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• Why doesn't java.util.Set have get(int index)?

  - by Marty Pitt

  I'm sure there's a good reason, but could someone please explain why the java.util.Set interface lacks get(int Index), or any similar get() method? It seems that sets are great for putting things into, but I can't find an elegant way of retrieving a single item from it. If I know I want the first item, I can use set.iterator().next(), but otherwise it seems I have to cast to an Array to retrieve an item at a specific index? What are the appropriate ways of retrieving data from a set? (other than using an iterator) I'm sure the fact that it's excluded from the API means there's a good reason for not doing this -- could someone please enlighten me? EDIT: Some extremely great answers here, and a few saying "more context". The specific scneario was a dbUnit test, where I could reasonalby assert that the returned set from a query had only 1 item, and I was trying to access that item. However, the question is more valid without the scenario, as it remains more focussed : What's the difference between set & list. Thanks to all for the fantastic answers below.

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• Using an SHA1 with Microsoft CAPI

  - by Erik Jõgi

  I have an SHA1 hash and I need to sign it. The CryptSignHash() method requires a HCRYPTHASH handle for signing. I create it and as I have the actual hash value already then set it: CryptCreateHash(cryptoProvider, CALG_SHA1, 0, 0, &hash); CryptSetHashParam(hash, HP_HASHVAL, hashBytes, 0); The hashBytes is an array of 20 bytes. However the problem is that the signature produced from this HCRYPTHASH handle is incorrect. I traced the problem down to the fact that CAPI actually doesn't use all 20 bytes from my hashBytes array. For some reason it thinks that SHA1 is only 4 bytes. To verify this I wrote this small program: HCRYPTPROV cryptoProvider; CryptAcquireContext(&cryptoProvider, NULL, NULL, PROV_RSA_FULL, 0); HCRYPTHASH hash; HCRYPTKEY keyForHash; CryptCreateHash(cryptoProvider, CALG_SHA1, keyForHash, 0, &hash); DWORD hashLength; CryptGetHashParam(hash, HP_HASHSIZE, NULL, &hashLength, 0); printf("hashLength: %d\n", hashLength); And this prints out hashLength: 4 ! Can anyone explain what I am doing wrong or why Microsoft CAPI thinks that SHA1 is 4 bytes (32 bits) instead of 20 bytes (160 bits).

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• Why Does Private Access Remain Non-Private in .NET Within a Class?

  - by AMissico

  While cleaning some code today written by someone else, I changed the access modifier from Public to Private on a class variable/member/field. I expected a long list of compiler errors that I use to "refactor/rework/review" the code that used this variable. Imagine my surprise when I didn't get any errors. After reviewing, it turns out that another instance of the Class can access the private members of another instance declared within the Class. Totally unexcepted. Is this normal? I been coding in .NET since the beginning and never ran into this issue, nor read about it. I may have stumbled onto it before, but only "vaguely noticed" and move on. Can anyone explain this behavoir to me? Am I doing something wrong? I found this behavior in both C# and VB.NET. The code seems to take advantage of the ability to access private variables. Sincerely, Totally Confused Class Foo Private _int As Integer Private _foo As Foo Private _jack As Jack Private _fred As Fred Public Sub SetPrivate() _foo = New Foo _foo._int = 3 'TOTALLY UNEXPECTED _jack = New Jack '_jack._int = 3 'expected compile error because Foo doesn't know Jack _fred = New Fred '_fred._int = 3 'expected compile error because Fred hides from Foo End Sub Private Class Fred Private _int As Integer End Class End Class Class Jack Private _int As Integer End Class

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• heap sort function explanation needed

