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Articles indexed in March 2012

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• What is the difference between all-static-methods and applying a singleton pattern?

  - by shahensha

  I am making a database to store information about the users of my website (I am using stuts2 and hence Java EE technology). For the database I'll be making a DBManager. Should I apply singleton pattern here or rather make all it's methods static? I will be using this DBManager for basic things like adding, deleting and updating User profiles. Along with it, I'll use for all other querying purposes, for instance to find out whether a username already exists and to get all users for administrative purposes and stuff like that. My questions What is the benefit of singleton pattern? Which thing is most apt here? All static methods or a singleton pattern? Please compare both of them. P.S. The database is bigger than this. Here I am talking only about the tables which I'll be using for storing User Information.

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• What is meant by Scope of a variable?

  - by Appy

  I think of the scope of a variable as - "The scope of a particular variable is the range within a program's source code in which that variable is recognized by the compiler". That statement is from "Scope and Lifetime of Variables in C++", which I read many months ago. Recently I came across this in LeMoyne-Owen College courses: What exactly is the difference between the scope of variables in C# and (C99, C++, Java) when However a variable still must be declared before it can be used

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• What is the the best way to become an iPhone developer?

  - by Noah89

  I have no experience as a programmer but I'd like to become a iPhone developer. Some people tell me to learn java because it is a Object Oriented Language. Other people tell me to go with C++. However, everyone advises me to actually learn any language and learn what programming is all about before I actually develop for iPhone. Please, let me know what would be the best choice and what books would be good for a total beginner and any website that offers any good tutorials.

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• Why choose an established CMS as opposed to building one from scratch?

  - by SkonJeet

  A lot of my research over the next few weeks will be into different CMS's. I've already had a brief look at episerver and umbraco. While reading into these systems I can't help but think that providing content management features are achievable without learning the details and structure of many of these (rather large) CMS platforms. I have, in the past, been given projects whereby my role as a developer must be kept separate to that of an editor (makes sense). i.e. It was my task to develop the design and functionality of the site and my clients' job to update the content. I've achieved this by also implementing a sort of 'portal' on which there were a couple of pages that would accept text input and picture uploads etc. (basically, whatever content they wanted), record this new content to the database and then by design the code-behind would read all this from the database into relevant controls (repeaters for example). For me, this has been an effective enough way of my clients managing the content to deploy with my solutions. I know that I am wrong - and that CMS's are preferable to those that are built from the ground up - but other than the matter of cost, why?

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• What are the differences between Bigloo and ECL?

  - by Pubby

  I've been looking to embed Lisp in some C++ code. Two options I'm interested in is Bigloo Scheme and ECL. Reading through the docs they seem to support a very similar feature set. Obviously Bigloo is Scheme and ECL is CLisp, but what other differences do they have? In particular I'm interested in the following criteria: Ease of embedding (for C++, not just C) Performance Style of coding Size Tail call support I'm targeting this question towards someone who has used both.

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• Static class vs Singleton class in C# [closed]

  - by Floradu88

  Possible Duplicate: What is the difference between all-static-methods and applying a singleton pattern? I need to make a decision for a project I'm working of whether to use static or singleton. After reading an article like this I am inclined to use singleton. What is better to use static class or singleton? Edit 1 : Client Server Desktop Application. Please provide code oriented solutions.

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• Is there a language offering LISP-like macros with a more complex syntax?

  - by blubb

  LISP's macros are extremely powerful constructs, and the inability to introspect and modify the program itself beyond the method signature level has always struck me as a limitation. Yet I favour "complex" syntax because it tends to be closer to natural language. So far I have failed to find a language which combines a powerful macro mechanism such as LISP's with a naturally looking syntax (1). Is anyone aware of such a language? Footnote: I would consider python to have a naturally looking syntax as it allows constructs like this: if 0 < a < 5 and b in list. The avoidance of braces to structure blocks is irrelevant in this case, though.

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• Is it common in companies that non-techs are doing analyzes

  - by Kubi

  It's been 2 months since I started working at an international big consulting company. I like my colleagues personally but it's like a joke since my first day. Analysts (people who has no idea about the tech. background) are planning the workflow and functions. In my case, none of my friends here even wrote even a single line of html. When I say Html, I doubt if they know what I mean. But they are deciding about really key decisions in a web system implementation project. Is this always like this?

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• How to improve testing your own code

  - by Peter

  Today I checked in a change on some code which turned out to be not working at all due to something rather stupid yet very crucial. I feel really bad about it and I hope I finally learn something from it. The stupid thing is, I've done these things before and I always tell myself, next time I won't be so stupid... Then it happens again and I feel even worse about it. I know you should keep your chin up and learn from your mistakes but here's the thing: I try to improve myself, I just don't see how I can prevent these things from happening. So, now I'm asking you guys: Do you have certain groundrules when testing your code?

