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• Force an object to be allocated on the heap

  - by Warren Seine

  A C++ class I'm writing uses shared_from_this() to return a valid boost::shared_ptr<>. Besides, I don't want to manage memory for this kind of object. At the moment, I'm not restricting the way the user allocates the object, which causes an error if shared_from_this() is called on a stack-allocated object. I'd like to force the object to be allocated with new and managed by a smart pointer, no matter how the user declares it. I thought it could be done through a proxy or an overloaded new operator, but I can't find a proper way of doing that. Is there a common design pattern for such usage? If it's not possible, how can I test it at compile time?

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• Simple prime number program - Weird issue with threads C#

  - by Para

  Hi! This is my code: using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading; namespace FirePrime { class Program { static bool[] ThreadsFinished; static bool[] nums; static bool AllThreadsFinished() { bool allThreadsFinished = false; foreach (var threadFinished in ThreadsFinished) { allThreadsFinished &= threadFinished; } return allThreadsFinished; } static bool isPrime(int n) { if (n < 2) { return false; } if (n == 2) { return true; } if (n % 2 == 0) { return false; } int d = 3; while (d * d <= n) { if (n % d == 0) { return false; } d += 2; } return true; } static void MarkPrimes(int startNumber,int stopNumber,int ThreadNr) { for (int j = startNumber; j < stopNumber; j++) nums[j] = isPrime(j); lock (typeof(Program)) { ThreadsFinished[ThreadNr] = true; } } static void Main(string[] args) { int nrNums = 100; int nrThreads = 10; //var threadStartNums = new List<int>(); ThreadsFinished = new bool[nrThreads]; nums = new bool[nrNums]; //var nums = new List<bool>(); nums[0] = false; nums[1] = false; for(int i=2;i<nrNums;i++) nums[i] = true; int interval = (int)(nrNums / nrThreads); //threadStartNums.Add(2); //int aux = firstStartNum; //int i = 2; //while (aux < interval) //{ // aux = interval*i; // i=i+1; // threadStartNums.Add(aux); //} int startNum = 0; for (int i = 0; i < nrThreads; i++) { var _thread = new System.Threading.Thread(() => MarkPrimes(startNum, Math.Min(startNum + interval, nrNums), i)); startNum = startNum + interval; //set the thread to run in the background _thread.IsBackground = true; //start our thread _thread.Start(); } while (!AllThreadsFinished()) { Thread.Sleep(1); } for (int i = 0; i < nrNums; i++) if(nums[i]) Console.WriteLine(i); } } } This should be a pretty simple program that is supposed to find and output the first nrNums prime numbers using nrThreads threads working in parallel. So, I just split nrNums into nrThreads equal chunks (well, the last one won't be equal; if nrThreads doesn't divide by nrNums, it will also contain the remainder, of course). I start nrThreads threads. They all test each number in their respective chunk and see if it is prime or not; they mark everything out in a bool array that keeps a tab on all the primes. The threads all turn a specific element in another boolean array ThreadsFinished to true when they finish. Now the weird part begins: The threads never all end. If I debug, I find that ThreadNr is not what I assign to it in the loop but another value. I guess this is normal since the threads execute afterwards and the counter (the variable i) is already increased by then but I cannot understand how to make the code be right. Can anyone help? Thank you in advance. P.S.: I know the algorithm is not very efficient; I am aiming at a solution using the sieve of Eratosthenes also with x given threads. But for now I can't even get this one to work and I haven't found any examples of any implementations of that algorithm anywhere in a language that I can understand.

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• <= vs < when proving big-o notation

  - by user600197

  We just started learning big-o in class. I understand the general concept that f(x) is big-o of g(x) if there exists two constants c,k such that for all xk |f(x)|<=c|g(x)|. I had a question whether or not it is required that we include the <= to sign or whether it is just sufficient to put the < sign? For example: suppose f(x)=17x+11 and we are to prove that this is O(x^2). Then if we take c=28 and xk=1 we know that 17x+11<=28x^2. So since we know that x will always be greater than 1 this implies that 28x^2 will always be greater than 17x+11. So, do we really need to include the equal sign (<=) or is it okay if we just write (<)? Thanks in advance.

