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• std::stringstream GCC Abnormal Behavior

  - by FlorianZ

  I have a very interesting problem with compiling a short little program on a Mac (GCC 4.2). The function below would only stream chars or strings into the stringstream, but not anything else (int, double, float, etc.) In fact, the fail flag is set if I attempt to convert for example an int into a string. However, removing the preprocessor flag: _GLIBCXX_DEBUG=1, which is set by default in XCode for the debug mode, will yield the desired results / correct behavior. Here is the simple function I am talking about. value is template variable of type T. Tested for int, double, float (not working), char and strings (working). template < typename T > const std::string Attribute<T>::getValueAsString() const { std::ostringstream stringValue; stringValue << value; return stringValue.str(); } Any ideas what I am doing wrong, why this doesn't work, or what the preprocessor flag does to make this not work anymore? Thanks!

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• What is a simple way to add a timer to a method

  - by John

  The following is in C#. I'm trying to do something very simple (I think). I have a method that loads an XML document XDocument doc = XDocument.Load(uri); , but I don't want to tie up pc resources if there are issues (connectivity, document size, etc.). So I'd like to be able to add a timeout variable that will cut the method off after a given number of seconds. I'm a newbie when it comes to asynchronous programming and find it confusing that there are so many examples written so many different ways . . . and none of them appear simple. I'd like a simple solution, if possible. Here's my thoughts so far on possible solution paths: 1) A method that wraps the existing load public XDocument LoadXDocument(string uri, int timeout){ //code } 2) A wrapper, but as an extension method XDocument doc = XDocument.LoadWithTimeout(string uri, int timeout); 3) A generic extension method. Object obj = SomeStaticClass.LoadWithTimeout(??? method, int timeout); 3), on its face seems really nice, because it would mean being able to generically add timeouts to many different method calls and not specifically tied to one type of object, but I suspect that it is either i)impossible or ii) very difficult. Please assist. Thanks.

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• Why would an image (the Mandelbrot) be skewed and wrap around?

  - by Sean D

  So I just wrote a little snippet to generate the Mandelbrot fractal and imagine my surprise when it came out all ugly and skewed (as you can see at the bottom). I'd appreciate a point in the direction of why this would even happen. It's a learning experience and I'm not looking for anyone to do it for me, but I'm kinda at a dead end debugging it. The offending generation code is: module Mandelbrot where import Complex import Image main = writeFile "mb.ppm" $ imageMB 1000 mandelbrotPixel x y = mb (x:+y) (0:+0) 0 mb c x iter | magnitude x > 2 = iter | iter >= 255 = 255 | otherwise = mb c (c+q^2) (iter+1) where q = x --Mandelbrot --q = (abs.realPart $ x) :+ (abs.imagPart $ x) --Burning Ship argandPlane x0 x1 y0 y1 width height = [(x,y)| y<-[y1,(y1-dy)..y0], --traverse from x<-[x0,(x0+dx)..x1]] --top-left to bottom-right where dx = (x1 - x0)/width dy = (y1 - y0)/height drawPicture :: (a->b->c)->(c->Colour)->[(a,b)]->Image drawPicture function colourFunction plane = map (colourFunction.uncurry function) plane imageMB s = createPPM s s $ drawPicture mandelbrotPixel (\x->[x,x,x]) $ argandPlane (-1.8) (-1.7) (0.02) 0.055 s' s' where s' = fromIntegral s And the image code (which I'm fairly confident in) is: module Image where type Colour = [Int] type Image = [Colour] createPPM :: Int -> Int -> Image -> String createPPM w h i = concat ["P3 ", show w, " ", show h, " 255\n", unlines.map (unwords.map show) $ i]

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• Efficiently select top row for each category in the set

