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  • Duplicate IP address detection with multiple NICs

    - by sfink
    I am using arping -D to detect duplicate IP addresses within a network when setting up servers. (The network is controlled by someone else, and we have had many issues with IP allocation in the past.) It works fine as long as my host has a single NIC on a given VLAN, but when my host has more than one (I have one with 9 NICs on one VLAN and 1 on the other), arping -D always returns false collisions. The problem is that all 9 of my NICs respond to an ARP request for any of the IPs on those NICs. (These are real physical NICs, not aliases or anything.) I send out one ARP request packet, and get 9 ARP is-at ARP replies, one for each MAC address. I could implement my own solution by sniffing packets and checking for any replies with a MAC address other than the local NICs', but it seems like there ought to be an easier way.

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  • RAID FS detection at boot time

    - by alex
    An excerpt from dmesg: md: Autodetecting RAID arrays. md: Scanned 2 and added 2 devices. md: autorun ... md: considering sdb1 ... md: adding sdb1 ... md: adding sda1 ... md: created md1 md: bind<sda1> md: bind<sdb1> md: running: <sdb1><sda1> raid1: raid set md1 active with 2 out of 2 mirrors md1: detected capacity change from 0 to 1500299198464 md: ... autorun DONE. md1: unknown partition table EXT3-fs (md1): error: couldn't mount because of unsupported optional features (240) EXT2-fs (md1): error: couldn't mount because of unsupported optional features (240) EXT4-fs (md1): mounted filesystem with ordered data mode Is it OK that kernel tries to mount an ext4 raid as ext3, ext2 first? Is there a way to tell it to skip those two steps? Just in case: /dev/md1 / ext4 noatime 0 1 TIA.

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  • PHP Browser Game Question - Pretty General Language Suitability and Approach Question

    - by JimBadger
    I'm developing a browser game, using PHP, but I'm unsure if the way I'm going about doing it is to be encouraged anymore. It's basically one of those MMOs where you level up various buildings and what have you, but, you then commit some abstract fighting entity that the game gives you, to an automated battle with another player (producing a textual, but hopefully amusing and varied combat report). Basically, as soon as two players agree to fight, PHP functions on the "fight.php" page run queries against a huge MySQL database, looking up all sorts of complicated fight moves and outcomes. There are about three hundred thousand combinations of combat stance, attack, move and defensive stances, so obviously this is quite a resource hungry process, and, on the super cheapo hosted server I'm using for development, it rapidly runs out of memory. The PHP script for the fight logic currently has about a thousand lines of code in it, and I'd say it's about half-finished as I try to add a bit of AI into the fight script. Is there a better way to do something this massive than simply having some functions in a PHP file calling the MySQL Database? I taught myself a modicum of PHP a while ago, and most of the stuff I read online (ages ago) about similar games was all PHP-based. but a) am I right to be using PHP at all, and b) am I missing some clever way of doing things that will somehow reduce server resource requirements? I'd consider non PHP alternatives but, if PHP is suitable, I'd rather stick to that, so there's no overhead of learning something new. I think I'd bite that bullet if it's the best option for a better game, though.

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  • Differentiate procedural language(c) from oop languages(c++)

    - by niko
    I have been trying to differentiate c and c++(or oop languages) but I don't understand where the difference is. Note I have never used c++ but I asked my friends and some of them to differentiate c and c++ They say c++ has oop concepts and also the public, private modes for definition of variables and which c does not have though. Seriously I have done vb.net programming for a while 2 to 3 months, I never faced a situation to use class concepts and modes of definition like public and private. So I thought what could be the use for these? My friend explained me a program saying that if a variable is public, it can be accessed anywhere I said why not declare it as a global variable like in c? He did not get back to my question and he said if a variable is private it cannot be accessed by some other functions I said why not define it as a local variable, even these he was unable to answer. No matter where I read private variables cannot be accessed whereas public variables can be then why not make public as global and private as local whats the difference? whats the real use of public and private ? please don't say it can be used by everyone, I suppose why not we use some conditions and make the calls? I have heard people saying security reasons, a friend said if a function need to be accessed it should be inherited first. He explained saying that only admin should be able to have some rights and not all so that functions are made private and inherited only by the admin to use Then I said why not we use if condition if ( login == "admin") invoke the function he still did not answer these question. Please clear me with these things, I have done vb.net and vba and little c++ without using oop concepts because I never found their real use while I was writing the code, I'm a little afraid am I too back in oop concepts?

