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• How to use boost::fusion::transform on heterogeneous containers?

  - by Kyle

  Boost.org's example given for fusion::transform is as follows: struct triple { typedef int result_type; int operator()(int t) const { return t * 3; }; }; // ... assert(transform(make_vector(1,2,3), triple()) == make_vector(3,6,9)); Yet I'm not "getting it." The vector in their example contains elements all of the same type, but a major point of using fusion is containers of heterogeneous types. What if they had used make_vector(1, 'a', "howdy") instead? int operator()(int t) would need to become template<typename T> T& operator()(T& const t) But how would I write the result_type? template<typename T> typedef T& result_type certainly isn't valid syntax, and it wouldn't make sense even if it was, because it's not tied to the function.

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• How do the operators < and > work with pointers?

  - by Øystein

  Just for fun, I had a std::list of const char*, each element pointing to a null-terminated text string, and ran a std::list::sort() on it. As it happens, it sort of (no pun intended) did not sort the strings. Considering that it was working on pointers, that makes sense. According to the documentation of std::list::sort(), it (by default) uses the operator < between the elements to compare. Forgetting about the list for a moment, my actual question is: How do these (, <, =, <=) operators work on pointers in C++ and C? Do they simply compare the actual memory addresses? char* p1 = (char*) 0xDAB0BC47; char* p2 = (char*) 0xBABEC475; e.g. on a 32-bit, little-endian system, p1 p2 because 0xDAB0BC47 0xBABEC475? Testing seems to confirm this, but I thought it'd be good to put it on StackOverflow for future reference. C and C++ both do some weird things to pointers, so you never really know...

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• GWT - problems with constants in css

  - by hba

  Hi, I'm new to GWT; I'm building a small sample app. I have several CSS files. I'm able to successfully use the ClientBundle and CssResource to assign styles to the elements defined in my UiBinder script. Now I'd like to take it one step further and introduce CSS constants using @def css-rule. The @def works great when I define a constant and use it in the same CSS file. However I cannot use it in another CSS file. When I try to use the @eval rule to evaluate an existing constant the compiler throws an execption: "cannot make a static reference to the non-static method ". Here is an example of what I'm trying to do: ConstantStyle.css @def BACKGROUND red; ConstantStyle.java package abc; import ...; interface ConstantStyle extends cssResource { String BACKGROUND(); } MyStyle.css @eval BACKGROUND abc.ConstantStyle.BACKGROUND(); .myClass {background-color: BACKGROUND;} MyStyle.java package abc; import ...; interface ConstantStyle extends cssResource { String myClass; } MyResources.java package abc; import ...; interface MyResources extends ClientBundle { @Source("ConstantStyle.css") ConstantStyle constantStyle(); @Source("MyStyle.css") MyStyle myStyle(); } Thanks in advance!

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• loop is cut one element of the array

  - by Walaa

  The problem is : Write a program that reads a number n and then declares an array of n elements. The program then fills the array with the first n numbers, where each number is two to the power of the previous. Finally, display array’s contents. My code : import java.util.*; public class Q1 { static Scanner scan = new Scanner (System.in); public static void main(String args [] ) { int num; int i = 0; System.out.println("Enter a number :"); num = scan.nextInt(); double [] a=new double[num]; a[0]= num ; for ( ;i<=a.length-1 ; i++) { a[i+1] = Math.pow(2,a[i]); System.out.println((int)(a[i]) ); } } } The error is : ----jGRASP exec: java Q1 Enter a number : 4 4 16 65536 Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 4 at Q1.main(Q1.java:16) ----jGRASP wedge2: exit code for process is 1. why it says that? And the number by user printed twice!