  - by VladV

  I need to select a top row for each category from a known set (somewhat similar to this question). The problem is, how to make this query efficient on the large number of rows. For example, let's create a table that stores temperature recording in several places. CREATE TABLE #t ( placeId int, ts datetime, temp int, PRIMARY KEY (ts, placeId) ) -- insert some sample data SET NOCOUNT ON DECLARE @n int, @ts datetime SELECT @n = 1000, @ts = '2000-01-01' WHILE (@n>0) BEGIN INSERT INTO #t VALUES (@n % 10, @ts, @n % 37) IF (@n % 10 = 0) SET @ts = DATEADD(hour, 1, @ts) SET @n = @n - 1 END Now I need to get the latest recording for each of the places 1, 2, 3. This way is efficient, but doesn't scale well (and looks dirty). SELECT * FROM ( SELECT TOP 1 placeId, temp FROM #t WHERE placeId = 1 ORDER BY ts DESC ) t1 UNION ALL SELECT * FROM ( SELECT TOP 1 placeId, temp FROM #t WHERE placeId = 2 ORDER BY ts DESC ) t2 UNION ALL SELECT * FROM ( SELECT TOP 1 placeId, temp FROM #t WHERE placeId = 3 ORDER BY ts DESC ) t3 The following looks better but works much less efficiently (30% vs 70% according to the optimizer). SELECT placeId, ts, temp FROM ( SELECT placeId, ts, temp, ROW_NUMBER() OVER (PARTITION BY placeId ORDER BY ts DESC) rownum FROM #t WHERE placeId IN (1, 2, 3) ) t WHERE rownum = 1 The problem is, during the latter query execution plan a clustered index scan is performed on #t and 300 rows are retrieved, sorted, numbered, and then filtered, leaving only 3 rows. For the former query three times one row is fetched. Is there a way to perform the query efficiently without lots of unions?

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• CRM 2011 - Set/Retrieve work hours programmatically

  - by Philip Rich

  I am attempting to retrieve a resources work hours to perform some logic I require. I understand that the CRM scheduling engine is a little clunky around such things, but I assumed that I would be able to find out how the working hours were stored in the DB eventually... So a resource has associated calendars and those calendars have associated calendar rules and inner calendars etc. It is possible to look at the start/end and frequency of aforementioned calendar rules and query their codes to work out whether a resource is 'working' during a given period. However, I have not been able to find the actual working hours, the 9-5 shall we say in any field in the DB. I even tried some SQL profiling while I was creating a new schedule for a resource via the UI, but the results don't show any work hours passing to SQL. For those with the patience the intercepted SQL statement is below:- EXEC Sp_executesql N'update [CalendarRuleBase] set [ModifiedBy]=@ModifiedBy0, [EffectiveIntervalEnd]=@EffectiveIntervalEnd0, [Description]=@Description0, [ModifiedOn]=@ModifiedOn0, [GroupDesignator]=@GroupDesignator0, [IsSelected]=@IsSelected0, [InnerCalendarId]=@InnerCalendarId0, [TimeZoneCode]=@TimeZoneCode0, [CalendarId]=@CalendarId0, [IsVaried]=@IsVaried0, [Rank]=@Rank0, [ModifiedOnBehalfBy]=NULL, [Duration]=@Duration0, [StartTime]=@StartTime0, [Pattern]=@Pattern0 where ([CalendarRuleId] = @CalendarRuleId0)', N'@ModifiedBy0 uniqueidentifier,@EffectiveIntervalEnd0 datetime,@Description0 ntext,@ModifiedOn0 datetime,@GroupDesignator0 ntext,@IsSelected0 bit,@InnerCalendarId0 uniqueidentifier,@TimeZoneCode0 int,@CalendarId0 uniqueidentifier,@IsVaried0 bit,@Rank0 int,@Duration0 int,@StartTime0 datetime,@Pattern0 ntext,@CalendarRuleId0 uniqueidentifier', @ModifiedBy0='EB04662A-5B38-E111-9889-00155D79A113', @EffectiveIntervalEnd0='2012-01-13 00:00:00', @Description0=N'Weekly Single Rule', @ModifiedOn0='2012-03-12 16:02:08', @GroupDesignator0=N'FC5769FC-4DE9-445d-8F4E-6E9869E60857', @IsSelected0=1, @InnerCalendarId0='3C806E79-7A49-4E8D-B97E-5ED26700EB14', @TimeZoneCode0=85, @CalendarId0='E48B1ABF-329F-425F-85DA-3FFCBB77F885', @IsVaried0=0, @Rank0=2, @Duration0=1440, @StartTime0='2000-01-01 00:00:00', @Pattern0=N'FREQ=WEEKLY;INTERVAL=1;BYDAY=SU,MO,TU,WE,TH,FR,SA', @CalendarRuleId0='0A00DFCF-7D0A-4EE3-91B3-DADFCC33781D' The key parts in the statement are the setting of the pattern:- @Pattern0=N'FREQ=WEEKLY;INTERVAL=1;BYDAY=SU,MO,TU,WE,TH,FR,SA' However, as mentioned, no indication of the work hours set. Am I thinking about this incorrectly or is CRM doing something interesting around these work hours? Any thoughts greatly appreciated, thanks.