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• Modular Architecture for Processing Pipeline

  - by anjruu

  I am trying to design the architecture of a system that I will be implementing in C++, and I was wondering if people could think of a good approach, or critique the approach that I have designed so far. First of all, the general problem is an image processing pipeline. It contains several stages, and the goal is to design a highly modular solution, so that any of the stages can be easily swapped out and replaced with a piece of custom code (so that the user can have a speed increase if s/he knows that a certain stage is constrained in a certain way in his or her problem). The current thinking is something like this: struct output; /*Contains the output values from the pipeline.*/ class input_routines{ public: virtual foo stage1(...){...} virtual bar stage2(...){...} virtual qux stage3(...){...} ... } output pipeline(input_routines stages); This would allow people to subclass input_routines and override whichever stage they wanted. That said, I've worked in systems like this before, and I find the subclassing and the default stuff tends to get messy, and can be difficult to use, so I'm not giddy about writing one myself. I was also thinking about a more STLish approach, where the different stages (there are 6 or 7) would be defaulted template parameters. Can anyone offer a critique of the pattern above, thoughts on the template approach, or any other architecture that comes to mind?

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• What syntax element do you hate most in a programming language you use frequently? [closed]

  - by Timwi

  No matter how much you love a programming language, there are always a few details in it that aren’t quite as nice as they could be. In this question, I would like to specifically focus on syntax elements. In a programming language that you use frequently (perhaps your favourite programming language, or perhaps the one you are forced to use at work), which syntax element do you find most unreadable, unclear, inconvenient or unpleasant?

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• RTOS experience

  - by Subbu

  I have been working as an embedded software engineer on mostly 8 bit micro-controller firmware and desktop/mobile applications development for the past five years. My work on a WinCE project (in which I got introduced to .NET CF) was short lived. I did use core APIs for interrupt processing, peripheral communication, etc...but again, not exactly a pure RTOS environment. In order to get together more solid experience for growing more in the embedded field, I want to work more with RTOSes. Will buying an evaluation board with an RTOS and putting together a project at home be regarded as a good experience or will an online course be more useful? I am just not clear as to what will be regarded as good experience. Any suggestions or directions will greatly help me. I have a passion for the field but just a need a point in the right direction.

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• How to store prices that have effective dates?

  - by lal00

  I have a list of products. Each of them is offered by N providers. Each providers quotes us a price for a specific date. That price is effective until that provider decides to set a new price. In that case, the provider will give the new price with a new date. The MySQL table header currently looks like: provider_id, product_id, price, date_price_effective Every other day, we compile a list of products/prices that are effective for the current day. For each product, the list contains a sorted list of the providers that have that particular product. In that way, we can order certain products from whoever happens to offer the best price. To get the effective prices, I have a SQL statement that returns all rows that have date_price_effective >= NOW(). That result set is processed with a ruby script that does the sorting and filtering necessary to obtain a file that looks like this: product_id_1,provider_1,provider_3,provider8,provider_10... product_id_2,provider_3,provider_2,provider1,provider_10... This works fine for our purposes, but I still have an itch that a SQL table is probably not the best way to store this kind of information. I have that feeling that this kind of problema has been solved previously in other more creative ways. Is there a better way to store this information other than in SQL? or, if using SQL, is there a better approach than the one I'm using?

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• changed /etc permission in oneiric (ubuntu11.10) by using "sudo chmod 665 /etc" cant use sudo now

  - by GuruDevil

  i screwed up big time. i changed the permission of /etc in ubuntu 11.10 by using following command sudo chmod 665 /etc now when ever i try to use sudo it gives the following error: sudo: can't open /etc/sudoers: Permission denied sudo: no valid sudoers sources found, quitting any help will be greatly appreciated because i am new to ubuntu....i have already tried using su but it doesnt even login as root and even i give it the right password it always say Authentication Failure......i dont want to login as root coz its risky and even a newbie in linux like me is not stupid enough to have such control...i just want to use my sudo again......i have tried to go into recovery mode as well but i cant get in to recovery mode......HELP please!!!

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• ERROR with Ubuntu: Cannot open the disk 'D:\My Documents\My Virtual Machines\Ubuntu\Ubuntu-1.vmdk' or one of the snapshot disks it depends on

  - by leiyu

  Cannot open the disk 'D:\My Documents\My Virtual Machines\Ubuntu\Ubuntu-1.vmdk' or one of the snapshot disks it depends on. Reason: The physical disk is already in use. ====================== When I powered on my Ubuntu on VMwave, a window showed up within words above. I tried to remove the old hard disk in settings and created a new one, but it still doesnot work. Also, I tried to delete the .lck files and even the doc. BUT....... Has someone solved this problem? PLEASE do me a favour!!Many thanks!!