  - by Codeguru

  Hello, Can someone clearly explain me how these functions of heap sort are working?? void heapSort(int numbers[], int array_size) { int i, temp; for (i = (array_size / 2)-1; i >= 0; i--) siftDown(numbers, i, array_size); for (i = array_size-1; i >= 1; i--) { temp = numbers[0]; numbers[0] = numbers[i]; numbers[i] = temp; siftDown(numbers, 0, i-1); } } void siftDown(int numbers[], int root, int bottom) { int done, maxChild, temp; done = 0; while ((root*2 <= bottom) && (!done)) { if (root*2 == bottom) maxChild = root * 2; else if (numbers[root * 2] > numbers[root * 2 + 1]) maxChild = root * 2; else maxChild = root * 2 + 1; if (numbers[root] < numbers[maxChild]) { temp = numbers[root]; numbers[root] = numbers[maxChild]; numbers[maxChild] = temp; root = maxChild; } else done = 1; } }

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• Java Function Analysis

  - by khan

  Okay..I am a total Python guy and have very rarely worked with Java and its methods. The condition is that I have a got a Java function that I have to explain to my instructor and I have got no clue about how to do so..so if one of you can read this properly, kindly help me out in breaking it down and explaining it. Also, i need to find out any flaw in its operation (i.e. usage of loops, etc.) if there is any. Finally, what is the difference between 'string' and 'string[]' types? public static void search(String findfrom, String[] thething){ if(thething.length > 5){ System.err.println("The thing is quite long"); } else{ int[] rescount = new int[thething.length]; for(int i = 0; i < thething.length; i++){ String[] characs = findfrom.split("[ \"\'\t\n\b\f\r]", 0); for(int j = 0; j < characs.length; j++){ if(characs[j].compareTo(thething[i]) == 0){ rescount[i]++; } } } for (int j = 0; j < thething.length; j++) { System.out.println(thething[j] + ": " + rescount[j]); } } }

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• How to install Zend Framework on Windows

  - by sombe

  "installing Zend Framework is so easy!!!!" yeah right... Ok I'm working with a beginner's book and the ONE thing that is not excessively detailed is the most important part: Installing the darn thing. After browsing the quickstart guide for hours, all it said was: "download Zend [...] add the include directory (bla bla) and YOU'RE DONE!" right, i'm done using Zend. Ok, not really, not yet anyway. I beg of you people, I wanna go to bed, please tell me how (in simple 6th grade detail) to install the framework. I've got the unzipped folder in my htdocs directory, and I placed zf.bat+zf.php in the htdocs root. What's next? thank you so much. EDIT: Thanks guys for all the answers. Unfortunately I haven't been able to work with this or find a good enough resource to explain it to me in plain english. It seems that this framework adheres more so to programmers than to beginners. I've since yesterday read a little on CakePHP and found that it was incredibly easy to install and tune. As oppose to Zend Framework, where I had to dig in my "environment variables", configure "httpd.conf" and almost tie the knot between my computer driver cables to just get it running, CakePHP has already allowed me to put together a nice newbie application. In conclusion, I very much appreciate all of your help. I hope someone else venturing on ZF will be more successful with it. Thanks!

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• Problem in Building mplsh-run in lshkit