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• Using Generics to return a literal string or from Dictionary<string, object>

  - by Mike

  I think I outsmarted myself this time. Feel free to edit the title also I could not think of a good one. I am reading from a file and then in that file will be a string because its like an xml file. But in the file will be a literal value or a "command" to get the value from the workContainer so <Email>[email protected]</Email> or <Email>[? MyEmail ?]</Email> What I wanted to do instead of writing ifs all over the place to put it in a generic function so logic is If Container command grab from container else grab string and convert to desired type Its up to the user to ensure the file is ok and the type is correct so another example is so <Answer>3</Answer> or <Answer>[? NumberOfSales ?]</Answer> This is the procedure I started to work on public class WorkContainer:Dictionary<string, object> { public T GetKeyValue<T>(string Parameter) { if (Parameter.StartsWith("[? ")) { string key = Parameter.Replace("[? ", "").Replace(" ?]", ""); if (this.ContainsKey(key)) { return (T)this[key]; } else { // may throw error for value types return default(T); } } else { // Does not Compile if (typeof(T) is string) { return Parameter } // OR return (T)Parameter } } } The Call would be mail.To = container.GetKeyValue<string>("[email protected]"); or mail.To = container.GetKeyValue<string>("[? MyEmail ?]"); int answer = container.GetKeyValue<int>("3"); or answer = container.GetKeyValue<int>("[? NumberOfSales ?]"); But it does not compile?

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• Java: Comparing a class with another within that class using a my own .equals

  - by user1670252

  I am making a method .equals replacing the equals method used. It accepts a object. I want it to check if that object equals the class that runs the .equals class. I know I want to compare all the private methods I have to that object. Is there a way to do this without making another private class to get the private variables from the object? How do I do this to compare equality not identity? I am stuck on this. Do i have to use == to compare? Also looking online i see others use recursion. If this is the way i have to do it can you show and explain it to me? so an example i have public boolean equals(Object o) { this is in a class we will call bobtheBuilder (first thing to pop in my head) I want to check if the object o is equal to the class he has private object array and a private int. I assume I want to check if the array and int of this class equal the array and int of the object.

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• How can I identify an element from a list within another list

  - by Alex

  I have been trying to make a block of code that finds the index of the largest bid for each item. Then I was going to use the index as a way to identify the person who paid that much moneys name. However no matter what i try I can't link the person and what they have gained from the auction together. Here is the code I have been writing: It has to be able to work with any information inputted def sealedBids(): n = int(input('\nHow many people are in the group? ')) z = 0 g = [] s = [] b = [] f = [] w = []#goes by number of items q = [] while z < n: b.append([]) z = z + 1 z = 0 while z < n: g.append(input('Enter a bidders name: ')) z = z + 1 z = 0 i = int(input('How many items are being bid on?')) while z < i: s.append(input('Enter the name of an item: ')) w.append(z) z = z + 1 z = 0 for j in range(n):#specifies which persons bids your taking for k in range(i):#specifies which item is being bid on b[j].append(int(input('How much money has {0} bid on the {1}? '.format(g[j], s[k])))) print(' ') for j in range(n):#calculates fair share f.append(sum(b[j])/n) for j in range(i):#identifies which quantity of money was the largest for each item for k in range(n): if w[j] < b[k][j]: w[j] = b[k][j] q.append(k) any advice is much appreciated.