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  • Idle state detection for server

    - by odinmillion
    Windows OS has a service that detects idle state. Details: Task Idle Conditions The computer is considered idle if all the processors and all the disks were idle for more than 90% of the past 15 minutes and if there is no keyboard or mouse input during this period of time. When the Task Scheduler service detects that the computer is idle, the service only waits for user input to mark the end of the idle state. It is very useful for usual PCs that have keyboard amd mouse. We can use standard task scheduler to start some process like defrag when PC in idle state and stop when PC isn't in idle state. But what should we use when we using a standalone server without keyboard and mouse? Server sometimes receives commands by TCP/IP and starts CPU and HDD activity. But sometimes CPU and HDD activity at zero level. I would like to use this periods of time to start defrag or another process. But this started at "idle" state processes should be terminated when another commands will appear. So, standard idle state conditions cant help me because we have not got user input to stop idle state. I need more customizable idle state detector. Automatically started processes shouldn't influence to idle state, but PC should go away from idle state when another process will apperar. What should I use? Maybe exists some advansed task scheduler? Or I should write some useful utility on C#? I hope that it is a standard task and all useful utilities already compiled :)

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  • Cross-language Extension Method Calling

    - by Tom Hines
    Extension methods are a concise way of binding functions to particular types. In my last post, I showed how Extension methods can be created in the .NET 2.0 environment. In this post, I discuss calling the extensions from other languages. Most of the differences I find between the Dot Net languages are mainly syntax.  The declaration of Extensions is no exception.  There is, however, a distinct difference with the framework accepting excensions made with C++ that differs from C# and VB.  When calling the C++ extension from C#, the compiler will SOMETIMES say there is no definition for DoCPP with the error: 'string' does not contain a definition for 'DoCPP' and no extension method 'DoCPP' accepting a first argument of type 'string' could be found (are you missing a using directive or an assembly reference?) If I recompile, the error goes away. The strangest problem with calling the C++ extension from C# is that I first must make SOME type of reference to the class BEFORE using the extension or it will not be recognized at all.  So, if I first call the DoCPP() as a static method, the extension works fine later.  If I make a dummy instantiation of the class, it works.  If I have no forward reference of the class, I get the same error as before and recompiling does not fix it.  It seems as if this none of this is supposed to work across the languages. I have made a few work-arounds to get the examples to compile and run. Note the following examples: Extension in C# using System; namespace Extension_CS {    public static class CExtension_CS    {  //in C#, the "this" keyword is the key.       public static void DoCS(this string str)       {          Console.WriteLine("CS\t{0:G}\tCS", str);       }    } } Extension in C++ /****************************************************************************\  * Here is the C++ implementation.  It is the least elegant and most quirky,  * but it works. \****************************************************************************/ #pragma once using namespace System; using namespace System::Runtime::CompilerServices;     //<-Essential // Reference: System.Core.dll //<- Essential namespace Extension_CPP {        public ref class CExtension_CPP        {        public:               [Extension] // or [ExtensionAttribute] /* either works */               static void DoCPP(String^ str)               {                      Console::WriteLine("C++\t{0:G}\tC++", str);               }        }; } Extension in VB ' Here is the VB implementation.  This is not as elegant as the C#, but it's ' functional. Imports System.Runtime.CompilerServices ' Public Module modExtension_VB 'Extension methods can be defined only in modules.    <Extension()> _       Public Sub DoVB(ByVal str As String)       Console.WriteLine("VB" & Chr(9) & "{0:G}" & Chr(9) & "VB", str)    End Sub End Module   Calling program in C# /******************************************************************************\  * Main calling program  * Intellisense and VS2008 complain about the CPP implementation, but with a  * little duct-tape, it works just fine. \******************************************************************************/ using System; using Extension_CPP; using Extension_CS; using Extension_VB; // vitual namespace namespace TestExtensions {    public static class CTestExtensions    {       /**********************************************************************\        * For some reason, this needs a direct reference into the C++ version        * even though it does nothing than add a null reference.        * The constructor provides the fake usage to please the compiler.       \**********************************************************************/       private static CExtension_CPP x = null;   // <-DUCT_TAPE!       static CTestExtensions()       {          // Fake usage to stop compiler from complaining          if (null != x) {} // <-DUCT_TAPE       }       static void Main(string[] args)       {          string strData = "from C#";          strData.DoCPP();          strData.DoCS();          strData.DoVB();       }    } }   Calling program in VB  Imports Extension_CPP Imports Extension_CS Imports Extension_VB Imports System.Runtime.CompilerServices Module TestExtensions_VB    <Extension()> _       Public Sub DoCPP(ByVal str As String)       'Framework does not treat this as an extension, so use the static       CExtension_CPP.DoCPP(str)    End Sub    Sub Main()       Dim strData As String = "from VB"       strData.DoCS()       strData.DoVB()       strData.DoCPP() 'fake    End Sub End Module  Calling program in C++ // TestExtensions_CPP.cpp : main project file. #include "stdafx.h" using namespace System; using namespace Extension_CPP; using namespace Extension_CS; using namespace Extension_VB; void main(void) {        /*******************************************************\         * Extension methods are called like static methods         * when called from C++.  There may be a difference in         * syntax when calling the VB extension as VB Extensions         * are embedded in Modules instead of classes        \*******************************************************/     String^ strData = "from C++";     CExtension_CPP::DoCPP(strData);     CExtension_CS::DoCS(strData);     modExtension_VB::DoVB(strData); //since Extensions go in Modules }

