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• named-checkzone reports 'ns.example.com.ns' has no address records (A or AAAA)

  - by hydroparadise

  The first thing I see wrong is that its a recursion problem. But I'm not sure where the problems lie in my reverse lookup file. ns should report back as ns.example.com but instead getting ns.example.com.ns. Of course it wouldn't find any entries for that name because there isn't one, nor is it supposed to. Here's my reverse file: $TTL 86400 @ IN SOA ns.example.com root.example.com. ( 16071990 ; Serial 3600 ; Refresh 1800 ; Retry 604800 ; Expire 86400 ; Minimum TTL ) @ IN NS ns.example.com It's not extraordinarily complicated. What my question is, what other files affect the output for named-checkzone when checking a name against the revers file?

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• Mark Zuckerberg tops the list of 50 Highest Rated CEOs. 3 Indian CEOs feature in the list.

  - by Gopinath

  Mark Zuckerberg, the CEO of Facebook is rated as the best CEO according to a report released by the popular employee reviews website Glassdoor.com. 50,000 employees reviews submitted to Glassdoor in the past 1 year are considered for preparing the rating list and Zukerberg topped the list with 99 percent approval to the question “Do you approve of the way your CEO is leading the company?”. Wow! That’s an amazing support to Zukergerg from his employees though stock market and share holders are not with him. Coincidently Facebook is also rated as the best company to work by Glassdoor in a recent survey. Here is the list of top 10 CEOs Mark Zuckerberg, Facebook; 99.3% Approval Bill McDermott & Jim Hagemann Snabe, SAP; 99% Approval Dominic Barton, McKinsey & Company; 97% Approval Jim Turley, Ernst & Young; 96% Approval John E. Schlifske, Northwestern Mutual; 96% Approval Frank D’Souza, Cognizant Technology Solutions; 96% Approval Joe Tucci, EMC; 96% Approval Paul E. Jacobs, QUALCOMM; 95% Approval Richard K. Davis, U.S. Bank; 95% Approval Pierre Nanterme, Accenture; 95% Approval 3 Indian CEOs in the top 50 list – TCS, Wipro & MindTree The list featured three Indian CEOs and all the three are leading Software IT Services organizations in India and creating thousands of IT jobs.  Natarajan Chandrasekaran – the CEO of TCS is at 25th position, Krishnakumar Natarajan – the CEO of MindTree is at 28th position and  Wipro’s T.K.Kurien is at 44th position. Glad to see Indian CEO joining the global ranks. Tech Heavy Weights Google, Apple, Amazon & Microsoft aren’t in top 10 Another thing to note from this report is that the CEO’s of technology heavy weights Google, Apple, Amazon and Microsoft are not in the top10 list- looks like their employees are not really happy with their bosses. At least not as happy as their peers at Facebook. Google CEO’s Larry Page is at 11th position, Jeff Bezos of Amazon at 16th position and Tim Cook of Apple is at 18th position. Well the Microsoft CEO is not even in the list of top 50!! You can read the complete list of ratings at Glassdoor.com’s blog. Photo Credit: Andrew Feinberg

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• Functional programming and stateful algorithms

  - by bigstones

  I'm learning functional programming with Haskell. In the meantime I'm studying Automata theory and as the two seem to fit well together I'm writing a small library to play with automata. Here's the problem that made me ask the question. While studying a way to evaluate a state's reachability I got the idea that a simple recursive algorithm would be quite inefficient, because some paths might share some states and I might end up evaluating them more than once. For example, here, evaluating reachability of g from a, I'd have to exclude f both while checking the path through d and c: So my idea is that an algorithm working in parallel on many paths and updating a shared record of excluded states might be great, but that's too much for me. I've seen that in some simple recursion cases one can pass state as an argument, and that's what I have to do here, because I pass forward the list of states I've gone through to avoid loops. But is there a way to pass that list also backwards, like returning it in a tuple together with the boolean result of my canReach function? (although this feels a bit forced) Besides the validity of my example case, what other techniques are available to solve this kind of problems? I feel like these must be common enough that there have to be solutions like what happens with fold* or map. So far, reading learnyouahaskell.com I didn't find any, but consider I haven't touched monads yet. (if interested, I posted my code on codereview)

