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• File IO with Streams - Best Memory Buffer Size

  - by AJ

  I am writing a small IO library to assist with a larger (hobby) project. A part of this library performs various functions on a file, which is read / written via the FileStream object. On each StreamReader.Read(...) pass, I fire off an event which will be used in the main app to display progress information. The processing that goes on in the loop is vaired, but is not too time consuming (it could just be a simple file copy, for example, or may involve encryption...). My main question is: What is the best memory buffer size to use? Thinking about physical disk layouts, I could pick 2k, which would cover a CD sector size and is a nice multiple of a 512 byte hard disk sector. Higher up the abstraction tree, you could go for a larger buffer which could read an entire FAT cluster at a time. I realise with today's PC's, I could go for a more memory hungry option (a couple of MiB, for example), but then I increase the time between UI updates and the user perceives a less responsive app. As an aside, I'm eventually hoping to provide a similar interface to files hosted on FTP / HTTP servers (over a local network / fastish DSL). What would be the best memory buffer size for those (again, a "best-case" tradeoff between perceived responsiveness vs. performance).

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• JQuery transition animation

  - by kk-dev11

  This program randomly selects two employees from a json-object Employees array, winnerPos is already defined. For better user experience I programmed these functions to change pictures one by one. The animation stops when the randomly selected person is shown on the screen. The slideThrough function will be triggered when the start button is pressed. function slideThrough() { counter = 0; start = true; clearInterval(picInterval); picInterval = setInterval(function () { changePicture(); }, 500); } function changePicture() { if (start) { if (counter > winnerPos) { setWinner(); start = false; killInterval(); } else { var employee = Employees[counter]; winnerPic.fadeOut(200, function () { this.src = 'img/' + employee.image; winnerName.html(employee.name); $(this).fadeIn(300); }); counter++; } } } The problem is the animation doesn't work smoothly. At first it works, but not perfect. The second time the transition happens in an irregular way, i.e. different speed and fadeIn/fadeOut differs from picture to picture. Could anyone help me to fine-tune the transition?

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• header location won't work in php

  - by Jayden Kelly

  I am making a login page for my website but the header location won't work. here is the code of login.php: <?php include ( './includes/header.php' ); if (isset($_POST['submit'])) { $username = $_POST['username']; $password = $_POST['password']; $check_username = mysql_query("SELECT username FROM users WHERE username='$username'"); $numrows = mysql_num_rows($check_username); if ($numrows != 1) { echo 'That User doesn\'t exist.'; } else { $check_password = mysql_query("SELECT password FROM users WHERE password='$password' && username='$username'"); while ($row = mysql_fetch_assoc($check_password)) { $password_db = $row['password']; if ($password_db == $password) { $_SESSION['username'] = $username; header("Location: members.php"); } } } } ?> <h2>Login to Your Account</h2> <form action='login.php' method='POST'> <input type='text' name='username' value='Username ...' onclick='value=""'/><p /> <input type='password' name='password' value='Password ...' onclick='value=""'/><p /> <input type='submit' name='submit' value='Login to my Account' /> </form> I would really appreciate it if someone could help me, thanks. P.S. If you need the php part of the header file it is here: <?php session_start(); include ( './includes/functions.php' ); include ( './includes/connect_to_mysql.php' ); ?>

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• Selective replication with CouchDB

  - by FRotthowe

  I'm currently evaluating possible solutions to the follwing problem: A set of data entries must be synchonized between multiple clients, where each client may only view (or even know about the existence of) a subset of the data. Each client "owns" some of the elements, and the decision who else can read or modify those elements may only be made by the owner. To complicate this situation even more, each element (and each element revision) must have an unique identifier that is equal for all clients. While the latter sounds like a perfect task for CouchDB (and a document based data model would fit my needs perfectly), I'm not sure if the authentication/authorization subsystem of CouchDB can handle these requirements: While it should be possible to restict write access using validation functions, there doesn't seem to be a way to authorize read access. All solutions I've found for this problem propose to route all CouchDB requests through a proxy (or an application layer) that handles authorization. So, the question is: Is it possible to implement an authorization layer that filters requests to the database so that access is granted only to documents that the requesting client has read access to and still use the replication mechanism of CouchDB? Simplified, this would be some kind of "selective replication" where only some of the documents, and not the whole database is replicated. I would also be thankful for directions to some detailed information about how replication works. The CouchDB wiki and even the "Definite Guide" Book are not too specific about that.