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• C Typecast: How to

  - by Jean

  #include<stdio.h> int main(void) { unsigned short a,e,f ; // 2 bytes data type unsigned int temp1,temp2,temp4; // 4 bytes data type unsigned long temp3; // 8 bytes data type a=0xFFFF; e=((a*a)+(a*a))/(2*a); // Line 8 //e=(((unsigned long)(a*a)+(unsigned long)(a*a)))/(unsigned int)(2*a); temp1=a*a; temp2=a*a; temp3=(unsigned long)temp1+(unsigned long)temp2; // Line 14 temp4=2*a; f=temp3/temp4; printf("%u,%u,%lu,%u,%u,%u,%u\n",temp1,temp2,temp3,temp4,e,f,a); return(1); } How do I fix the arithmetic (At Line 8 by appropriate typecasting of intermediate results) so that overflows are taken care of ? Currently it prints 65534 instead of expected 65535. Why is the typecast necessary for Line 14 ?

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• Error when running a basic Hadoop code

  - by Abhishek Shivkumar

  I am running a hadoop code that has a partitioner class inside the job. But, when I run the command hadoop jar Sort.jar SecondarySort inputdir outputdir I am getting a runtime error that says class KeyPartitioner not org.apache.hadoop.mapred.Partitioner. I have ensured that the KeyPartitioner class has extended the Partitioner class, but why am I getting this error? Here is the driver code: JobConf conf = new JobConf(getConf(), SecondarySort.class); conf.setJobName(SecondarySort.class.getName()); conf.setJarByClass(SecondarySort.class); conf.setInputFormat(TextInputFormat.class); conf.setOutputFormat(TextOutputFormat.class); conf.setMapOutputKeyClass(StockKey.class); conf.setMapOutputValueClass(Text.class); conf.setPartitionerClass((Class<? extends Partitioner<StockKey, DoubleWritable>>) KeyPartitioner.class); conf.setMapperClass((Class<? extends Mapper<LongWritable, Text, StockKey, DoubleWritable>>) StockMapper.class); conf.setReducerClass((Class<? extends Reducer<StockKey, DoubleWritable, Text, Text>>) StockReducer.class); and here is the code of the partitioner class: public class KeyPartitioner extends Partitioner<StockKey, Text> { @Override public int getPartition(StockKey arg0, Text arg1, int arg2) { int partition = arg0.name.hashCode() % arg2; return partition; } }

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• Blackberry - custom logic for checkboxes group

  - by SWATI

  if i click on any checkbox all previous checkboxes must get checked "my logic works" if i uncheck a checkbox then all checkboxes after it must get unchecked "how to do that" MyLogic works for storm but not for other models what to do //well what i want to do is i have 5 checkboxes class myscreen { chk_service = new CheckboxField[5]; chk_service[0]= new CheckboxField("1",true) chk_service[1]= new CheckboxField("2",false) chk_service[2]= new CheckboxField("3",false) chk_service[3]= new CheckboxField("4",false) chk_service[4]= new CheckboxField("5",false) CheckboxFieldChangeListener obj = new CheckboxFieldChangeListener(chk_service); chk_service[0].setChangeListener(obj); chk_service[1].setChangeListener(obj); chk_service[2].setChangeListener(obj); chk_service[3].setChangeListener(obj); chk_service[4].setChangeListener(obj); hm4 = new HorizontalFieldManager(); hm4.add(chk_service[0]); hm4.add(chk_service[1]); hm4.add(chk_service[2]); hm4.add(chk_service[3]); hm4.add(chk_service[4]); add(hm4); } public CheckboxFieldChangeListener (CheckboxField[] arrFields) { m_arrFields = arrFields; } public void fieldChanged(Field field, int context) { if(true == ((CheckboxField) field).getChecked()) { for(int i = 0; i < m_arrFields.length; i++) { if(m_arrFields[i]==field) { //a[j]=i; j++; break; } else { CheckboxField oField = m_arrFields[i]; oField.setChecked(true); } } } a[k] = j; if(false == ((CheckboxField) field).getChecked()) { for(int i =field.getIndex(); i < m_arrFields.length; i++) { if(m_arrFields[i]==field) { //a[j]=i; j++; break; } else { CheckboxField oField = m_arrFields[i]; oField.setChecked(false); } } } } }