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• Reverse lookup SERVFAIL

  - by Quan Tran

  I just set up a DNS server and a web server using Virtualbox. The IP address of the DNS server is 192.168.56.101 and the web server 192.168.56.102. Here are my configuration files for the DNS server: named.conf: // // named.conf // // Provided by Red Hat bind package to configure the ISC BIND named(8) DNS // server as a caching only nameserver (as a localhost DNS resolver only). // // See /usr/share/doc/bind*/sample/ for example named configuration files. // options { directory "/var/named"; dump-file "/var/named/data/cache_dump.db"; statistics-file "/var/named/data/named_stats.txt"; memstatistics-file "/var/named/data/named_mem_stats.txt"; //query-source address * port 53; //forward first; forwarders { 8.8.8.8; 8.8.4.4; }; listen-on port 53 { 127.0.0.1; 192.168.56.0/24; }; allow-query { localhost; 192.168.56.0/24; }; recursion yes; dnssec-enable yes; dnssec-validation yes; dnssec-lookaside auto; /* Path to ISC DLV key */ bindkeys-file "/etc/named.iscdlv.key"; managed-keys-directory "/var/named/dynamic"; }; logging { channel default_debug { file "data/named.run"; severity debug 10; print-category yes; print-time yes; print-severity yes; }; }; zone "quantran.com" in { type master; file "named.quantran.com"; }; zone "56.168.192.in-addr.arpa" in { type master; file "named.192.168.56"; allow-update { none; }; }; include "/etc/named.rfc1912.zones"; include "/etc/named.root.key"; named.quantran.com: $TTL 86400 quantran.com. IN SOA dns1.quantran.com. root.quantran.com. ( 100 ; serial 3600 ; refresh 600 ; retry 604800 ; expire 86400 ) IN NS dns1.quantran.com. dns1.quantran.com. IN A 192.168.56.101 www.quantran.com. IN A 192.168.56.102 named.192.168.56: $TTL 86400 $ORIGIN 56.168.192.in-addr.arpa. @ IN SOA dns1.quantran.com. root.quantran.com. ( 100 ; serial 3600 ; refresh 600 ; retry 604800 ; expire 86400 ) ; minimum IN NS dns1.quantran.com. 101.56.168.192.in-addr.arpa. IN PTR dns1.quantran.com. 102 IN PTR www.quantran.com. When I try a normal lookup from the host (I configured so that the only nameserver the host uses is the DNS server 192.168.56.101): quan@quantran:~$ host www.quantran.com www.quantran.com has address 192.168.56.102 quan@quantran:~$ host dns1.quantran.com dns1.quantran.com has address 192.168.56.101 But when I try a reverse lookup: quan@quantran:~$ host -v 192.168.56.101 192.168.56.101 Trying "101.56.168.192.in-addr.arpa" Using domain server: Name: 192.168.56.101 Address: 192.168.56.101#53 Aliases: Host 101.56.168.192.in-addr.arpa not found: 2(SERVFAIL) Received 45 bytes from 192.168.56.101#53 in 0 ms quan@quantran:~$ host -v 192.168.56.102 192.168.56.101 Trying "102.56.168.192.in-addr.arpa" Using domain server: Name: 192.168.56.101 Address: 192.168.56.101#53 Aliases: Host 102.56.168.192.in-addr.arpa not found: 2(SERVFAIL) Received 45 bytes from 192.168.56.101#53 in 0 ms So why can't I perform a reverse lookup? Anything wrong with the zone configuration files? Thanks in advance :) Oh, here is the output from the log file /var/named/data/named.run when I perform the reverse lookup: quan@quantran:~$ host 192.168.56.102 192.168.56.101 Using domain server: Name: 192.168.56.101 Address: 192.168.56.101#53 Aliases: Host 102.56.168.192.in-addr.arpa not found: 2(SERVFAIL) /var/named/data/named.run: 02-Jun-2014 15:18:11.950 client: debug 3: client 192.168.56.1#51786: UDP request 02-Jun-2014 15:18:11.950 client: debug 5: client 192.168.56.1#51786: using view '_default' 02-Jun-2014 15:18:11.950 security: debug 3: client 192.168.56.1#51786: request is not signed 02-Jun-2014 15:18:11.950 security: debug 3: client 192.168.56.1#51786: recursion available 02-Jun-2014 15:18:11.950 client: debug 3: client 192.168.56.1#51786: query 02-Jun-2014 15:18:11.950 client: debug 10: client 192.168.56.1#51786: ns_client_attach: ref = 1 02-Jun-2014 15:18:11.950 query-errors: debug 1: client 192.168.56.1#51786: query failed (SERVFAIL) for 102.56.168.192.in-addr.arpa/IN/PTR at query.c:5428 02-Jun-2014 15:18:11.950 client: debug 3: client 192.168.56.1#51786: error 02-Jun-2014 15:18:11.950 client: debug 3: client 192.168.56.1#51786: send 02-Jun-2014 15:18:11.950 client: debug 3: client 192.168.56.1#51786: sendto 02-Jun-2014 15:18:11.951 client: debug 3: client 192.168.56.1#51786: senddone 02-Jun-2014 15:18:11.951 client: debug 3: client 192.168.56.1#51786: next 02-Jun-2014 15:18:11.951 client: debug 10: client 192.168.56.1#51786: ns_client_detach: ref = 0 02-Jun-2014 15:18:11.951 client: debug 3: client 192.168.56.1#51786: endrequest 02-Jun-2014 15:18:11.951 client: debug 3: client @0xb537e008: udprecv Also, I made some changes to the log section in named.conf.

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• Is it possible to implement an infinite IEnumerable without using yield with only C# code?

