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• Tar dereference only 1 level

  - by Bart van Heukelom

  I use the following pseudo-script to create a TAR of my installed software mkdir tmp ln -s /path/to/app1/bin tmp/app1 ln -s /and/path/going/to/the-app-2 tmp/app2 tar -c --dereference -f apps.tar tmp I need the --dereference option here to follow the links I just made in tmp. The reason I make the links in the first place is to store the directories with a different name in the archive than they have on the filesystem. Until now it has worked fine. However, I now have the situation that /path/to/app1 also contains links, and those I don't want to follow. Is this possible with some changes to the tar command? Or do I need to completely switch around the way I build the archive?

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• OpenVPN Configuration - Windows 7 client & debian server

  - by Guillaume

  I recently formatted my Windows 7 computer and lost my client's config files for OpenVPN. I recovered the certificates and default config that were left on the server but I haven't managed to make the whole thing work again. I assume the server's config and routing table are OK because it was working before (although quite some time ago). Would any of you experts be able to help? server.conf # Serveur TCP/666 mode server proto udp port 666 dev tun # Cles et certificats ca ca.crt cert server.crt key server.key dh dh1024.pem tls-auth ta.key 0 cipher AES-256-CBC # Reseau server 10.8.0.0 255.255.255.0 #push "redirect-gateway def1 bypass-dhcp" push "dhcp-option DNS 208.67.222.222" push "dhcp-option DNS 208.67.220.220" push "redirect-gateway def1" keepalive 10 120 # Securite user nobody group nogroup chroot /etc/openvpn/jail persist-key persist-tun comp-lzo # Log verb 3 mute 20 status openvpn-status.log log-append /var/log/openvpn.log client.conf # Client client dev tun proto udp remote *my server's ip address*:666 cipher AES-256-CBC # Cles ca ca.crt cert client1.crt key client1.key tls-auth ta.key 1 # Securite nobind persist-key persist-tun comp-lzo verb 3 Routing table on debian server when OpenVPN server is running: Destination Gateway Genmask Indic Metric Ref Use Iface 10.8.0.2 * 255.255.255.255 UH 0 0 0 tun0 10.8.0.0 10.8.0.2 255.255.255.0 UG 0 0 0 tun0 my server's ip * 255.255.255.0 U 0 0 0 eth0 default 72815.trg.dedic 0.0.0.0 UG 0 0 0 eth0 Routing table on Windows 7 client (OpenVPN not working) =========================================================================== Interface List 19...00 f0 8a 1b 6e 5c ......TAP-Win32 Adapter V9 12...90 2e 34 33 84 7b ......Atheros AR8151 PCI-E Gigabit Ethernet Controller ( NDIS 6.20) 1...........................Software Loopback Interface 1 12...00 00 00 00 00 00 00 e0 Microsoft ISATAP Adapter 13...00 00 00 00 00 00 00 e0 Teredo Tunneling Pseudo-Interface 16...00 00 00 00 00 00 00 e0 Microsoft ISATAP Adapter #2 =========================================================================== IPv4 Route Table =========================================================================== Active Routes: Network Destination Netmask Gateway Interface Metric 0.0.0.0 0.0.0.0 192.168.1.1 192.168.1.11 20 127.0.0.0 255.0.0.0 On-link 127.0.0.1 306 127.0.0.1 255.255.255.255 On-link 127.0.0.1 306 127.255.255.255 255.255.255.255 On-link 127.0.0.1 306 192.168.1.0 255.255.255.0 On-link 192.168.1.11 276 192.168.1.11 255.255.255.255 On-link 192.168.1.11 276 192.168.1.255 255.255.255.255 On-link 192.168.1.11 276 224.0.0.0 240.0.0.0 On-link 127.0.0.1 306 224.0.0.0 240.0.0.0 On-link 192.168.1.11 276 255.255.255.255 255.255.255.255 On-link 127.0.0.1 306 255.255.255.255 255.255.255.255 On-link 192.168.1.11 276 =========================================================================== Persistent Routes: None IPv6 Route Table =========================================================================== Active Routes: [...] =========================================================================== Persistent Routes: None And when the link is established between my client and the server: The server's routing table stays the same. The client's becomes: =========================================================================== Interface List 19...00 f0 8a 1b 6e 5c ......TAP-Win32 Adapter V9 12...90 2e 34 33 84 7b ......Atheros AR8151 PCI-E Gigabit Ethernet Controller ( NDIS 6.20) 1...........................Software Loopback Interface 1 12...00 00 00 00 00 00 00 e0 Microsoft ISATAP Adapter 13...00 00 00 00 00 00 00 e0 Teredo Tunneling Pseudo-Interface 16...00 00 00 00 00 00 00 e0 Microsoft ISATAP Adapter #2 =========================================================================== IPv4 Route Table =========================================================================== Active Routes: Network Destination Netmask Gateway Interface Metric 0.0.0.0 0.0.0.0 192.168.1.1 192.168.1.11 20 0.0.0.0 128.0.0.0 10.8.0.5 10.8.0.6 30 10.8.0.1 255.255.255.255 10.8.0.5 10.8.0.6 30 10.8.0.4 255.255.255.252 On-link 10.8.0.6 286 10.8.0.6 255.255.255.255 On-link 10.8.0.6 286 10.8.0.7 255.255.255.255 On-link 10.8.0.6 286 my server's ip 255.255.255.255 192.168.1.1 192.168.1.11 20 127.0.0.0 255.0.0.0 On-link 127.0.0.1 306 127.0.0.1 255.255.255.255 On-link 127.0.0.1 306 127.255.255.255 255.255.255.255 On-link 127.0.0.1 306 128.0.0.0 128.0.0.0 10.8.0.5 10.8.0.6 30 192.168.1.0 255.255.255.0 On-link 192.168.1.11 276 192.168.1.11 255.255.255.255 On-link 192.168.1.11 276 192.168.1.255 255.255.255.255 On-link 192.168.1.11 276 224.0.0.0 240.0.0.0 On-link 127.0.0.1 306 224.0.0.0 240.0.0.0 On-link 192.168.1.11 276 224.0.0.0 240.0.0.0 On-link 10.8.0.6 286 255.255.255.255 255.255.255.255 On-link 127.0.0.1 306 255.255.255.255 255.255.255.255 On-link 192.168.1.11 276 255.255.255.255 255.255.255.255 On-link 10.8.0.6 286 =========================================================================== Persistent Routes: None What's working: Server and client do connect to each other, SSL certificates are OK. The client gets an IP (10.8.0.6) from the server OpenVPN client is started as an administrator. But: I cannot ping the other one on either side. 'Gateway' value is empty on client's side (in the adapter's "status" window). Client has got no internet access when the link is up. Ideal configuration: I only want the client to be able to use the server's Internet access and access its resources (MySQL server in particular). I do not need or want the server to access the client's local network. The client needs to be able to access it's local network, although all Internet traffic should be redirected to the VPN link. I spent a considerable amount of time on this but it's still not working, any help would be much appreciated. Thanks :)