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• Memory leaks while using array of double

  - by Gacek

  I have a part of code that operates on large arrays of double (containing about 6000 elements at least) and executes several hundred times (usually 800) . When I use standard loop, like that: double[] singleRow = new double[6000]; int maxI = 800; for(int i=0; i<maxI; i++) { singleRow = someObject.producesOutput(); //... // do something with singleRow // ... } The memory usage rises for about 40MB (from 40MB at the beggining of the loop, to the 80MB at the end). When I force to use the garbage collector to execute at every iteration, the memory usage stays at the level of 40MB (the rise is unsignificant). double[] singleRow = new double[6000]; int maxI = 800; for(int i=0; i<maxI; i++) { singleRow = someObject.producesOutput(); //... // do something with singleRow // ... GC.Collect() } But the execution time is 3 times longer! (it is crucial) How can I force the C# to use the same area of memory instead of allocating new ones? Note: I have the access to the code of someObject class, so if it would be needed, I can change it.

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• SQL SERVER FOR XML SYNTAX

  - by Raj73

  How can I get an output as follows using FOR XML / sql query. I am not sure how I can get the Column Values as Elements instead of the tables' column Names. I am using sql server 2005 I HAVE TABLE SCEMA AS FOLLOWS CREATE TABLE PARENT ( PID INT, PNAME VARCHAR(20) ) CREATE TABLE CHILD ( PID INT, CID INT, CNAME VARCHAR(20) ) CREATE TABLE CHILDVALUE ( CID INT, CVALUE VARCHAR(20) ) INSERT INTO PARENT VALUES (1, 'SALES1') INSERT INTO PARENT VALUES (2, 'SALES2') INSERT INTO CHILD VALUES (1, 1, 'FOR01') INSERT INTO CHILD VALUES (1, 2, 'FOR02') INSERT INTO CHILD VALUES (2, 3, 'FOR03') INSERT INTO CHILD VALUES (2, 4, 'FOR04') INSERT INTO CHILDVALUE VALUES (1, '250000') INSERT INTO CHILDVALUE VALUES (2, '400000') INSERT INTO CHILDVALUE VALUES (3, '500000') INSERT INTO CHILDVALUE VALUES (4, '800000') The Output I am looking for is as follows <SALE1> <FOR01>250000</FOR01> <FOR02>400000</FOR02> </SALE1> <SALE2> <FOR03>500000</FOR03> <FOR04>800000</FOR04> </SALE2>

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• Big-O for calculating all routes from GPS data

  - by HH

  A non-critical GPS module use lists because it needs to be modifiable, new routes added, new distances calculated, continuos comparisons. Well so I thought but my team member wrote something I am very hard to get into. His pseudo code int k =0; a[][] <- create mapModuleNearbyDotList -array //CPU O(n) for(j = 1 to n) // O(nlog(m)) for(i =1 to n) for(k = 1 to n) if(dot is nearby) adj[i][j]=min(adj[i][j], adj[i][k] + adj[k][j]); His ideas transformations of lists to tables His worst case time complexity is O(n^3), where n is number of elements in his so-called table. Exception to the last point with Finite structure: O(mlog(n)) where n is number of vertices and m is the amount of neighbour vertices. Questions about his ideas why to waste resources to transform constantly-modified lists to table? Fast? only point where I to some extent agree but cannot understand the same upper limits n for each for-loops -- perhaps he supposed it circular why does the code take O(mlog(n)) to proceed in time as finite structure? The term finite may be wrong, explicit?

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• How to paginate json data?

  - by Pandiya Chendur

  I used json data and iterated div elements to get my result.... function Iteratejsondata(HfJsonValue) { //var jsonObj = eval('(' + HfJsonValue + ')'); var jsonObj = JSON.parse(HfJsonValue); for (var i = jsonObj.Table.length - 1; i >= 0; i--) { var employee = jsonObj.Table[i]; $('<div class="resultsdiv"><br /><span class="resultName">' + employee.Emp_Name + '</span><span class="resultfields" style="padding-left:100px;">Category&nbsp;:</span>&nbsp;<span class="resultfieldvalues">' + employee.Desig_Name + '</span><br /><br /><span id="SalaryBasis" class="resultfields">Salary Basis&nbsp;:</span>&nbsp;<span class="resultfieldvalues">' + employee.SalaryBasis + '</span><span class="resultfields" style="padding-left:25px;">Salary&nbsp;:</span>&nbsp;<span class="resultfieldvalues">' + employee.FixedSalary + '</span><span style="font-size:110%;font-weight:bolder;padding-left:25px;">Address&nbsp;:</span>&nbsp;<span class="resultfieldvalues">' + employee.Address + '</span></div>').insertAfter('#ResultsDiv'); } $(".resultsdiv:even").addClass("resultseven"); $(".resultsdiv").hover(function() { $(this).addClass("resultshover"); }, function() { $(this).removeClass("resultshover"); }); } I get 22 records in total... Now i want to paginate these divs (i.e) 5 divs per page... Any suggestion...

