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  • template specialization of a auto_ptr<T>

    - by Chris Kaminski
    Maybe I'm overcomplicating things, but then again, I do sort of like clean interfaces. Let's say I want a specialization of auto_ptr for an fstream - I want a default fstream for the generic case, but allow a replacement pointer? tempate <> class auto_ptr<fstream> static fstream myfStream; fstream* ptr; public: auto_ptr() { // set ptr to &myfStream; } reset(fstream* newPtr) { // free old ptr if not the static one. ptr = newPtr }; } Would you consider something different or more elegant? And how would you keep something like the above from propagating outside this particular compilation unit? [The actual template is a boost::scoped_ptr.] EDIT: It's a contrived example. Ignore the fstream - it's about providing a default instance of object for an auto_ptr. I may not want to provide a specialized instance, but would like to keep the auto_ptr semantics for this static default object. class UserClass { public: auto_ptr<fstream> ptr; UserClass() { } } I may not provide an dynamic object at construction time - I still want it to have a meaningful default. Since I'm not looking at ownership-transfer semantics, it really shouldn't matter that my pointer class is pointing to a statically allocated object, no?

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  • Linq In Clause & Predicate building

    - by Michael G
    I have two tables. Report and ReportData. ReportData has a constraint ReportID. How can I write my linq query to return all Report objects where the predicate conditions are met for ReportData? Something like this in SQL: SELECT * FROM Report as r Where r.ServiceID = 3 and r.ReportID IN (Select ReportID FROM ReportData WHERE JobID LIKE 'Something%') This is how I'm building my predicate: Expression<Func<ReportData, bool>> predicate = PredicateBuilder.True<ReportData>(); predicate = predicate.And(x => x.JobID.StartsWith(QueryConfig.Instance.DataStreamName)); var q = engine.GetReports(predicate, reportsDataContext); reports = q.ToList(); This is my query construction at the moment: public override IQueryable<Report> GetReports(Expression<Func<ReportData, bool>> predicate, LLReportsDataContext reportDC) { if (reportDC == null) throw new ArgumentNullException("reportDC"); var q = reportDC.ReportDatas.Where(predicate).Where(r => r.ServiceID.Equals(1)).Select(r => r.Report); return q; }

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  • What is the best practice in regards to building composite dtos off of an aggregate root with domain

    - by Chance
    I'm trying to figure out the best approach/practice for assembling a composite data transfer object off of an aggregate root and would love to hear people's thoughts on this. For example, lets say I have a root that has a few domain objects as children. I want to assemble a specific view dto, based on some business logic, that either has attributes or full dto's of it's objects. What I'm struggling with is trying to figure out where that assembly should happen. I can see it going on the domain object of the aggregate root as there is some business logic associated with it. The benefits of this approach from what I've deduced thus far is that it should reduce the inevitable business logic from bleeding outisde of the domain object. It also allows for private methods that take care of tasks that could become more complex from an external builder. The downsides being that the domain object becomes much more entrenched in the application's workflow and represents much more than just the domain object. It also could become very large in the scenario where you need multiple composite Dtos. Alternatively, I could also see it belonging to some form of transfer object assembler where there is a builder for each domain object. The domain objects would still be responsible for GetDto() and UpdateFromDto(dto). Outside of that, the builder would handle the construction and deconstruction of composite dtos. The downside is kind of mentioned above, where I fear this will easily lead to developers unfamiliar with DDD bleeding a ton of business logic into the assembler which is what I want to desperately avoid. Any thoughts would be greatly apperciated.