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• Choose IP Adress for Process to use on launch [duplicate]

  - by user1436026

  This question already has an answer here: How to set which IP to use for a HTTP request? 2 answers Say my server has the following IP addresses: 123.456.78.0 123.467.79.1 123.456.77.1 123.456.68.0 etc... Say I want to launch a process, say wget from the command line. Normally, I would do something like this: wget http://www.google.com/ Except that I would like to choose the IP address that my server uses to make this request. Is there a way to use wget or launch another command with a choice of one of my own IP addresses, like the following pseudo command: with-ip 123.456.68.0 wget http://www.google.com/

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• Can't access Terminal anymore, only shows a cursor

  - by user138304

  I run OS X. Following these directions (Installing MySQL on Mac OS X) I added a file to /usr and the contents were PATH=/usr/local/mysql/bin:$PATH Actually I was trying to get the mysql command to work now I cannot access terminal. All I get is a cursor but no command line. I also cannot find the file I created in the Finder. I used command shift G to find the folder /usr and the file is not there. Edit: I Solved the problem by restarting my computer. I am really not sure what the problem was. I got the idea because Could not open a new pseudo-tty. appeared in my terminal after following slhck directions to remove my .profile file. I then searched google and found this; http://blogs.oreilly.com/digitalmedia/2008/03/fixing-terminal-tty-errors.html. Thanks

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• How can I get windows to release an IPv6 address