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• Modifying bundled properties from visitor

  - by ravenspoint

  How should I modify the bundled properties of a vertex from inside a visitor? I would like to use the simple method of sub-scripting the graph, but the graph parameter passed into the visitor is const, so compiler disallows changes. I can store a reference to the graph in the visitor, but this seems weird. /** A visitor which identifies vertices as leafs or trees */ class bfs_vis_leaf_finder:public default_bfs_visitor { public: /** Constructor @param[in] total reference to int variable to store total number of leaves @param[in] g reference to graph ( used to modify bundled properties ) */ bfs_vis_leaf_finder( int& total, graph_t& g ) : myTotal( total ), myGraph( g ) { myTotal = 0; } /** Called when the search finds a new vertex If the vertex has no children, it is a leaf and the total leaf count is incremented */ template <typename Vertex, typename Graph> void discover_vertex( Vertex u, Graph& g) { if( out_edges( u, g ).first == out_edges( u, g ).second ) { myTotal++; //g[u].myLevel = s3d::cV::leaf; myGraph[u].myLevel = s3d::cV::leaf; } else { //g[u].myLevel = s3d::cV::tree; myGraph[u].myLevel = s3d::cV::tree; } } int& myTotal; graph_t& myGraph; };

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• Obtaining command line arguments in a QT application

  - by morpheous

  The following snippet is from a little app I wrote using the QT framework. The idea is that the app can be run in batch mode (i.e. called by a script) or can be run interactively. It is important therefore, that I am able to parse command line arguments in order to know which mode in which to run etc. [Edit] I am debugging using QTCreator 1.3.1 on Ubuntu Karmic. The arguments are passed in the normal way (i.e. by adding them via the 'Project' settings in the QTCreator IDE). When I run the app, it appears that the arguments are not being passed to the application. The code below, is a snippet of my main() function. int main(int argc, char *argv[]) { //Q_INIT_RESOURCE(application); try { QApplication the_app(argc, argv); //trying to get the arguments into a list QStringList cmdline_args = QCoreApplication::arguments(); // Code continues ... } catch (const MyCustomException &e) { return 1; } return 0; } [Update] I have identified the problem - for some reason, although argc is correct, the elements of argv are empty strings. I put this little code snippet to print out the argv items - and was horrified to see that they were all empty. for (int i=0; i< argc; i++){ std::string s(argv[i]); //required so I can see the damn variable in the debugger std::cout << s << std::endl; } Does anyone know what on earth is going on (or a hammer)?

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• Index question: Select * with WHERE clause. Where and how to create index

  - by Mestika

  Hi, I’m working on optimizing some of my queries and I have a query that states: select * from SC where c_id ="+c_id” The schema of ** SC** looks like this: SC ( c_id int not null, date_start date not null, date_stop date not null, r_t_id int not null, nt int, t_p decimal, PRIMARY KEY (c_id, r_t_id, date_start, date_stop)); My immediate bid on how the index should be created is a covering index in this order: INDEX(c_id, date_start, date_stop, nt, r_t_id, t_p) The reason for this order I base on: The WHERE clause selects from c_id thus making it the first sorting order. Next, the date_start and date_stop to specify a sort of “range” to be defined in these parameters Next, nt because it will select the nt Next the r_t_id because it is a ID for a specific type of my r_t table And last the t_p because it is just a information. I don’t know if it is at all necessary to order it in a specific way when it is a SELECT ALL statement. I should say, that the SC is not the biggest table. I can say how many rows it contains but a estimate could be between <10 and 1000. The next thing to add is, that the SC, in different queries, inserts the data into the SC, and I know that indexes on tables which have insertions can be cost ineffective, but can I somehow create a golden middle way to effective this performance. Don't know if it makes a different but I'm using IBM DB2 version 9.7 database Sincerely Mestika

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• C++: calling member functions within constructor?

