Lit_coefficient should be higher. And then we can normalize the ratings according to the Lit_coefficient of user. Could there be a better algorithm/solution for the same?

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• Is the way I'm implementing my genetic algorithm right?

  - by Mhjr

  In my graduation project, I am asked to use a genetic algorithm (any variation of it can be chosen) to generate valid timetables. What I did was make a simple program that generates unique sequences representing genes, the sequence is described below: (sorry if it's mathematically incorrect) The only variable in the sequence is the room element, so basically the program takes a tree that goes like this: [Course] -(contains)-> [Units] -(contains)-> [Offerings] -(contains)-> [Instructors] -(contains)-> [Rooms] Each course can have n units (duplicates). Each unit can have n offerings (lectures,lab session, excercises,...). Each offering has only 1 instructor. Each instructor (or the whole lecture composed from the four elements of the sequence) has multiple rooms. When a timetable is initialized, one of these sequences that differ in rooms will be taken into the timetable, so the difference in genes (sequences) of each timetable will be just the rooms random choice and the difference between chromosomes (timetables) will be time placements of these genes (sequences). My question is, before I proceed in implementing what I described, is it valid? Is the representation used here for chromosomes a permutation representation?

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• The clock problem - to if or not to if?

  - by trejder

  Let's say, we have a simple digital clock. To "power" it, we use a routine executed every second. We update seconds part in it. But, what about minutes and hours part? What is better / more professional / offers better performance: Ignore all checking and update hour, minute and seconds part each time, every second. Use if + a variable for checking, if 60 (or 3600) seconds passed and update minute / hour part only at that precise moments. This leads us to a question, what is better -- unnecessary drawings (first approach) or extra ifs? I've just spotted a Javascript digital clock, one of millions similar on one of billions pages. And I noticed that all three parts (hours, minutes and seconds) are updated every second, though first changes its value only once per 3600 seconds and second once per 60 seconds. I'm not to experienced developer, so I might me wrong. But everything, what I've learnt up until now, tells me, that if are far better then executing drawing / refreshing sequences only to draw the same content.

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• How to Install WebLogic 12c ZIP on Linux

  - by Bruno.Borges

  I knew that WebLogic had this small ZIP distribution, of only 184M, but what I didn't know was that it is so easy to install it on Linux machines, specially for development purposes, that I thought I had to blog about it. You may want to check this blog, where I found the missing part on this how to, but I'm blogging this again because I wanted to put it in a simpler way, straight to the point. And if you are looking for a how to for Mac, check Arun Gupta's post.  So, here's the step-by-step: 1 - Download the ZIP distribution (don't worry if your system is x86_64)Don't forget to accept the OTN Free Developer License Agreement! 2 - Choose where to install your WebLogic server and your domain, and set as your MW_HOME environment variableI will use /opt/middleware/weblogic for this how to export MW_HOME=/opt/middleware/weblogicMake sure this path exists in your system. 'mydomains' will be used to keep your WebLogic domain. mkdir -p $MW_HOME/mydomain 3 - If you don't have your JAVA_HOME environment variable still configured, do it. Point it to where your JDK is installed. export JAVA_HOME=/usr/lib/jvm/default-java 4 - Unzip the downloaded file into MW_HOME unzip wls1211_dev.zip -d $MW_HOME 5 - Go to that directory and run configure.sh cd $MW_HOME ./configure.sh 6 - Call the setEnvs.sh script . $MW_HOME/wlserver/server/bin/setWLSEnv.sh7 - Create your development domain. It will ask you for username and password. I like to use weblogic / welcome1cd $MW_HOME/mydomain $JAVA_HOME/bin/java $JAVA_OPTIONS -Xmx1024m \ -Dweblogic.management.allowPasswordEcho=true weblogic.Server8 - Start WebLogic and access its web console(sh startWebLogic.sh &); sleep 10; firefox http://localhost:7001/consoleUsually, it takes only 10 seconds to start a domain, and 5 more to deploy the Administration Console (on my laptop). :-)Enjoy!

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• Is it bad practice for a module to contain more information than it needs?

  - by gekod

  I just wanted to ask for your opinion on a situation that occurs sometimes and which I don't know what would be the most elegant way to solve it. Here it goes: We have module A which reads an entry from a database and sends a request to module B containing ONLY the information from the entry module B would need to accomplish it's job (to keep modularity I just give it the information it needs - module B has nothing to do with the rest of the information from the read DB entry). Now after finishing it's job, module B has to reply to a module C if it succeeded or failed. To do this module B replies with the information it has gotten from module A and some variable meaning success or fail. Now here comes the problem: module C needs to find that entry again BUT the information it has gotten from module B is not enough to uniquely find the exact same entry again. I don't think that module A giving more information to module B which it doesn't need to do it's job but which it could then give back to module C would be a good practice because this would mean giving some module information it doesn't really need. What do you think?