  - by Mark Robinson

  I have a windows system with an IPv4 address and an IPv6 address and I'm trying to figure out how to release my IPv6 address. I've tried ipconfig /release6 and I get this error An error occurred while releasing interface Local Area Connection : The system cannot find the file specified. An error occurred while releasing interface Loopback Pseudo-Interface 1 : The system cannot find the file specified. No operation can be performed on isatap.{6B874193-B28A-4446-B6E6-8ADAC22E5090} while it has its media disconnected. No operation can be performed on IP6Tunnel while it has its media disconnected. I still have my IPv6 address at the end. I can release IPv4 address using ipconfig /release

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• Duplicating keepass files instead of creating a new file

  - by BlakBat

  I'm currently using KeePass 2 and syncing them via dropbox. I have a few KeePass files (one for websites, one to store software licenses, etc...) Every time I need a new KeePass file, I just create a copy of the kbdx file, open it, remove all existing entries, change the key transformation rounds to another pseudo-random value. I do not change the master password. I want to know if this was unsafe practice, or was a security risk, compared to just creating a new KeePass file via the "File-New" menu. The reason I don't use the menu: i'm lazy enough to not want to reconfigure "database settings" every time.

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• PuTTY: how to properly emulate -t option

  - by John Sonderson

  On Linux the ssh command has a -t option whose man page reads: Force pseudo-tty allocation. This can be used to execute arbitrary screen-based programs on a remote machine, which can be very useful, e.g. when implementing menu services. Multiple -t options force tty allocate, even if ssh has no local tty. I would like to use this same option with PuTTY on Windows. In particular, I can see that PuTTY has a bunch of options under: Category - Connection - SSH - TTY and suspect it might be possible to achieve the same behavior via some of the (NUMEROUS!) settings found on this screen. Anyone know how to configure the following command: ssh -t USER,[email protected] create Thanks!

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• Software for "High-level" source code (C++) Management

  - by Korchkidu

  after a lot of small-medium projects, I have a lot of libraries and test programs here and there. Also, I must admit that some of the "best practices" I learnt are not that "good" IMHO. In particular, documenting your code and making a "high-level" documentation is not useful in practice: High-level documentation are not maintain up to date = I prefer to read the source code directly; Browsing generated developer documentation is a pain (IMHO) = I prefer to read the source code directly. For that reason, I am looking for a tool who could help me organize all my source code directories in a more "readable manner". What I need is a tool which: Maintains an UML diagram from C++ source code. I don't need source code generation from UML; USE CASE: I am in this super-tool, I notice a design issue, I change the source code, when I get back, the UML diagram is updated; Maintains easily browsable call graphs; Lists references to methods, variables, etc. For example, when I want to see where/when a method is called; Helps writing pseudo-code from C++; Embeds a nice C++ source code browser; Is Open Source would be great; Works at least on Win7. The focus of this tool should be to browse source code to understand what's going on. For example, when you have a newcomer and you need him to go through source code. Do you know any great tool? Thanks in advance. PS: please do not answer doxygen (great tool however).

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• Writing algorithm on 2D data set in plain english

  - by Alexandre P. Levasseur

  I have started an introductory Java class and the material is absolutely horrendous and I have to get excellent grades to be accepted into the master's degree, hence my very beginner question: In my assignment I have to write algorithms (no pseudo-code yet) to solve a board game (Sudoku). Essentially, the notes say that an algorithm is specification of the input(s), the output(s) and the treatments applied to the input to get the output. My question lies on the wording of algorithms because I could probably code it but I can't seem to put it on paper in a coherent way. The game has a 9x9 board and one of the algorithms to write has to find the solution by looking at 3 squares (either horizontal or vertical) and see if one of the three sub-squares match the number you are looking for. If none match then the number you are looking to place is in one of the other 2 set of 3 sub-squares (see image to get a better idea). I really can't get my head around how to formulate the solution into the terms described above or maybe it's just too simple, here's what I was thinking: Input: A 2-dimensional set of data of size 9 by 9 to be solved and a number to search for. Ouput: A 2-dimensional set of data of size 9 by 9 either solved or partially solved. Treatment: Scan each set of 3x9 and 9x3 squares. For each line or column of a 3x3 square check if the number matches a line (or column). If it does then move to the next line (or column). If not then proceed to the next 3x3 square in the same line (or column). Rinse and repeat. Does that make sense as an algorithm written in plain english ? I'm not looking for an answer to the algorithm per se but rather on the formulation of algorithms in plain english.