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  • Fastest Functional Language

    - by Farouk
    I've recently been delving into functional programming especially Haskell and F#, the prior more so. After some googling around I could not find a benchmark comparison of the more prominent functional languages (Scala,F# etc). I know it's not necessarily fair to some of the languages (Scala comes to mind) given that they are hybrids, but I just wanna know which outperforms which on what operations and overall.

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  • very slow bridge detection

    - by deddihp
    hello everyone, I have setup some bridge interface with 4 ethernet port. My problem is, when they detect some network topology change, the bridge really need a lot of time to have done it. Is there any solution, so the bridge can detect topology change faster ? thanks.

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  • Mac OS ? Assembly Language Esoteria

    - by veryfoolish
    I've been playing around with assembly and object files in general on Mac OS ? and was wondering if somebody could provide some edification. Specifically, I'm wondering what the extra code GCC generates when compiling the C file in the following example does. I have a toy C program so I can comprehend the assembly output. int main() { int a = 5; int b = 5; int c = a + b; } Running this through gcc -S creates the following assembly: .text .globl _main _main: LFB2: pushq %rbp LCFI0: movq %rsp, %rbp LCFI1: movl $5, -4(%rbp) movl $5, -8(%rbp) movl -8(%rbp), %eax addl -4(%rbp), %eax movl %eax, -12(%rbp) leave ret LFE2: .section __TEXT,__eh_frame,coalesced,no_toc+strip_static_syms+live_support EH_frame1: .set L$set$0,LECIE1-LSCIE1 .long L$set$0 LSCIE1: .long 0x0 .byte 0x1 .ascii "zR\0" .byte 0x1 .byte 0x78 .byte 0x10 .byte 0x1 .byte 0x10 .byte 0xc .byte 0x7 .byte 0x8 .byte 0x90 .byte 0x1 .align 3 LECIE1: .globl _main.eh _main.eh: LSFDE1: .set L$set$1,LEFDE1-LASFDE1 .long L$set$1 LASFDE1: .long LASFDE1-EH_frame1 .quad LFB2-. .set L$set$2,LFE2-LFB2 .quad L$set$2 .byte 0x0 .byte 0x4 .set L$set$3,LCFI0-LFB2 .long L$set$3 .byte 0xe .byte 0x10 .byte 0x86 .byte 0x2 .byte 0x4 .set L$set$4,LCFI1-LCFI0 .long L$set$4 .byte 0xd .byte 0x6 .align 3 LEFDE1: .subsections_via_symbols The LCFI1 section seems to contain the actual logic for the program, but I'm not sure what the misc. other stuff is for... also, is there any scheme these labels are following? I'm sorry this is such a vague question. I'd appreciate anything, including being pointed to a resource where I can find out more about this. Thanks!

