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• When to use reinterpret_cast?

  - by HeretoLearn

  I am little confused with the applicability of reinterpret_cast vs static_cast. From what I have read the general rules are to use static cast when the types can be interpreted at compile time hence the word static. This is the cast the C++ compiler uses internally for implicit casts also. reinterpret_cast are applicable in two scenarios, convert integer types to pointer types and vice versa or to convert one pointer type to another. The general idea I get is this is unportable and should be avoided. Where I am a little confused is one usage which I need, I am calling C++ from C and the C code needs to hold on to the C++ object so basically it holds a void*. What cast should be used to convert between the void * and the Class type? I have seen usage of both static_cast and reinterpret_cast? Though from what I have been reading it appears static is better as the cast can happen at compile time? Though it says to use reinterpret_cast to convert from one pointer type to another?

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• Python to C/C++ const char question

  - by tsukemonoki

  I am extending Python with some C++ code. One of the functions I'm using has the following signature: int PyArg_ParseTupleAndKeywords(PyObject *arg, PyObject *kwdict, char *format, char **kwlist, ...); (link: http://docs.python.org/release/1.5.2p2/ext/parseTupleAndKeywords.html) The parameter of interest is kwlist. In the link above, examples on how to use this function are given. In the examples, kwlist looks like: static char *kwlist[] = {"voltage", "state", "action", "type", NULL}; When I compile this using g++, I get the warning: warning: deprecated conversion from string constant to ‘char*’ So, I can change the static char* to a static const char*. Unfortunately, I can't change the Python code. So with this change, I get a different compilation error (can't convert char** to const char**). Based on what I've read here, I can turn on compiler flags to ignore the warning or I can cast each of the constant strings in the definition of kwlist to char *. Currently, I'm doing the latter. What are other solutions? Sorry if this question has been asked before. I'm new.

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• XmlSerializer construction with same named extra types

  - by NoizWaves

  Hey, I am hitting trouble constructing an XmlSerializer where the extra types contains types with the same Name (but unique Fullname). Below is an example that illustrated my scenario. Type definitions in external assembly I cannot manipulate: public static class Wheel { public enum Status { Stopped, Spinning } } public static class Engine { public enum Status { Idle, Full } } Class I have written and have control over: public class Car { public Wheel.Status WheelStatus; public Engine.Status EngineStatus; public static string Serialize(Car car) { var xs = new XmlSerializer(typeof(Car), new[] {typeof(Wheel.Status),typeof(Engine.Status)}); var output = new StringBuilder(); using (var sw = new StringWriter(output)) xs.Serialize(sw, car); return output.ToString(); } } The XmlSerializer constructor throws a System.InvalidOperationException with Message "There was an error reflecting type 'Engine.Status'" This exception has an InnerException of type System.InvalidOperationException and with Message "Types 'Wheel.Status' and 'Engine.Status' both use the XML type name, 'Status', from namespace ''. Use XML attributes to specify a unique XML name and/or namespace for the type." Given that I am unable to alter the enum types, how can I construct an XmlSerializer that will serialize Car successfully?

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• Using an empty column as a divider in a JTable.

  - by Catalina Island

  I'm trying to use an empty column as a divider between pairs of columns in a JTable. Here's a picture and code for what I have so far. I know I can change the look using a custom TableCellRenderer. Before I go down that road, is there a better way to do this? Any ideas appreciated. import javax.swing.*; import javax.swing.table.*; public class TablePanel extends JPanel { public static void main(String[] args) { SwingUtilities.invokeLater(new Runnable() { @Override public void run() { JFrame f = new JFrame("TablePanel"); f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE); f.add(new TablePanel()); f.pack(); f.setVisible(true); } }); } public TablePanel() { TableModel dataModel = new MyModel(); JTable table = new JTable(dataModel); table.getColumnModel().getColumn(MyModel.DIVIDER).setMaxWidth(0); JScrollPane jsp = new JScrollPane(table); jsp.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS); this.add(jsp); } private static class MyModel extends AbstractTableModel { private static final int DIVIDER = 2; private final String[] names = { "A1", "A2", "", "B1", "B2" }; @Override public int getRowCount() { return 32; } @Override public int getColumnCount() { return names.length; } @Override public String getColumnName(int col) { if (col == DIVIDER) return ""; return names[col]; } @Override public Object getValueAt(int row, int col) { if (col == DIVIDER) return ""; return (row + 1) / 10.0; } @Override public Class<?> getColumnClass(int col) { if (col == DIVIDER) return String.class; return Number.class; } } }

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• Does allocation speed depend on the garbage collector being used?