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• 2.5D game development

  - by ne5tebiu

  2.5D ("two-and-a-half-dimensional"), 3/4 perspective and pseudo-3D are terms used to describe either: graphical projections and techniques which cause a series of images or scenes to fake or appear to be three-dimensional (3D) when in fact they are not, or gameplay in an otherwise three-dimensional video game that is restricted to a two-dimensional plane. (Information taken from Wikipedia.org) I have a question based on 2.5D game development. As stated before, 2.5D uses graphical projections and techniques to make fake 3d or a gameplay restricted to a two-dimensional plane. A good example is a TQ Digital made game: Zero Online (screenshot) the whole map is made of 2d images and only NPCs and players are 3d. The maps were drawn manually by hand without any 3d software rendering. As I'm playing the game I feel like I'm going from a lower part of the map (ground) to a higher one (some metal platform) and it feels like I'm moving in 3 dimensions. But when I look closely, I see that the player size didn't change and the shadow too but I'm still feeling like I'm somehow higher then before (I had rendered a simple map myself that I made in 3dmax but it didn't quite give the result I wanted). How to accomplish such an effect?

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• DNS: forward part of a managed domain to one host, but sub domain services to another (Google Apps)

  - by Paul Zee

  I was going to post this as a comment against DNS: Forward domain to another host, but I don't seem able to do that. I'm in a similar situation. I have a DNS registered/managed by enom, except with the slight twist that the domain was originally registered with enom through a Google Apps account creation. The domain currently supports a Google Apps site/account. I now want to direct the bare primary domain and www entries to a hosting provider for the website component, but leave the Google Apps setup intact for its services such as calendar, mail etc. For now, I'm leaving the domain managed by enom. Also note that when I registered my account with the hosting provider, I gave the same domain name as the existing domain (e.g. example.com), so at their end I'm working with the same domain name in cpanel, etc. In my case, the existing enom DNS entries don't have an A record for the www.example.com, or the bare example.com domain. Instead, there are 4 x @ records with the Google Apps IP Address, 2 x TXT records with what I assume are Google Apps site verification strings/tokens, and a bunch of CNAME records for the various features of Google Apps (mail, calendar, docs, sites, etc). So, my questions: How do I point the www.example.com and example.com DNS entries at enom to my web site hosting provider, while leaving the domain managed by enom, and the Google Apps services working as they are now (with the obvious exception of Google Sites)? How do I setup the example.com mail-related DNS records (MX, etc) at the web site hosting provider, so that outbound email to [email protected] gets correctly sent to the google apps mail account, and doesn't get trapped inside the pseudo domain within the hosting providers servers?

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• Huge procedurally generated 'wilderness' worlds

  - by The Communist Duck

  Hi. I'm sure you all know of games like Dwarf Fortress - massive, procedural generated wilderness and land. Something like this, taken from this very useful article. However, I was wondering how I could apply this to a much larger scale; the scale of Minecraft comes to mind (isn't that something like 8x the size of the Earth's surface?). Pseudo-infinite, I think the best term would be. The article talks about fractal perlin noise. I am no way an expert on it, but I get the general idea (it's some kind of randomly generated noise which is semi-coherent, so not just random pixel values). I could just define regions X by X in size, add some region loading type stuff, and have one bit of noise generating a region. But this would result in just huge amounts of islands. On the other extreme, I don't think I can really generate a supermassive sheet of perlin noise. And it would just be one big island, I think. I am pretty sure Perlin noise, or some noise, would be the answer in some way. I mean, the map is really nice looking. And you could replace the ascii with tiles, and get something very nice looking. Anyone have any ideas? Thanks. :D -TheCommieDuck

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• Designing a Content-Based ETL Process with .NET and SFDC