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  • Suggestions for a CMS markup language for PHP

    - by Yanick Rochon
    As a learning experience, and as project, I am attempting to write a CMS module for ZF2. One of the functionality I would like to have is the possibility of adding dynamic contents in the pages by calling PHP functions in the view scripts. However, I do not want to give the users freedom in writing PHP code directly inside the page content, but rather implement custom view helpers (or widgets) to handle logic. For example: calling partial, partialLoop, url, etc. specifying arguments and all. I liked the idea of extending Markdown but this would get complicated when trying to add custom CSS class to elements, etc. Then I had the idea of simply doing a preg_replace on some patterns. For example, the string : ### partialLoop:['partials/display.phtml',[{id:'p1',price:4.99},{id:'p2',price:12.34}]] ### would be replaced by <?php echo $this->partialLoop('partials/display.phtml', array(array('id'=>'p1','price'=>4.99),array('id'=>'p2','price'=>12.34))) ?> Obviously, there would be some caching done so the page content is not rendered everytime. Does this sound good? If not, what would be a good way of doing this? Or is there a project already being developed for doing this? (I'd like to avoid heavy third party libs and something fairly or fully compatible with ZF2 would be nice.) Thanks.

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  • What to do if I am working on a language that I don't like

    - by Sayem Ahmed
    Hi there, I really don't know if this is the right place to ask this question, but if it isn't, then I guess someone will notify. Anyway, I am working in a software development farm which is currently using PowerBuilder to develop a mid-size ERP solution. The work environment and company management are so great that it may be the best in the whole Bangladesh. Only problem is the technology that are currently being used, which is this PowerBuilder. Now I am a guy who tends to prefer modern development technologies, like DI containers, ORM, TDD, JQuery etc. PowerBuilder is a great tool too, but I couldn' like the application techniques used to build PB applications. These techniques are so inheritance-dependent that many a times these create a great deal of sufferings. I remember two days ago I had to change some processing logic in a core user object and as a result I had to test and re-test all the forms that the application have(apparently, there are almost 20 forms there, each of them with 3-4 kinds of functionalities). Also, learning PB is tough, because online material on this thing is very, very low. I can't afford to read all the documentation that PB provide because I have hard deadlines on the work that I have to do. Another thing with PB is that applications tend to rely on business logic that are implemented on databases which causes debugging to be a nightmare. As a result, I don't feel motivated enough to work in this IDE/System/Framework (or whatever) anymore. My productivity has greatly decreased, and I am not delivering quality code. I think I have the following options available to me - Remain in the current job, keep delivering worse code and let my productivity decrease day by day, taking salaries and bonuses but not delivering quality codes/doing my job the way I should, Search for a new job. At this point number 2 seems a good option, but there are also some issues. As I mentioned before, our management may be the best in the country. Our company owner is himself a software developer with 24 years of experience in software development. He is currently our Team Leader and System Analyst. He is by far the greatest manager and boss I have ever seen. He understands developer's mentality very well(as he IS himself a developer). He is also a great, kind and generous guy. Our company is only a start-up company with 10 developers. Among them, only 3-4 people knows about the business logic behind the ERP, and I am one of them. If I switch my current job, it may hamper the development of this product which I really don't want. I couldn't decide what to do in this situation, so I turned to the community for advice.

