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  • Is it possible to apply inheritance to a Singleton class?

    - by Bragaadeesh
    Hi, Today I faced one question in interview. Is it possible to apply inheritance concept on Singleton Classes. I said since the constructor is private, we cannot extend that Singleton class (can someone please validate this). Next thing he asked me is to apply inheritance on that Singleton class. So, I made the Singleton's constructor as protected thinking that child's constructor also has be protected. But I was wrong the child can have a modifier either equal to or higher than that. So, I asked him to give a real world example on such a case. He was not able to give me one and said that I cant ask questions and wanted me to tell whether this scenario is possible or not. I went kind of blank. My question here is, Is this possible? Even if its possible, what is the use of it? What real world scenario would demand such a use. Thanks

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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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  • T-SQL Operations on a Calculated Date Field

    - by firedrawndagger
    Can I do WHERE operations on a calculated date field? I have a lookup field, which has been written badly in SQL and unfortunately I can't change it. But basically it stores dates as characters such as "July-2010" or "June-2009" (along with other non date data). I want to extract the dates first (which I did using a LIKE opertor) and then extract data based on a date range. SELECT BusinessUnit, Lookup, ReleaseDate FROM ( SELECT TOP 10 LookupColumn As Lookup, BU as BusinessUnit, CONVERT(DATETIME, REPLACE(LookupColumn,'-',' ')) as ReleaseDate FROM [dbo].[LookupTable] WHERE LookupColumn LIKE N'%-2010' ) MyTable ORDER BY ReleaseDate WHERE ReleaseDate = '2010-02-01' I'm having issues with WHERE operator. I would assume creating a subquery to encapsulate the calculated field would allow me to do operations with it such as WHERE but maybe I'm wrong. Bottom line is it possible to do operations on calculated fields?

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  • Dynamic name of NSMutableDictionary?

    - by Bruno
    Hi everyone I load from a txt file many info, and I would like, if possible, to dynamically create NSmutable dictionary with the elements of the txt. For example, each is like that: id of element | date | text What I'm asking is the equivalent of the NSString stringWithFormat:. Can we do the same for an Mutable Dictionary? To be more practical, let's say the NSString *date is equal to "23/12/2009" (for europe). I want to create a dictionary called 23/12/2009 without declaring *23/12/2009 but just something like dictionaryWithFormat: @"%@", date]; I'm stuck on this, and I don't even know if it is possible. If not, what's the best way to approach that? Thanks everyone Regards

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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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  • MySQL Query WHERE Including CASE or IF?

    - by handfix
    Strange problem. My Query looks like SELECT DISTINCT ID, `etcetc`, `if/elses over muliple joined tables` FROM table1 AS `t1` # some joins, eventually unrelated in that context WHERE # some standard where statements, they work/ CASE WHEN `t1`.`field` = "foo" THEN (`t1`.`anOtherField` != 123 AND `t1`.`anOtherField` != 456 AND `t1`.`anOtherOtherField` != "some String") WHEN `t1`.`field` = "bar" THEN `t1`.`aSecondOtherField` != 12345 END #ORDER BY CASE etc. Standard Stuff Apperantly MySQL returns a wrong rowcount and I think my problem is in the logic of the WHERE ... CASE statement. Maybe with the brackets? Maybe I should go for operator OR and not AND? Should my the second WHEN include brackets also, even when I only compare one field? Should I use IF and not CASE? Basically I want to exclude some rows with specific values IF theres a specific value in field foo or bar I would try that all out, but it takes a huge amount of time to complete that query... :(

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  • Python: Access members of a set

    - by emu
    Say I have a set myset of custom objects that may be equal although their references are different (a == b and a is not b). Now if I add(a) to the set, Python correctly assumes that a in myset and b in myset even though there is only len(myset) == 1 object in the set. That is clear. But is it now possible to extract the value of a somehow out from the set, using b only? Suppose that the objects are mutable and I want to change them both, having forgotten the direct reference to a. Put differently, I am looking for the myset[b] operation, which would return exactly the member a of the set. It seems to me that the type set cannot do this (faster than iterating through all its members). If so, is there at least an effective work-around?