  - by Patrick

  As my firm makes the transition to using SFDC as our main operational system, we've spun together a couple of SFDC portals where we can post customer-specific documents to be viewed at will. As such, we've had the need for pseudo-ETL applications to be implemented that are able to extract metadata from the documents our analysts generate internally (most are industry-standard PDFs, XML, or MS Office formats) and place in networked "queue" folders. From there, our applications scoop of the queued documents and upload them to the appropriate SFDC CRM Content Library along with some select pieces of metadata. I've mostly used DbAmp to broker communication with SFDC (DbAmp is a Linked Server provider that allows you to use SQL conventions to interact with your SFDC Org data). I've been able to create [console] applications in C# that work pretty well, and they're usually structured something like this: static void Main() { // Load parameters from app.config. // Get documents from queue. var files = someInterface.GetFiles(someFilterOrRegexPattern); foreach (var file in files) { // Extract metadata from the file. // Validate some attributes of the file; add any validation errors to an in-memory // structure (e.g. List<ValidationErrors>). if (isValid) { var fileData = File.ReadAllBytes(file); // Upload using some wrapper for an ORM or DAL someInterface.Upload(fileData, meta.Param1, meta.Param2, ...); } else { // Bounce the file } } // Report any validation errors (via message bus or SMTP or some such). } And that's pretty much it. Most of the time I wrap all these operations in a "Worker" class that takes the needed interfaces as constructor parameters. This approach has worked reasonably well, but I just get this feeling in my gut that there's something awful about it and would love some feedback. Is writing an ETL process as a C# Console app a bad idea? I'm also wondering if there are some design patterns that would be useful in this scenario that I'm clearly overlooking. Thanks in advance!

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• conky stopped displaying after daul monitors setup -- works when I detect monitors

  - by synaptik

  I just recently installed Ubuntu 12.04 on a clean install. I previously was using 11.10. I am also using a new laptop with a Dell docking-station and two external monitors. When I try to use the .conkyrc file that I used previously, my conky display simply doesn't show up anywhere. However, after I went to System Settings Displays and made some slight change that caused the monitors to refresh, then conky appeared as it should. Here is my .conkyrc file: background yes use_xft yes xftfont DejaVu Sans Mono:size=8 xftalpha 0.8 out_to_console no update_interval 2.0 total_run_times 0 draw_shades no short_units yes # Create own window instead of using desktop (required in nautilus) own_window yes # If own_window is yes, you may use type normal, desktop or override own_window_type override # Use pseudo transparency with own_window? own_window_transparent yes double_buffer yes default_color f0e68c color1 white color2 AD0303 alignment bottom_left gap_x 2 gap_y 30 no_buffers yes use_spacer right pad_percents 3 xftfont Terminus:size=10 TEXT $stippled_hr cpu1: ${color1}${cpu cpu1}% ${color} cpu2: ${color1}${cpu cpu2}% ${color} load: ${color1}$loadavg ${color} hot proc: ${color1}${top cpu 1}% - ${top name 1}${color} $stippled_hr big proc: ${color1}${top_mem mem_res 1} - ${top_mem name 1}${color} memory: ${color1}$mem/$memmax $memperc%${color} $stippled_hr disk: ${color1}${fs_used /}/${fs_size /}${color} swap: ${color1}${swap}/${swapmax}${color} ${diskiograph_read 15,120 color1 0077ff 750} ${diskiograph_write 15,120 color1 0077ff 750} $stippled_hr download: ${color1}${downspeed wlan0} /s${color} ${downspeedgraph eth0 20,120 104E8B 0077ff} upload: ${color1}${upspeed wlan0} /s${color} ${upspeedgraph eth0 20,120 104E8B 0077ff} How can I fix it so that I don't have to tamper with the Displays settings in order for conky to show up?

