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  • c++ float subtraction rounding error

    - by Volkan Ozyilmaz
    I have a float value between 0 and 1. I need to convert it with -120 to 80. To do this, first I multiply with 200 after 120 subtract. When subtract is made I had rounding error. Let's look my example. float val = 0.6050f; val *= 200.f; Now val is 121.0 as I expected. val -= 120.0f; Now val is 0.99999992 I thought maybe I can avoid this problem with multiplication and division. float val = 0.6050f; val *= 200.f; val *= 100.f; val -= 12000.0f; val /= 100.f; But it didn't help. I have still 0.99 on my hand. Is there a solution for it? Edit: After with detailed logging, I understand there is no problem with this part of code. Before my log shows me "0.605", after I had detailed log and I saw "0.60499995946884155273437500000000000000000000000000" the problem is in different place.

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  • NullPointerException on Activity Testint Tutorial

    - by Bendik
    Hello, I am currently trying the activity testing tutorial (Found here), and have a problem. It seems that whenever I try to call something inside the UIThread, I get a java.lang.NullPointerException. public void testSpinnerUI() { mActivity.runOnUiThread( new Runnable() { public void run() { mSpinner.requestFocus(); } }); } This gives me: Incomplete: java.lang.NullPointerException and nothing else. I have tried this on two different samples now, with the same result. I tried with a try/catch clause around the mSpinner.requestFocus() call, and it seems that mSpinner is null inside the thread. I have set it properly up with the setUp() function found in the same sample, and a quick assertNotNull( mSpinner ) shows me that mSpinner is in fact not null after the setUp() function. What can be the cause of this? EDIT; ok, some more testing has been done. It seems that the application that is being tested resets between each test. This essentially makes me have to reinstantiate all variables between each test. Is this normal?

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  • Class lookup structure array in C++

    - by wyatt
    I'm trying to create a structure array which links input strings to classes as follows: struct {string command; CommandPath cPath;} cPathLookup[] = { {"set an alarm", AlarmCommandPath}, {"send an email", EmailCommandPath}, {"", NULL} }; which will be used as follows: CommandPath *cPath = NULL; string input; getline(cin, input); for(int i = 0; cPathLookup[i] != ""; i++) { if(cPathLookup[i].command == input) cPath = new cPathLookup[i].cPath; } Obviously, this code is meaningless, but I think my intention is apparent - depending on input, I'd like cPath to be initialized as either a new AlarmCommandPath or a new EmailCommandPath. I could handle it with a function returning an instance depending on input, but a whole sequence of ifs just seems inelegant. I should also note that, in case it's not apparent and important, that AlarmCommandPath and EmailCommandPath are derived from CommandPath, and CommandPath is an abstract class. Thanks for any help you can offer. EDIT: I just noticed that, in spite of CommandPath being abstract, I have a declaration: CommandPath *cPath = NULL; in working code. Why does that compile?

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  • Context.Items.Add on an XML return type?

    - by Scott Schluer
    So I have the following code contained within an HttpModule in an application I've been asked to support: app.Context.Response.ContentType = "text/xml"; app.Context.Items.Add("IpixRoomId", ipixRoomId); app.Context.Items.Add("IpixId", ipixId); app.Context.Response.Cache.SetCacheability(HttpCacheability.NoCache); app.Context.RewritePath(rewriteUrl, true); What's the purpose of adding data to Context.Items when the content type is XML? EDIT: For clarification, I'm calling up this URL: http://website.com/virtualtour/1971/6284/panorama2flash.swf I assume the SWF file (I know very little about Flash) makes another call to http://website.com/virtualtour/config.xml. The code I pasted above only executes on calls to config.xml. So since it's only the SWF file and config.xml being requested from the server, I'm a little confused. Can the .SWF file have access to HttpContext.Current.Items? Other than the HttpModule, there is no .NET involved in the code, it's a straight request to the SWF file which triggers a call to config.xml but it seems that those Context.Items contain the data needed to make the SWF file display the right virtual tour. I'm just missing where that link happens. It can't happen in the XML, so maybe in Flash?

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  • (Python/Pyramid) Better ways to have standard list/form editors?