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• Handling large datasets with PHP/Drupal

  - by jo

  Hi all, I have a report page that deals with ~700k records from a database table. I can display this on a webpage using paging to break up the results. However, my export to PDF/CSV functions rely on processing the entire data set at once and I'm hitting my 256MB memory limit at around 250k rows. I don't feel comfortable increasing the memory limit and I haven't got the ability to use MySQL's save into outfile to just serve a pre-generated CSV. However, I can't really see a way of serving up large data sets with Drupal using something like: $form = array(); $table_headers = array(); $table_rows = array(); $data = db_query("a query to get the whole dataset"); while ($row = db_fetch_object($data)) { $table_rows[] = $row->some attribute; } $form['report'] = array('#value' => theme('table', $table_headers, $table_rows); return $form; Is there a way of getting around what is essentially appending to a giant array of arrays? At the moment I don't see how I can offer any meaningful report pages with Drupal due to this. Thanks

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• Is there a way to receive data as unsigned char over UDP on Qt?

  - by user269037

  I need to send floating point numbers using a UDP connection to a Qt application. Now in Qt the only function available is qint64 readDatagram ( char * data, qint64 maxSize, QHostAddress * address = 0, quint16 * port = 0 ) which accepts data in the form of signed character buffer. I can convert my float into a string and send it but it will obviously not be very efficient converting a 4 byte float into a much longer sized character buffer. I got hold of these 2 functions to convert a 4 byte float into an unsinged 32 bit integer to transfer over network which works fine for a simple C++ UDP program but for Qt I need to receive the data as unsigned char. Is it possible to avoid converting the floatinf point data into a string and then sending it? uint32_t htonf(float f) { uint32_t p; uint32_t sign; if (f < 0) { sign = 1; f = -f; } else { sign = 0; } p = ((((uint32_t)f)&0x7fff)<<16) | (sign<<31); // Whole part and sign. p |= (uint32_t)(((f - (int)f) * 65536.0f))&0xffff; // Fraction. return p; } float ntohf(uint32_t p) { float f = ((p>>16)&0x7fff); // Whole part. f += (p&0xffff) / 65536.0f; // Fraction. if (((p>>31)&0x1) == 0x1) { f = -f; } // Sign bit set. return f; }

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• Sys. engineer has decided to dynamically transform all XSLs into DLLs on website build process. DLL

  - by John Sullivan

  Hello, OS: Win XP. Here is my situation. I have a browser based application. It is "wrapped" in a Visual Basic application. Our "Systems Engineer Senior" has decided to spawn DLL files from all of our XSL pages (many of which have duplicate names) upon building a new instance of the website and have the active server pages (ASPX) use the DLL instead. This has created a "known issue" in which ~200 DLL naming conflicts occur and, thus, half of our application is broken. I think a solution to this problem is that, thankfully, we're generating the names of the DLLs and linking them up with our application dynamically. Therefore we can do something kludgy like generate a hash and append it to the end of the DLL file name when we build our website, then always reference the DLL that had some kind of random string / hash appended to its name. Aside from outright renaming the DLLs, is there another way to have multiple DLLs with the same name register for one application? I think the answer is "No, only between different applications using a special technique." Please confirm. Another question I have on my mind is whether this whole idea is a good practice -- converting our XSL pages (which we use in mass -- every time a response from our web app occurs) into DLL functions that call a "function" to do what the XSL page did via an active server page (ASPX), when we were before just sending an XML response to an XSL page via aspx.

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• Getting values from another winform and passing it to current!

  - by klm9971

  Hello: I have 2 windows forms. The 1st one who gets active during start of the program has a button in which another 2nd windows form appears which has text field in which user type their name and HIT okay. Now in the 1st form I have a variable name: nameproccessed which takes the name from the second form. But the problem is my button which is in the 1st form has more functions besides taking name, how can I stop the flow of the compiler to take first the name from the second form and then process the rest execution of the function??? Here is the snippet of my code: //1st form //Class1 public string _nameProcessed = ""; private void btnGetSomething_Click(object sender, EventArgs e) { showdial(); //some more functionalities in this function!!! } private void showdial() { InputName inm = new InputName(); inm.Show(); } //2nd form //Class2 public string name; private void btnEnterName_Click(object sender, EventArgs e) { name = tbxName.Text; Class1 ict = new Class1(); ict._nameProcessed = name; this.Close(); } Now I want to take the 'name' from the second form put it on the _nameprocessed in the 1st form and then execute the rest of the function. How can I do that? Any help!