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• My New Job

  - by Stuart Brierley

  Last year I started a new job with a logistics company in the North of England, where I was responsible for the management, design and development of IT Integration strategies, architectures and solutions using BizTalk Server 2009.  This included the design and implementation of the BizTalk Server 2009 infrastructure, the definition of development standards, mentoring a fellow developer in the ways of BizTalk and migrating a number of existing solutions from Softshare over to BizTalk 2009. Unfortunately I then realised that, following this initial set up, there didn't actually seem to be that much BizTalk work for me to get stuck into and reluctantly I have now moved on from this role to a very similar role with the country's largest office supplies company.  Based in Sheffield, we distribute office supplies on a UK wide basis and computer supplies across Europe. The situation here is slightly different than when I first joined my previous employer.  Whereas that was a green field installation with no previous BizTalk solutions in place, my new employer currently has a number of live BizTalk 2000 (!) and BizTalk 2006 solutions in place.  Unfortunately the infrastructure around these is less than ideal; with no clear distinction between development and test environments and no source control what so ever! We are currently building a proposal for a new BizTalk Server 2010 implementation, where I am hopeful of being able to implement fully independent development, test and pseudo-live environments, alongside an enterprise level live installation.  We should also be introducing Team Foundation Server to the development process, thereby giving us some much needed source control capabilities. Following this is likely to be a period of migration for the existing BizTalk Solutions, along with the onward development of new projects and initiatives - I'm hoping to be a busy man for the forseeable future :o)

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• Arbitrary Rotation about a Sphere

  - by Der

  I'm coding a mechanic which allows a user to move around the surface of a sphere. The position on the sphere is currently stored as theta and phi, where theta is the angle between the z-axis and the xz projection of the current position (i.e. rotation about the y axis), and phi is the angle from the y-axis to the position. I explained that poorly, but it is essentially theta = yaw, phi = pitch Vector3 position = new Vector3(0,0,1); position.X = (float)Math.Sin(phi) * (float)Math.Sin(theta); position.Y = (float)Math.Sin(phi) * (float)Math.Cos(theta); position.Z = (float)Math.Cos(phi); position *= r; I believe this is accurate, however I could be wrong. I need to be able to move in an arbitrary pseudo two dimensional direction around the surface of a sphere at the origin of world space with radius r. For example, holding W should move around the sphere in an upwards direction relative to the orientation of the player. I believe I should be using a Quaternion to represent the position/orientation on the sphere, but I can't think of the correct way of doing it. Spherical geometry is not my strong suit. Essentially, I need to fill the following block: public void Move(Direction dir) { switch (dir) { case Direction.Left: // update quaternion to rotate left break; case Direction.Right: // update quaternion to rotate right break; case Direction.Up: // update quaternion to rotate upward break; case Direction.Down: // update quaternion to rotate downward break; } }

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• What is the best practice for when to check if something needs to be done?

  - by changokun

  Let's say I have a function that does x. I pass it a variable, and if the variable is not null, it does some action. And I have an array of variables and I'm going to run this function on each one. Inside the function, it seems like a good practice is to check if the argument is null before proceeding. A null argument is not an error, it just causes an early return. I could loop through the array and pass each value to the function, and the function will work great. Is there any value to checking if the var is null and only calling the function if it is not null during the loop? This doubles up on the checking for null, but: Is there any gained value? Is there any gain on not calling a function? Any readability gain on the loop in the parent code? For the sake of my question, let's assume that checking for null will always be the case. I can see how checking for some object property might change over time, which makes the first check a bad idea. Pseudo code example: for(thing in array) { x(thing) } Versus: for(thing in array) { if(thing not null) x(thing) } If there are language-specific concerns, I'm a web developer working in PHP and JavaScript.

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• Should I give the answer to a failed interview coding exercise?

  - by GlenH7

  We had a senior level interview candidate fail a nuance of the FizzBuzz question*. I mean, really, utterly, completely, failed the question - not even close. I even coached him through to thinking about using a loop and that 3 and 5 were really worth considering as special cases. He blew it. Just for QA purposes, I gave the same exact question to three teammates; gave them 5 minutes; and then came back to collect their pseudo-code. All of them nailed it and hadn't seen the question before. Two asked what the trick was... On a different logic exercise, the candidate showed some understanding of some of the features available within the language he chose to use (C#). So it's not as if he had never written a line of code. But his logic still stunk. My question is whether or not I should have given him the answer to the logic questions. He knew he blew them, and acknowledged it later in the interview. On the other hand, he never asked for the answer or what I was expecting to see. I know coding exercises can be used to set candidates up for failure (again, see second link from above). And I really tried to help him home in on answering the core of the question. But this was a senior level candidate and Fizz-Buzz is, frankly, ridiculously easy even with accounting for interview jitters. I felt like I should have shown him a way of solving the problem so that he could at least learn from the experience. But again, he didn't ask. What's the right way to handle that situation? *Okay, that's not the link to the actual FizzBuzz question, but it is a good P.SE discussion around FizzBuzz and links to the various aspects of it.