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• How do I fix broken installation?

  - by Daniel

  Let me start off by saying I'm dual booting 11.04 and Windows 7 on a Thinkpad T61p. The problem may have arisen when I hit the power button during normal startup. I'm fully aware how stupid this is. I don't know why I did it. I did it. Now, I can't get in to Ubuntu. Windows works fine. But when I try to start Ubuntu normally, it seems to run some checks, and does not start up. Sometimes, I see a black screen, and it tells me that it's running certain checks, and then, [ok]. Like... Battery Check Somethingorother [ok] It'll give me 1-5 of these. And then it just does nothing, and I have to turn it off. When I try to start in safe mode... I tried low graphics mode, and after going through a couple of dialogue boxes, I'm brought right back to the safe mode dialogue box. And if I hit 'resume,' a shell pushes up (still that grey on black "your computer is broken" type shell) and asks me to log in. I do, and try to run unity. It tells me something along the lines of: WARNING no DISPLAY variable set and then sets it to " :0" , which doesn't work. And then I can't do anything, really, and I have to restart. (I don't know how to do this from the command line, so I just hard reset. That command would be helpful). Does anybody have any idea how I can get Ubuntu working right again? FTP is less pleasant in Explorer than it is in Nautilus or w/e it is now.

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• Input of mouseclick not always registered in XNA Update method

  - by LordrAider

  I have a problem that not all inputs of my mouse events seem to be registered. The update logic is checking a 2 dimensional array of 10x10 . It's logic for a jewel matching game. So when i switch my jewel I can't click on another jewel for like half a second. I tested it with a click counter variable and it doesn't hit the debugger when i click the second time after the jewel switch. Only if I do the second click after waiting half a second longer. Could it be that the update logic is too heavy that while he is executing update logic my click is happening and he doesn't register it? What am I not seeing here :)? Or doing wrong. It is my first game. My function of the update methode looks like this. public void UpdateBoard() { MouseState currentMouseState; currentMouseState = Mouse.GetState(); if (currentMouseState.LeftButton == ButtonState.Pressed && prevMouseState.LeftButton != ButtonState.Pressed) { UpdatingLogic = true; // this.CheckDropJewels(currentMouseState); //this.CheckMatches(3); //this.RemoveMatches(); this.CheckForSwitch(currentMouseState); this.MarkJewel(currentMouseState); UpdatingLogic = false; //reIndexMissingJewels = true; reIndexSwitchedJewels = true; } prevMouseState = currentMouseState; this.ReIndex(); this.UpdateJewels(); }

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• What are some techniques I can use to refactor Object Oriented code into Functional code?

  - by tieTYT

  I've spent about 20-40 hours developing part of a game using JavaScript and HTML5 canvas. When I started I had no idea what I was doing. So it started as a proof of concept and is coming along nicely now, but it has no automated tests. The game is starting to become complex enough that it could benefit from some automated testing, but it seems tough to do because the code depends on mutating global state. I'd like to refactor the whole thing using Underscore.js, a functional programming library for JavaScript. Part of me thinks I should just start from scratch using a Functional Programming style and testing. But, I think refactoring the imperative code into declarative code might be a better learning experience and a safer way to get to my current state of functionality. Problem is, I know what I want my code to look like in the end, but I don't know how to turn my current code into it. I'm hoping some people here could give me some tips a la the Refactoring book and Working Effectively With Legacy Code. For example, as a first step I'm thinking about "banning" global state. Take every function that uses a global variable and pass it in as a parameter instead. Next step may be to "ban" mutation, and to always return a new object. Any advice would be appreciated. I've never taken OO code and refactored it into Functional code before.

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• Matrices: Arrays or separate member variables?

  - by bjz

  I'm teaching myself 3D maths and in the process building my own rudimentary engine (of sorts). I was wondering what would be the best way to structure my matrix class. There are a few options: Separate member variables: struct Mat4 { float m11, m12, m13, m14, m21, m22, m23, m24, m31, m32, m33, m34, m41, m42, m43, m44; // methods } A multi-dimensional array: struct Mat4 { float[4][4] m; // methods } An array of vectors struct Mat4 { Vec4[4] m; // methods } I'm guessing there would be positives and negatives to each. From 3D Math Primer for Graphics and Game Development, 2nd Edition p.155: Matrices use 1-based indices, so the first row and column are numbered 1. For example, a12 (read “a one two,” not “a twelve”) is the element in the first row, second column. Notice that this is different from programming languages such as C++ and Java, which use 0-based array indices. A matrix does not have a column 0 or row 0. This difference in indexing can cause some confusion if matrices are stored using an actual array data type. For this reason, it’s common for classes that store small, fixed size matrices of the type used for geometric purposes to give each element its own named member variable, such as float a11, instead of using the language’s native array support with something like float elem[3][3]. So that's one vote for method one. Is this really the accepted way to do things? It seems rather unwieldy if the only benefit would be sticking with the conventional math notation.