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• How can I write a function template for all types with a particular type trait?

  - by TC

  Consider the following example: struct Scanner { template <typename T> T get(); }; template <> string Scanner::get() { return string("string"); } template <> int Scanner::get() { return 10; } int main() { Scanner scanner; string s = scanner.get<string>(); int i = scanner.get<int>(); } The Scanner class is used to extract tokens from some source. The above code works fine, but fails when I try to get other integral types like a char or an unsigned int. The code to read these types is exactly the same as the code to read an int. I could just duplicate the code for all other integral types I'd like to read, but I'd rather define one function template for all integral types. I've tried the following: struct Scanner { template <typename T> typename enable_if<boost::is_integral<T>, T>::type get(); }; Which works like a charm, but I am unsure how to get Scanner::get<string>() to function again. So, how can I write code so that I can do scanner.get<string>() and scanner.get<any integral type>() and have a single definition to read all integral types? Update: bonus question: What if I want to accept more than one range of classes based on some traits? For example: how should I approach this problem if I want to have three get functions that accept (i) integral types (ii) floating point types (iii) strings, respectively.

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• Intelligent search and generation of Java code, preferrably using Python?

  - by Ipsquiggle

  Basically, I do lots of one-off code generation, large-scale refactorings, etc. etc. in Java. My tool language of choice is Python, but I'll take whatever solutions you can offer. Here is a simplified illustration of what I would like, in a pseudocode Generating an implementation for an interface search within my project: for each Interface as iName: write class(name=iName+"Impl", implements=iName) search within the body of iName: for each Method as mName: write method(name=mName, body="// TODO implement this...") Basically, the tool I'm searching for would allow me to: parse files according to their Java structure ("search for interfaces") search for words contextualized by language elements and types ("variables of type SomeClass", "doStuff() method calls on SomeClass instances") to run searches with structural context ("within the body of the current result") easily replace or generate code (with helpers to generate, as above, or functions for replacing, "rename the interface to Foo", "insert the line Blah.Blah()", etc.) The point is, I don't want to spend a lot of time writing these things, as they are usually throwaway. But sometimes I need something just a little smarter than what grep offers. It wouldn't be too hard to write up a simplistic version of this, but if I'm going to use something like this at all, I'd expect it to be robust. Any suggestions of a tool/library that will help me accomplish this?

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• Using parameterized function calls in SELECT statements. MS SQL Server

  - by geekzlla

  I have taken over some code from a previous developer and have come across this SQL statement that calls several SQL functions. As you can see, the function calls in the select statement pass a parameter to the function. How does the SQL statement know what value to replace the variable with? For the below sample, how does the query engine know what to replace nDeptID with when it calls, fn_SelDeptName_DeptID(nDeptID)? nDeptID IS a column in table Note. SELECT STATEMENT: SELECT nCustomerID AS [Customer ID], nJobID AS [Job ID], dbo.fn_SelDeptName_DeptID(nDeptID) AS Department, nJobTaskID AS JobTaskID, dbo.fn_SelDeptTaskDesc_OpenTask(nJobID, nJobTaskID) AS Task, nStandardNoteID AS StandardNoteID, dbo.fn_SelNoteTypeDesc(nNoteID) AS [Note Type], dbo.fn_SelGPAStandardNote(nStandardNoteID) AS [Standard Note], nEntryDate AS [Entry Date], nUserName as [Added By], nType AS Type, nNote AS Note FROM Note WHERE nJobID = 844261 xORDER BY nJobID, Task, [Entry Date] ====================== Function fn_SelDeptName_DeptID: ALTER FUNCTION [dbo].[fn_SelDeptName_DeptID] (@iDeptID int) RETURNS varchar(25) -- Used by DataCollection for Job Tracking -- if the Deptartment isnt found return an empty string BEGIN -- Return the Department name for the given DeptID. DECLARE @strDeptName varchar(25) IF @iDeptID = 0 SET @strDeptName = '' ELSE BEGIN SET @strDeptName = (SELECT dName FROM Department WHERE dDeptID = @iDeptID) IF (@strDeptName IS NULL) SET @strDeptName = '' END RETURN @strDeptName END ========================== Thanks in advance.