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  • Meta tag depending of selected language and title

    - by lena
    Hi, I'm aware about Google ignore most of the time, meta tag and use content. (This is not the point here) I'm working on an existing web site, not created by me. I need a quick solution, I guess with variables. The website construction: (no known template system) index.html which is presentation page with language selection index.php which embeding menu, content, footer several content pages that are embedded by index.php What I need to do only for those 2 pages welcome_en.html and welcome_fr.html (these pages are embedded so no header possible on these page) to have different page title (browser title) and different META tag. Any solution is welcome Thanks extra information Language detection on index.php: <?php $lang = $_GET['lang']; $page = $_GET['page']; if ($_GET['page'] == "" || !$_GET['page']) { $page = "welcome"; } if ($_GET['lang'] == "" || !$_GET['lang']) { $lang = "_fr"; } ? <td><img src="images/ban02<?php echo "$lang" ?>.jpg" width="531" height="60" <?php if ($_GET['lang'] == "_fr" || $_GET['lang'] == "" || !$_GET['lang']) { echo "alt='text'";} else if ($_GET['lang'] == "_en") {echo "alt='text'"; } ?>></td> for the embeded menu, footer ect like this one <?php include "menu.php"; ?> for the embedded content <?php //echo "$page$lang.html"; $lang = preg_replace('/[^a-z0-9_ ]/i', '', $_GET['lang']); $page = preg_replace('/[^a-z0-9_ ]/i', '', $_GET['page']); include $page . $lang . ".html"; ?>

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  • Using shared_ptr to implement RCU (read-copy-update)?

    - by yongsun
    I'm very interested in the user-space RCU (read-copy-update), and trying to simulate one via tr1::shared_ptr, here is the code, while I'm really a newbie in concurrent programming, would some experts help me to review? The basic idea is, reader calls get_reading_copy() to gain the pointer of current protected data (let's say it's generation one, or G1). writer calls get_updating_copy() to gain a copy of the G1 (let's say it's G2), and only one writer is allowed to enter the critical section. After the updating is done, writer calls update() to do a swap, and make the m_data_ptr pointing to data G2. The ongoing readers and the writer now hold the shared_ptr of G1, and either a reader or a writer will eventually deallocate the G1 data. Any new readers would get the pointer to G2, and a new writer would get the copy of G2 (let's say G3). It's possible the G1 is not released yet, so multiple generations of data my co-exists. template <typename T> class rcu_protected { public: typedef T type; typedef std::tr1::shared_ptr<type> rcu_pointer; rcu_protected() : m_data_ptr (new type()) {} rcu_pointer get_reading_copy () { spin_until_eq (m_is_swapping, 0); return m_data_ptr; } rcu_pointer get_updating_copy () { spin_until_eq (m_is_swapping, 0); while (!CAS (m_is_writing, 0, 1)) {/* do sleep for back-off when exceeding maximum retry times */} rcu_pointer new_data_ptr(new type(*m_data_ptr)); // as spin_until_eq does not have memory barrier protection, // we need to place a read barrier to protect the loading of // new_data_ptr not to be re-ordered before its construction _ReadBarrier(); return new_data_ptr; } void update (rcu_pointer new_data_ptr) { while (!CAS (m_is_swapping, 0, 1)) {} m_data_ptr.swap (new_data_ptr); // as spin_until_eq does not have memory barrier protection, // we need to place a write barrier to protect the assignments of // m_is_writing/m_is_swapping be re-ordered bofore the swapping _WriteBarrier(); m_is_writing = 0; m_is_swapping = 0; } private: volatile long m_is_writing; volatile long m_is_swapping; rcu_pointer m_data_ptr; };

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  • MySQL SELECT combining 3 SELECTs INTO 1