    - by badcat
    I'm working on a number of Pyramid (former Pylons) projects, and often I have the need to display a list of some content (let's say user accounts, log entries or simply some other data). A user should be able to paginate through the list, click on a row and get a form where he/she can edit the contents of that row. Right now I'm always re-inventing the wheel by having Mako templates which use webhelpers for the pagination, Jquery UI for providing a dialog and I craft the editor form and AJAX requests on the client and server side by hand. As you may know, this eats up painfully much time. So what I'm wondering is: Is there a better way of providing lists, editor dialog and server/client communication about this, without having to re-invent the wheel every time? I heard Django takes off a big load of that by providing user accounts and other stuff out of the box; but in my case it's not just about user accounts, it can be any kind of data that is stored on the server-side in a SQL database, which should be able to be edited by a user. Thanks in advance!

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  • Sorting a very large text file in Java

    - by Alice
    Hi, I have a large text file I need to sort in Java. The format is: word [tab] frequency [new line] The algorithm for sorting is: Read some of the file, filtering for purlely alphabetic words. Once you have X number of alphabetic words, call Collections.sort and write the result to a file. Repeat until you have finished reading the file. Start reading two sorted files, comparing line by line for the word with higher frequency, and writing at the same time to a new file as to not load much into your memory Repeat until all files are merged into one large file Right now I've divided the large file into smaller ones (sorted by descending frequency) with 10,000 lines each. I know I need to somehow merge these files back together, but I'm not sure how to go about this. I've created a LinkedList to keep track of all the files created. The algorithm says to compare each line in the two files, except I've tried a case where , say file1 = 8,6,5,3,1 and file2 = 9,8,8,8,8. Then if I compare them line by line I would get file3 = 9,8,8,6,8,5,8,3,8,1 which is incorrectly sorted (they should be in decreasing order). I think I'm misunderstanding some part of the algorithm. If someone could point out what I should do instead, I'd greatly appreciate it. Thanks. edit: Yes this is an assignment. We aren't allowed to increase memory unfortunately :(

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  • How to implement instance numbering?

    - by Joan Venge
    I don't know if the title is clear but basically I am trying to implement something like this: public class Effect { public int InternalId ... public void ResetName() ... } When ResetName is called, this will reset the name of the object to: "Effect " + someIndex; So if I have 5 instances of Effect, they will be renamed to: "Effect 1" "Effect 2" "Effect 3" ... So I have another method (ResetNames) in another manager/container type that calls ResetName for each instance. And right now I have to pass an integer to ResetName while keeping a counter myself inside ResetNames. But this feels not as clean and this prevents me from calling ResetName myself outside the manager class, which is valid. How to do this better/cleaner? As for the InternalId, it's just some id that stores the creation order for everything. So I can't just rely on these, because the numbers are large, like 32000, etc. EDIT: Container ResetNames code: int count = 1; var effects = this.Effects.OrderBy ( n => n.InternalId ); foreach ( Effect effect in effects ) { effect.ResetName ( count ); ++count; }

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  • How to know the type of an object in a list?

    - by nacho4d
    Hi, I want to know the type of object (or type) I have in my list so I wrote this: void **list; //list of references list = new void * [2]; Foo foo = Foo(); const char *not_table [] = {"tf", "ft", 0 }; list[0] = &foo; list[1] = not_table; if (dynamic_cast<LogicProcessor*>(list[0])) { //ERROR here ;( printf("Foo was found\n"); } if (dynamic_cast<char*> (list[0])) { //ERROR here ;( printf("char was found\n"); } but I get : error: cannot dynamic_cast '* list' (of type 'void*') to type 'class Foo*' (source is not a pointer to class) error: cannot dynamic_cast '* list' (of type 'void*') to type 'char*' (target is not pointer or reference to class) Why is this? what I am doing wrong here? Is dynamic_cast what I should use here? Thanks in advance EDIT: I know above code is much like plain C and surely sucks from the C++ point of view but is just I have the following situation and I was trying something before really implementing it: I have two arrays of length n but both arrays will never have an object at the same index. Hence, or I have array1[i]!=NULL or array2[i]!=NULL. This is obviously a waste of memory so I thought everything would be solved if I could have both kind of objects in a single array of length n. I am looking something like Cocoa's (Objective-C) NSArray where you don't care about the type of the object to be put in. Not knowing the type of the object is not a problem since you can use other method to get the class of a certain later. Is there something like it in c++ (preferably not third party C++ libraries) ? Thanks in advance ;)