  - by sinelaw

  This isn't a practical problem, it's more of a riddle. Problem I'm curious to know if there's a way to implement something equivalent to the following, but without using yield: IEnumerable<T> Infinite<T>() { while (true) { yield return default(T); } } Rules You can't use the yield keyword Use only C# itself directly - no IL code, no constructing dynamic assemblies etc. You can only use the basic .NET lib (only mscorlib.dll, System.Core.dll? not sure what else to include). However if you find a solution with some of the other .NET assemblies (WPF?!), I'm also interested. Don't implement IEnumerable or IEnumerator. Notes The closest I've come yet: IEnumerable<int> infinite = null; infinite = new int[1].SelectMany(x => new int[1].Concat(infinite)); This is "correct" but hits a StackOverflowException after 14399 iterations through the enumerable (not quite infinite). I'm thinking there might be no way to do this due to the CLR's lack of tail recursion optimization. A proof would be nice :)

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• PCRE limits exceeded, but triggering rules are SQL related

  - by Wolfe

  [Mon Oct 15 17:12:13 2012] [error] [client xx.xx.xx.xx] ModSecurity: Rule 1d4ad30 [id "300014"][file "/usr/local/apache/conf/modsec2.user.conf"][line "349"] - Execution error - PCRE limits exceeded (-8): (null). [hostname "domain.com"] [uri "/admin.php"] [unique_id "UHx8LEUQwYEAAGutKkUAAAEQ"] And similar are spamming my error log for apache. It's only the admin side.. and only these two lines in the config: line 349: #Generic SQL sigs SecRule ARGS "(or.+1[[:space:]]*=[[:space:]]1|(or 1=1|'.+)--')" "id:300014,rev:1,severity:2,msg:'Generic SQL injection protection'" And line 356: SecRule ARGS "(insert[[:space:]]+into.+values|select.*from.+[a-z|A-Z|0-9]|select.+from|bulk[[:space:]]+insert|union.+select|convert.+\(.*from)" Is there a way to fix this problem? Can someone explain what is going on or if these rules are even valid to cause this error? I know it's supposedly a recursion protection.. but these protect against SQL injection so I'm confused.

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• Deleting a row from self-referencing table

  - by Jake Rutherford

  Came across this the other day and thought “this would be a great interview question!” I’d created a table with a self-referencing foreign key. The application was calling a stored procedure I’d created to delete a row which caused but of course…a foreign key exception. You may say “why not just use a the cascade delete option?” Good question, easy answer. With a typical foreign key relationship between different tables which would work. However, even SQL Server cannot do a cascade delete of a row on a table with self-referencing foreign key. So, what do you do?…… In my case I re-wrote the stored procedure to take advantage of recursion:   -- recursively deletes a Foo ALTER PROCEDURE [dbo].[usp_DeleteFoo]      @ID int     ,@Debug bit = 0    AS     SET NOCOUNT ON;     BEGIN TRANSACTION     BEGIN TRY         DECLARE @ChildFoos TABLE         (             ID int         )                 DECLARE @ChildFooID int                        INSERT INTO @ChildFoos         SELECT ID FROM Foo WHERE ParentFooID = @ID                 WHILE EXISTS (SELECT ID FROM @ChildFoos)         BEGIN             SELECT TOP 1                 @ChildFooID = ID             FROM                 @ChildFoos                             DELETE FROM @ChildFoos WHERE ID = @ChildFooID                         EXEC usp_DeleteFoo @ChildFooID         END                                    DELETE FROM dbo.[Foo]         WHERE [ID] = @ID                 IF @Debug = 1 PRINT 'DEBUG:usp_DeleteFoo, deleted - ID: ' + CONVERT(VARCHAR, @ID)         COMMIT TRANSACTION     END TRY     BEGIN CATCH         ROLLBACK TRANSACTION         DECLARE @ErrorMessage VARCHAR(4000), @ErrorSeverity INT, @ErrorState INT         SELECT @ErrorMessage = ERROR_MESSAGE(), @ErrorSeverity = ERROR_SEVERITY(), @ErrorState = ERROR_STATE()         IF @ErrorState <= 0 SET @ErrorState = 1         INSERT INTO ErrorLog(ErrorNumber,ErrorSeverity,ErrorState,ErrorProcedure,ErrorLine,ErrorMessage)         VALUES(ERROR_NUMBER(), @ErrorSeverity, @ErrorState, ERROR_PROCEDURE(), ERROR_LINE(), @ErrorMessage)         RAISERROR (@ErrorMessage, @ErrorSeverity, @ErrorState)     END CATCH   This procedure will first determine any rows which have the row we wish to delete as it’s parent. It then simply iterates each child row calling the procedure recursively in order to delete all ancestors before eventually deleting the row we wish to delete.

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• How to authenticate users in nested groups in Apache LDAP?

  - by mark

  I've working LDAP authentication with the following setup AuthName "whatever" AuthType Basic AuthBasicProvider ldap AuthLDAPUrl "ldap://server/OU=SBSUsers,OU=Users,OU=MyBusiness,DC=company,DC=local?sAMAccountName?sub?(objectClass=*)" Require ldap-group CN=MySpecificGroup,OU=Security Groups,OU=MyBusiness,DC=company,DC=local This works, however I've to put all users I want to authenticate into MySpecificGroup. But on LDAP server I've configured that MySpecificGroup also contains the group MyOtherGroup with another list of users. But those users in MyOtherGroup are not authenticated, I've to manually add them all to MySpecificGroup and basically can't use the nested grouping. I'm using Windows SBS 2003. Is there a way to configure Apache LDAP to do this? Or is there a problem with possible infinite recursion and thus not allowed?