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• How can I find installed web applications?

  - by Jo-Erlend Schinstad

  I've installed LAMP Server using tasksel. I've installed phpMyAdmin, which I know from experience gets in /phpmyadmin. That works. Then I installed drupal6. I assumed that it would get in /drupal, but that's not the case. How can I find that kind of information? Of course, in this case, I'm looking for my Drupal install, but I would like to avoid having to spend so much time every time I install a web application, so I'm looking for a generic way.

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• How can i fix some broken packages PyQt packages?

  - by Jorge

  I'm trying to install PyQt but i've met some difficulties (i.e packages that won't be updated and stuff like that). I'm not very proficient with Ubuntu, so some help is needed. Here's the output i get from the terminal: sudo apt-get install python-qt4 Reading package lists... Done Building dependency tree Reading state information... Done Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation: The following packages have unmet dependencies: python-qt4 : Depends: libqt4-declarative (>= 4:4.7.0~rc1) but it is not going to be installed Depends: libqt4-designer (>= 4:4.7.0) but it is not going to be installed Depends: libqt4-help (>= 4:4.7.0) but it is not going to be installed Depends: libqt4-script (>= 4:4.7.0) but it is not going to be installed Depends: libqt4-scripttools (>= 4:4.7.0) but it is not going to be installed Depends: libqt4-svg (>= 4:4.7.0) but it is not going to be installed Depends: libqt4-test (>= 4:4.7.0) but it is not going to be installed Depends: libqt4-xmlpatterns (>= 4:4.7.0) but it is not going to be installed E: Broken packages

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• One of my user accounts logs in without desktop environment

  - by Bill Cheatham

  When I log in to my main user account on Ubuntu 11.10 ,the desktop environment (unity bar, clock, volume control, etc.) is not there. All I have is the desktop background with a menu bar across the top which appears to be for nautilus (options like File-New folder). My other accounts log in like normal. I have recently followed these instructions to give my main user account access to an OSX partition, but I think I have logged in successfully since then. I am able to get a terminal by pressing ctrl+alt+t, but when I typed unity the whole thing crashed. Is there anything I can do to fix this? I have a separate administrator account I can use if needed.

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• HP Pavilion G6 1209 temperature higher than usual and fan working in 11.10

  - by vanjadjurdjevic

  Installing Ubuntu on this new machine i had various problems, so I asked around ask ubuntu for a solution. This is the latest one! :D When I start the pc it shows the temperature around 50-55. When I open chromium it shows 60+ (61,62,63). It even gets to 67-68 when multi-tasking 2 apps. The fan is working slightly louder than in windows 7. Talking about windows 7, the temperature is 45-50 when idle, 50-53 when working in browser. Im already loosing it with this machine. You can find specs here It says 'technishe daten' below the picture. Click that tab and you will reach the specs.

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• Installing 10.10+ with Radeon HD 6970 Video Card

  - by Ben Lacy

  I built a new PC that has a Diamond Radeon HD 6970 graphics card, and no on-board graphics. When I boot from the Ubuntu disc, it runs through some initial booting stuff, and then gets to a loading screen that just has the Ubuntu logo and some progress bar/dot thingies. After this screen is finished, it goes black and says it cannot display video mode. I've seen many people that say to simply install the ati drivers. However, I don't believe this is an option, because I can't even get to the boot screen that asks me if I want to run the system off of the LiveCD, boot to hard disk, etc... Is there a way to somehow boot to a CLI before getting to the screen that would normally let me choose that? I'm at a loss as far as what to do. Also: Yes, the CD boots fine on other machines. (I've also burnt a couple discs just to be sure) Yes, the graphics card is fine. I normally dual-boot with Windows 7, and it runs on Windows just fine. Thanks for any help!

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• Why does my cursor jump when typing in ubuntu 11.10

  - by Stephen Myall

  When typing in Ubuntu my cursor jumps around and its not application specific. It doesn't matter or Im filing in a web form, writing an e-mail or using LibreOffice or Lyx. Im using a Sony Vaio 64bit machine. i read a previous question (link below) on this subject which indicates it may have something to do with the touchpad settings. as this has occurred in previous Ubuntu distros Im guess it is somekind of hardware issue. How do you turn of the touchpad when typing to avoid the cursor jumping around? I'd be grateful if anyone can make this stop Stephen

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• UBS drive on Ubuntu on VM Virtualbox

  - by Raama

  OSX is my host OS I have windows xp and Ubuntu 10.10 on guest OS. They both work great. When I eject USB flash drive from host OS, it appears in windows guest OS but it does not appear in Ubuntu Guest OS. I never run both guest OS at the same time. its always either or. I am running, VM virtualbox 4.1.10 and installed latest guest additions and also installed VM virtualbox extension pack. Thanks for your help

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• Can't start ubuntu 11.10, Stops at login screen!