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  • Bash script to find a directory, list it's contents and sub-folders info

    - by lithiumion
    Hi I want to write a script that will: 1- locate folder "store" on a *nix filesystem 2- move into that folder 3- print list of contents with last modification date 4- calculate sub-folders size This folder's absolute path changes from server to server, but the folder name remains the same always. There is a config file that contains the correct path to that folder though, but it doesn't give absolute bath to it. Sample Config: Account ON DIR-Store /hdd1 Scheduled YES ?According to the config file the absolute path would be "/hdd1/backup/store/" I need the script to grep the "/hdd1" or anything beyond the word "Config-Store", add "/backup/store/" to it, move into folder "store", print list of it's contents, and calculate sub-folders size. Until now I manually edit the script on each server to reflect the path to the "store" folder. Here is a sample script: #!/bin/bash echo " " echo " " echo "Moving Into Directory" cd /hdd1/backup/store/ echo "Listing Directory Content" echo " " ls -alh echo "*******************************" sleep 2 echo " " echo "Calculating Backup Size" echo " " du -sh store/* echo "********** Done! **********" I know I could use grep cat /etc/store.conf | grep DIR-Store Just don't know how to get around selecting the path, adding the "/backup/store/" and moving ahead. Any help will be appreciated

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  • Is a web-server (e.g servlets) a good solution for an IM server?

    - by John
    I'm looking at a new app, broadly speaking an IM application with a strong client-server model - all communications go through a server so they can be logged centrally. The server will be Java in some form, clients could at this point be anything from a .NET Desktop app to Flex/Silverlight, to a simple web-interface using JS/AJAX. I had anticipated doing the server using standard J2EE so I get a thread-safe, multi-user server for 'free'... to make things simple let's say using Servlets (but in practice SpringMVC would be likely). This all seemed very neat but I'm concerned if the stateless nature of Servlets is the best approach. If my memory of servlets (been a year or two) is right, each time a client sent a HTTP request, typically a new message entered by the user, the servlet could not assume it had the user/chat in memory and might have to get it from the DB... regardless it has to look it up. Then it either has to use some PUSH system to inform other members of the chat, or cache that there are new messages, for other clients who poll the server using AJAX or similar - and when they poll it again has to lookup the chat, including new messages, and send the new data. I'm wondering if a better system would be the server is running core Java, and implements a socket-based communication with clients. This allows much more immediate data transfer and is more flexible if say the IM client included some game you could play. But then you're writing a custom server and sockets don't sound very friendly to a browser-based client on current browsers. Am I missing some big piece of the puzzle here, it kind of feels like I am? Perhaps a better way to ask the question would simply be "if the client was browser-based using HTML/JS and had to run on IE7+,FF2+ (i.e no HTML5), how would you implement the server?" edit: if you are going to suggest using XMPP, I have been trying to get my head around this in another question, so please consider if that's a more appropriate place to discuss this specifically.

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  • Using NHibernate's HQL to make a query with multiple inner joins

    - by Abu Dhabi
    The problem here consists of translating a statement written in LINQ to SQL syntax into the equivalent for NHibernate. The LINQ to SQL code looks like so: var whatevervar = from threads in context.THREADs join threadposts in context.THREADPOSTs on threads.thread_id equals threadposts.thread_id join posts1 in context.POSTs on threadposts.post_id equals posts1.post_id join users in context.USERs on posts1.user_id equals users.user_id orderby posts1.post_time where threads.thread_id == int.Parse(id) select new { threads.thread_topic, posts1.post_time, users.user_display_name, users.user_signature, users.user_avatar, posts1.post_body, posts1.post_topic }; It's essentially trying to grab a list of posts within a given forum thread. The best I've been able to come up with (with the help of the helpful users of this site) for NHibernate is: var whatevervar = session.CreateQuery("select t.Thread_topic, p.Post_time, " + "u.User_display_name, u.User_signature, " + "u.User_avatar, p.Post_body, p.Post_topic " + "from THREADPOST tp " + "inner join tp.Thread_ as t " + "inner join tp.Post_ as p " + "inner join p.User_ as u " + "where tp.Thread_ = :what") .SetParameter<THREAD>("what", threadid) .SetResultTransformer(Transformers.AliasToBean(typeof(MyDTO))) .List<MyDTO>(); But that doesn't parse well, complaining that the aliases for the joined tables are null references. MyDTO is a custom type for the output: public class MyDTO { public string thread_topic { get; set; } public DateTime post_time { get; set; } public string user_display_name { get; set; } public string user_signature { get; set; } public string user_avatar { get; set; } public string post_topic { get; set; } public string post_body { get; set; } } I'm out of ideas, and while doing this by direct SQL query is possible, I'd like to do it properly, without defeating the purpose of using an ORM. Thanks in advance! EDIT: The database looks like this: http://i41.tinypic.com/5agciu.jpg (Can't post images yet.)