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• Defining a function that is both a generator and recursive [on hold]

  - by user96454

  I am new to python, so this code might not necessarily be clean, it's just for learning purposes. I had the idea of writing this function that would display the tree down the specified path. Then, i added the global variable number_of_py to count how many python files were in that tree. That worked as well. Finally, i decided to turn the whole thing into a generator, but the recursion breaks. My understanding of generators is that once next() is called python just executes the body of the function and "yields" a value until we hit the end of the body. Can someone explain why this doesn't work? Thanks. import os from sys import argv script, path = argv number_of_py = 0 lines_of_code = 0 def list_files(directory, key=''): global number_of_py files = os.listdir(directory) for f in files: real_path = os.path.join(directory, f) if os.path.isdir(real_path): list_files(real_path, key=key+' ') else: if real_path.split('.')[-1] == 'py': number_of_py += 1 with open(real_path) as g: yield len(g.read()) print key+real_path for i in list_files(argv[1]): lines_of_code += i print 'total number of lines of code: %d' % lines_of_code print 'total number of py files: %d' % number_of_py

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• Java: How to manage UDP client-server state

  - by user92947

  I am trying to write a Java application that works similar to MapReduce. There is a server and several workers. Workers may come and go as they please and the membership to the group has a soft-state. To become a part of the group, the worker must send a UDP datagram to the server, but to continue to be part of the group, the worker must send the UDP datagram to the server every 5 minutes. In order to accommodate temporary errors, a worker is allowed to miss as many as two consecutive periodic UDP datagrams. So, the server must keep track of the current set of workers as well as the last time each worker had sent a UDP datagram. I've implemented a class called WorkerListener that implements Runnable and listens to UDP datagrams on a particular UDP port. Now, to keep track of active workers, this class may maintain a HashSet (or HashMap). When a datagram is received, the server may query the HashSet to check if it is a new member. If so, it can add the new worker to the group by adding an entry into the HashSet. If not, it must reset a "timer" for the worker, noting that it has just heard from the corresponding worker. I'm using the word timer in a generic sense. It doesn't have to be a clock of sorts. Perhaps this could also be implemented using int or long variables. Also, the server must run a thread that continuously monitors the timers for the workers to see that a client that times out on two consecutive datagram intervals, it is removed from the HashSet. I don't want to do this in the WorkerListener thread because it would be blocking on the UDP datagram receive() function. If I create a separate thread to monitor the worker HashSet, it would need to be a different class, perhaps WorkerRegistrar. I must share the HashSet with that thread. Mutual exclusion must also be implemented, then. My question is, what is the best way to do this? Pointers to some sample implementation would be great. I want to use the barebones JDK implementation, and not some fancy state maintenance API that takes care of everything, because I want this to be a useful demonstration for a class that I am teaching. Thanks

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• Composing programs from small simple pieces: OOP vs Functional Programming

  - by Jay Godse

  I started programming when imperative programming languages such as C were virtually the only game in town for paid gigs. I'm not a computer scientist by training so I was only exposed to Assembler and Pascal in school, and not Lisp or Prolog. Over the 1990s, Object-Oriented Programming (OOP) became more popular because one of the marketing memes for OOP was that complex programs could be composed of loosely coupled but well-defined, well-tested, cohesive, and reusable classes and objects. And in many cases that is quite true. Once I learned object-oriented programming my C programs became better because I structured them more like classes and objects. In the last few years (2008-2014) I have programmed in Ruby, an OOP language. However, Ruby has many functional programming (FP) features such as lambdas and procs, which enable a different style of programming using recursion, currying, lazy evaluation and the like. (Through ignorance I am at a loss to explain why these techniques are so great). Very recently, I have written code to use methods from the Ruby Enumerable library, such as map(), reduce(), and select(). Apparently this is a functional style of programming. I have found that using these methods significantly reduce code volume, and make my code easier to debug. Upon reading more about FP, one of the marketing claims made by advocates is that FP enables developers to compose programs out of small well-defined, well-tested, and reusable functions, which leads to less buggy code, and low code volume. QUESTIONS: Is the composition of complex program by using FP techniques contradictory to or complementary to composition of a complex program by using OOP techniques? In which situations is OOP more effective, and when is FP more effective? Is it possible to use both techniques in the same complex program? Do the techniques overlap or contradict each other?

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• bind: blackhole for invalid recursive queries?

  - by Udo G

  I have a name server that's publicly accessible since it is the authoritative name server for a couple of domains. Currently the server is flooded with faked type ANY requests for isc.org, ripe.net and similar (that's a known distributed DoS attack). The server runs BIND and has allow-recursion set to my LAN so that these requests are rejected. In such cases the server responds just with authority and additional sections referring the root servers. Can I configure BIND so that it completely ignores these requests, without sending a response at all?

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• WGet or cURL: Mirror Site from http://site.com And No Internal Access

  - by alharaka

  I have tried wget -m wget -r and a whole bunch of variations. I am getting some of the images on http://site.com, one of the scripts, and none of the CSS, even with the fscking -p parameter. The only HTML page is index.html and there are several more referenced, so I am at a loss. curlmirror.pl on the cURL developers website does not seem to get the job done either. Is there something I am missing? I have tried different levels of recursion with only this URL, but I get the feeling I am missing something. Long story short, some school allows its students to submit web projects, but they want to know how they can collect everything for the instructor who will grade it, instead of him going to all the externally hsoted sites.