  - by Martinpizza

  I have been trying to dual boot ubuntu with windows 7 via WUBI on my custom built pc but without success. When i start the computer i can choose windows or ubuntu i choose ubuntu and when i should get to the login screen the screen just stays purple/pink. Tried safe mode but cant get in there either. I have tried reinstall but did not work either. :( The second time i install ubuntu the screen was purple/pink and the screen was cut of so the left side was on the right side and right side on left side (hard to describe) Third time installing (The last time) it is just like the first time please help!!!! cant get nowhere without help i am kinda new at ubuntu and its creepy commands. Had ubuntu on my old computer. I think the problem is my hardware so here is my computer specs: Amd Fx 6100 Amd HIS Radeon HD 6950 ICEQ X Asus Sabertooth 990fx 1TB Harddrive I have no idea the name on it Please Help me!! Sorry for my bad English! :D

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• How to resize / enlarge / grow a non-LVM ext4 partition

  - by Mischa

  I have already searched the forums, but couldnt find a good suitable answer: I have an Ubuntu Server 10.04 as KVM Host and a guest system, that also runs 10.04. The host system uses LVM and there are three logical volumes, which are provided to the guest as virtual block devices - one for /, one for /home and one for swap. The guest had been partitioned without LVM. I have already enlarged the logical volume in the host system - the guest successfully sees the bigger virtual disk. However, this virtual disk contains one "good old" partition, which still has the old small size. The output of fdisk -l is me@produktion:/$ LC_ALL=en_US sudo fdisk -l Disk /dev/vda: 32.2 GB, 32212254720 bytes 255 heads, 63 sectors/track, 3916 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x000c8ce7 Device Boot Start End Blocks Id System /dev/vda1 * 1 3917 31455232 83 Linux Disk /dev/vdb: 2147 MB, 2147483648 bytes 244 heads, 47 sectors/track, 365 cylinders Units = cylinders of 11468 * 512 = 5871616 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x000f2bf7 Device Boot Start End Blocks Id System /dev/vdb1 1 366 2095104 82 Linux swap / Solaris Partition 1 has different physical/logical beginnings (non-Linux?): phys=(0, 32, 33) logical=(0, 43, 28) Partition 1 has different physical/logical endings: phys=(260, 243, 47) logical=(365, 136, 44) Disk /dev/vdc: 225.5 GB, 225485783040 bytes 255 heads, 63 sectors/track, 27413 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00027f25 Device Boot Start End Blocks Id System /dev/vdc1 1 9138 73398272 83 Linux The output of parted print all is Model: Virtio Block Device (virtblk) Disk /dev/vda: 32.2GB Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 1049kB 32.2GB 32.2GB primary ext4 boot Model: Virtio Block Device (virtblk) Disk /dev/vdb: 2147MB Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 1049kB 2146MB 2145MB primary linux-swap(v1) Model: Virtio Block Device (virtblk) Disk /dev/vdc: 225GB Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 1049kB 75.2GB 75.2GB primary ext4 What I want to achieve is to simply grow or resize the partition /dev/vdc1 so that it uses the whole space provided by the virtual block device /dev/vdc. The problem is, that when I try to do that with parted, it complains: (parted) select /dev/vdc Using /dev/vdc (parted) print Model: Virtio Block Device (virtblk) Disk /dev/vdc: 225GB Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 1049kB 75.2GB 75.2GB primary ext4 (parted) resize 1 WARNING: you are attempting to use parted to operate on (resize) a file system. parted's file system manipulation code is not as robust as what you'll find in dedicated, file-system-specific packages like e2fsprogs. We recommend you use parted only to manipulate partition tables, whenever possible. Support for performing most operations on most types of file systems will be removed in an upcoming release. Start? [1049kB]? End? [75.2GB]? 224GB Error: File system has an incompatible feature enabled. Compatible features are has_journal, dir_index, filetype, sparse_super and large_file. Use tune2fs or debugfs to remove features. So what can I do? This is a headless production system. What is a safe way to grow this partition? I CAN unmount it, though - so this is not the problem.

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• How to connect to a serverside process on Ubuntu running in a VM?

  - by Jenko

  I am running Ubuntu 11.10 in VirtualBox, on Windows 7. I'm trying to setup a serverside process like Apache on it. How do I configure VirtualBox to allow access to the Ubuntu server process from other computers on the network? I can access the internet from Ubuntu. The Windows 7 computer is on a WiFi network using DHCP. The WiFi network has a dynamic IP with the network provider. This is my current configuration:

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