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  • Heap Algorithmic Issue

    - by OberynMarDELL
    I am having this algorithmic problem that I want to discuss about. Its not about find a solution but about optimization in terms of runtime. So here it is: Suppose we have a race court of Length L and a total of N cars that participate on the race. The race rules are simple. Once a car overtakes an other car the second car is eliminated from the race. The race ends when no more overtakes are possible to happen. The tricky part is that the k'th car has a starting point x[k] and a velocity v[k]. The points are given in an ascending order, but the velocities may differ. What I've done so far: Given that a car can get overtaken only by its previous, I calculated the time that it takes for each car to reach its next one t = (x[i] - x[i+1])/(v[i] - v[i+1]) and I insert these times onto a min heap in O(n log n). So in theory I have to pop the first element in O(logn), find its previous, pop it as well , update its time and insert it in the heap once more, much like a priority queue. My main problem is how I can access specific points of a heap in O(log n) or faster in order to keep the complexity in O(n log n) levels. This program should be written on Haskell so I would like to keep things simple as far as possible EDIT: I Forgot to write the actual point of the race. The goal is to find the order in which cars exit the game

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  • Problem with overlapping divs - CSS

    - by Chaitanya
    html, body {margin: 0px; padding: 0px;} #pageContainer{ margin: auto; padding: auto;} #contentContainer{ margin:150px; width:1100px; height: 100%; overflow: hidden; } #leftContainer{ width: 80%; min-height: 800px; background: #009900; float:left;} #left1{ margin:80px 0 0 80px; height: 550px; top:0px; z-index:1; background: #000000;} #left2{ margin:80px 0 0 80px; height: 500px; top:110px; z-index:2000; background:#99FFFF; } #rightContainer{ width: 20%; height: inherit; background: black; float:right;} / CSS Document */ I require 2 overlapping divs, which look like the one below. ---------------------- | | | ------------------ | | ' '| | ' '| | ' '| | ' '| | ' '| | ' '| | ' '| ---------------------- ' ' ' ' ------------------- <div id="pageContainer"> <div id="contentContainer"> <div id="leftContainer"> Am the left container <div id="left1"> <div id="left2"> </div> </div> </div> <div id="rightContainer"> </div> </div> </div> The problem is am failing to get the overlap. Where am I going wrong? Edit 1: topx was a typo, corrected it.

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  • Rails Nested Attributes Doesn't Insert ID Correctly

    - by MunkiPhD
    I'm attempting to edit a model's nested attributes, much as outline here, replicated here: <%= form_for @person do |person_form| %> <%= person_form.text_field :name %> <% for address in @person.addresses %> <%= person_form.fields_for address, :index => address do |address_form|%> <%= address_form.text_field :city %> <% end %> <% end %> <% end %> In my code, I have the following: <%= form_for(@meal) do |f| %> <!-- some other stuff that's irrelevant... --> <% for subitem in @meal.meal_line_items %> <%= f.fields_for subitem, :index => subitem do |line_item_form| %> <%= line_item_form.label :servings %><br/> <%= line_item_form.text_field :servings %><br/> <%= line_item_form.label :food_id %><br/> <%= line_item_form.text_field :food_id %><br/> <% end %> <% end %> <%= f.submit %> <% end %> This works great, except, when I look at the HTML, it's creating the inputs that look like the following, failing to input the correct id and instead placing the memory representation(?) of the model: <input type="text" value="2" size="30" name="meal[meal_line_item][#<MealLineItem:0x00000005c5d618>][servings]" id="meal_meal_line_item_#<MealLineItem:0x00000005c5d618>_servings">