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• Jquery + Prototype Question

  - by mikeyhill

  I recently inherited a site which is botched in all sorts of ways. I'm more of a php guy and initially the js was working just fine. I made no changes to the javascript or the any of the include files but after making a few content edits I'm getting errors from firebug. a.dispatchEvent is not a function emptyFunction()protot...ects.js (line 2) emptyFunction()protot...ects.js (line 2) fireContentLoadedEvent()protot...ects.js (line 2) [Break on this error] var Prototype={Version:'1.6.0.2',Brows...pe,Enumerable);Element.addMethods(); protot...ects.js (line 2) this.m_eTarget.setStyle is not a function [Break on this error] this.m_eTarget.setStyle( { position: 'relative', overflow:'hidden'} ); protot...ects.js (line 43) uncaught exception: [Exception... "Component returned failure code: 0x80070057 (NS_ERROR_ILLEGAL_VALUE)" nsresult: "0x80070057 (NS_ERROR_ILLEGAL_VALUE)" location: "JS frame :: js/prototype_effects.js :: anonymous :: line 2" data: no] Googling around I found several posts that sometimes jquery+prototype don't play well and rearranging the scripts could fix this issue, however being that I didn't touch these sections I'm not sure where I even need to begin to debug. The previous developer incorporated a head.inc file which loads up prototype, scriptaculous and then many of the pages are in a sub-template loading up jquery for functions like lightbox. The site is temp housed at http://dawn.mikeyhill.com Any help is appreciated.

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• Implementing comparision operators via 'tuple' and 'tie', a good idea?

  - by Xeo

  (Note: tuple and tie can be taken from Boost or C++11.) When writing small structs with only two elements, I sometimes tend to choose a std::pair, as all important stuff is already done for that datatype, like operator< for strict-weak-ordering. The downsides though are the pretty much useless variable names. Even if I myself created that typedef, I won't remember 2 days later what first and what second exactly was, especially if they are both of the same type. This gets even worse for more than two members, as nesting pairs pretty much sucks. The other option for that is a tuple, either from Boost or C++11, but that doesn't really look any nicer and clearer. So I go back to writing the structs myself, including any needed comparision operators. Since especially the operator< can be quite cumbersome, I thought of circumventing this whole mess by just relying on the operations defined for tuple: Example of operator<, e.g. for strict-weak-ordering: bool operator<(MyStruct const& lhs, MyStruct const& rhs){ return std::tie(lhs.one_member, lhs.another, lhs.yet_more) < std::tie(rhs.one_member, rhs.another, rhs.yet_more); } (tie makes a tuple of T& references from the passed arguments.) Edit: The suggestion from @DeadMG to privately inherit from tuple isn't a bad one, but it got quite some drawbacks: If the operators are free-standing (possibly friends), I need to inherit publicly With casting, my functions / operators (operator= specifically) can be easily bypassed With the tie solution, I can leave out certain members if they don't matter for the ordering Are there any drawbacks in this implementation that I need to consider?

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• Pthread - setting scheduler parameters

  - by Andna

  I wanted to use read-writer locks from pthread library in a way, that writers have priority over readers. I read in my man pages that If the Thread Execution Scheduling option is supported, and the threads involved in the lock are executing with the scheduling policies SCHED_FIFO or SCHED_RR, the calling thread shall not acquire the lock if a writer holds the lock or if writers of higher or equal priority are blocked on the lock; otherwise, the calling thread shall acquire the lock. so I wrote small function that sets up thread scheduling options. void thread_set_up(int _thread) { struct sched_param *_param=malloc(sizeof (struct sched_param)); int *c=malloc(sizeof(int)); *c=sched_get_priority_min(SCHED_FIFO)+1; _param->__sched_priority=*c; long *a=malloc(sizeof(long)); *a=syscall(SYS_gettid); int *b=malloc(sizeof(int)); *b=SCHED_FIFO; if (pthread_setschedparam(*a,*b,_param) == -1) { //depending on which thread calls this functions, few thing can happen if (_thread == MAIN_THREAD) client_cleanup(); else if (_thread==ACCEPT_THREAD) { pthread_kill(params.main_thread_id,SIGINT); pthread_exit(NULL); } } } sorry for those a,b,c but I tried to malloc everything, still I get SIGSEGV on the call to pthread_setschedparam, I am wondering why?