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• Is NAN suitable for communicating that an invalid parameter was involved in a calculation?

  - by Arman

  I am currently working on a numerical processing system that will be deployed in a performance-critical environment. It takes inputs in the form of numerical arrays (these use the eigen library, but for the purpose of this question that's perhaps immaterial), and performs some range of numerical computations (matrix products, concatenations, etc.) to produce outputs. All arrays are allocated statically and their sizes are known at compile time. However, some of the inputs may be invalid. In these exceptional cases, we still want the code to be computed and we still want outputs not "polluted" by invalid values to be used. To give an example, let's take the following trivial example (this is pseudo-code): Matrix a = {1, 2, NAN, 4}; // this is the "input" matrix Scalar b = 2; Matrix output = b * a; // this results in {2, 4, NAN, 8} The idea here is that 2, 4 and 8 are usable values, but the NAN should signal to the receipient of the data that that entry was involved in an operation that involved an invalid value, and should be discarded (this will be detected via a std::isfinite(value) check before the value is used). Is this a sound way of communicating and propagating unusable values, given that performance is critical and heap allocation is not an option (and neither are other resource-consuming constructs such as boost::optional or pointers)? Are there better ways of doing this? At this point I'm quite happy with the current setup but I was hoping to get some fresh ideas or productive criticism of the current implementation.

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• Is there a way to add unique items to an array without doing a ton of comparisons?

  - by hydroparadise

  Please bare with me, I want this to be as language agnostic as possible becuase of the languages I am working with (One of which is a language called PowerOn). However, most languanges support for loops and arrays. Say I have the following list in an aray: 0x 0 Foo 1x 1 Bar 2x 0 Widget 3x 1 Whatsit 4x 0 Foo 5x 1 Bar Anything with a 1 should be uniqely added to another array with the following result: 0x 1 Bar 1x 1 Whatsit Keep in mind this is a very elementry example. In reality, I am dealing with 10's of thousands of elements on the old list. Here is what I have so far. Pseudo Code: For each element in oldlist For each element in newlist Compare If values oldlist.element equals newlist.element, break new list loop If reached end of newlist with with nothing equal from oldlist, add value from old list to new list End End Is there a better way of doing this? Algorithmicly, is there any room for improvement? And as a bonus qeustion, what is the O notation for this type of algorithm (if there is one)?

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• Is '@' Error Suppression a Valid Technique for Testing for an Optional Array Key?

  - by MikeSchinkel

  Rarst and I were debating offline about the use of the '@' error suppression operator in PHP, specifically for use to test for existence of "optional" array keys, i.e. array keys that are being used as a switch here a their lack of existence in the array is functionally equivalent to the array having the key with a value equaling false. Here is pseudo-code for this scenario: function do_something( $args = array() ) { if ( @$args['switch'] ) { // Do something with this switch } // continue on... } vs. this approach: function do_something( $args = array() ) { if ( ! empty( $args['switch'] ) && $args['switch'] ) { // Do something with this switch } // continue on... } Of course in most use-cases, suppressing errors would not be A Good Thing(tm). However in this use-case where an array is passed with an optional element, it seems to me that it is actually a very good technique but I could be wrong and would like to hear other's opinions on the subject before I make up my mind. I do know that there are alleged performance hits for using the former approach but I'd like to know how they compare with the alternative and if they performance hits really matter in real world scenarios? P.S. I decided to post this because, after debating this offline with Rarst, he asked a more general question here on Programmers but didn't actually give a detailed example of the specific use-case we were debating. And since I'm pretty sure he'll want to use the out-of-context answers on that other question as justification for why the above is "bad" I decided I needed to get opinions on this specific use-case.

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• How do I use depth testing and texture transparency together in my 2.5D world?