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  • Codifying a natural language requirements spec

    - by ProfK
    I have a fairly technical functionality requirements spec, expressed in English prose, produced by my project manager. It is structured as a collection of UI tabs, where the requirements for each tab are expressed as a lit of UI fields and a list of business rules for the tab. Most business rules are for UI fields on a tab, e.g: a) Must be alphanumeric, max length 20. b) Must be a dropdown, with values from table x. c) Is mandatory. d) Is mandatory under certain conditions, e.g. another field is just populated, or has a specific value. Then other business rules get a little more complex. The spec is for a job application, so the central business object (table) is the Applicant, and we have several other tables with one-to-many relationships with applicant, such as Degree, HighSchool, PreviousEmployer, Diploma, etc. e) One such complex rule says a status field can only be assigned a certain value if a many-side record exists in at least one of the many-side tables. E.g. the Applicant has at least one HighSchool or at least one Diploma record. I am looking for advice on how to codify these requirements into a more structured specification defined in terms of tables, fields, and relationships, especially for the conditional rules for fields and for the presence of related records. Any suggestions and advice will be most welcome, but I would be overjoyed if i could find an already defined system or structure for expressing things like this.

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  • CentOS 6.3 X86_64 RAM detection

    - by Peter
    I have a machine with 8GB ram (BIOS sees it, so my motherboard and CPU supports it), and I installed CentOS 6.3 on it. When it starts up, it only see 3.1GB. uname says: 2.6.32-279.1.1.el6.x86_64 #1 SMP BIOS-provided physical RAM map: BIOS-e820: 0000000000000000 - 000000000009fc00 (usable) BIOS-e820: 000000000009fc00 - 00000000000a0000 (reserved) BIOS-e820: 00000000000e0000 - 0000000000100000 (reserved) BIOS-e820: 0000000000100000 - 00000000cf65f000 (usable) BIOS-e820: 00000000cf65f000 - 00000000cf6e8000 (ACPI NVS) BIOS-e820: 00000000cf6e8000 - 00000000cf6ec000 (usable) BIOS-e820: 00000000cf6ec000 - 00000000cf6ff000 (ACPI data) BIOS-e820: 00000000cf6ff000 - 00000000cf700000 (usable) dmesg | grep -i memory says: initial memory mapped : 0 - 20000000 init_memory_mapping: 0000000000000000-00000000cf700000 Reserving 129MB of memory at 48MB for crashkernel (System RAM: 3319MB) PM: Registered nosave memory: 000000000009f000 - 00000000000a0000 PM: Registered nosave memory: 00000000000a0000 - 00000000000e0000 PM: Registered nosave memory: 00000000000e0000 - 0000000000100000 PM: Registered nosave memory: 00000000cf65f000 - 00000000cf6e8000 PM: Registered nosave memory: 00000000cf6ec000 - 00000000cf6ff000 Memory: 3184828k/3398656k available (5152k kernel code, 1016k absent, 212812k reserved, 7166k data, 1260k init) please try 'cgroup_disable=memory' option if you don't want memory cgroups Initializing cgroup subsys memory Freeing initrd memory: 16136k freed Non-volatile memory driver v1.3 agpgart-intel 0000:00:00.0: detected 8192K stolen memory crash memory driver: version 1.1 Freeing unused kernel memory: 1260k freed Freeing unused kernel memory: 972k freed Freeing unused kernel memory: 1732k freed Update: Memtest see all the 8GB, and dmidecode -t 17 | grep Size too. But free -m still see only 3.1 GB. Question: How can I repair/modify the system, to see all the 8GB RAM? Thanks in advance!

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  • Is the C programming language still used?