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• Setting up a shared media drive

  - by Sam Brightman

  I want to have a shared media drive be transparently usable to all users, whilst also sticking to FHS and Ubuntu standards. The former takes priority if necessary. I currently mount it at /media/Stuff but /media is supposed to be for external media, I believe. The main issue is setting permissions so that access to read and write to the drive can be granted to multiple users working within the same directories. InstallingANewHardDrive seems both slightly confused and not what I want. It claims that this sets ownership for the top-level directory (despite the recursion flag): sudo chown -R USERNAME:USERNAME /media/mynewdrive And that this will let multiple users create files and sub-directories but only delete their own: sudo chgrp plugdev /media/mynewdrive sudo chmod g+w /media/mynewdrive sudo chmod +t /media/mynewdrive However, the group writeable bit does not seem to get inherited, which is troublesome for keeping things organised (prevents creation inside sub-folders originally made by another user). The sticky bit is probably also unwanted for the same reason, although currently it seems that one userA (perhaps the owner of the mount-point?) can delete the userB's files, but not vice-versa. This is fine, as long as userB can create files inside the directory of userA. So: What is the correct mount point? Is plugdev the correct group? Most importantly, how to set up permissions to maintain an organised media drive? I do not want to be running cron jobs to set permissions regularly!

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• Obtain reference to Parent object during instantiation

  - by GoldBishop

  I have a situation where a custom class is a property of another class. What i need to be able to do, if it is possible at all, is obtain a reverse to the "parent" class (ie the the class that holds the current class as a property). For Instance: Public Class Class1 ... public readonly property Prop11 as Class2 public property Prop12 as String ... End Class Public Class Class2 ... private _par as Class1 private _var21 as string ... Public Sub New(...) me._par = ???? ... End Sub public readonly property Prop21 as string Get return me._par.Prop12 & me._var21 End Get End Property ... End Class Ultimately, i am trying to access other properties within Class1 from Class2 as they do have substance for information from within Class2. There are several other classes within Class1 that provide descriptive information to other classes contained within it as properties but the information is not extensible to all of the classes through Inheritance, as Class1 is being used as a resource bin for the property classes and the application itself. Diagram, lazy design ;): Application <- Class1.Prop12 Application <- Class1.Prop11.Prop21 Question: Is it possible to get a recursion through this design setup?

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• Traverse tree with results. Maybe type in Java?

  - by Angelo.Hannes

  I need to check a tree's node state. It can either be OK or NOT_OK. But that state is dependent on its children. So for a node to be OK, every of its children needs to be OK. If one or more of its children is NOT_OK the whole node is NOT_OK. To determine the state of a node I need to aggregate some properties of the node. So I thought of two possible implementations. And they are more or less covered in this question: Why is Option/Maybe considered a good idea and checked exceptions are not? Exception I could pass the properties up the recursion path, and throw an exception if something went wrong. Maybe I implement an Maybe type and let it either hold an error or the aggregated properties. Maybe it is more an Either. I tend towards the last option. And I'm thinking of an enum with two objects. Where I can additionally set those aggregated properties. Am I on the right track? I'm not familiar with the new JDK8 functional stuff. But I'm stuck on JDK7 anyway, so please focus on JDK7.

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• A generic Re-usable C# Property Parser utility [on hold]

  - by Shyam K Pananghat

  This is about a utility i have happened to write which can parse through the properties of a data contracts at runtime using reflection. The input required is a look like XPath string. since this is using reflection, you dont have to add the reference to any of your data contracts thus making pure generic and re- usable.. you can read about this and get the full c# sourcecode here. Property-Parser-A-C-utility-to-retrieve-values-from-any-Net-Data-contracts-at-runtime Now about the doubts which i have about this utility. i am using this utility enormously i many places of my code I am using Regex repeatedly inside a recursion method. does this affect the memmory usage or GC collection badly ?do i have to dispose this manually. if yes how ?. The statements like obj.GetType().GetProperty() and obj.GetType().GetField() returns .net "object" which makes difficult or imposible to introduce generics here. Does this cause to have any overheads like boxing ? on an overall, please suggest to make this utility performance efficient and more light weight on memmory

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• Why is quicksort better than other sorting algorithms in practice?

  - by Raphael

  This is a repost of a question on cs.SE by Janoma. Full credits and spoils to him or cs.SE. In a standard algorithms course we are taught that quicksort is O(n log n) on average and O(n²) in the worst case. At the same time, other sorting algorithms are studied which are O(n log n) in the worst case (like mergesort and heapsort), and even linear time in the best case (like bubblesort) but with some additional needs of memory. After a quick glance at some more running times it is natural to say that quicksort should not be as efficient as others. Also, consider that students learn in basic programming courses that recursion is not really good in general because it could use too much memory, etc. Therefore (and even though this is not a real argument), this gives the idea that quicksort might not be really good because it is a recursive algorithm. Why, then, does quicksort outperform other sorting algorithms in practice? Does it have to do with the structure of real-world data? Does it have to do with the way memory works in computers? I know that some memories are way faster than others, but I don't know if that's the real reason for this counter-intuitive performance (when compared to theoretical estimates).