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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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  • 3 fixed Columns (header and footer) using DIVs, NO Absolute DIVs, IE friendly, ALL columns stretch e

    - by Phillip Schein
    Left to right, Col1 id 560px wide with 10 px padding, middle column, 250px wide with 5px padding and Col3 (siderbar) is 200px wide with 3px padding. Background coloR, no matter text length in any column should stretch vertically equal. No javascript (jQuery workarounds) to make it work. It needs to be pure Semantic Markup with CSS. Each Column should have a nested column of color were content will go. Column 1 should be SEO prominant which means the highest nested column for Google and other Search Engines to crawl. I have used 'The Holy Grail" layout, articles at "A List Apart" and these solution are so convoluted that they push the main columns left and than the nested columns push them with padding back right. This is crazy! I try to adjust these examples, but they're not editable by just adjusting a width in the CSS or the padding, etc. Can you please help me?

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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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  • 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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  • How to check if string contains a string in string array

    - by Abu Hamzah
    edit: the order might change as you can see in the below example, both string have same name but different order.... How would you go after checking to see if the both string array match? the below code returns true but in a reality its should return false since I have extra string array in the _check what i am trying to achieve is to check to see if both string array have same number of strings. string _exists = "Adults,Men,Women,Boys"; string _check = "Men,Women,Boys,Adults,fail"; if (_exists.All(s => _check.Contains(s))) //tried Equal { return true; } else { return false; }

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  • Assigning two strings together getting Access Read Violation

    - by Jay Bell
    I am trying to pass a string to a class mutator and set the private member to that string here is the code that is sending the string void parseTradePairs(Exchange::Currency *curr, std::string *response, int begin, int exit) { int start; int end; string temp; string dataResponse; CURL *tempCurl; initializeCurl(tempCurl); int location = response->find("marketid", begin); if(location <= exit) { start = location + 11; begin = response->find("label", start); end = begin - start - 3; findStrings(start, end, temp, response); getMarketInfo(tempCurl, temp, dataResponse); curr->_coin->setExch(temp); // here is the line of code that is sending the string dataResponse >> *(curr->_coin); curr->_next = new Exchange::Currency(curr, curr->_position + 1); parseTradePairs(curr->_next, response, begin, exit); } } and here is the mutator within the coin class that is receiving the string and assigning it to _exch void Coin::setExch(string exch) { _exch = exch; } I have stepped through it and made sure that exch has the string in it. "105" but soon as it hits _exch = exch; I get the reading violation. I tried passing as pointer as well. I do not believe it should go out of scope. and the string variable in the class is initialized to zero in the default constructor but again that should matter unless I am trying to read from it instead of writing to it. /* defualt constructor */ Coin::Coin() { _id = ""; _label = ""; _code= ""; _name = ""; _marketCoin = ""; _volume = 0; _last = 0; _exch = ""; } Exchange::Exchange(std::string str) { _exch = str; _currencies = new Currency; std::string pair; std::string response; CURL *curl; initializeCurl(curl); getTradePairs(curl, response); int exit = response.find_last_of("marketid"); parseTradePairs(_currencies, &response, 0, exit); } int main(void) { CURL *curl; string str; string id; Coin coin1; initializeCurl(curl); Exchange ex("cryptsy"); curl_easy_cleanup(curl); system("pause"); return 0; } class Exchange { public: typedef struct Currency { Currency(Coin *coin, Currency *next, Currency *prev, int position) : _coin(coin), _next(next), _prev(prev), _position(position) {} Currency(Currency *prev, int position) : _prev(prev), _position(position), _next(NULL), _coin(&Coin()){} Currency() : _next(NULL), _prev(NULL), _position(0) {} Coin *_coin; Currency *_next; Currency *_prev; int _position; }; /* constructor and destructor */ Exchange(); Exchange(std::string str); ~Exchange(); /* Assignment operator */ Exchange& operator =(const Exchange& copyExchange); /* Parse Cryptsy Pairs */ friend void parseTradePairs(Currency *curr, std::string *response, int begin, int exit); private: std::string _exch; Currency *_currencies; }; here is what i changed it to to fix it. typedef struct Currency { Currency(Coin *coin, Currency *next, Currency *prev, int position) : _coin(coin), _next(next), _prev(prev), _position(position) {} Currency(Currency *prev, int position) : _prev(prev), _position(position), _next(NULL), _coin(&Coin()){} Currency() { _next = NULL; _prev = NULL; _position = 0; _coin = new Coin(); } Coin *_coin; Currency *_next; Currency *_prev; int _position; };