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  • Call from a singleton class to a function which in turn calls that class's method

    - by dare2be
    Hello, I am still looking for a way to phrase it properly (I'm not a native speaker...). So I have this class SQL which implements the singleton pattern (for obvious reasons) and I also have this function, checkUsr(), which queries the database using one of SQL's methods. Everything works fine as long as I don't call checkUsr() from within the SQL class. When I do so, the scripts just exits and a blank page is displayed - no errors are returned, no exception is thrown... What's happening? And how do I work around this problem? EDIT: class SQL { public static function singleton() { static $instance; if(!isset($instance)) $instance = new SQL; return $instance; } public function tryLoginAuthor( $login, $sha1 ) { (...) } } function checkUsr() { if (!isset($_SESSION['login']) || !isset($_SESSION['sha1'])) throw new Exception('Not logged in', 1); $SQL = SQL::singleton(); $res = $SQL->tryLoginAuthor($_SESSION['login'], $_SESSION['sha1']); if (!isset($res[0])) throw new Exception('Not logged in', 1); }

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  • ListView and wrap_content

    - by gaiapac
    I want to create an activity with a ListView on the left and a TextView on the right, side by side. I write the following xml, but the ListView occupies the entire page and it don't worry about the wrap_content. Why? How can I resolve it? <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="horizontal" > <ListView android:id="@+id/lv" android:layout_width="wrap_content" android:layout_height="match_parent" /> <TextView android:id="@+id/tv" android:layout_width="wrap_content" android:layout_height="match_parent" /> </LinearLayout> EDIT: my onCreate @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); ListView lv = (ListView) findViewById(R.id.lv); String[] values = new String[] { "Test1", "Test2", "Test3", "Test4" }; ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,R.layout.left, R.id.tv1, values); lv.setAdapter(adapter); }

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  • Controlling race condition at startup.

    - by Will Hartung
    I have some code that I want to have some one time initialisation performed. But this code doesn't have a definite lifecycle, so my logic can be potentially invoked by multiple threads before my initialisation is done. So, I want to basically ensure that my logic code "waits" until initialisation is done. This is my first cut. public class MyClass { private static final AtomicBoolean initialised = new AtomicBoolean(false); public void initialise() { synchronized(initialised) { initStuff(); initialised.getAndSet(true); initialised.notifyAll(); } } public void doStuff() { synchronized(initialised) { if (!initialised.get()) { try { initialised.wait(); } catch (InterruptedException ex) { throw new RuntimeException("Uh oh!", ex); } } } doOtherStuff(); } } I basically want to make sure this is going to do what I think it's going to do -- block doStuff until the initialised is true, and that I'm not missing a race condition where doStuff might get stuck on a Object.wait() that will never arrive. Edit: I have no control over the threads. And I want to be able to control when all of the initialisation is done, which is why doStuff() can't call initialise(). I used an AtomicBoolean as it was a combination of a value holder, and an object I could synchronize. I could have also simply had a "public static final Object lock = new Object();" and a simple boolean flag. AtomicBoolean conveniently gave me both. A Boolean can not be modified. The CountDownLatch is exactly what I was looking for. I also considered using a Sempahore with 0 permits. But the CountDownLatch is perfect for just this task.

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  • Jquery Selecting Multiple Classes, Loading External Files

    - by WillingLearner
    I have 2 links, with the class dynamicLoad. <ul class="navbar"> <li><a href="Page3-News.html" class="dynamicLoad news">NEWS</a></li> <li><a href="Page2-Events.html" class="dynamicLoad">EVENTS</a></li> </ul> and then I have this already working code, which loads external pages into a div named #MainWrapper: <script type="text/javascript"> $( document ).ready( function() { $( 'a.dynamicLoad' ).click( function( e ) { e.preventDefault(); // prevent the browser from following the link e.stopPropagation(); // prevent the browser from following the link $( '#MainWrapper' ).load( $( this ).attr( 'href' ) ); }); }); </script> How do I edit this code and my links, so that i can target the 1st link with the classes of both dynamicLoad and news, and then, load another script and/or pages into the main wrapper, without breaking its already working functionality?

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  • Why does a checkbox remain checked in FF3 but not in IE, Chrome or ...