  - by Yijinsei

  Hi guy, been trying out this for quite some time but I'm still unable to built mplsh-run from lshkit Not sure if this would help to explain my situation during the building process /tmp/cc17kth4.o: In function `lshkit::MultiProbeLshRecallTable::reset(lshkit::MultiProbeLshModel, unsigned int, double, double)': mplsh-run.cpp:(.text._ZN6lshkit24MultiProbeLshRecallTable5resetENS_18MultiProbeLshModelEjdd[lshkit::MultiProbeLshRecallTable::reset(lshkit::MultiProbeLshModel, unsigned int, double, double)]+0x230): undefined reference to `lshkit::MultiProbeLshModel::recall(double) const' /tmp/cc17kth4.o: In function `void lshkit::MultiProbeLshIndex<unsigned int>::query_recall<lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> > >(float const*, float, lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> >&) const': mplsh-run.cpp:(.text._ZNK6lshkit18MultiProbeLshIndexIjE12query_recallINS_11TopkScannerINS_6MatrixIfE8AccessorENS_6metric5l2sqrIfEEEEEEvPKffRT_[void lshkit::MultiProbeLshIndex<unsigned int>::query_recall<lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> > >(float const*, float, lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> >&) const]+0x2c4): undefined reference to `lshkit::MultiProbeLsh::genProbeSequence(float const*, std::vector<unsigned int, std::allocator<unsigned int> >&, unsigned int) const' /tmp/cc17kth4.o: In function `void lshkit::MultiProbeLshIndex<unsigned int>::query<lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> > >(float const*, unsigned int, lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> >&)': mplsh-run.cpp:(.text._ZN6lshkit18MultiProbeLshIndexIjE5queryINS_11TopkScannerINS_6MatrixIfE8AccessorENS_6metric5l2sqrIfEEEEEEvPKfjRT_[void lshkit::MultiProbeLshIndex<unsigned int>::query<lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> > >(float const*, unsigned int, lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> >&)]+0x4a): undefined reference to `lshkit::MultiProbeLsh::genProbeSequence(float const*, std::vector<unsigned int, std::allocator<unsigned int> >&, unsigned int) const' collect2: ld returned 1 exit status the command that i used to built mplsh-run is g++ -I./lshkit/include -L/usr/lib -lm -lgsl -lgslcblas -lboost_program_options-mt mplsh-run.cpp Do you guys have any clue on how I could solve this?

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• PHP Notice: Undefined property: stdClass:

  - by 4D

  I've got an array coming back from a Flash app created in Flash Builder 4. I have a service setup that queries and brings data back from the DB successfully, however the Update script is generating the Undefined Property errors. I'm still learning both PHP and Flash Builder, and don't fully understand what the $this- commands do. If anyone can suggest where this script is going wrong, it is basically just generated by Flash Builder and is not something I've developed myself, I would appreciate it? Also if someone can explain $this- to me that would be awesome too? I've seen them before, but then I've seen scripts doing the same thing that do not use them, so is this an old way of doing things? Really appreciate any input anyone can give. public function updateItem($item) { // TODO Auto-generated method stub // Update an existing record in the database and return the item // Sample code \' $this->connect(); $sql = "UPDATE tbltrust SET inst_code = '$item->inst_code', trust_name = '$item->trust_name', trust_code = '$item->trust_code' WHERE trust_key = '$item->trust_key'"; mysqli_query($this->connection, $sql) or die('Query failed: ' . mysqli_error($this->connection)); mysqli_close($this->connection); }

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• Complicated SQL query

  - by Yandawl

  Please bare with me this is difficult to explain xD http://img90.imageshack.us/i/croppercapture1.png/ This is based on an undergraduate degree course where a student takes many units (say 4 core units and 1 optional unit per year). tblAwardCoreUnits and tblAwardOptUnits store which units are optional and core for which award, hence the relationship to tblAward and tblStudentCoreUnits and tblStudentOptUnits store the particular instances of those units which a particular student is taking. Secondly, a unit can have multiple events (say a lecture and a unit) and each of those events has sessions in which a student can attend, hence tblEvents, tblSessions and tblAttendances. The query I am trying to produce is to get a list of all level one students, grouped by their award that lists the percentage of attendances in all the units in the current level. I've tried and tried with this and the following is the best I've managed to come up with so far... I'd REALLY appreciate any help you can give with this! SELECT tblStudents.enrolmentNo, tblStudents.forename, tblStudents.surname, tblAwards.title, (SELECT COUNT((tblAttendances.attended + tblAttendances.authorisedAbsence)) AS SumOfAttendances FROM tblAttendances INNER JOIN (tblStudents ON tblStudents.enrolmentNo = tblAttendances.enrolmentNo)) / FROM tblUnits, tblAwards INNER JOIN ((tblStudents INNER JOIN tblStudentOptUnit ON tblStudents.studentID = tblStudentOptUnit.studentID) INNER JOIN tblStudentCoreUnit ON tblStudents.studentID = tblStudentCoreUnit.studentID) ON tblAwards.awardID = tblStudents.awardID WHERE (((tblStudents.level)="1") AND ((tblStudents.status)="enrolled")) GROUP BY tblAwards.title ORDER BY tblStudents.forname;