  - by jkff

  My app is allocating a ton of objects (1mln per second; most objects are byte arrays of size ~80-100 and strings of the same size) and I think it might be the source of its poor performance. The app's working set is only tens of megabytes. Profiling the app shows that GC time is negligibly small. However, I suspect that perhaps the allocation procedure depends on which GC is being used, and some settings might make allocation faster or perhaps make a positive influence on cache hit rate, etc. Is that so? Or is allocation performance independent on GC settings under the assumption that garbage collection itself takes little time?

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• C++ object in memory

  - by Neo_b

  Hello. Is there a standard in storing a C++ objects in memory? I wish to set a char* pointer to a certain address in memory, so that I can read certain objects' variables directly from the memory byte by byte. When I am using Dev C++, the variables are stored one by one right in the memory address of an object in the order that they were defined. Now, can it be different while using a different compiler (like the variables being in a different order, or somewhere else)? Thank you in advance. :-)

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• How to deal with callback to your UIController after your UIController unloads?

  - by erotsppa

  Suppose your controller is a table view and one of the cells you are going off to do a length task (say download a thumbnail) to be viewed in the cell. Typically you would have the network call do a callback to your controller when it is done downloading. The callback can then reload the table or do some other form of UI update (hides a spinner etc). However, what if the controller is unloaded? Say the user navigated away from this controller and it got released? What happens? Will the callback still work despite the controller now not in memory? Also, if the callback operates on some objects (say the UITableView) what happens when the controller is deallocated? I suppose the controller can release all the objects and the callback would just be calling methods on nil to prevent crash. But is this the convention?

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• Is this the correct way to reloadData on a UITableView?

  - by Sheehan Alam

  I am trying to append objects to my data source and then reload the table. Is this the correct way of approaching it? self.items is my datasource //Copy current items self.itemsCopy = [self.items mutableCopy];//[[NSMutableArray alloc] initWithArray:self.items copyItems:NO]; NSLog(@"Copy Size before append: %d",[itemsCopy count]); //Get new items int lastMsgID = [self getLastMessageID]; [self.coreData getMoreMessages:self.title lastID:lastMsgID]; //This will update self.items with 30 objects //Append new items [itemsCopy addObjectsFromArray:self.items]; //Empty items and copy itemsCopy [self.items removeAllObjects]; self.items = [self.itemsCopy mutableCopy]; NSLog(@"Actual Size after append: %d",[self.items count]); //Reload data [tableView reloadData];

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• C# What would happen to GC if I run process with priority = RealTime?

  - by Bobb

  I have a C# app which runs with priority RealTime. It was all fine until I made few hectic changes in past 2 days. Now it runs out of memory in few hours. I am trying to find whether it is a memory leak I created of this is because I consume lot more objects than before and GC simply cant collect them because it runs with same priority. My question is - what could happen to GC when it tries to collect objects in application with RealTime priority (there is also at least one thread running with Highest thread priority)? (P.S. by realtime priority I mean Process.GetCurrentProcess().PriorityClass = ProcessPriorityClass.RealTime)

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• DataGridView cells not editable when using an outside thread call