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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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  • 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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  • 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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  • Mysql query help needed

    - by Me-and-Coding
    Hi, i have two tables category and hotels where category.id should be equal to hotels.catid. Now how do i select 3 rows from each different category from the hotels table. I have this query: select h.* from hotels h inner join category c on h.catid = c.id order by h.catid, h.hid this selects all records, but i want to select three rows per different category so in all it should return 9 rows with 3 rows for each category. If this can not be done in mysql, you could also suggest php code please. Thanks

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  • Use currently logged-in user in query

    - by Degan
    I am using VisualWebDeveloperExpress2008 with Access as the membership provider. I have some cases where I want users to edit their own data. This would involve a query where the UserId should equal the UserID of the user who is using the site. I am expecting to use WHERE UserId = ?, but I have not found out where to direct "?". The IDE gives several choices, but I am uncertain which to choose. This, while it looks promising does not work: <SelectParameters> <asp:ProfileParameter Name="UserID" PropertyName="UserId" Type="Int32" /> </SelectParameters> What is best to use for the Select Parameter?

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  • Core Data NSFetchedResultsController sorting in certain sequence

    - by Moze
    I'm writing iphone app that has UITableView and uses Core Data. Data in UITableView is shown using NSFetchedResultsController. I use NSPredicate operator "IN" to fetch only needed entries. NSArray *filterArray = [NSArray arrayWithObjects:@"789", @"963", @"445", @"198", nil]; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"id IN %@", filterArray]; Now the problem is that I need to show entries in same sequence they are in filterArray. How can I do it? How I can create NSSortDescriptor that would sort all entries in that way? I tried without sort descriptor, but I get error that NSFetchedResultsController needs sortDescriptor to be set.

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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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  • VBA for filtering columns

    - by Ampi Severe
    I have a big database-like sheet, first row contains headers. I would like a subset of rows of this table based on column values. Two issues: 1) VBA-wise I would like to loop through the columns, when the values for all necessary columns all match, copy the entire row into a new sheet. 2) The subset of rows is based on a list. This should be the first column to be looped through. For example I want all rows where the value in column A is equal to one of the values in my list. Is there any possibility to autofilter strings based on a list (column) of strings? EDIT Thanks to @Doug Glancy the autofiltering works now, so I've removed my (horrible) code and issue 1 is solved.

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  • Using adaptive step sizes with scipy.integrate.ode

    - by Mike
    The (brief) documentation for scipy.integrate.ode says that two methods (dopri5 and dop853) have stepsize control and dense output. Looking at the examples and the code itself, I can only see a very simple way to get output from an integrator. Namely, it looks like you just step the integrator forward by some fixed dt, get the function value(s) at that time, and repeat. My problem has pretty variable timescales, so I'd like to just get the values at whatever time steps it needs to evaluate to achieve the required tolerances. That is, early on, things are changing slowly, so the output time steps can be big. But as things get interesting, the output time steps have to be smaller. I don't actually want dense output at equal intervals, I just want the time steps the adaptive function uses.

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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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  • 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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  • Extended maxima transform in Matlab

    - by garvin
    I use imtophat to apply a filter to an m x n array. I then find the local max using imextendedmax(). I get mostly 0's everywhere except for 1's in the general areas where I am expecting a local max. The weird thing is, though, that I don't get just one local max. Instead in these places I get MANY elements with 1's such as 00011100000 00111111000 00000110000 yet the values there are close but NOT equal so I would expect that there would be one that is higher than all of the rest. So I'm wondering a) if this is a bug and how I might fix it and b) how you would choose choose the element of these 1's with the highest value.

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