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• No idea how to solve SICP exercise 1.11

  - by Javier Badia

  This is not homework. Exercise 1.11: A function f is defined by the rule that f(n) = n if n<3 and f(n) = f(n - 1) + 2f(n - 2) + 3f(n - 3) if n 3. Write a procedure that computes f by means of a recursive process. Write a procedure that computes f by means of an iterative process. Implementing it recursively is simple enough. But I couldn't figure out how to do it iteratively. I tried comparing with the Fibonacci example given, but I didn't know how to use it as an analogy. So I gave up (shame on me) and Googled for an explanation, and I found this: (define (f n) (if (< n 3) n (f-iter 2 1 0 n))) (define (f-iter a b c count) (if (< count 3) a (f-iter (+ a (* 2 b) (* 3 c)) a b (- count 1)))) After reading it, I understand the code and how it works. But what I don't understand is the process needed to get from the recursive defintion of the function to this. I don't get how the code formed in someone's head. Could you explain the thought process needed to arrive at the solution?

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• Using PHP to get the source code of a URL I must be logged in to reach

  - by Maxwell

  I am trying to write a PHP script that will get the source code of a page in my Amazon account. However, to reach that page, I must be logged in. From what I understand, I should be able to accomplish this by posting the correct request headers, and then capturing the HTML response. Is that correct? If so, I'd really appreciate it if someone could explain to me how exactly I would do this. If it's not right, I'd love to hear the correct way of doing it! I've used Firebug to get the request and response headers I need. It's just a matter of what to do with them now. I read elsewhere on this site that you can't send a request with the PHP post method, and that perhaps using cURL is the way to go. I really know nothing about cURL, so the more info the better. Also, feel free to point me to some useful tutorials on this topic. Thanks! Max

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• Serializing and deserializing a map with key as string

  - by Grace K

  Hi! I am intending to serialize and deserialize a hashmap whose key is a string. From Josh Bloch's Effective Java, I understand the following. P.222 "For example, consider the case of a harsh table. The physical representation is a sequence of hash buckets containing key-value entries. Which bucket an entry is placed in is a function of the hash code of the key, which is not, in general guaranteed to be the same from JVM implementation to JVM implementation. In fact, it isn't even guranteed to be the same from run to run on the same JVM implementation. Therefore accepting the default serialized form for a hash table would constitute a serious bug. Serializing and deserializing the hash table could yield an object whose invariants were seriously corrupt." My questions are: 1) In general, would overriding the equals and hashcode of the key class of the map resolve this issue and the map can be correctly restored? 2) If my key is a String and the String class is already overriding the hashCode() method, would I still have problem described above. (I am seeing a bug which makes me think this is probably still a problem even though the key is String with overriding hashCode.) 3)Previously, I get around this issue by serializing an array of entries (key, value) and when deserializing I would reconstruct the map. I am wondering if there is a better approach. 4) If the answers to question 1 and 2 are that I still can't be guaranteed. Could someone explain why? If the hashCodes are the same would they go to the same buckets across JVMs? Thanks, Grace

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• Common Lisp condition system for transfer of control

  - by Ken

  I'll admit right up front that the following is a pretty terrible description of what I want to do. Apologies in advance. Please ask questions to help me explain. :-) I've written ETLs in other languages that consist of individual operations that look something like: // in class CountOperation IEnumerable<Row> Execute(IEnumerable<Row> rows) { var count = 0; foreach (var row in rows) { row["record number"] = count++; yield return row; } } Then you string a number of these operations together, and call The Dispatcher, which is responsible for calling Operations and pushing data between them. I'm trying to do something similar in Common Lisp, and I want to use the same basic structure, i.e., each operation is defined like a normal function that inputs a list and outputs a list, but lazily. I can define-condition a condition (have-value) to use for yield-like behavior, and I can run it in a single loop, and it works great. I'm defining the operations the same way, looping through the inputs: (defun count-records (rows) (loop for count from 0 for row in rows do (signal 'have-value :value `(:count ,count @,row)))) The trouble is if I want to string together several operations, and run them. My first attempt at writing a dispatcher for these looks something like: (let ((next-op ...)) ;; pick an op from the set of all ops (loop (handler-bind ((have-value (...))) ;; records output from operation (setq next-op ...) ;; pick a new next-op (call next-op))) But restarts have only dynamic extent: each operation will have the same restart names. The restart isn't a Lisp object I can store, to store the state of a function: it's something you call by name (symbol) inside the handler block, not a continuation you can store for later use. Is it possible to do something like I want here? Or am I better off just making each operation function explicitly look at its input queue, and explicitly place values on the output queue?