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• Deleting first and last element of a linked list in C

  - by LuckySlevin

  struct person { int age; char name[100]; struct person *next; }; void delfirst(struct person **p)// For deleting the beginning { struct person *tmp,*m; m = (*p); tmp = (*p)->next; free(m); return; } void delend(struct person **p)// For deleting the end { struct person *tmp,*m; tmp=*p; while(tmp->next!=NULL) { tmp=tmp->next; } m->next=tmp; free(tmp); m->next = NULL; return; } I'm looking for two seperate functions to delete the first and last elements of a linked list. Here is what i tried. What do you suggest? Especially deleting first is so problematic for me.

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• What is the best way to store static data in C# that will never change

  - by Luke101

  I have a class that stores data in asp.net c# application that never changes. I really don't want to put this data in the database - I would like it to stay in the application. Here is my way to store data in the application: public class PostVoteTypeFunctions { private List<PostVoteType> postVotes = new List<PostVoteType>(); public PostVoteTypeFunctions() { PostVoteType upvote = new PostVoteType(); upvote.ID = 0; upvote.Name = "UpVote"; upvote.PointValue = PostVotePointValue.UpVote; postVotes.Add(upvote); PostVoteType downvote = new PostVoteType(); downvote.ID = 1; downvote.Name = "DownVote"; downvote.PointValue = PostVotePointValue.DownVote; postVotes.Add(downvote); PostVoteType selectanswer = new PostVoteType(); selectanswer.ID = 2; selectanswer.Name = "SelectAnswer"; selectanswer.PointValue = PostVotePointValue.SelectAnswer; postVotes.Add(selectanswer); PostVoteType favorite = new PostVoteType(); favorite.ID = 3; favorite.Name = "Favorite"; favorite.PointValue = PostVotePointValue.Favorite; postVotes.Add(favorite); PostVoteType offensive = new PostVoteType(); offensive.ID = 4; offensive.Name = "Offensive"; offensive.PointValue = PostVotePointValue.Offensive; postVotes.Add(offensive); PostVoteType spam = new PostVoteType(); spam.ID = 0; spam.Name = "Spam"; spam.PointValue = PostVotePointValue.Spam; postVotes.Add(spam); } } When the constructor is called the code above is ran. I have some functions that can query the data above too. But is this the best way to store information in asp.net? if not what would you recommend?

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• Why is function's length information of other shared lib in ELF?

  - by minastaros

  Our project (C++, Linux, gcc, PowerPC) consists of several shared libraries. When releasing a new version of the package, only those libs should change whose source code was actually affected. With "change" I mean absolute binary identity (the checksum over the file is compared. Different checksum - different version according to the policy). (I should mention that the whole project is always built at once, no matter if any code has changed or not per library). Usually this can by achieved by hiding private parts of the included Header files and not changing the public ones. However, there was a case where just a delete was added to the destructor of a class TableManager (in the TableManager.cpp file!) of library libTableManager.so, and yet the binary/checksum of library libB.so (which uses class TableManager ) has changed. TableManager.h: class TableManager { public: TableManager(); ~TableManager(); private: int* myPtr; } TableManager.cpp: TableManager::~TableManager() { doSomeCleanup(); delete myPtr; // this delete has been added } By inspecting libB.so with readelf --all libB.so, looking at the .dynsym section, it turned out that the length of all functions, even the dynamically used ones from other libraries, are stored in libB! It looks like this (length is the 668 in the 3rd column): 527: 00000000 668 FUNC GLOBAL DEFAULT UND _ZN12TableManagerD1Ev So my questions are: Why is the length of a function actually stored in the client lib? Wouldn't a start address be sufficient? Can this be suppressed somehow when compiling/linking of libB.so (kind of "stripping")? We would really like to reduce this degree of dependency...