  - by joslinm

  Hi, I'm not able to edit my datagridview cells when a number of identical calls takes place on another thread. Here's the situation: Dataset table is created in the main window The program receives in files and processes them on a background thread in class TorrentBuilder : BackgroundWorker creating an array objects of another class Torrent My program receives those objects from the BW result and adds them into the dataset The above happens either on my main window thread or in another thread: I have a separate thread watching a folder for files to come in, and when they do come in, they proceed to call TorrentBuilder.RunWorkerAsynch() from that thread, receive the result, and call an outside class that adds the Torrent objects into the table. When the files are received by the latter thread, the datagridview isn't editable. All of the values come up properly into the datagridview, but when I click on a cell to edit it: I can write letters and everything, but when I click out of it, it immediately reverts back to its original value. If I restart the program, I can edit the same cells just fine. If the values are freshly added from the main window thread, I can edit the cells just fine. The outside thread is called from my main window thread, and sits there in the background. I don't believe it to be ReadOnly because I would have gotten an exception. Here's some code: From my main window class: private void dataGridView_DragDrop(object sender, DragEventArgs e) { ArrayList al = new ArrayList(); string[] files = (string[])e.Data.GetData(DataFormats.FileDrop); foreach (string file in files) { string extension = Path.GetExtension(file); if (Path.GetExtension(file).Equals(".zip") || Path.GetExtension(file).Equals(".rar")) { foreach (string unzipped in dh.UnzipFile(file)) al.Add(unzipped); } else if (Path.GetExtension(file).Equals(".torrent")) { al.Add(file); } } dataGridViewProgressBar.Visible = true; tb.RunWorkerCompleted += new RunWorkerCompletedEventHandler(tb_DragDropCompleted); tb.ProgressChanged += new ProgressChangedEventHandler(tb_DragDropProgress); tb.RunWorkerAsync() } void tb_DragDropCompleted(object sender, RunWorkerCompletedEventArgs e) { data.AddTorrents((Torrent[])e.Result); builder.Dispose(); dh.MoveProcessedFiles(data); dataGridViewProgressBar.Visible = false; } From my outside Thread while (autocheck) { if (torrentFiles != null) { builder.RunWorkerAsync(torrentFiles); while (builder.IsBusy) Thread.Sleep(500); } } void builder_RunWorkerCompleted(object sender, System.ComponentModel.RunWorkerCompletedEventArgs e) { data.AddTorrents((Torrent[])e.Result); builder.Dispose(); dh.MoveProcessedFiles(xml); data.Save(); //Save just does an `AcceptChanges()` and saves to a XML file }

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• Want to make object transparent

  - by Himadri

  I am working with directx. I am displaying two objects on my window. They are intersecting each other. I find the intersecting object. My problem is- I want two original objects to be transparent and the resulting intersected part to be opaque, so that the intersected part can be seen clearly. I found some question related to transparency but they are related to transparency of window. But I want the object to be transparent.

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• can't save form content to database, help plsss!!

  - by dana

  i'm trying to save 100 caracters form user in a 'microblog' minimal application. my code seems to not have any mystakes, but doesn't work. the mistake is in views.py, i can't save the foreign key to user table models.py looks like this: class NewManager(models.Manager): def create_post(self, post, username): new = self.model(post=post, created_by=username) new.save() return new class New(models.Model): post = models.CharField(max_length=120) date = models.DateTimeField(auto_now_add=True) created_by = models.ForeignKey(User, blank=True) objects = NewManager() class NewForm(ModelForm): class Meta: model = New fields = ['post'] # widgets = {'post': Textarea(attrs={'cols': 80, 'rows': 20}) def save_new(request): if request.method == 'POST': created_by = User.objects.get(created_by = user) date = request.POST.get('date', '') post = request.POST.get('post', '') new_obj = New(post=post, date=date, created_by=created_by) new_obj.save() return HttpResponseRedirect('/') else: form = NewForm() return render_to_response('news/new_form.html', {'form': form},context_instance=RequestContext(request)) i didn't mention imports here - they're done right, anyway. my mistake is in views.py, when i try to save it says: local variable 'created_by' referenced before assignment it i put created_py as a parameter, the save needs more parameters... it is really weird help please!!

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• MemoryStream instance timing help

  - by rod

  Hi All, Is it ok to instance a MemoryStream at the top of my method, do a bunch of stuff to it, and then use it? For instance: public static byte[] TestCode() { MemoryStream m = new MemoryStream(); ... ... whole bunch of stuff in between ... ... //finally using(m) { return m.ToArray(); } } Updated code public static byte[] GetSamplePDF() { using (MemoryStream m = new MemoryStream()) { Document document = new Document(); PdfWriter.GetInstance(document, m); document.Open(); PopulateTheDocument(document); document.Close(); return m.ToArray(); } } private static void PopulateTheDocument(Document document) { Table aTable = new Table(2, 2); aTable.AddCell("0.0"); aTable.AddCell("0.1"); aTable.AddCell("1.0"); aTable.AddCell("1.1"); document.Add(aTable); for (int i = 0; i < 20; i++) { document.Add(new Phrase("Hello World, Hello Sun, Hello Moon, Hello Stars, Hello Sea, Hello Land, Hello People. ")); } } My point was to try to reuse building the byte code. In other words, build up any kind of document and then send it to TestCode() method.