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• Does unboxing just return a pointer to the value within the boxed object on the heap?

  - by Charles

  I this MSDN Magazine article, the author states (emphasis mine): Note that boxing always creates a new object and copies the unboxed value's bits to the object. On the other hand, unboxing simply returns a pointer to the data within a boxed object: no memory copy occurs. However, it is commonly the case that your code will cause the data pointed to by the unboxed reference to be copied anyway. I'm confused by the sentence I've bolded and the sentence that follows it. From everything else I've read, including this MSDN page, I've never before heard that unboxing just returns a pointer to the value on the heap. I was under the impression that unboxing would result in you having a variable containing a copy of the value on the stack, just as you began with. After all, if my variable contains "a pointer to the value on the heap", then I haven't got a value type, I've got a pointer. Can someone explain what this means? Was the author on crack? (There is at least one other glaring error in the article). And if this is true, what are the cases where "your code will cause the data pointed to by the unboxed reference to be copied anyway"? I just noticed that the article is nearly 10 years old, so maybe this is something that changed very early on in the life of .Net.

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• PHP static function self:: in joomla JFactory class explanation?

  - by Carbon6

  Hi I'm looking at the code of Joomla and trying to figure out what exactly happends in this function. index.php makes a call to function $app = JFactory::getApplication('site'); jfactory.php code public static function getApplication($id = null, $config = array(), $prefix='J') { if (!self::$application) { jimport('joomla.application.application'); self::$application = JApplication::getInstance($id, $config, $prefix); } return self::$application; } application.php code.. public static function getInstance($client, $config = array(), $prefix = 'J') { static $instances; if (!isset($instances)) { $instances = array(); } ....... more code ........ return $instances[$client]; } Now I cannot figure out in function getApplication why is self:$application used. self::$application = JApplication::getInstance($id, $config, $prefix); $application is always null, what is the purpose of using this approach. I tryied modifying it to $var = JApplication::getInstance($id, $config, $prefix); and returnig it but it doesn't work. I would be very glad if someone with more knowledge could explain what is happening here detailed as possible. Many thanks.

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• Assemblies mysteriously loaded into new AppDomains

  - by Eric

  I'm testing some code that does work whenever assemblies are loaded into an appdomain. For unit testing (in VS2k8's built-in test host) I spin up a new, uniquely-named appdomain prior to each test with the idea that it should be "clean": [TestInitialize()] public void CalledBeforeEachTestMethod() { AppDomainSetup appSetup = new AppDomainSetup(); appSetup.ApplicationBase = @"G:\<ProjectDir>\bin\Debug"; Evidence baseEvidence = AppDomain.CurrentDomain.Evidence; Evidence evidence = new Evidence( baseEvidence ); _testAppDomain = AppDomain.CreateDomain( "myAppDomain" + _appDomainCounter++, evidence, appSetup ); } [TestMethod] public void MissingFactoryCausesAppDomainUnload() { SupportingClass supportClassObj = (SupportingClass)_testAppDomain.CreateInstanceAndUnwrap( GetType().Assembly.GetName().Name, typeof( SupportingClass ).FullName ); try { supportClassObj.LoadMissingRegistrationAssembly(); Assert.Fail( "Should have nuked the app domain" ); } catch( AppDomainUnloadedException ) { } } [TestMethod] public void InvalidFactoryMethodCausesAppDomainUnload() { SupportingClass supportClassObj = (SupportingClass)_testAppDomain.CreateInstanceAndUnwrap( GetType().Assembly.GetName().Name, typeof( SupportingClass ).FullName ); try { supportClassObj.LoadInvalidFactoriesAssembly(); Assert.Fail( "Should have nuked the app domain" ); } catch( AppDomainUnloadedException ) { } } public class SupportingClass : MarshalByRefObject { public void LoadMissingRegistrationAssembly() { MissingRegistration.Main(); } public void LoadInvalidFactoriesAssembly() { InvalidFactories.Main(); } } If every test is run individually I find that it works correctly; the appdomain is created and has only the few intended assemblies loaded. However, if multiple tests are run in succession then each _testAppDomain already has assemblies loaded from all previous tests. Oddly enough, the two tests get appdomains with different names. The test assemblies that define MissingRegistration and InvalidFactories (two different assemblies) are never loaded into the unit test's default appdomain. Can anyone explain this behavior?