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• PHP classes, parse syntax errors when using 'var' to declare variables

  - by jon

  I am a C# guy trying to translate some of my OOP understanding over to php. I'm trying to make my first class object, and are hitting a few hitches. Here is the beginning of the class: <?php require("Database/UserDB.php"); class User { private var $uid; private var $username; private var $password; private var $realname; private var $email; private var $address; private var $phone; private var $projectArray; public function _construct($username) { $userArray = UserDB::GetUserArray($username); $uid = $userArray['uid']; $username = $userArray['username']; $realname = $userArray['realname']; $email = $userArray['email']; $phone = $userArray['phone']; $i = 1; $projectArray = UserDB::GetUserProjects($this->GetID()); while($projectArray[$i] != null) { $projectArray[$i] = new Project($projectArray[$i]); } UserDB.php is where I have all my static functions interacting with the Database for this User Class. I am getting errors using when I use var, and I'm getting confused. I know I don't HAVE to use var, or declare the variables at all, but I feel it is a better practice to do so. the error is "unexpected T_VAR, expecting T_VARIABLE" When I simply remove var from the declarations it works. Why is this?

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• Getting rid of function's argument

  - by Max

  It is better to explain my intention with code. So right now I have the following code: class A, IInterfaceUsedByB { } class B { void func(A someObject) { func2(someObject, 1); func3(someObject, "string"); func4(someObject, new MyObject()); } func2(A someObject, int val); func3(A someObject, string val); func4(A someObject, C val); } Where func2, func3, func4 do need references to someObject. I want to change this to void func() { with(someObject, () => { func2(1); func3("string"); func4(new MyObject()); } ); } Or even better to void func(someObject) { func2(1); func3("string"); func4(new MyObject()); } So that I don't have to drag this someObject around, but I should still be able to use it inside func2,3,4. I can use any of the three languages (C#, F# or IronPython) for this. UPDATE In the ideal solution class B would be independent of A. func* functions only depend on a small interface of A consisting of 2 methods.

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• How to break out from nested doseqs

  - by fizbin

  Hi, I have a question regarding nested doseq loops. In the start function, once I find an answer I set the atom to true, so that the outer loop validation with :while fails. However it seems that it doesn't break it, and the loops keep on going. What's wrong with it? I am also quite confused with the usage of atoms, refs, agents (Why do they have different names for the update functions when then the mechanism is almost the same?) etc. Is it okay to use an atom in this situation as a flag? Obviously I need a a variable like object to store a state. (def pentagonal-list (map (fn [a] (/ (* a (dec (* 3 a))) 2)) (iterate inc 1))) (def found (atom false)) (defn pentagonal? [a] (let [y (/ (inc (Math/sqrt (inc (* 24 a)))) 6) x (mod (* 10 y) 10)] (if (zero? x) true false))) (defn both-pent? [a b] (let [sum (+ b a) diff (- a b)] (if (and (pentagonal? sum) (pentagonal? diff)) true false))) (defn start [] (doseq [x pentagonal-list :while (false? @found)] (doseq [y pentagonal-list :while (<= y x)] (if (both-pent? x y) (do (reset! found true) (println (- x y)))))))

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• [c++] accessing the hidden 'this' pointer

  - by Kyle

  I have a GUI architecture wherein elements fire events like so: guiManager->fireEvent(BUTTON_CLICKED, this); Every single event fired passes 'this' as the caller of the event. There is never a time I dont want to pass 'this', and further, no pointer except for 'this' should ever be passed. This brings me to a problem: How can I assert that fireEvent is never given a pointer other than 'this', and how can I simplify (and homogenize) calls to fireEvent to just: guiManager->fireEvent(BUTTON_CLICKED); At this point, I'm reminded of a fairly common compiler error when you write something like this: class A { public: void foo() {} }; class B { void oops() { const A* a = new A; a->foo(); } }; int main() { return 0; } Compiling this will give you ../src/sandbox.cpp: In member function ‘void B::oops()’: ../src/sandbox.cpp:7: error: passing ‘const A’ as ‘this’ argument of ‘void A::foo()’ discards qualifiers because member functions pass 'this' as a hidden parameter. "Aha!" I say. This (no pun intended) is exactly what I want. If I could somehow access the hidden 'this' pointer, it would solve both issues I mentioned earlier. The problem is, as far as I know you can't (can you?) and if you could, there would be outcries of "but it would break encapsulation!" Except I'm already passing 'this' every time, so what more could it break. So, is there a way to access the hidden 'this', and if not are there any idioms or alternative approaches that are more elegant than passing 'this' every time?

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• Need a design approach or suggestion for a simple structure using Servlet.