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• How to get the Host value inside ~/.ssh/config

  - by iconoclast

  Within a ~/.ssh/config or ssh_config file, %h will give you the HostName value, but how do you get the Host ("alias") value? Why would I want to do that? Well, here's an example Host some_host_alias HostName 1.2.3.4 User my_user_name PasswordAuthentication no IdentityFile ~/.ssh/some_host_alias.rsa.id LocalCommand some_script.sh %h # <---- this is the critical line If I pass %h to the script, then it uses 1.2.3.4, which fails to give it all the options it needs to connect to that machine. I need to pass some_host_alias, but I can't find the % variable for that. (And: yes! I'm aware of the risk of recursion. That's solved inside the script.) UPDATE: Kenster pointed out that I could just hard-code the Host value as an argument to the script. Of course this will work in the example I gave, but it won't work if I'm using pattern matching for the Host.

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• How often do you review fundamentals?

  - by mlnyc

  So I've been out of school for a year and a half now. In school, of course we covered all the fundamentals: OS, databases, programming languages (i.e. syntax, binding rules, exception handling, recursion, etc), and fundamental algorithms. the rest were more in-depth topics on things like NLP, data mining, etc. Now, a year ago if you would have told me to write a quicksort, or reverse a singly-linked list, analyze the time complexity of this 'naive' algorithm vs it's dynamic programming counterpart, etc I would have been able to give you a decent and hopefully satisfying answer. But if you would have asked me more real world questions I might have been stumped (things like how would handle logging for an application, or security difference between GET and POST, differences between SQL Server and Oracle SQL, anything I list on my resume as currently working with [jQuery questions, ColdFusion questions, ...] etc) Now, I feel things are the opposite. I haven't wrote my own sort since graduating, and I don't really have to worry much about theoretical things that do not naturally fall into problems I am trying to solve. For example, I might give you some great SQL solutions using an analytical function that I would have otherwise been stumped on or write a cool web application using angular or something but ask me to write an algo for insertAfter(Element* elem) and I might not be able to do it in a reasonable time frame. I guess my question here to the experienced programmers is how do you balance the need to both learn and experiment with new technologies (fun!), working on personal projects (also fun!) working and solving real world problems in a timeboxed environment (so I might reach out to a library that does what I want rather than re-invent the wheel so that I can focus on the problem I am trying to solve) (work, basically), and refreshing on old theoretical material which is still valid for interviews and such (can be a drag)? Do you review older material (such as famous algorithms, dynamic programming, Big-O analysis, locking implementations) regularly or just when you need it? How much time do you dedicate to both in your 'deliberate practice' and do you have a certain to-do list of topics that you want to work on?

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• Is this a good implementation of a loop in Prolog?

  - by Carles Araguz

  First of all, let me tell you that this happens to be the first time I ask something here, so if it's not the right place to do so, please forgive me. I'm developing a rather complex software that has a Prolog core implementing a FSM. Since I don't want it to stop (ever), I'm trying to write a good loop-like predicate that would work using Prolog's recursion. After a few unsuccessful tries (mainly because of stack problems) I ended up having something similar to this: /* Finite State Transition Network */ transition(st0,evnt0,st1). transition(st1,evnt1,st2). transition(st2,evnt2,st0). fsm_state(state(st0),system(Energy,ActivePayloads),[]) :- /* ... */ transition(st0,evnt0,NextState), !, fsm_state(state(NextState),system(Energy,ActivePayloads),[]). fsm_state(state(st1),system(Energy,ActivePayloads),[]) :- /* ... */ transition(st1,evnt1,NextState), !, fsm_state(state(NextState),system(Energy,ActivePayloads),[0,1,2]). fsm_state(state(st2),system(Energy,ActivePayloads),[P|Params]) :- /* ... */ transition(st2,evnt2,NextState), !, fsm_state(state(NextState),system(Energy,ActivePayloads),[]). start :- Sys = system(10,[]), fsm_state(state(s0),Sys,[]). Is this a good approach?

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• dynatree: how can i select child node programmatically

  - by Muhammad Adeel Zahid

  hello everyone i m using jquery's dynaTree in my application and i want to select the all the child nodes programmably when a node is selected. the structure of my tree is as follows <div id = "tree"> <ul> <li>package 1 <ul> <li>module 1.1 <ul> <li> document 1.1.1</li> <li> document 1.1.2</li> </ul> </li> <li>module 1.2 <ul> <li>document 1.2.1</li> <li>document 1.2.2</li> </ul> </li> </ul> </li> <li> package 2 <ul> <li> module 2.1 <ul> <li>document 2.1.1</li> <li>document 2.1.1</li> </ul> </li> </ul> </li> </ul> </div> now what i want is that when i click on tree node with title "package 1" all its child nodes i.e (module 1.1, document 1.1.1, document 1.1.2, module 1.2, document 1.2.1, document 1.2.2) should also be selected below is the approach i tried to use $("#tree").dynatree({ onSelect: function(flag, dtnode) { // This will happen each time a check box is selected/deselected var selectedNodes = dtnode.tree.getSelectedNodes(); var selectedKeys = $.map(selectedNodes, function(node) { //alert(node.data.key); return node.data.key; }); // Set the hidden input field's value to the selected items $('#SelectedItems').val(selectedKeys.join(",")); if (flag) { child = dtnode.childList; alert(child.length); for (i = 0; i < child.length; i++) { var x = child[i].select(true); alert(i); } } }, checkbox: true, onActivate: function(dtnode) { //alert("You activated " + dtnode.data.key); } }); in the if(flag) condition i get all the child nodes of element that is selected by user and it gives me the correct value that i can see from alert(child.length) statement. then i run the loop to select all the children but loop never goes beyond the statement var x = child[i].select(true); and i can never see the statement alert(i) being executed. the result of above statement is that if i select package 1, module 1.1 and document 1.1.1 is also selected but never does it execute alert(i) statement neither other children of package 1 are selected. in my view when first time child[i].select(true) statement is executed it also triggers the on select event of its children thus making a recursion kind of thing is my thinking correct? no matter recursion or what why on earth does it not complete the loop and execute very next instruction alert(i). please help me in solving this problem. i m dying to see that alert any suggestion and help is highly appriciated thanks Adeel