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• C# iterator is executed twice when composing two IEnumerable methods

  - by achristoph

  I just started learning about C# iterator but got confused with the flow of the program after reading the output of the program. The foreach with uniqueVals seems to be executed twice. My understanding is that the first few lines up to the line before "Nums in Square: 3" should not be there. Can anyone help to explain why this happens? The output is: Unique: 1 Adding to uniqueVals: 1 Unique: 2 Adding to uniqueVals: 2 Unique: 2 Unique: 3 Adding to uniqueVals: 3 Nums in Square: 3 Unique: 1 Adding to uniqueVals: 1 Square: 1 Number returned from Unique: 1 Unique: 2 Adding to uniqueVals: 2 Square: 2 Number returned from Unique: 4 Unique: 2 Unique: 3 Adding to uniqueVals: 3 Square: 3 Number returned from Unique: 9 static class Program { public static IEnumerable<T> Unique<T>(IEnumerable<T> sequence) { Dictionary<T, T> uniqueVals = new Dictionary<T, T>(); foreach (T item in sequence) { Console.WriteLine("Unique: {0}", item); if (!uniqueVals.ContainsKey(item)) { Console.WriteLine("Adding to uniqueVals: {0}", item); uniqueVals.Add(item, item); yield return item; Console.WriteLine("After Unique yield: {0}", item); } } } public static IEnumerable<int> Square(IEnumerable<int> nums) { Console.WriteLine("Nums in Square: {0}", nums.Count()); foreach (int num in nums) { Console.WriteLine("Square: {0}", num); yield return num * num; Console.WriteLine("After Square yield: {0}", num); } } static void Main(string[] args) { var nums = new int[] { 1, 2, 2, 3 }; foreach (int num in Square(Unique(nums))) Console.WriteLine("Number returned from Unique: {0}", num); Console.Read(); } }

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• Code Golf: Find the possible ways on a numpad

  - by ikar

  I was bored today at school and so I tried to amuse myself using my calculator and a "game" I've invented which isn't really a game but keeps the boringness away. Also some time has passed since the last real code-golf here, so I decided to create this one. Imagine a simplified numpad like you know it from your phone (I'll leave the 0 out for this code-golf as it kinda destroys all the fun) 1 2 3 4 5 6 7 8 9 Now the rules of the game were always: At the end every digit must have been visited exactly once You can start at any digit you want You can always move one digit up, down, left or right. You can't move diagonally! There a quite a lot of possible ways (or not; I haven't found out yet), here some trivial examples: > > v v < < > > | The output of the golf-program should look something like the above, I'll try to explain: Symbols: Go right < Go left ^ Go up v Go down | End of the way Example solutions: (Program output can either be the numbers pressed in the right order from beginning point to end, or an (ASCII) picture like above) 147852369 569874123 523698741 So if we speak out the example above it would be: Start at 1, move right to 2, move right to 3, go down to 6, go left to 5, go left to 4, go down to 7, go right to 8 then go right to 9 and we are finished! Now there are many different ways possible: You could as well start at 5 and go around it in a circle. So the task would be: Write a program that can compute (using brute-force or whatever) the possible solutions for the numpad problem described above. (Friendly rethorical question with smiley removed because it made some people think that this is homework)