    - by Pankaj Upadhyay
    I am a C# programmer, and most of my development is for websites along with a few Windows application. As far as C goes, I haven't used it in a long time, as there was no need to. It came to me as a surprise when one of my friends said that she needs to learn C for testing jobs, while I was helping her learn C#. I figured that someone would only learn C for testing only if there is development done in C. In my knowledge, all the development related to COM and hardware design are also done in C++. Therefore, learning C doesn't make sense if you need to use C++. I also don't believe in historic significance, so why waste time and money in learning C? Is C is still used in any kind of new software development or anything else?

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  • C Programming Language and UNIX Pioneer Passes Away

    According to a statement given to the New York Times by Ritchie's brother Bill, Dennis Ritchie was living alone at his home in Berkeley Heights, New Jersey, prior to his death. Richie's health had reportedly deteriorated, and his last years were made difficult by the after effects of treatments for prostate cancer and heart disease. In addition to his brother Bill, Ritchie is survived by his sister Lynn and his other brother John. Dennis Ritchie was born in Bronxville, New York, in 1941. His father was an engineer with Bell Labs and his mother was a homemaker. His family eventually moved...

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  • Ideas for attack damage algorithm (language irrelevant)

    - by Dillon
    I am working on a game and I need ideas for the damage that will be done to the enemy when your player attacks. The total amount of health that the enemy has is called enemyHealth, and has a value of 1000. You start off with a weapon that does 40 points of damage (may be changed.) The player has an attack stat that you can increase, called playerAttack. This value starts off at 1, and has a possible max value of 100 after you level it up many times and make it farther into the game. The amount of damage that the weapon does is cut and dry, and subtracts 40 points from the total 1000 points of health every time the enemy is hit. But what the playerAttack does is add to that value with a percentage. Here is the algorithm I have now. (I've taken out all of the gui, classes, etc. and given the variables very forward names) double totalDamage = weaponDamage + (weaponDamage*(playerAttack*.05)) enemyHealth -= (int)totalDamage; This seemed to work great for the most part. So I statrted testing some values... //enemyHealth ALWAYS starts at 1000 weaponDamage = 50; playerAttack = 30; If I set these values, the amount of damage done on the enemy is 125. Seemed like a good number, so I wanted to see what would happen if the players attack was maxed out, but with the weakest starting weapon. weaponDamage = 50; playerAttack = 100; the totalDamage ends up being 300, which would kill an enemy in just a few hits. Even with your attack that high, I wouldn't want the weakest weapon to be able to kill the enemy that fast. I thought about adding defense, but I feel the game will lose consistency and become unbalanced in the long run. Possibly a well designed algorithm for a weapon decrease modifier would work for lower level weapons or something like that. Just need a break from trying to figure out the best way to go about this, and maybe someone that has experience with games and keeping the leveling consistent could give me some ideas/pointers.

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  • CON6714 - Mixed-Language Development: Leveraging Native Code from Java

    - by Darryl Gove
    Here's the abstract from my JavaOne talk: There are some situations in which it is necessary to call native code (C/C++ compiled code) from Java applications. This session describes how to do this efficiently and how to performance-tune the resulting applications. The objectives for the session are: Explain reasons for using native code in Java applications Describe pitfalls of calling native code from Java Discuss performance-tuning of Java apps that use native code I'll cover how to call native code from Java, debugging native code, and then I'll dig into performance tuning the code. The talk is not going too deep on performance tuning - focusing on the JNI specific topics; I'll do a bit more about performance tuning in my OpenWorld talk later in the day.

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  • Language parsing to find important words