    - by sirrocco
    So - I have a checkbox <asp:CheckBox ID="chkOrder" runat="server" Visible='<%#IsCheckBoxVisible() %>' Checked="false" OnCheckedChanged="chkOrder_CheckedChanged" AutoPostBack="true" EnableViewState="false"></asp:CheckBox> the one above. Now, the checkbox is in a gridview and on databound - for all the rows in the gridview the checkbox is set to false. The problem is that the first checkbox is still true checked. In IE the problem doesn't exist, same for Chrome. I'm running out of options. Also if i use $("checkboxName").attr("checked"); // verified on jquery ready function. In FF it is true; IE false; Chrome false. Any tips? EDIT Now get ready for this : in the generated html - there is NO checked attribute. The diff between FF and IE is exactly the same. Another thing - the grid that contains the checkboxes has an ajax panel on it and when I page the grid, try to go to page 2 - the checkedChanged in codebehind is triggered.

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  • removing a case clause: bash expansion in sed regexp: X='a\.b' ; Y=';;' sed -n '/${X}/,/${Y}/d'

    - by ChrisSM
    I'm trying to remove a case clause from a bash script. The clause will vary, but will always have backslashes as part of the case-match string. I was trying sed but could use awk or a perl one-liner within the bash script. The target of the edit is straightforward, resembles: $cat t.sh case N in a\.b); #[..etc., varies] ;; esac I am running afoul of the variable expansion escaping backslashes, semicolons or both. If I 'eval' I strip my backslash escapes. If I don't, the semi-colons catch me up. So I tried subshell expansion within the sed. This fouls the interpreter as I've written it. More escaping the semi-colons doesn't seem to help. X='a\.b' ; Y=';;' sed -i '/$(echo ${X} | sed -n 's/\\/\\\\/g')/,/$(echo ${Y} | sed -n s/\;/\\;/g')/d t.sh And this: perl -i.bak -ne 'print unless /${X}/ .. /{$Y}/' t.sh # which empties t.sh and eval perl -i.bak -ne \'print unless /${X}/ .. /{$Y}/' t.sh # which does nothing

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  • Form wont stay on top. How do I keep my excel form from hiding behind other windows after I browse

    - by ScottK
    I have a vb.net program that opens up an excel workbook and runs a macro ("Report") in that workbook when a button is clicked. //Workbook with macro and form xlWorkbook = xlApp.Workbooks.Open("W:Data\Excel Program.xls") //Macro: xlApp.Run("Report") //Macro opens form from workbook. I browse for my two .csv files //and then click a button to run code that creates my reports. //form closes, show the excel report after its created xlApp.Visible = True After I browse my first file and select it so that its location is displayed in my text box, the excel form then hides behind any open windows. I want this form to stay on top. It is after this code executes that the form will hide behind all other open windows: Private Sub btnBrowseFile1_Click() Dim fileName1 As String fileName1 = Application.GetOpenFilename("CSV file (*.csv), *.csv") If fileName1 <> "False" Then Me.txtFileName1.text = fileName1 End If End Sub EDIT: I still have no luck with this problem. When the excel macro is opened from a vb program I have this hiding issue...but only after browsing for a file. Why does the focus leave the form and go to Windows after browsing a file? Any one have any suggestions?

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  • How to iteratively generate k elements subsets from a set of size n in java?

    - by Bea Metitiri
    Hi, I'm working on a puzzle that involves analyzing all size k subsets and figuring out which one is optimal. I wrote a solution that works when the number of subsets is small, but it runs out of memory for larger problems. Now I'm trying to translate an iterative function written in python to java so that I can analyze each subset as it's created and get only the value that represents how optimized it is and not the entire set so that I won't run out of memory. Here is what I have so far and it doesn't seem to finish even for very small problems: public static LinkedList<LinkedList<Integer>> getSets(int k, LinkedList<Integer> set) { int N = set.size(); int maxsets = nCr(N, k); LinkedList<LinkedList<Integer>> toRet = new LinkedList<LinkedList<Integer>>(); int remains, thresh; LinkedList<Integer> newset; for (int i=0; i<maxsets; i++) { remains = k; newset = new LinkedList<Integer>(); for (int val=1; val<=N; val++) { if (remains==0) break; thresh = nCr(N-val, remains-1); if (i < thresh) { newset.add(set.get(val-1)); remains --; } else { i -= thresh; } } toRet.add(newset); } return toRet; } Can anybody help me debug this function or suggest another algorithm for iteratively generating size k subsets? EDIT: I finally got this function working, I had to create a new variable that was the same as i to do the i and thresh comparison because python handles for loop indexes differently.