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• Recursion in assembly?

  - by Davis

  I'm trying to get a better grasp of assembly, and I am a little confused about how to recursively call functions when I have to deal with registers, popping/pushing, etc. I am embedding x86 assembly in C++. Here I am trying to make a method which given an array of integers will build a linked list containing these integers in the order they appear in the array. I am doing this by calling a recursive function: insertElem (struct elem *head, struct elem *newElem, int data) -head: head of the list -data: the number that will be inserted at the end of a list -newElem: points to the location in memory where I will store the new element (data field) My problem is that I keep overwriting the registers instead of a typical linked list. For example, if I give it an array {2,3,1,8,3,9} my linked-list will return the first element (head) and only the last element, because the elements keep overwriting each other after head is no longer null. So here my linked list looks something like: 2--9 instead of 2--3--1--8--3--9 I feel like I don't have a grasp on how to organize and handle the registers. newElem is in EBX and just keeps getting rewritten. Thanks in advance!

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• Simplest way to mix sequences of types with iostreams?

  - by Kylotan

  I have a function void write<typename T>(const T&) which is implemented in terms of writing the T object to an ostream, and a matching function T read<typename T>() that reads a T from an istream. I am basically using iostreams as a plain text serialisation format, which obviously works fine for most built-in types, although I'm not sure how to effectively handle std::strings just yet. I'd like to be able to write out a sequence of objects too, eg void write<typename T>(const std::vector<T>&) or an iterator based equivalent (although in practice, it would always be used with a vector). However, while writing an overload that iterates over the elements and writes them out is easy enough to do, this doesn't add enough information to allow the matching read operation to know how each element is delimited, which is essentially the same problem that I have with a single std::string. Is there a single approach that can work for all basic types and std::string? Or perhaps I can get away with 2 overloads, one for numerical types, and one for strings? (Either using different delimiters or the string using a delimiter escaping mechanism, perhaps.)

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• How to find an XPath query to Element/Element without namespaces (XmlSerializer, fragment)?

  - by Veksi

  Assume this simple XML fragment in which there may or may not be the xml declaration and has exactly one NodeElement as a root node, followed by exactly one other NodeElement, which may contain an assortment of various number of different kinds of elements. <?xml version="1.0"> <NodeElement xmlns="xyz"> <NodeElement xmlns=""> <SomeElement></SomeElement> </NodeElement> </NodeElement> How could I go about selecting the inner NodeElement and its contents without the namespace? For instance, "//*[local-name()='NodeElement/NodeElement[1]']" (and other variations I've tried) doesn't seem to yield results. As for in general the thing that I'm really trying to accomplish is to Deserialize a fragment of a larger XML document contained in a XmlDocument. Something like the following var doc = new XmlDocument(); doc.LoadXml(File.ReadAllText(@"trickynodefile.xml")); //ReadAllText to avoid Unicode trouble. var n = doc.SelectSingleNode("//*[local-name()='NodeElement/NodeElement[1]']"); using(var reader = XmlReader.Create(new StringReader(n.OuterXml))) { var obj = new XmlSerializer(typeof(NodeElementNodeElement)).Deserialize(reader); I believe I'm missing just the right XPath expression, which seem to be rather elusive. Any help much appreciated!

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• Best implementation of Java Queue?