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• Direct3D Rotation Matrix from Vector and vice-versa

  - by Beta Carotin

  I need to compute a rotation matrix from a direction vector, and a direction vector from a rotation matrix. The up direction should correspond to the z-axis, forward is y and right is x; D3DXMATRIX m; // the rotation matrix D3DXVECTOR3 v; // this is the direction vector wich is given D3DXVECTOR3 r; // resulting direction vector float len = D3DXVec3Length(&v); // length of the initial direction vector // compute matrix D3DXMatrixLookAtLH(&m, &v, &D3DXVECTOR3(0,0,0), &D3DXVECTOR3(0,0,1)); // use the matrix on a vector { 0, len, 0 } D3DXVec3TransformCoord(&r, &D3DXVECTOR3(0,len,0), &m); Now, the vector r should be equal to v, but it isnt. What exactly do I have to do to get the results I need?

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• Insert error when sending post array to activerecord

  - by Gonzalo

  I am using CodeIgniter + phpActiveRecord. I am getting all the records from the $_POST array and I want to send that same array to my activeRecord class to insert the data into the DB. This line doesn't seem to be working but I can't get the error because the page is just blank: Car::create($this->input->post()); If the names of the fields are equal to the names of the columns in the table, should it what I pasted above work? ==========SOLVED======== It is possible to do it, and in the model of the object one can add var $name_of_the_field_which_you_don't_process = FALSE; And that's it.

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• How to retrieve large data from oracle database using vbscript

  - by allenzzzxd

  Hi guys, I'm now working on vbscript to do some test. Actuelly, I want to retrieve a large amount of data from an oracle database, so I write the code like this: sql = "Select * from CORE_DB where MC = '" & mstr & "' " Set myrs = db_execute_query(curConnection, sql) Then I count the rows in myrs,there are 248 rows. So then I do a For loop to retrieve some fields of each row. For k = 0 To db_get_rows_count(myrs) But then I found that the content of the row k when k 133 was always equal to k = 133. So this makes an error. As I think, there may be a limit size of mrys ? Could anyone light me about this? Thanks a lot in advance

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• Why isn't Perl's File::GlobMapper exporting globmap?

  - by justintime

  The following is pretty well copied from the documentation. use File::GlobMapper qw( globmap ); for my $pair (globmap '<*.tar.gz>' => '<#1.tgz>' ) { } And it gives String found where operator expected at globmapper_test1.pl line 4, near "globmap '<*.tar.gz>'" (Do you need to predeclare globmap?) (Using ActivePerl 5.10.0 on Windows) Side questions - if GlobMapper only exports one function, why is it set so you have to export it explicitly?

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• help implementing algorithm

  - by davit-datuashvili

  http://en.wikipedia.org/wiki/All_nearest_smaller_values this is site of the problem and here is my code but i have some trouble to implement it import java.util.*; public class stack{ public static void main(String[]args){ int x[]=new int[]{ 0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15 }; Stack<Integer> st=new Stack<Integer>(); for (int a:x){ while (!st.empty() && st.pop()>=a){ System.out.println( st.pop()); if (st.empty()){ break; } else{ st.push(a); } } } } } and here is pseudo code from site S = new empty stack data structure for x in the input sequence: while S is nonempty and the top element of S is greater than or equal to x: pop S if S is empty: x has no preceding smaller value else: the nearest smaller value to x is the top element of S push x onto S

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• jQuery Running a function in a context and adding to a variable

  - by Mark

  For this question I'm going to give a simplified example of what I want to do, and the function I want to learn to write. var collection = ''; <div id='container'> <span>1</span> <span>2</span> <span>3</span> </div> What I want to do this, for every span in the div, take its text, add it to the collection. So ideally it would look like: $('#container').addtoCollection(collection); The method would be something like: $(this).find('span').each(function () { collection = collection + $(this).text(); }). Where the first this would equal #container. So in the end you can do: console.log(collection); and get: 123 How do I write the function that does this? Thanks!

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• help implementing All Nearest Smaller Values algorithm

  - by davit-datuashvili

  http://en.wikipedia.org/wiki/All_nearest_smaller_values this is site of the problem and here is my code but i have some trouble to implement it import java.util.*; public class stack{ public static void main(String[]args){ int x[]=new int[]{ 0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15 }; Stack<Integer> st=new Stack<Integer>(); for (int a:x){ while (!st.empty() && st.pop()>=a){ System.out.println( st.pop()); if (st.empty()){ break; } else{ st.push(a); } } } } } and here is pseudo code from site S = new empty stack data structure for x in the input sequence: while S is nonempty and the top element of S is greater than or equal to x: pop S if S is empty: x has no preceding smaller value else: the nearest smaller value to x is the top element of S push x onto S

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• Is there a shorthand way to denullify a string in C#?