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• Can using non primitive Integer/ Long datatypes too frequently in the application, hurt the performance??

  - by Marcos

  I am using Long/Integer data types very frequently in my application, to build Generic datatypes. I fear that using these wrapper objects instead of primitive data types may be harmful for performance since each time it needs to create objects which is an expensive operation. but also it seems that I have no other choice(when I have to use primtives with generics) rather than just using them. However, still it would be great if you can suggest if there is anything I could do to make it better. or any way if I could just avoid it ?? Also What may be the downsides of this ? Suggestions welcomed!

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• PHP array of object(stdClass) fusion/intersect?

  - by Gremo

  $arr1 is an associative array of anonymus objects: array 15898 => object(stdClass)[8] public 'date' => int $arr2 is another associative array with two (or more, it's not fixed) properties: array 15898 => object(stdClass)[10] public 'fruits' public 'drinks' I can't find any function for intersect and content fusion when dealing with objects. Basically i'd like to obtain: array 15898 => object(stdClass)[8] public 'date' => int public 'fruits' public 'drinks' Question is: is this even possible?

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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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• Show a django relationship in a template

  - by kevin_82

  I have a django model as follows: class Person(models.Model): name = models.CharField(max_length=255) class Relationship(models.Model): parent = models.ForeignKey(Person) child = models.ForeignKey(Person) description = models.TextField(blank=True) In my view, I pass a certain person, and the relationships in which he/she is parent: person = Person.objects.filter(name ='some name') descendant_relationships = Relationship.objects.filter(parent = person) An I want to show this person's descendants in a list in a template: <ul> {% for item in descendant_relationships%} <li> {{item.child.name}} - {{item.description}} </li> {% endfor %} </ul> But this template code will not show the children of children (i.e. grandchildren, great-grandchildren etc.). How can I get these lower level descendants to show up? I imagine recursion is necessary somewhere, but where?

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• Teacher confused about MVC?

  - by Gideon

  I have an assignment to create a game in java using MVC as a pattern. The thing is that stuff I read about MVC aren't really what the teacher is telling me. What I read is that the Model are the information objects, they are manipulated by the controllers. So in a game the controller mutates the placement of the objects and check if there is any collision etc. What my teacher told me is that I should put everything that is universal to the platform in the models and the controllers should only tell the model which input is given. That means the game loop will be in a model class, but also collision checks etc. So what I get from his story is that the View is the screen, the Controller is the unput handeler, and the Model is the rest. Can someone point me in the right direction?

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• How do I pull `static final` constants from a Java class into a Clojure namespace?

  - by Joe Holloway

  I am trying to wrap a Java library with a Clojure binding. One particular class in the Java library defines a bunch of static final constants, for example: class Foo { public static final int BAR = 0; public static final int SOME_CONSTANT = 1; ... } I had a thought that I might be able to inspect the class and pull these constants into my Clojure namespace without explicitly def-ing each one. For example, instead of explicitly wiring it up like this: (def *foo-bar* Foo/BAR) (def *foo-some-constant* Foo/SOME_CONSTANT) I'd be able to inspect the Foo class and dynamically wire up *foo-bar* and *foo-some-constant* in my Clojure namespace when the module is loaded. I see two reasons for doing this: A) Automatically pull in new constants as they are added to the Foo class. In other words, I wouldn't have to modify my Clojure wrapper in the case that the Java interface added a new constant. B) I can guarantee the constants follow a more Clojure-esque naming convention I'm not really sold on doing this, but it seems like a good question to ask to expand my knowledge of Clojure/Java interop. Thanks

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• How should flushing be handled in a doctrine EntityManager instance shared across different services in symfony2?