  - by Georges Oates Larsen

  I am working (In java) on a recursive image processing algorithm that recursively traverses the pixels of the image, outward from a center point. Unfortunately... That causes stack overflows, so I have decided to switch to a Queue-based algorithm. Now, this is all fine and dandy -- But considering the fact that its queue will be analyzing THOUSANDS of pixels in a very short amount of time, while constantly popping and pushing, WITHOUT maintaining a predictable state (It could be anywhere between length 100, and 20000); The queue implementation needs to have significantly fast popping and pushing abilities. A linked list seems attractive due to its ability to push elements unto its self without rearranging anything else in the list, but in order for it to be fast enough, it would need easy access to both its head, AND its tail (or second-to-last node if it were not doubly-linked). Sadly, though I cannot find any information related to the underlying implementation of linked lists in Java, so it's hard to say if a linked list is really the way to go... This brings me to my question... What would be the best implementation of the Queue interface in Java for what I intend to do? (I do not wish to edit or even access anything other than the head and tail of the queue -- I do not wish to do any sort of rearranging, or anything. On the flip side, I DO intend to do a lot of pushing and popping, and the queue will be changing size quite a bit, so preallocating would be inefficient)

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• Masonry js won't bunch images vertically

  - by user1449737

  The images are being aligned horizontally correctly but they are all spaced out vertically.. Take a look here http://brstudios.co.uk/testing to see what I mean properly.. My mark up is as followed (simplified): <html> <head> <script type="text/javascript" src="http://code.jquery.com/jquery-latest.js"></script> <script type="text/javascript" src="http://masonry.desandro.com/jquery.masonry.min.js"></script> <script type="text/javascript" src="https://raw.github.com/desandro/imagesloaded/master/jquery.imagesloaded.min.js"></script> <script type="text/javascript"> var $container = $('.portfolio-container'); $container.imagesLoaded(function(){ $container.masonry({ itemSelector : '.break', columnWidth : 429 }); }); </script> <style type="text/css"> .break { float: left; width: 429px; margin: 10px 20px; } </style> </head> <body> <div class="portfolio-container"> <?php do { ?> <div class="break"> // Contents taken from MySQL // </div> <?php } while ($row_displayPosts = mysql_fetch_assoc($displayPosts)); ?> </div> </body> </html> I think part of it is working but as you can see by the link provided it isn't moving the elements together vertically. Does anyone have any pointers?

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• Invoke Command When "ENTER" Key Is Pressed In XAML

  - by bitxwise

  I want to invoke a command when ENTER is pressed in a TextBox. Consider the following XAML: <UserControl ... xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity" ...> ... <TextBox> <i:Interaction.Triggers> <i:EventTrigger EventName="KeyUp"> <i:InvokeCommandAction Command="{Binding MyCommand}" CommandParameter="{Binding Text}" /> </i:EventTrigger> </i:Interaction.Triggers> </TextBox> ... </UserControl> and that MyCommand is as follows: public ICommand MyCommand { get { return new DelegateCommand<string>(MyCommandExecute); } } private void MyCommandExecute(string s) { ... } With the above, my command is invoked for every key press. How can I restrict the command to only invoke when the ENTER key is pressed? I understand that with Expression Blend I can use Conditions but those seem to be restricted to elements and can't consider event arguments. I have also come across SLEX which offers its own InvokeCommandAction implementation that is built on top of the Systems.Windows.Interactivity implementation and can do what I need. Another consideration is to write my own trigger, but I'm hoping there's a way to do it without using external toolkits.

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• Sending information between JavaScript and Web Services using AJAX

  - by COB-CSU-AM

  Alright so I'm using Microsoft's Web Services and AJAX to get information from a SQL database for use with java script on the client side. And I'm wondering what the best method is. Before I started working on the project, the web services were setup to return a C# List filled with some objects. Those objects variables (ints, strings, etc.) contain the data I want to use. Of course, java script can't do much with this, to the best of my knowledge. I then modified the web service to return a 2D Array, but java script got confused, and to the best of my knowledge can't handle 2D array's returned from C#. I then tried to use a regular array, but then a found the length property of an array in JS doesn't carry over, so I couldn't preform a for loop through all the items, because there wasn't anyway of knowing how many elements there were. The only other thing I can thing of is returning a string with special char's to separate the data, but this seems way too convoluted. Any suggestions? Thanks in advance!