    - by Matt Huggins
    I'm looking for some input and theory on how to approach a lexical topic. Let's say I have a collection of strings, which may just be one sentence or potentially multiple sentences. I'd like to parse these strings to and rip out the most important words, perhaps with a score that denotes how likely the word is to be important. Let's look at a few examples of what I mean. Example #1: "I really want a Keurig, but I can't afford one!" This is a very basic example, just one sentence. As a human, I can easily see that "Keurig" is the most important word here. Also, "afford" is relatively important, though it's clearly not the primary point of the sentence. The word "I" appears twice, but it is not important at all since it doesn't really tell us any information. I might expect to see a hash of word/scores something like this: "Keurig" => 0.9 "afford" => 0.4 "want" => 0.2 "really" => 0.1 etc... Example #2: "Just had one of the best swimming practices of my life. Hopefully I can maintain my times come the competition. If only I had remembered to take of my non-waterproof watch." This example has multiple sentences, so there will be more important words throughout. Without repeating the point exercise from example #1, I would probably expect to see two or three really important words come out of this: "swimming" (or "swimming practice"), "competition", & "watch" (or "waterproof watch" or "non-waterproof watch" depending on how the hyphen is handled). Given a couple examples like this, how would you go about doing something similar? Are there any existing (open source) libraries or algorithms in programming that already do this?

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  • Default language in Windows 7

    - by Rodnower
    Hello, I have Windows 7, and I set up English like default language, but every time I open new window keyboard layout become be non English, but second language, and it occurs only when I login with local admin, when I login with domain user, all work fine... Any idea what this voodoo is? Thank you for ahead.

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  • How fast does a language get outdated?

    - by Dummy Derp
    I started learning Java recently. I started learning it using books that I picked up from the library, some that I bought, and here and there from Java documentation. The book that I use for Java was published in the year 2011. In 2012, Java8 will be released followed by Java9 in the year 2013. The questions are: How do I keep myself updated about developments in Java without having to buy a tome for Java8 and/or Java9 Is a book published in 2008 an outdated book for studying JSP and Servelets? I'm talking about Head First Servlets and JSP

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  • Webserver security, intrusion detection, and file intregrity

    - by enfield
    I would like to add some type of tracking / alerting on some linux webservers running PHP and Apache. In doing searches I have come across a lot of info from 2006-2009. Would like to revisit things and see what others are doing now. The main purpose here is to track when any files are changed and if so alert me somehow. The same goes for IDS and hopefully something that can reside on same server? Since some of these are small scale projects I would prefer opensource/free solutions that are really effective. Although I would still like to hear of other alternatives if someone has the experience and the cost can be justified.

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  • How do we keep dependent data structures up to date?

    - by Geo
    Suppose you have a parse tree, an abstract syntax tree, and a control flow graph, each one logically derived from the one before. In principle it is easy to construct each graph given the parse tree, but how can we manage the complexity of updating the graphs when the parse tree is modified? We know exactly how the tree has been modified, but how can the change be propagated to the other trees in a way that doesn't become difficult to manage? Naturally the dependent graph can be updated by simply reconstructing it from scratch every time the first graph changes, but then there would be no way of knowing the details of the changes in the dependent graph. I currently have four ways to attempt to solve this problem, but each one has difficulties. Nodes of the dependent tree each observe the relevant nodes of the original tree, updating themselves and the observer lists of original tree nodes as necessary. The conceptual complexity of this can become daunting. Each node of the original tree has a list of the dependent tree nodes that specifically depend upon it, and when the node changes it sets a flag on the dependent nodes to mark them as dirty, including the parents of the dependent nodes all the way down to the root. After each change we run an algorithm that is much like the algorithm for constructing the dependent graph from scratch, but it skips over any clean node and reconstructs each dirty node, keeping track of whether the reconstructed node is actually different from the dirty node. This can also get tricky. We can represent the logical connection between the original graph and the dependent graph as a data structure, like a list of constraints, perhaps designed using a declarative language. When the original graph changes we need only scan the list to discover which constraints are violated and how the dependent tree needs to change to correct the violation, all encoded as data. We can reconstruct the dependent graph from scratch as though there were no existing dependent graph, and then compare the existing graph and the new graph to discover how it has changed. I'm sure this is the easiest way because I know there are algorithms available for detecting differences, but they are all quite computationally expensive and in principle it seems unnecessary so I'm deliberately avoiding this option. What is the right way to deal with these sorts of problems? Surely there must be a design pattern that makes this whole thing almost easy. It would be nice to have a good solution for every problem of this general description. Does this class of problem have a name?

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