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• escape sequence in c

  - by prp

  int main() { char *arr="\\0\1\8234\0"; int i=0; while(arr[i]) { switch(arr[i]) { case '0': printf("is no"); break; case '00': printf("is debugging\n"); break; case 0: printf("It is Avishkar\n"); break; case '\\': printf("This "); break; case '\1': printf("t s"); break; case '8': printf("o s"); break; case '2': printf("imp"); break; case '3': printf("le as"); break; case 2: case 3: case 4: case 8: printf("This "); break; default: printf(" it seems\n"); break;} i++; } } please explain the o/p ? i am not able to get it..

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• Dynamic/Generic ViewModelBase?

  - by Shimmy

  I am learning MVVM now and I understand few things (more than but few are here..): Does every model potentially exposed (thru a VM) to the View is having a VM? For example, if I have a Contact and Address entity and each contact has an Addresses (many) property, does it mean I have to create a ContactViewModel and an AddressViewModel etc.? Do I have to redeclare all the properties of the Model again in the ViewModel (i.e. FirstName, LastName blah blah)? why not have a ViewModelBase and the ContactViewMode will be a subclass of ViewModelBase accessing the Entity's properties itself? and if this is a bad idea that the View has access to the entity (please explain why), then why not have the ViewModelBase be a DynamicObject (view the Dictionary example @ the link page), so I don't have to redeclare all the properties and validation over and over in the two tiers (M & VM) - because really, the View is anyway accessing the ViewModel's fields via reflection anyway. I think MVVM was the hardest technology I've ever learned. it doesn't have out-the-box support and there are to many frameworks and methods to achieve it, and in the other hand there is no arranged way to learn it (as MVC for instance), learning MVVM means browsing and surfing around trying to figure out what's better. Bottom line, what I mean by this section is please go and vote to MSFT to add MVVM support in the BCL and generators for VMs and Vs according to the Ms. Thanks

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• How do I implement configurations and settings?

  - by Malvolio

  I'm writing a system that is deployed in several places and each site needs its own configurations and settings. A "configuration" is a named value that is necessary to a particular site (e.g., the database URL, S3 bucket name); every configuration is necessary, there is not usually a default, and it's typically string-valued. A setting is a named value but it just tweaks the behavior of the system; it's often numeric or Boolean, and there's usually some default. So far, I've been using property files or thing like them, but it's a terrible solution. Several times, a developer has added a requirement for a configuration but not added the value to file for the live configuration, so the new release passed all the tests, then failed when released to live. Better, of course, for every file to be compiled — so if there's a missing configuration, or one of the wrong type, it won't get past the compiler — and inject the site-specific class into the build for each site. As a bones, a Scala file can easy model more complex values, especially lists, but also maps and tuples. The downside is, the files are sometimes maintained by people who aren't developers, so it has to be pretty self-explanatory, which was the advantage of property files. (Someone explain XML configurations to me: all the complexity of a compilable file but the run-time risk of a property file.) What I'm looking for is an easy pattern for defining a group required names and allowable values. Any suggestions?

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• How do you deserialize a collection with child collections?

  - by Stuart Helwig

  I have a collection of custom entity objects one property of which is an ArrayList of byte arrays. The custom entity is serializable and the collection property is marked with the following attributes: [XmlArray("Images"), XmlArrayItem("Image",typeof(byte[]))] So I serialize a collection of these custom entities and pass them to a web service, as a string. The web service receives the string and byte array in tact, The following code then attempts to deserialize the collection - back into custom entities for processing... XmlSerializer ser = new XmlSerializer(typeof(List<myCustomEntity>)); StringReader reader = new StringReader(xmlStringPassedToWS); List<myCustomEntity> entities = (List<myCustomEntity>)ser.Deserialize(reader); foreach (myCustomEntity e in entities) { // ...do some stuff... foreach (myChildCollection c in entities.ChildCollection { // .. do some more stuff.... } } I've checked the XML resulting from the initial serialization and it does contain byte array - the child collection, as does the StringReader built above. After the deserialization process, the resulting collection of custom entites is fine, except that each object in the collection does not contain any items in its child collection. (i.e. it doesn't get to "...do some more stuff..." above. Can someone please explain what I am doing wrong? Is it possible to serialize ArrayLists within a generic collection of custom entities?