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• Totem crashes immediately after startup in 12.10

  - by Sakib Hasan

  I did a fresh install of Ubuntu 12.10 and did sudo apt-get update && sudo apt-get update. Then I installed ubuntu-restricted-extras, audacious and vlc from Software Center. After that I tried launch Totem Movie player but in terminal following error comes up: (totem:9295): Gdk-ERROR **: The program 'totem' received an X Window System error. This probably reflects a bug in the program. The error was 'BadDrawable (invalid Pixmap or Window parameter)'. (Details: serial 1808 error_code 9 request_code 152 minor_code 9) (Note to programmers: normally, X errors are reported asynchronously; that is, you will receive the error a while after causing it. To debug your program, run it with the GDK_SYNCHRONIZE environment variable to change this behavior. You can then get a meaningful backtrace from your debugger if you break on the gdk_x_error() function.) Trace/breakpoint trap (core dumped) I tried purge and again install. But the error remains. What should I do?

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• Where to find common database abbreviations in Spanish

  - by jmh_gr

  I'm doing a little pro bono work for an organization in Central America. I'm ok at Spanish and my contacts are perfectly fluent but are not techincal people. Even if they don't care what I call some fields in a database I still want to make as clean a schema as possible, and I'd like to know what some typical abbreviations are for field / variable names in Spanish. I understand abbreviations and naming conventions are entirely personal. I'm not asking for the "correct" or "best" way to abbreviate database object names. I'm just looking for references to lists of typical abbreviations that would be easily recognizable to a techincally competent native Spanish speaker. I believe I am a decent googler but I've had no luck on this one. For example, in my company (where English is the primary language) 'Date' is always shortened to 'DT', 'Code' to 'CD', 'Item' to 'IT', etc. It's easy for the crowds of IT temp workers who revolve through on various projects to figure out that 'DT' stands for 'Date', 'YR' for 'Year', or 'TN' for 'Transaction' without even having to consult the official abbreviations list.

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• Designing communications for extensibility

  - by Thomas S.

  I am working on the design stages of an application that will a) collect data from various sources (in my case that's scientific data from serial ports), keeping track of the age of the data, b) generate real-time statistics (e.g. running averages) c) display, record, and otherwise handle the data (and statistics). I anticipate that I will be adding both data producers and consumers over time, and would like to design this application abstractly so that I will be able to trivially add functionality with a small amount of interface code. What I'm stumbling on is deciding what communication infrastructure I should use to handle the interfaces. In particular, how should I make the processed data and statistics available to multiple consumers? Some things I've considered: Writing to several named pipes (variable number). Each consumer reads from one of them. Using FUSE to make a userspace filesystem where a read() returns the latest line of data even if another process has already read it. Making a TCP server, and having consumers connect and request data individually. Simply writing the consumers as part of the same program that aggregates the data. So I would like to hear your all's advice on deciding how to interface these functions in the best way to keep them separate and allow room for extenstions.

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• Boundary conditions for testing

  - by Loggie

  Ok so in a programming test I was given the following question. Question 1 (1 mark) Spot the potential bug in this section of code: void Class::Update( float dt ) { totalTime += dt; if( totalTime == 3.0f ) { // Do state change m_State++; } } The multiple choice answers for this question were. a) It has a constant floating point number where it should have a named constant variable b) It may not change state with only an equality test c) You don't know what state you are changing to d) The class is named poorly I wrongly answered this with answer C. I eventually received feedback on the answers and the feedback for this question was Correct answer is a. This is about understanding correct boundary conditions for tests. The other answers are arguably valid points, but do not indicate a potential bug in the code. My question here is, what does this have to do with boundary conditions? My understanding of boundary conditions is checking that a value is within a certain range, which isn't the case here. Upon looking over the question, in my opinion, B should be the correct answer when considering the accuracy issues of using floating point values.

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• What’s ‘default’ for?