  - by akshay

  Hi I have to design such that whenever user pass a query I process it using servlet and then call the js page to draw the chart 1 user writes a query on a page 2 the page call the servelt class public class MyServlet extends Httpservlet implements DataSourceServlet {..... return data The user see a beautiful string like this.. google.visualization.Query.setResponse......... /Tiger'},{v:80.0}, {v:false}]}]}}); 3 when the user hits on different html page myhtml.js it draws the chart. I want the Myservlet class itself call the myhtml.js page and draw the chart directly. and want to eliminate the beautiful string google.visualization.Query.setResponse......... /Tiger'},{v:80.0}, {v:false}]}]}}); from coming on user's browser What should i do? I tried using functions to call another page like request dispatcher(), redirect() calling myhtml.js page directly after myservlet process the query results. But i get the result like this google.visualization.Query.setResponse......... /Tiger'},{v:80.0}, {v:false}]}]}}); and the entire myhtml.js code page below it on the browsers that to without the chart been draw. Is there anyway to element the beautiful string from coming on clients browser and only show them the chart been drawn ? :) This is the small tutorial i am following http://code.google.com/apis/visualization/documentation/dev/dsl_get_started.html

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• C++ creating generic template function specialisations

  - by Fire Lancer

  I know how to specialise a template function, however what I want to do here is specialise a function for all types which have a given method, eg: template<typename T> void foo(){...} template<typename T, if_exists(T::bar)>void foo(){...}//always use this one if the method T::bar exists T::bar in my classes is static and has different return types. I tried doing this by having an empty base class ("class HasBar{};") for my classes to derive from and using boost::enable_if with boost::is_base_of on my "specialised" version. However the problem then is that for classes that do have bar, the compiler cant resolve which one to use :(. template<typename T> typename boost::enable_if<boost::is_base_of(HasBar, T>, void>::type f() {...} I know that I could use boost::disable_if on the "normal" version, however I do not control the normal version (its provided by a third party library and its expected for specialisations to be made, I just don't really want to make explicit specialisations for my 20 or so classes), nor do I have that much control over the code using these functions, just the classes implementing T::bar and the function that uses it. Is there some way to tell the compiler to "always use this version if possible no matter what" without altering the other versions?

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• C++ reference variables

  - by avd

  I have these two functions (with Point2D & LineVector (has 2 Point2D member variables) classes and SQUARE macro predefined) inline float distance(const Point2D &p1,const Point2D &p2) { return sqrt(SQUARE(p2.getX()-p1.getX())+SQUARE(p2.getY()-p1.getY())); } inline float maxDistance(const LineVector &lv1,const LineVector &lv2) { return max(distance(lv1.p1,lv2.p2),distance(lv1.p2,lv2.p1)); } but it gives compilation error in maxDistance() function (line 238) saying: /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/stl_iterator_base_types.h: In instantiation of `std::iterator_traits<Point2D>': quadrilateral.cpp:238: instantiated from here /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/stl_iterator_base_types.h:129: error: no type named `iterator_category' in `class Point2D' /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/stl_iterator_base_types.h:130: error: no type named `value_type' in `class Point2D ' /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/stl_iterator_base_types.h:131: error: no type named `difference_type' in `class Point2D' /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/stl_iterator_base_types.h:132: error: no type named `pointer' in `class Point2D' /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/stl_iterator_base_types.h:133: error: no type named `reference' in `class Point2D' Please suggest what is the error?

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• How security of the systems might be improved using database procedures?

  - by Centurion

  The usage of Oracle PL/SQL procedures for controlling access to data often emphasized in PL/SQL books and other sources as being more secure approach. I'v seen several systems where all business logic related with data is performed through packages, procedures and functions, so application code becomes quite "dumb" and is only responsible for visualization part. I even heard some devs call such approaches and driving architects as database nazi :) because all logic code resides in database. I do know about DB procedure performance benefits, but now I'm interested in a "better security" when using thick client model. I assume such design mostly used when Oracle (and maybe MS SQL Server) databases are used. I do agree such approach improves security but only if there are not much users and every system user has a database account, so we might control and monitor data access through standard database user security. However, how such approach could increase the security for an average web system where thick clients are used: for example one database user with DML grants on all tables, and other users are handled using "users" and"user_rights" tables? We could use DB procedures, save usernames into context use that for filtering but vulnerability resides at the root - if the main database account is compromised than nothing will help. Of course in a real system we might consider at least several main users (for example frontend_db_user, backend_db_user).

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