  - by powerboy

  The following code raises a runtime error: #include <iostream> #include <iterator> #include <ext/slist> class IntList : public __gnu_cxx::slist<int> { public: typedef IntList::iterator iterator; IntList() { tail_ = begin(); } // seems that there is a problem here void append(const int node) { tail_ = insert_after(tail_, node); } private: iterator tail_; }; int main() { IntList list; list.append(1); list.append(2); list.append(3); for (IntList::iterator i = list.begin(); i != list.end(); ++i) { std::cout << *i << " "; } return 0; } Seems that the problem is in the constructor IntList(). Is it because it calls the member function begin()?

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• C++ compiler error on template specialization

  - by user231536

  I would like to specialize a template method for a class C that is itself templated by an int parameter. How do I do this? template <int D=1> class C { static std::string foo () { stringstream ss; ss << D << endl; return ss.str();} }; template <class X> void test() { cout << "This is a test" << endl;} template <> template <int D> void test<C<D> > () {cout << C<D>::foo() << endl;} The specialization for test() fails with "Too many template parameter lists in declaration of void test()".

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• C++ arrays as parameters, EDIT: now includes variable scoping

  - by awshepard

  Alright, I'm guessing this is an easy question, so I'll take the knocks, but I'm not finding what I need on google or SO. I'd like to create an array in one place, and populate it inside a different function. I define a function: void someFunction(double results[]) { for (int i = 0; i<100; ++i) { for (int n = 0; n<16; ++n) //note this iteration limit { results[n] += i * n; } } } That's an approximation to what my code is doing, but regardless, shouldn't be running into any overflow or out of bounds issues or anything. I generate an array: double result[16]; for(int i = 0; i<16; i++) { result[i] = -1; } then I want to pass it to someFunction someFunction(result); When I set breakpoints and step through the code, upon entering someFunction, results is set to the same address as result, and the value there is -1.000000 as expected. However, when I start iterating through the loop, results[n] doesn't seem to resolve to *(results+n) or *(results+n*sizeof(double)), it just seems to resolve to *(results). What I end up with is that instead of populating my result array, I just get one value. What am I doing wrong? EDIT Oh fun, I have a typo: it wasn't void someFunction(double results[]). It was: void someFunction(double result[])... So perhaps this is turning into a scoping question. If my double result[16] array is defined in a main.cpp, and someFunction is defined in a Utils.h file that's included by the main.cpp, does the result variable in someFunction then wreak havoc on the result array in main?

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• Constructor issue

  - by laura

  This is the code that I worked on and I don't understand what it's happening on constructor Package obj2(); On output are displayed only the values 4 (Package obj1(4)) and 2 (Package obj3(2)) #include <iostream> using namespace std; class Package { private: int value; public: Package() { cout<<"constructor #1"<<endl; value = 7; cout << value << endl; } Package(int v) { cout<<"constructor #2"<<endl; value = v; cout << value << endl; } ~Package() { cout<<"destructor"<<endl; cout << value << endl; } }; int main() { Package obj1(4); Package obj2(); Package obj3(2); }

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• novice needing help on shuffeling an array

  - by steffen Myklebust

  Please help a TOTAL beginner.! I found this post: http://stackoverflow.com/questions/56648/whats-the-best-way-to-shuffle-an-nsmutablearray And as i try to deploy this in my own code, I cant get it working... :-( Can anyone help me to resolve this code? To me it looks like the shuffle function is not called..? here is my code: // // shuffle2ViewController.h // shuffle2 #import @interface shuffle2ViewController : UIViewController { NSMutableArray *puzzles; int *randomSort; } - (void)shuffle; @end //============================= // shuffle2ViewController.m ´#import "shuffle2ViewController.h" @implementation shuffle2ViewController (void)viewDidLoad { [super viewDidLoad]; NSMutableArray *puzzles = [NSMutableArray arrayWithObjects:@"1",@"2",@"3", @"4",@"5",@"6",@"7",@"8",@"9", @"10",@"11",@"12", nil]; // Call the shuffle function [self shuffle]; // print to log int i; NSLog(@"NEW OLD"); NSLog(@"================="); for (i = 0; i < 12; ++i) NSLog(@" %2i %@", i + 1, [puzzles objectAtIndex:i]); } int randomSort(id obj1, id obj2, void *context ) { // returns random number -1 0 1 return (random()%3 - 1); } (void)shuffle { // call custom sort function [puzzles sortUsingFunction:randomSort context:nil]; } Giving this result: NEW OLD ================= 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 11 11 12 12