  - by Moose Factory

  Is there a shorthand way to denullify a string in C#? It would be the equivalent of (if 'x' is a string): string y = x == null ? "" : x; I guess I'm hoping there's some operator that would work something like: string y = #x; Wishful thinking, huh? The closest I've got so far is an extension method on the string class: public static string ToNotNull(this string value) { return value == null ? "" : value; } which allows me to do: string y = x.ToNotNull(); Any improvements on that, anyone?

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• C++: conjunction of binds?

  - by Helltone

  Suppose the following two functions: #include <iostream> #include <cstdlib> // atoi #include <cstring> // strcmp #include <boost/bind.hpp> bool match1(const char* a, const char* b) { return (strcmp(a, b) == 0); } bool match2(int a, const char* b) { return (atoi(b) == a); } Each of these functions takes two arguments, but can be transformed into a callable object that takes only one argument by using (std/boost)bind. Something along the lines of: boost::bind(match1, "a test"); boost::bind(match2, 42); I want to be able to obtain, from two functions like these that take one argument and return bool, a callable object that takes two arguments and returns the && of the bools. The type of the arguments is arbitrary. Something like an operator&& for functions that return bool.

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• How to show a page after a specific time period?

  - by Mahfuz

  I want to build an online quiz test site. Suppose, exam will start at 10:00 am and a student login to give exam at 9:45 am. Whenever the student clicks 'Take Exam' button, he/she cannot not get access to the question paper because the exam time is 10:00 am and there are still 15 minutes before the exam start. Now I want to put some Javascript or PHP code that will prohibit the students to give exam earlier and if a students come early, it will show a stopwatch which display the remaining time before exam time and when the current time is equal to exam time then he/she will be directly redirected to the question paper page.

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• Does std::multiset guarantee insertion order?

  - by Naveen

  I have a std::multiset which stores elements of class A. I have provided my own implementation of operator< for this class. My question is if I insert two equivalent objects into this multiset is their order guaranteed? For example, first I insert a object a1 into the set and then I insert an equivalent object a2 into this set. Can I expect the a1 to come before a2 when I iterate through the set? If no, is there any way to achieve this using multiset?

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• Scala match/compare enumerations

  - by williamstw

  I have an enumeration that I want to use in pattern matches in an actor. I'm not getting what i'd expect and, now, I'm suspecting I'm missing something simple. My enumeration, object Ops extends Enumeration { val Create = Value("create") val Delete = Value("delete") } Then, I create an Ops from a String: val op = Ops.valueOf("create") Inside my match, I have: case (Ops.Create, ...) But Ops.Create doesn't seem to equal ops.valueOf("create") The former is just an atom 'create' and the later is Some(create) Hopefully, this is enough info for someone to tell me what I'm missing... Thanks

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• MySQL Join Comma Separated Field

  - by neeraj

  I have two tables. First Table is a batch table that contain comma separated student id in field "batch" batch -------------- id batch -------------- 1 1,2 2 3,4 Second Table is marks marks ---------------------- id studentid subject marks 1 1 English 50 2 2 English 40 3 3 English 70 4 1 Math 65 5 4 English 66 6 5 English 75 7 2 Math 55 How we can find those students of first batch id =1 who have scored more than 45 marks in English without using sub query. Problem i found to get this done using a single query is that we can not use IN as an association operator in JOIN statement What changes are required in below query to make it work? SELECT * FROM batch INNER JOIN marks ON marks.studentid IN(batch.batch) where batch.id = 1

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• PHP - Using strcpsn() to protect against SQL injection?

  - by MichaelMitchell

  I am making a sort of form validation system and I need to check the SQL database to see if the username is already there. So, my question, is it effective to use a little if statement like this to protect against an attack? if (strcspn($string, "/\?!@#$%^&*()[]{}|:;<>,.\"\'-+=" == strlen($string)){ return true; } So essentially, if the string contains any of these characters, "/\?!@#$%^&*()[]{}|:;<>,.\"\'-+=", then the length will not equal that of the original $string. I am just wondering if this is sufficient to protect, or if there is more that I must do. Thanks.

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• Storing expression template functors

  - by UncaughtException

  Hello guys, at the moment I'm really interested in expression templates and want to code a library for writing and differentiating mathematical functions with a lambda-style syntax. At the moment, I'm able to write (_x * _x)(2); and get the correct result 4. But I would really like to do something like MathFunction f = _x * _x; f(2);, but I don't have any ideas on how to cope with the recursive expression templates on the right side. Is it possible to achieve this without using the 'auto'-Keyword instead of MathFunction or having to make the operator() virtual? Thanks for your help!