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• Parsing URL error

  - by user577875

  It didn't seem like there was a post about this, so here goes. I've been working on a simple app to grab my time table from my school, and get it on my phone. Currently I'm working on the port on android but I've hit an issue. I get the error: java.io.IOException: -1 error loading URL urladress. Code: public void updateTimeTable(){ //Get UID and Birthday SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getBaseContext()); String uid = prefs.getString("uid", "000000"); String fods = prefs.getString("fodsdag", "000000"); //Set URL String url = "http://unv1.aalborg-stu.dk/cgi-bin/elevskema.pl?ugen=0&unavn=" + uid + "&fodsdag=" + fods; try { Document doc = Jsoup.connect(url).get(); Elements td = doc.getElementsByTag("td"); //ArrayList<String> tdArray = new ArrayList<String>(); // for (Element tds : td) { // String tdText = tds.text(); // tdArray.add(tdText); //} //String[] data = tdArray.toArray(new String[tdArray.size()]); } catch (IOException e ){ Log.e("Parser", "shite", e); } Context context = getApplicationContext(); CharSequence text = url; int duration = Toast.LENGTH_SHORT; Toast toast = Toast.makeText(context, text, duration); toast.show(); } I've commented some lines out to identify where the issue is, and it seems it's at the actual parsing. Anywho, screenshot of the error I get: Screenshot I got about 4 days worth of Java experience so forgive me if it's something silly. Best Regards

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• Populating a Datagrid with variable number of columns and rows in Flex

  - by Rie Mino

  I am trying to figure out how to manage a Datagrid based on an XML object like this: <matrix rows="5" columns="5"> <column> <row>0.5</row> <row>0.21</row> </column> <column> <row>0.6</row> <row>0.9</row> </column> <column> <row>0.5</row> <row>0.5</row> </column> <column> <row>0.8</row> <row>0.4</row> </column> </matrix> I will need to populate the Datagrid column names based on a different XML object and use the above XML to populate each of the column's rows. I currently am able to create the Datagrid and populate its column headers but I am unsure as to how to how to add the rows for each column. The above XML will be update with new row and column elements added and deleted. This, of course, will be bound to the Datagrid to show updates. Thanks in advanced for your help.

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• Array indexOf implementation for Internet Explorer

  - by Daemon

  There are plenty of solutions on how to get the indexOf implementation into the Array prototype so that it works under Internet Explorer, however I've stumbled upon an issue that doesn't seem to be addressed anywhere I've looked so far. Using the pretty well agreed upon implementation at MDC, I have the following code that's being problematic now: // indexOf support for IE (from MDC) if (!Array.prototype.indexOf) { Array.prototype.indexOf = function(elt /*, from*/) { var len = this.length >>> 0; var from = Number(arguments[1]) || 0; from = (from < 0) ? Math.ceil(from) : Math.floor(from); if (from < 0) from += len; for (; from < len; from++) { if (from in this && this[from] === elt) return from; } return -1; }; } var i = [1,2,3,4]; for (j in i) { alert(i[j]); } I am expecting to receive 4 alerts, each one containing one of the elements of the array. In Firefox and Chrome, that's exactly what I see, however in IE8 I get an additional alert containing the indexOf function code. What can be done to avoid this?

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• Ruby and RSS2 Feed not displaying image

  - by pcasa

  Trying to create a simple RSS2 Feed that I could later pass on to FeedBurner but can't get RSS feed to display images at all. Also, from what I have read having xml.instruct! on top might cause IE to complain it's not a valid feed. Is this true? My Code looks like xml.instruct! xml.rss "version" => "2.0", "xmlns:dc" => "http://purl.org/dc/elements/1.1/" do xml.channel do xml.title "Store" xml.link url_for :only_path => false, :controller => 'products' xml.description "Store" xml.pubDate @products.first.updated_at.rfc822 if @products.any? @products.each do |product| xml.item do xml.title product.name xml.pubDate (product.updated_at.rfc822) xml.image do xml.url domain_host + product.product_image.url(:small) xml.title "Store" xml.link url_for :only_path => false, :controller => 'products' end xml.link url_for :only_path => false, :controller => 'products', :action => 'show', :id => product.permalink xml.description product.fine_print xml.guid url_for :only_path => false, :controller => 'products', :action => 'show', :id => product.permalink end end end end