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• Help! I'm a Haskell Newbie

  - by Darknight

  I've only just dipped my toe in the world of Haskell as part of my journey of programming enlightenment (moving on from, procedural to OOP to concurrent to now functional). I've been trying an online Haskell Evaluator. However I'm now stuck on a problem: Create a simple function that gives the total sum of an array of numbers. In a procedural language this for me is easy enough (using recursion) (c#) : private int sum(ArrayList x, int i) { if (!(x.Count < i + 1)) { int t = 0; t = x.Item(i); t = sum(x, i + 1) + t; return t; } } All very fine however my failed attempt at Haskell was thus: let sum x = x+sum in map sum [1..10] this resulted in the following error (from that above mentioned website): Occurs check: cannot construct the infinite type: a = a -> t Please bear in mind I've only used Haskell for the last 30 minutes! I'm not looking simply for an answer but a more explanation of it. Thanks in advanced.

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• C++: inheritance problem

  - by Helltone

  It's quite hard to explain what I'm trying to do, I'll try: Imagine a base class A which contains some variables, and a set of classes deriving from A which all implement some method bool test() that operates on the variables inherited from A. class A { protected: int somevar; // ... }; class B : public A { public: bool test() { return (somevar == 42); } }; class C : public A { public: bool test() { return (somevar > 23); } }; // ... more classes deriving from A Now I have an instance of class A and I have set the value of somevar. int main(int, char* []) { A a; a.somevar = 42; Now, I need some kind of container that allows me to iterate over the elements i of this container, calling i::test() in the context of a... that is: std::vector<...> vec; // push B and C into vec, this is pseudo-code vec.push_back(&B); vec.push_back(&C); bool ret = true; for(i = vec.begin(); i != vec.end(); ++i) { // call B::test(), C::test(), setting *this to a ret &= ( a .* (&(*i)::test) )(); } return ret; } How can I do this? I've tried two methods: forcing a cast from B::* to A::*, adapting a pointer to call a method of a type on an object of a different type (works, but seems to be bad); using std::bind + the solution above, ugly hack; changing the signature of bool test() so that it takes an argument of type const A& instead of inheriting from A, I don't really like this solution because somevar must be public.

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• Why it's can be compiled in GNU/C++, can't compiled in VC++2010 RTM?

  - by volnet

  #include #include #include #include "copy_of_auto_ptr.h" #ifdef _MSC_VER #pragma message("#include ") #include // http://gcc.gnu.org/onlinedocs/gcc/Diagnostic-Pragmas.html#Diagnostic-Pragmas #endif /* case 1-4 is the requirement of the auto_ptr. which form http://ptgmedia.pearsoncmg.com/images/020163371X/autoptrupdate/auto_ptr_update.html */ /* case 1. (1) Direct-initialization, same type, e.g. */ std::auto_ptr source_int() { // return std::auto_ptr(new int(3)); std::auto_ptr tmp(new int(3)); return tmp; } /* case 2. (2) Copy-initialization, same type, e.g. */ void sink_int(std::auto_ptr p) { std::cout source_derived() { // return std::auto_ptr(new Derived()); std::auto_ptr tmp(new Derived()); return tmp; } /* case 4. (4) Copy-initialization, base-from-derived, e.g. */ void sink_base( std::auto_ptr p) { p-go(); } int main(void) { /* // auto_ptr */ // case 1. // auto_ptr std::auto_ptr p_int(source_int()); std::cout p_derived(source_derived()); p_derived-go(); // case 4. // auto_ptr sink_base(source_derived()); return 0; } In Eclipse(GNU C++.exe -v gcc version 3.4.5 (mingw-vista special r3)) it's two compile error: Description Resource Path Location Type initializing argument 1 of void sink_base(std::auto_ptr<Base>)' from result ofstd::auto_ptr<_Tp::operator std::auto_ptr<_Tp1() [with _Tp1 = Base, _Tp = Derived]' auto_ptr_ref_research.cpp auto_ptr_ref_research/auto_ptr_ref_research 190 C/C++ Problem Description Resource Path Location Type no matching function for call to `std::auto_ptr::auto_ptr(std::auto_ptr)' auto_ptr_ref_research.cpp auto_ptr_ref_research/auto_ptr_ref_research 190 C/C++ Problem But it's right in VS2010 RTM. Questions: Which compiler stand for the ISO C++ standard? The content of case 4 is the problem "auto_ptr & auto_ptr_ref want to resolve?"