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• Core Data - JSON (TouchJSON) on iPhone

  - by Urizen

  I have the following code which seems to go on indefinitely until the app crashes. It seems to happen with the recursion in the datastructureFromManagedObject method. I suspect that this method: 1) looks at the first managed object and follows any relationship property recursively. 2) examines the object at the other end of the relationship found at point 1 and repeats the process. Is it possible that if managed object A has a to-many relationship with object B and that relationship is two-way (i.e an inverse to-one relationship to A from B - e.g. one department has many employees but each employee has only one department) that the following code gets stuck in infinite recursion as it follows the to-one relationship from object B back to object A and so on. If so, can anyone provide a fix for this so that I can get my whole object graph of managed objects converted to JSON. #import "JSONUtils.h" @implementation JSONUtils - (NSDictionary*)dataStructureFromManagedObject:(NSManagedObject *)managedObject { NSDictionary *attributesByName = [[managedObject entity] attributesByName]; NSDictionary *relationshipsByName = [[managedObject entity] relationshipsByName]; //getting the values correspoinding to the attributes collected in attributesByName NSMutableDictionary *valuesDictionary = [[managedObject dictionaryWithValuesForKeys:[attributesByName allKeys]] mutableCopy]; //sets the name for the entity being encoded to JSON [valuesDictionary setObject:[[managedObject entity] name] forKey:@"ManagedObjectName"]; NSLog(@"+++++++++++++++++> before the for loop"); //looks at each relationship for the given managed object for (NSString *relationshipName in [relationshipsByName allKeys]) { NSLog(@"The relationship name = %@",relationshipName); NSRelationshipDescription *description = [relationshipsByName objectForKey:relationshipName]; if (![description isToMany]) { NSLog(@"The relationship is NOT TO MANY!"); [valuesDictionary setObject:[self dataStructureFromManagedObject:[managedObject valueForKey:relationshipName]] forKey:relationshipName]; continue; } NSSet *relationshipObjects = [managedObject valueForKey:relationshipName]; NSMutableArray *relationshipArray = [[NSMutableArray alloc] init]; for (NSManagedObject *relationshipObject in relationshipObjects) { [relationshipArray addObject:[self dataStructureFromManagedObject:relationshipObject]]; } [valuesDictionary setObject:relationshipArray forKey:relationshipName]; } return [valuesDictionary autorelease]; } - (NSArray*)dataStructuresFromManagedObjects:(NSArray*)managedObjects { NSMutableArray *dataArray = [[NSArray alloc] init]; for (NSManagedObject *managedObject in managedObjects) { [dataArray addObject:[self dataStructureFromManagedObject:managedObject]]; } return [dataArray autorelease]; } //method to call for obtaining JSON structure - i.e. public interface to this class - (NSString*)jsonStructureFromManagedObjects:(NSArray*)managedObjects { NSLog(@"-------------> just before running the recursive method"); NSArray *objectsArray = [self dataStructuresFromManagedObjects:managedObjects]; NSLog(@"-------------> just before running the serialiser"); NSString *jsonString = [[CJSONSerializer serializer] serializeArray:objectsArray]; return jsonString; } - (NSManagedObject*)managedObjectFromStructure:(NSDictionary*)structureDictionary withManagedObjectContext:(NSManagedObjectContext*)moc { NSString *objectName = [structureDictionary objectForKey:@"ManagedObjectName"]; NSManagedObject *managedObject = [NSEntityDescription insertNewObjectForEntityForName:objectName inManagedObjectContext:moc]; [managedObject setValuesForKeysWithDictionary:structureDictionary]; for (NSString *relationshipName in [[[managedObject entity] relationshipsByName] allKeys]) { NSRelationshipDescription *description = [[[managedObject entity]relationshipsByName] objectForKey:relationshipName]; if (![description isToMany]) { NSDictionary *childStructureDictionary = [structureDictionary objectForKey:relationshipName]; NSManagedObject *childObject = [self managedObjectFromStructure:childStructureDictionary withManagedObjectContext:moc]; [managedObject setValue:childObject forKey:relationshipName]; continue; } NSMutableSet *relationshipSet = [managedObject mutableSetValueForKey:relationshipName]; NSArray *relationshipArray = [structureDictionary objectForKey:relationshipName]; for (NSDictionary *childStructureDictionary in relationshipArray) { NSManagedObject *childObject = [self managedObjectFromStructure:childStructureDictionary withManagedObjectContext:moc]; [relationshipSet addObject:childObject]; } } return managedObject; } //method to call for obtaining managed objects from JSON structure - i.e. public interface to this class - (NSArray*)managedObjectsFromJSONStructure:(NSString *)json withManagedObjectContext:(NSManagedObjectContext*)moc { NSError *error = nil; NSArray *structureArray = [[CJSONDeserializer deserializer] deserializeAsArray:[json dataUsingEncoding:NSUTF32BigEndianStringEncoding] error:&error]; NSAssert2(error == nil, @"Failed to deserialize\n%@\n%@", [error localizedDescription], json); NSMutableArray *objectArray = [[NSMutableArray alloc] init]; for (NSDictionary *structureDictionary in structureArray) { [objectArray addObject:[self managedObjectFromStructure:structureDictionary withManagedObjectContext:moc]]; } return [objectArray autorelease]; } @end