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• wpf treeview does not show child objects

  - by gangt

  I have an object with child object(s) and I load it using linq. And I assign it to a treeView's itemssource. treeView.DisplayMemberPath = "Name"; treeView.ItemsSource = tasks; It shows only the parent nodes (task.name), I couldn't figure out how to add children (TaskItems.name). All the examples show HierarchicalData in xaml. I need to do it in code-behind, just like the above code. Is it possible? public class Task { public int Id; public string Name; public bool IsActive; public List<TaskItem> TaskItems = new List<TaskItem>(); } public class TaskItem { public int TaskId; public string Name; public string Value; } -------------- var tasks1 = from t in xd.Descendants("taskheader") select new Task { Id = (int)t.Element("id"), Name = t.Element("name").Value, IsActive = t.Element("isactive").Value == "1", TaskItems = t.Elements("taskdetail").Select(e => new TaskItem { TaskId = (int)e.Element("taskid"), Name = (string)e.Element("name"), Value = (string)e.Element("value"), }).ToList() }; -------------- List<Task> tasks = new List<Task>(); tasks = tasks1;

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• Webkit browsers rendering CSS different than Mozilla Firefox...Why??

  - by JAG2007

  I'm styling a form that was already marked up (made some markup changes), and I normally work in Firefox to style so I can use firebug and the web developer toolbar. On this project, I noticed that my styles are displaying quite differently for one particular area (several elements) in webkit based browsers Chrome and Safari, than in Firefox (we won't even get into Internet Explorer, although it is siding with the Firefox display). I can't figure out though why the styles are displaying so differently. Normally there is some rule that I'm neglecting that Firefox just takes for granted, and the others need it specified. But here I'm not getting why it's displaying this way. In particular I'm referring to the bottom area of the form where users can enter their contact info, then submit the form. I'll attach screen shots for reference as to the discrepancy. Here's the URL so feel free to check it out on your own. Although be advised that this is a production page (already released) so if you try out the form, you WILL BE added to CURE's contact database. http://www.helpcurenow.org/survey2010 Here's the screen shots: Firefox (the way I intend it to look) Chrome, and then Safari - strange change to submit button As a bonus, if anybody wants to help me with figuring out why on earth IE7 wants to not show the background behind the questions only, and how to fix that I would be much obliged! Thanks very much.

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• is there something equivalent to 'Address of' or offset operator in .net?

  - by Gio

  We have nested stuctures as such, used as an interface for some device drivers. On occasion we have to update individual elements. An 'address of' operator would be helpful, but an 'offset' function or operator is what I'm really looking for, but not sure how to go about it. In other words, how far is structureN.elementX away from the start of the structure in bytes? [StructLayout(LayoutKind.Sequential)] public struct s1 { UInt16 elem1; UInt16 elem2; UInt16 elem3; } [StructLayout(LayoutKind.Sequential)] public struct s2 { UInt16 elem1; UInt16 elem2; UInt16 elem3; } [StructLayout(LayoutKind.Sequential)] public struct driver { public S1 s1; public S2 s2; } For instance we need to send the device driver some data to update driver.s1.elem3, by way of providing an offset address, data block and length. We would update our local copy, then call the device api with the afore mentioned data. Not sure I have to do this with 'unsafe' method calls. Any help?