  - by nbolton

  Note: I've already found an answer (which I will post after this question) - I was just wondering if I was doing it right, or if there is a better way. I'm making a "2.5D" isometric game using OpenGL ES (JOGL). By "2.5D", I mean that the world is 3D, but it is rendered using 2D isometric tiles. The original problem I had to solve was that my textures had to be rendered in order (from back to front), so that the tiles overlapped properly to create the proper effect. After some reading, I quickly realised that this is the "old hat" 2D approach. This became difficult to do efficiently, since the 3D world can be modified by the player (so stuff can appear anywhere in 3D space) - so it seemed logical that I take advantage of the depth buffer. This meant that I didn't have to worry about rendering stuff in the correct order. However, I faced a problem. If you use GL_DEPTH_TEST and GL_BLEND together, it creates an effect where objects are blended with the background before they are "sorted" by z order (meaning that you get a weird kind of overlap where the transparency should be). Here's some pseudo code that should illustrate the problem (incidentally, I'm using libgdx for Android). create() { // ... // some other code here // ... Gdx.gl.glEnable(GL10.GL_DEPTH_TEST); Gdx.gl.glEnable(GL10.GL_BLEND); } render() { Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT); Gdx.gl.glBlendFunc(GL10.GL_SRC_ALPHA, GL10.GL_ONE_MINUS_SRC_ALPHA); // ... // bind texture and create vertices // ... } So the question is: How do I solve the transparency overlap problem?

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• Non-Profit Technololgy for Non-Profits?

  - by TomJ

  I've been looking around for a way to give back to the community, but I haven't found my right fit yet, so an idea came to mind: A non-profit technology "company" that targets non-profits. Do these exist? I've been doing some google searches and can only find software that is targeted for non-profits that is created by for-profit companies or that charges what I believe to be an outrages amount, conferences directed towards non-profits and technology they may use -- or articles complaining about the digital divide and how non-profits view technology as key but dont have the funds or the knowledge to employ it. Pseudo "Business Model" An open source 501(3)(c) organization that targets directly targets non-profits to fill the "digital divide." Most services would be free and consulting fees would be charged for customization. Donations would be accepted and government grants would be sought after. This would enable non-profits to keep pace with the for-profits in the technology sector, but at little to no cost. Perhaps the first "industry" to be targeted would be those that fill key social needs like unemployment, or food banks.

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• Can anyone explain step-by-step how the as3isolib depth-sorts isometric objects?

  - by Rob Evans

  The library manages to depth-sort correctly, even when using items of non-1x1 sizes. I took a look through the code but it's a big project to go through line by line! There are some questions about the process such as: How are the x, y, z values of each object defined? Are they the center points of the objects or something else? I noticed that the IBounds defines the bounds of the object. If you were to visualise a cuboid of 40, 40, 90 in size, where would each of the IBounds metrics be? I would like to know how as3isolib achieves this although I would also be happy with a generalised pseudo-code version. At present I have a system that works 90% of the time but in cases of objects that are along the same horizontal line, the depth is calculated as the same value. The depth calculation currently works like this: x = object horizontal center point y = object vertical center point originX and Y = the origin point relative to the object so if you want the origin to be the center, the value would be originX = 0.5, originY = 0.5. If you wanted the origin to be vertical center, horizontal far right of the object it would be originX = 1.0, originY = 0.5. The origin adjusts the position that the object is transformed from. AABB_width = The bounding box width. AABB_height = The bounding box height. depth = x + (AABB_width * originX) + y + (AABB_height * originY) - z; This generates the same depth for all objects along the same horizontal x.

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• Transform coordinates from 3d to 2d without matrix or built in methods

  - by Thomas

  Not to long ago i started to create a small 3D engine in javascript to combine this with an html5 canvas. One of the issues I run into is how can you transform 3d to 2d coords. Since I cannot use matrices or built in transformation methods I need another way. I've tried implementing the next explanation + pseudo code: http://freespace.virgin.net/hugo.elias/routines/3d_to_2d.htm Unfortunately no luck there. I've replace all the input variables with data from my own camera and object classes. I have the following data: An object with a rotation, position vector and an array of 4 3d coords (its just a plane) a camera with a position and rotation vector the viewport - a square 600 x 600 surface. The example uses a zoom factor which I've set as 1 Most hits on google use either matrix calculations or don't implement camera rotation. Basic transformation should be like this: screen.x = x / z * zoom screen.y = y / z * zoom Can anyone point me in the right direction or explain to me howto achieve this? edit: Thanks for all your posts, I haven't been able to apply all this to my project yet but I hope to do this soon.

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