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  • Need help optimizing this Django aggregate query

    - by Chris Lawlor
    I have the following model class Plugin(models.Model): name = models.CharField(max_length=50) # more fields which represents a plugin that can be downloaded from my site. To track downloads, I have class Download(models.Model): plugin = models.ForiegnKey(Plugin) timestamp = models.DateTimeField(auto_now=True) So to build a view showing plugins sorted by downloads, I have the following query: # pbd is plugins by download - commented here to prevent scrolling pbd = Plugin.objects.annotate(dl_total=Count('download')).order_by('-dl_total') Which works, but is very slow. With only 1,000 plugins, the avg. response is 3.6 - 3.9 seconds (devserver with local PostgreSQL db), where a similar view with a much simpler query (sorting by plugin release date) takes 160 ms or so. I'm looking for suggestions on how to optimize this query. I'd really prefer that the query return Plugin objects (as opposed to using values) since I'm sharing the same template for the other views (Plugins by rating, Plugins by release date, etc.), so the template is expecting Plugin objects - plus I'm not sure how I would get things like the absolute_url without a reference to the plugin object. Or, is my whole approach doomed to failure? Is there a better way to track downloads? I ultimately want to provide users some nice download statistics for the plugins they've uploaded - like downloads per day/week/month. Will I have to calculate and cache Downloads at some point? EDIT: In my test dataset, there are somewhere between 10-20 Download instances per Plugin - in production I expect this number would be much higher for many of the plugins.

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  • What is the point of having a key_t if what will be the key to access shared memory is the return value of shmget()?

    - by devoured elysium
    When using shared memory, why should we care about creating a key key_t ftok(const char *path, int id); in the following bit of code? key_t key; int shmid; key = ftok("/home/beej/somefile3", 'R'); shmid = shmget(key, 1024, 0644 | IPC_CREAT); From what I've come to understand, what is needed to access a given shared memory is the shmid, not the key. Or am I wrong? If what we need is the shmid, what is the point in not just creating a random key every time? Edit @link text one can read: What about this key nonsense? How do we create one? Well, since the type key_t is actually just a long, you can use any number you want. But what if you hard-code the number and some other unrelated program hardcodes the same number but wants another queue? The solution is to use the ftok() function which generates a key from two arguments. Reading this, it gives me the impression that what one needs to attach to a shared-memory block is the key. But this isn't true, is it? Thanks

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  • Vista seems to prevent .net from reading/updating file attributes.

    - by CFP
    Hello everyone! The following function copies a file from Source & Path to Dest & Path, normally setting file attributes to normal before copying. Yet, a user of my app has reported it to fail when copying readonly files, returning a permissions-related error. The user is however running the code as administrator, and the error happens - quite strangely - on the SetLastWriteTimeUtc line. Although the code reports that the file attributes are set to normal, windows explorer shows that they are set to read only. Sub CopyFile(ByVal Path As String, ByVal Source As String, ByVal Dest As String) If IO.File.Exists(Dest & Path) Then IO.File.SetAttributes(Dest & Path, IO.FileAttributes.Normal) IO.File.Copy(Source & Path, Dest & Path, True) If Handler.GetSetting(ConfigOptions.TimeOffset, "0") <> "0" Then IO.File.SetAttributes(Dest & Path, IO.FileAttributes.Normal) IO.File.SetLastWriteTimeUtc(Dest & Path, IO.File.GetLastWriteTimeUtc(Dest & Path).AddHours(Handler.GetSetting(ConfigOptions.TimeOffset, "0"))) End If IO.File.SetAttributes(Dest & Path, IO.File.GetAttributes(Source & Path)) End Sub I just fail to see the problem in this code, so after long hours of searching for the solution, I thought one of SO VB.Net Gurus might help :) Thanks a lot. Edit: The actual error is Access to the path '(..)' is denied. at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath) at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy) at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize) at System.IO.File.OpenFile(String path, FileAccess access, SafeFileHandle& handle) at System.IO.File.SetLastWriteTimeUtc(String path, DateTime lastWriteTimeUtc)

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