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• Convert a Dynamic[] construct to a numerical list

  - by Leo Alekseyev

  I have been trying to put together something that allows me to extract points from a ListPlot in order to use them in further computations. My current approach is to select points with a Locator[]. This works fine for displaying points, but I cannot figure out how to extract numerical values from a construct with head Dynamic[]. Below is a self-contained example. By dragging the gray locator, you should be able to select points (indicated by the pink locator and stored in q, a list of two elements). This is the second line below the plot. Now I would like to pass q[[2]] to a function, or perhaps simply display it. However, Mathematica treats q as a single entity with head Dynamic, and thus taking the second part is impossible (hence the error message). Can anyone shed light on how to convert q into a regular list? EuclideanDistanceMod[p1_List, p2_List, fac_: {1, 1}] /; Length[p1] == Length[p2] := Plus @@ (fac.MapThread[Abs[#1 - #2]^2 &, {p1, p2}]) // Sqrt; test1 = {{1.`, 6.340196001221532`}, {1.`, 13.78779876355869`}, {1.045`, 6.2634018978377295`}, {1.045`, 13.754947081416544`}, {1.09`, 6.178367702583522`}, {1.09`, 13.72055251752498`}, {1.135`, 1.8183153704413153`}, {1.135`, 6.082497198000075`}, {1.135`, 13.684582525399742`}, {1.18`, 1.6809452373465104`}, {1.18`, 5.971583107298081`}, {1.18`, 13.646996905469383`}, {1.225`, 1.9480537697339537`}, {1.225`, 5.838386922625636`}, {1.225`, 13.607746407088161`}, {1.27`, 2.1183174369679234`}, {1.27`, 5.669799095595362`}, {1.27`, 13.566771130126131`}, {1.315`, 2.2572975468163463`}, {1.315`, 5.444014254828522`}, {1.315`, 13.523998701347882`}, {1.36`, 2.380307009155079`}, {1.36`, 5.153024664297602`}, {1.36`, 13.479342200528283`}, {1.405`, 2.4941312539733285`}, {1.405`, 4.861423833512566`}, {1.405`, 13.432697814928654`}, {1.45`, 2.6028066447609426`}, {1.45`, 4.619367407525507`}, {1.45`, 13.383942212133244`}}; DynamicModule[{p = {1.2, 10}, q = {1.3, 11}}, q := Dynamic@ First@test1[[ Ordering[{#, EuclideanDistanceMod[p, #, {1, .1}]} & /@ test1, 1, #1[[2]] < #2[[2]] &]]]; Grid[{{Show[{ListPlot[test1, Frame -> True, ImageSize -> 300], Graphics@Locator[Dynamic[p]], Graphics@ Locator[q, Appearance -> {Small}, Background -> Pink]}]}, {Dynamic@p}, {q},{q[[2]]}}]]

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• How to improve multi-threaded access to Cache (custom implementation)

  - by Andy

  I have a custom Cache implementation, which allows to cache TCacheable<TKey> descendants using LRU (Least Recently Used) cache replacement algorithm. Every time an element is accessed, it is bubbled up to the top of the LRU queue using the following synchronized function: // a single instance is created to handle all TCacheable<T> elements public class Cache() { private object syncQueue = new object(); private void topQueue(TCacheable<T> el) { lock (syncQueue) if (newest != el) { if (el.elder != null) el.elder.newer = el.newer; if (el.newer != null) el.newer.elder = el.elder; if (oldest == el) oldest = el.newer; if (oldest == null) oldest = el; if (newest != null) newest.newer = el; el.newer = null; el.elder = newest; newest = el; } } } The bottleneck in this function is the lock() operator, which limits cache access to just one thread at a time. Question: Is it possible to get rid of lock(syncQueue) in this function while still preserving the queue integrity?

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• How to treat Base* pointer as Derived<T>* pointer?

  - by dehmann

  I would like to store pointers to a Base class in a vector, but then use them as function arguments where they act as a specific class, see here: #include <iostream> #include <vector> class Base {}; template<class T> class Derived : public Base {}; void Foo(Derived<int>* d) { std::cerr << "Processing int" << std::endl; } void Foo(Derived<double>* d) { std::cerr << "Processing double" << std::endl; } int main() { std::vector<Base*> vec; vec.push_back(new Derived<int>()); vec.push_back(new Derived<double>()); Foo(vec[0]); Foo(vec[1]); delete vec[0]; delete vec[1]; return 0; } This doesn't compile: error: call of overloaded 'Foo(Base*&)' is ambiguous Is it possible to make it work? I need to process the elements of the vector differently, according to their int, double, etc. types.

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