  - by Strenium

  Sometimes there's a need to communicate explicitly that value variable is yet to be "initialized" or in other words - we’ve never changed it from its' default value. Perhaps "initialized" is not the right word since a value type will always have some sort of value (even a nullable one) but it's just that - how do we tell? Of course an 'int' would be 0, an 'enum' would the first defined value of a given enum and so on – we sure can make this kind of check "by hand" but eventually it would get a bit messy. There's a more elegant way with a use of little-known functionality of: 'default'Let’s just say we have a simple Enum: Simple Enum namespace xxx.Common.Domain{    public enum SimpleEnum    {        White = 1,         Black = 2,         Red = 3    }}   In case below we set the value of the enum to ‘White’ which happens to be a first and therefore default value for the enum. So the snippet below will set value of the ‘isDefault’ Boolean to ‘true’. 'True' Case SimpleEnum simpleEnum = SimpleEnum.White;bool isDefault; /* btw this one is 'false' by default */ isDefault = simpleEnum == default(SimpleEnum) ? true : false; /* default value 'white' */   Here we set the value to ‘Red’ and ‘default’ will tell us whether or not this the default value for this enum type. In this case: ‘false’. 'False' Case simpleEnum = SimpleEnum.Red; /* change from default */isDefault = simpleEnum == default(SimpleEnum) ? true : false; /* value is not default any longer */ Same 'default' functionality can also be applied to DateTimes, value types and other custom types as well. Sweet ‘n Short. Happy Coding!

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• Installing Django on Windows

  - by Pranav

  Ever needed to install Django in a Microsoft Windows environment, here is a quick start guide to make that happen: Read through the official Django installation documentation, it might just save you a world of hut down the road. Download Python for your version of Windows. Install Python, my preference here is to put it into the Program Files folder under a folder named Python<Version> Add your chosen Python installation path into your Windows path environment variable. This is an optional step, however it allows you to just type python in the command line and have it fire up the Python interpreter. An easy way of adding it is going into Control Panel, System and into the Environment Variables section. Download Django, you can either download a compressed file or if you’re comfortable with using version control – check it out from the Django Subversion repository. Create a folder named django under your <Python installation directory>\Lib\site-packages\ folder. Using my example above that would have been C:\Program Files\Python25\Lib\site-packages\. If you chose to download the compressed file, open it and extract the contents of the django folder into your newly created folder. If you’d prefer to check it out from Subversion, the normal check out points are http://code.djangoproject.com/svn/django/trunk/ for the latest development copy or a named release which you’ll find under http://code.djangoproject.com/svn/django/tags/releases/. Done, you now have a working Django installation on Windows. At this point, it’d be pertinent to confirm that everything is working properly, which you can do by following the first Django tutorial. The tutorial will make mention of django-admin.py, which is a utility which offers some basic functionality to get you off the ground. The file is located in the bin folder under your Django installation directory. When you need to use it, you can either type in the full path to it or simply add that file path into your environment variables as well. Hope this helps!

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• Trying to make a game with C++, using lists to store bullets and enemies, but they are not erased

  - by XD_dued

  I've been trying to make a pretty simple space shooter game with C++, and I have been having a lot of trouble trying to use lists to store enemies and bullets. Basically I followed the post here almost exactly to store my bullets: SDL Bullet Movement I've done something similar to store my enemies. However, when I call bullets.erase(it++), for some reason the bullet is not erased. When the bullet movement is run for the next frame, it tries to re delete the bullet and segfaults the program. When I comment out the erase line, it runs fine, but the bullets are then never erased from the list... Is there any reason why the elements of the list aren't being deleted? I also set it up to print the number of elements in the list for every iteration, and it does not go down after deleting. Thanks! EDIT: Here's the specific code I'm using to store my enemies and having them act: std::list<Grunt*> doGrunts(std::list<Grunt*> grunts) { for(std::list<Grunt*>::iterator it = grunts.begin(); it != grunts.end();) { if((*it)->getHull() == 0) { delete * it; grunts.erase(it++); } else { (**it).doUnit(grunts, it); ++it; } } } Grunt is my enemy class, and the list grunts is a global variable. Is that my problem? When I pass the global into the function it becomes local? I assumed lists would be a reference type so thought this wouldn't be a problem. Sorry if this was a dumb question, I'm very new to C++, this is the first major thing I'm working on.

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• Finite Numbers and ExplorerCanvas

  - by PhubarBaz

  I was working on my online mathematical graphing application, CloudGraph, and trying to make it work in IE. The app uses the HTML5 canvas element to draw graphs. Since IE doesn't support canvas yet I use ExplorerCanvas to provide that support for IE. However, it seems that when using excanvas, if you try to moveTo or drawTo a point that is not finite it loses it's mind and stops drawing anything else after that. I had no such problems in Firefox or Chrome so it took me awhile to figure out what was going on. Next I discovered that I needed a way to check if a variable was NaN or Inifinity or any other non-finite value so I could avoid calling moveTo() in that case. I started writing a long if statement, then I thought there has to be a better way. Sure enough there was. There just happens to be an isFinite() function built into Javascript just for this purpose. Who knew! It works great. Another difference I discovered with excanvas is that you must specify a starting point using a moveTo() when beginning a drawing path. Again, Chrome and Firefox are a lot more forgiving in this area so it took me a while to figure out why my lines weren't drawing. But, all is happy now and I'm a little wiser to the ways of the canvas.

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