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• Defend PHP; convince me it isn't horrible

  - by Jason L

  I made a tongue-in-cheek comment in another question thread calling PHP a terrible language and it got down-voted like crazy. Apparently there are lots of people here who love PHP. So I'm genuinely curious. What am I missing? What makes PHP a good language? Here are my reasons for disliking it: PHP has inconsistent naming of built-in and library functions. Predictable naming patterns are important in any design. PHP has inconsistent parameter ordering of built-in functions, eg array_map vs. array_filter which is annoying in the simple cases and raises all sorts of unexpected behaviour or worse. The PHP developers constantly deprecate built-in functions and lower-level functionality. A good example is when they deprecated pass-by-reference for functions. This created a nightmare for anyone doing, say, function callbacks. A lack of consideration in redesign. The above deprecation eliminated the ability to, in many cases, provide default keyword values for functions. They fixed this in PHP 5, but they deprecated the pass-by-reference in PHP 4! Poor execution of name spaces (formerly no name spaces at all). Now that name spaces exist, what do we use as the dereference character? Backslash! The character used universally for escaping, even in PHP! Overly-broad implicit type conversion leads to bugs. I have no problem with implicit conversions of, say, float to integer or back again. But PHP (last I checked) will happily attempt to magically convert an array to an integer. Poor recursion performance. Recursion is a fundamentally important tool for writing in any language; it can make complex algorithms far simpler. Poor support is inexcusable. Functions are case insensitive. I have no idea what they were thinking on this one. A programming language is a way to specify behavior to both a computer and a reader of the code without ambiguity. Case insensitivity introduces much ambiguity. PHP encourages (practically requires) a coupling of processing with presentation. Yes, you can write PHP that doesn't do so, but it's actually easier to write code in the incorrect (from a sound design perspective) manner. PHP performance is abysmal without caching. Does anyone sell a commercial caching product for PHP? Oh, look, the designers of PHP do. Worst of all, PHP convinces people that designing web applications is easy. And it does indeed make much of the effort involved much easier. But the fact is, designing a web application that is both secure and efficient is a very difficult task. By convincing so many to take up programming, PHP has taught an entire subgroup of programmers bad habits and bad design. It's given them access to capabilities that they lack the understanding to use safely. This has led to PHP's reputation as being insecure. (However, I will readily admit that PHP is no more or less secure than any other web programming language.) What is it that I'm missing about PHP? I'm seeing an organically-grown, poorly-managed mess of a language that's spawning poor programmers. So convince me otherwise!

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• Clustered MSDTC

  - by niel

  Hi I'm setting up a SQL cluster (SQL 2008), Windows 2008 R2. I enable the network access on local dtc and then create a DTC resource in my cluster . the problem is that when i start up the resource it does nto pull through my settings to enable network access. the log shows this: MSDTC started with the following settings: Security Configuration (OFF = 0 and ON = 1): Allow Remote Administrator = 0, Network Clients = 0, Trasaction Manager Communication: Allow Inbound Transactions = 0, Allow Outbound Transactions = 0, Transaction Internet Protocol (TIP) = 0, Enable XA Transactions = 0, Enable SNA LU 6.2 Transactions = 1, MSDTC Communications Security = Mutual Authentication Required, Account = NT AUTHORITY\NetworkService, Firewall Exclusion Detected = 0 Transaction Bridge Installed = 0 Filtering Duplicate Events = 1 where when i restart the local dtc service it says this: Security Configuration (OFF = 0 and ON = 1): Allow Remote Administrator = 0, Network Clients = 1, Trasaction Manager Communication: Allow Inbound Transactions = 1, Allow Outbound Transactions = 1, Transaction Internet Protocol (TIP) = 0, Enable XA Transactions = 1, Enable SNA LU 6.2 Transactions = 1, MSDTC Communications Security = No Authentication Required, Account = NT AUTHORITY\NetworkService, Firewall Exclusion Detected = 0 Transaction Bridge Installed = 0 Filtering Duplicate Events = 1 settings on both nodes in teh cluster is the same. I have reinstalled and restarted to many times to mention. Any ideas ?

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