  - by Jbm

  I have defined several services in symfony 2 which persist changes to the database. These services have the doctrine instance as one of their dependencies: a.given.service: class: Acme\TestBundle\Service\AGivenService arguments: [@doctrine] If I have two different services and both of them persist objects through the EntityManager, which is obtained like this from the doctrine instance: $em = $doctrine->getEntityManager(); Would all services always share the same EntityManager? If so, how should I handle flushing if I wanted to handle all the changes in a single transaction? I have checked this: http://docs.doctrine-project.org/projects/doctrine-orm/en/2.0.x/reference/transactions-and-concurrency.html and it explains how to handle different transactions in a request, but I want to achieve the opposite, which is having different changes in different services handled as a single transaction. Is there a better approach to handle multiple changes in different services? For now my best bet is having a front-end service in charge of calling the other services and doing the flushing afterwards. Backend services would persist objects but would not do any flushing.

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• In Django, how do I filter where language column = "null"?

  - by alex

  MyTable.objects.filter(where language column = null) How can that be done? Thanks.

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• Download multiple files in background in Android

  - by Addev

  Basically I'm trying to make a little app for watching offline content. So there's a moment where the user selects to download the contents (and the app should download about 300 small files and images). I'd like to show the user how does the process go if he enters the proper activity. Showing a list of all the files, telling what has been already downloaded, in progress or waiting for download. My problem is that I really don't know what approach to take for achieve this. Since the download should last until finished I imagine the solution is an Service, but whats best? an IntentService, a Bound Service or an Standard Service calling a startService() for each download? And how can I keep my objects updated for displaying them later? should I use a database or objects in memory? Thanks

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• Javascript: How to filter object array based on attributes?

  - by JGreig

  I have the following JavaScript JSON array of real estate home objects: var json = { 'homes' : [ { "home_id":"1", "price":"925", "sqft":"1100", "num_of_beds":"2", "num_of_baths":"2.0", }, { "home_id":"2", "price":"1425", "sqft":"1900", "num_of_beds":"4", "num_of_baths":"2.5", }, // ... (more homes) ... ]} var xmlhttp = eval('(' + json + ')'); homes = xmlhttp.homes; What I would like to do is be able to perform a filter on the object to return a subset of "home" objects. For example, I want to be able to filter based on: price, sqft, num_of_beds, and num_of_baths. Question: How can I perform something in javascript like the pseudo-code below: var newArray = homes.filter( price <= 1000 & sqft >= 500 & num_of_beds >=2 & num_of_baths >= 2.5); Note, the syntax does not have to be exactly like above. This is just an example.

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• Xcode automatically converts the object to NSArray

  - by Farrukh Javeid

  I have been working on an app and during the development, I am facing a very strange problem. I have a NSMutableArray tempSortedArray, which is full of objects of Store types. All the objects are valid as I can see them in my GUI, the problem arises when I iterate through the array, at index 90, which can be generally anyone, the XCode converts the Store object to NSMutableArray object. Any idea, why this is happening. This is the code to check out what I am doing: NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"cashBack" ascending:NO]; NSArray *sortDescriptors = [NSArray arrayWithObject:sortDescriptor]; NSArray *sortedArray = [storesArray sortedArrayUsingDescriptors:sortDescriptors]; for (int i = 0; i < [tempSortedArray count]; i++) { Store *currentStore = [tempSortedArray objectAtIndex:i]; NSLog(@"store class: %@", [currentStore.class description]); if (currentStore.cashBackTypeString != (id)[NSNull null]) { //do whatever is required to do here }

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• WPF Converter to look up in generic list

  - by user310046

  I have a list of data where I keep e.g. countries with code, name and some other data. List<Country> countries = <deserialized objects from file> which consist of objects like this: public class Country { public string Code { get; set;} public string Name { get; set;} } The object which use as a DataContext may look like this: public class Address { public string StreetName{ get; set;} public string CountryCode { get; set;} } Then in my XAML I want to do something like this to show the name of the country <TextBlock Text="{Binding Path=CountryCode, Converter={StaticResource CountryNameLookupConverter}}"/> But how can I make the CountryNameLookupConverter use the countries list I read from the xml file?

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