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• Using pipes inside a class in C++

  - by Paul

  I'm trying to use this tutorial to make plots with Gnuplot in C++. However I will be using the pipe to Gnuplot from within a class, but then I run into some problems: I've got a header file where I declare all variables etc. I need to declare the pipe-variable here too, but how do I do that? I've tried doing it straight away, but it doesn't work: Logger.h: class Logger { FILE pipe; } Logger.cpp: Logger::Logger() { //Constructor *pipe = popen("gnuplot -persist","w"); } Gives the error Logger.cpp:28: error: no match for ‘operator=’ in ‘*((Logger*)this)->Logger::pipe = popen(((const char*)"gnuplot -persist"), ((const char*)"w"))’ Suggestions?

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• how to interleaving lists

  - by user2829177

  I have two lists that could be not equal in lengths and I want to be able to interleave them. I want to be able to append the extra values in the longer list at the end of my interleaved list.I have this: a=xs b=ys minlength=[len(a),len(b)] extralist= list() interleave= list() for i in range((minval(minlength))): pair=a[i],b[i] interleave.append(pair) flat=flatten(interleave) c=a+b if len(b)>len(a): remainder=len(c)-len(a) for j in range(-remainder): extra=remainder[j] extralist.append(extra) if len(a)>len(b): remainder=len(c)-len(b) for j in range(-remainder): extra=remainder[j] final=flat+extralist return final but if I test it: >>> interleave([1,2,3], ["hi", "bye",True, False, 33]) [1, 'hi', 2, 'bye', 3, True] >>> The False and 33 don't appear. What is it that Im doing wrong?

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• C# (With .NET & Visual Studio) WebForms - How can I get the title of a page ..?

  - by Ashley Davies

  Prety long question; How can I do the following in C#: Open a webpage (Prefferably not visible) Check whether the page redirects to a different page (Site is down, 404, etc.) Check if the title is not equal to a said string Then seperately, (They need to click a confirm button) open their browser, and go to the adress of the first (It'll be the only one) hyperlink on the site. I literally have been looking on google for ages and haven't found anything similar to what I need. Whether you give me a link to a site with a tutorial on this area of programming or actual source code doesn't make a difference to me.

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• Design guidelines for cache mechanism

  - by Delashmate

  Hi All, I got assignment to write design for cache mechanism (this is work assignment, not homework), This is my first time writing a design document, Our program display images for doctors, and we want to reduce the parsing time of the images So we want to save the parsed data in advance (in files or inside database) Currently I have several design key ideas: Handle locks - each shared data structure should be handled, also files Test - add test to verify the data from the cache is equal to the data from the files To decouple the connection to the database- not to call directly to the database Cleanup mechanisem- to delete old files if the cahce directory exceed configurable threshold Support config file Support performance tool in the feature I will also add class diagram, data flow charts, and workflow What do you think I should add to the key ideas? Do you know good link to atricales about design? Thanks in advance, Dan

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• Is there a way to cause a new C++ class instance to fail, if certain conditions in the contructor ar

  - by Jim Fell

  As I understand it, when a new class is instantiated in C++, a pointer to the new class is returned, or NULL, if there is insufficient memory. I am writing a class that initializes a linked list in the constructor. If there is an error while initializing the list, I would like the class instantiator to return NULL. For example: MyClass * pRags = new MyClass; If the linked list in the MyClass constructor fails to initialize properly, I would like pRags to equal NULL. I know that I can use flags and additional checks to do this, but I would like to avoid that, if possible. Does anyone know of a way to do this? Thanks.

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• How Do I Update a Table From Another Table Only If the Result Count is 1?

  - by Russ Bradberry

  I have a table of 2 tables in a one to many relationship. I want to run an update script that will update the table with the FK of the related table only if there is one result (because if there is multiple then we need to decide which one to use, in another method) Here is what I have so far: UPDATE import_hourly_event_reports i SET i.banner_id = b.banner_id FROM banner b JOIN plan p ON b.plan_id = p.id WHERE b.campain_id = i.campaign_id AND b.size_id = i.size_id AND p.site_id = i.site_id HAVING COUNT(b.banner_id) = 1 As you can see, the HAVING clause doesn't quite work as I'd expect it. I only want to update the row in the import table with the id of the banner from the banner table if the count is equal to 1.

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• Byte order (endian) of int in NSLog?

  - by Eonil

  NSLog function accepts printf format specifiers. My question is about %x specifier. Does this print hex codes as sequence on memory? Or does it have it's own printing sequence style? unsigned int a = 0x000000FF; NSLog(@"%x", a); Results of above code on little or big endian processors are equal or different? And how about NSString's -initWithFormat method? Does it follows this rule equally?

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