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• Runing bcdedit from python in Windows 2008 SP2

  - by Lee-Man

  I do not know windows well, so that may explain my dilemma ... I am trying to run bcdedit in Windows 2008R2 from Python 2.6. My Python routine to run a command looks like this: def run_program(cmd_str): """Run the specified command, returning its output as an array of lines""" dprint("run_program(%s): entering" % cmd_str) cmd_args = cmd_str.split() subproc = subprocess.Popen(cmd_args, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True) (outf, errf) = (subproc.stdout, subproc.stderr) olines = outf.readlines() elines = errf.readlines() if Options.debug: if elines: dprint('Error output:') for line in elines: dprint(line.rstrip()) if olines: dprint('Normal output:') for line in olines: dprint(line.rstrip()) errf.close() outf.close() res = subproc.wait() dprint('wait result=', res) return (res, olines) I call this function thusly: (res, o) = run_program('bcdedit /set {current} MSI forcedisable') This command works when I type it from a cmd window, and it works when I put it in a batch file and run it from a command window (as Administrator, of course). But when I run it from Python (as Administrator), Python claims it can't find the command, returning: bcdedit is not recognized as an internal or external command, operable program or batch file Also, if I trying running my batch file from Python (which works from the command line), it also fails. I've also tried it with the full path to bcdedit, with the same results. What is it about calling bcdedit from Python that makes it not found? Note that I can call other EXE files from Python, so I have some level of confidence that my Python code is sane ... but who knows. Any help would be most appreciated.

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• Why does this extension method throw a NullReferenceException in VB.NET?

  - by Dan

  From previous experience I had been under the impression that it's perfectly legal (though perhaps not advisable) to call extension methods on a null instance. So in C#, this code compiles and runs: // code in static class static bool IsNull(this object obj) { return obj == null; } // code elsewhere object x = null; bool exists = !x.IsNull(); However, I was just putting together a little suite of example code for the other members of my development team (we just upgraded to .NET 3.5 and I've been assigned the task of getting the team up to speed on some of the new features available to us), and I wrote what I thought was the VB.NET equivalent of the above code, only to discover that it actually throws a NullReferenceException. The code I wrote was this: ' code in module ' <Extension()> _ Function IsNull(ByVal obj As Object) As Boolean Return obj Is Nothing End Function ' code elsewhere ' Dim exampleObject As Object = Nothing Dim exists As Boolean = Not exampleObject.IsNull() The debugger stops right there, as if I'd called an instance method. Am I doing something wrong (e.g., is there some subtle difference in the way I defined the extension method between C# and VB.NET)? Is it actually not legal to call an extension method on a null instance in VB.NET, though it's legal in C#? (I would have thought this was a .NET thing as opposed to a language-specific thing, but perhaps I was wrong.) Can anybody explain this one to me?

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• adding virtual function to the end of the class declaration avoids binary incompatibility?

  - by bob

  Could someone explain to me why adding a virtual function to the end of a class declaration avoids binary incompatibility? If I have: class A { public: virtual ~A(); virtual void someFuncA() = 0; virtual void someFuncB() = 0; virtual void other1() = 0; private: int someVal; }; And later modify this function to: class A { public: virtual ~A(); virtual void someFuncA(); virtual void someFuncB(); virtual void someFuncC(); virtual void other1() = 0; private: int someVal; }; I get a coredump from another .so compiled against the previous declaration. But if I put someFuncC() at the end of the class declaration (after "int someVal"), I don't see coredump anymore. Could someone tell me why this is? And does this trick always work? PS. compiler is gcc, does this work with other compilers?

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