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• "Abstract static" method - how?

  - by polyglot

  There are already several SO questions on why there is not abstract static method/field as such, but I'm wondering about how one would go about implementing the following psuedo-code: class Animal { abstract static int getNumberOfLegs(); // not possible } class Chicken inherits Animal { static int getNumberOfLegs() { return 2; } class Dog inherits Animal { static int getNumberOfLegs() { return 4; } Here is the problem: Assuming that I want make sure that every class that inherits Animal to contain getNumberOfLegs() method (i.e. almost like an interface, except I do want the abstract class to implement several methods that are common to all child classes, hence pure interface does not work here). getNumberOfLegs() obviously should be a static method (assuming that in a perfect world we dont' have crippled chicken and dogs so getNumberOfLegs is not instance-dependent). Without an "abstract static" method/field, one can either leave the method out from Animal class, then there is the risk that some child class do not have that method. Or one can make getNumberOfLegs an instance method, but then one would have to instantiate a class to find out how many legs that animal has - even though it is not necessary. How do one usually go about implementing this situation?

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• Port scanning using threadpool

  - by thenry

  I am trying to run a small app that scans ports and checks to see if they are open using and practicing with threadpools. The console window will ask a number and scans ports from 1 to X and will display each port whether they are open or closed. My problem is that as it goes through each port, it sometimes stops prematurely. It doesn't stop at just one number either, its pretty random. For example it I specify 200. The console will scroll through each port then stops at 110. Next time I run it, it stops at 80. Code Left out some of the things, assume all variables are declared where they should. First part is in Main. static void Main(string[] args) { string portNum; int convertedNum; Console.WriteLine("Scanning ports 1-X"); portNum = Console.ReadLine(); convertedNum = Convert.ToInt32(portNum); try { for (int i = 1; i <= convertedNum; i++) { ThreadPool.QueueUserWorkItem(scanPort, i); Thread.Sleep(100); } } catch (Exception e) { Console.WriteLine("exception " + e); } } static void scanPort(object o) { TcpClient scanner = new TcpClient(); try { scanner.Connect("127.0.0.1",(int)o); Console.WriteLine("Port {0} open", o); } catch { Console.WriteLine("Port {0} closed",o); } } }

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• Accessing derived class members with a base class pointer

  - by LRB

  I am making a simple console game in C++ I would like to know if I can access members from the 'entPlayer' class while using a pointer that is pointing to the base class ( 'Entity' ): class Entity { public: void setId(int id) { Id = id; } int getId() { return Id; } protected: int Id; }; class entPlayer : public Entity { string Name; public: entPlayer() { Name = ""; Id = 0; } void setName(string name) { Name = name; } string getName() { return Name; } }; Entity *createEntity(string Type) { Entity *Ent = NULL; if (Type == "player") { Ent = new entPlayer; } return Ent; } void main() { Entity *ply = createEntity("player"); ply->setName("Test"); ply->setId(1); cout << ply->getName() << endl; cout << ply->getId() << endl; delete ply; } How would I be able to call ply-setName etc? OR If it's not possible that way, what would be a better way?

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