    - by Martin Tóth
    Consider following tables in MySQL database: entries: creator_id INT entry TEXT is_expired BOOL other: creator_id INT entry TEXT userdata: creator_id INT name VARCHAR etc... In entries and other, there can be multiple entries by 1 creator. userdata table is read only for me (placed in other database). I'd like to achieve a following SELECT result: +------------+---------+---------+-------+ | creator_id | entries | expired | other | +------------+---------+---------+-------+ | 10951 | 59 | 55 | 39 | | 70887 | 41 | 34 | 108 | | 88309 | 38 | 20 | 102 | | 94732 | 0 | 0 | 86 | ... where entries is equal to SELECT COUNT(entry) FROM entries GROUP BY creator_id, expired is equal to SELECT COUNT(entry) FROM entries WHERE is_expired = 0 GROUP BY creator_id and other is equal to SELECT COUNT(entry) FROM other GROUP BY creator_id. I need this structure because after doing this SELECT, I need to look for user data in the "userdata" table, which I planned to do with INNER JOIN and select desired columns. I solved this problem with selecting "NULL" into column which does not apply for given SELECT: SELECT creator_id, COUNT(any_entry) as entries, COUNT(expired_entry) as expired, COUNT(other_entry) as other FROM ( SELECT creator_id, entry AS any_entry, NULL AS expired_entry, NULL AS other_enry FROM entries UNION SELECT creator_id, NULL AS any_entry, entry AS expired_entry, NULL AS other_enry FROM entries WHERE is_expired = 1 UNION SELECT creator_id, NULL AS any_entry, NULL AS expired_entry, entry AS other_enry FROM other ) AS tTemp GROUP BY creator_id ORDER BY entries DESC, expired DESC, other DESC ; I've left out the INNER JOIN and selecting other columns from userdata table on purpose (my question being about combining 3 SELECTs into 1). Is my idea valid? = Am I trying to use the right "construction" for this? Are these kind of SELECTs possible without creating an "empty" column? (some kind of JOIN) Should I do it "outside the DB": make 3 SELECTs, make some order in it (let's say python lists/dicts) and then do the additional SELECTs for userdata? Solution for a similar question does not return rows where entries and expired are 0. Thank you for your time.

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  • Making a jQuery plugin to feed Tumblr to site

    - by tylorreimer
    I have some experience with PHP and a little with JS but I'm far from anything proficient. I'm trying to make a jQuery plugin for my site that I can call in my HTML via something like this: $('.new').tumble({username: "tylor", count: 9}); Which would basically put the Tumblr list the code should make into the DIV with class 'new' in this case. Here is my code so far; the problem seems to be how to get it to pick up class/id from the original call (in the HTML) and use that in the jQuery. Here's the code so far: (function($) { $.fn.tumble = function(options){ var settings = $.extend({ username: null, // [string or array] required to get url for tumblr account count: 3, // [integer] how many posts to display? }, options); //url construction var url = "http://" + settings.username + ".tumblr.com"; var jsonurl = url + "/api/read/json?num=" + settings.count + "&callback=?"; $.getJSON(jsonurl, function(data) { var items = []; $.each(data.posts, function(id, url) { // Goes over each post in the JSON document retrieved from data URL var url = this.url; // Just assigns a variable to the url to avoid constantly writing "this.whatever" var photourl = this['photo-url-250']; // photo-url-xxx needs to be called this way due to integers in the name items.push('<li><a href="' + url + '">' + photourl + '</a></li>'); }); $('<ul/>', { // Creates an empty list html: items.join('') // Takes the values in the item array and puts 'em together }).appendTo('.new'); // I don't want this to have the class set in the jQuery itself }); //end json }; })( jQuery ); Any help you can lend would be wonderful. Thank you

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  • NUnit doesn't work well with Assert.AreEqual

    - by stasal
    Hi! I'm new to unit-testing and NUit in particular. I'm just typing some examples from the book which refers to Java and JUnit. But I'm using C# instead. The problem is: I've got a class with overriden methods such as Equals() and GetHashCode(), but when I am trying to compare two objects of this class with Assert.AreEqual() my code is not called, so I get an exception. Assert.True(MyClass.Equals(MyClass2)) does work well. But I don't wanna use this construction instead of Assert.AreEqual(). Where the problem can be? Here is the class: public class Money { public int amount; protected string currency; public Money(int amount, string currency) { this.amount = amount; this.currency = currency; } public new bool Equals(object obj) { if (obj == null) return false; Money money = (Money)obj; return (amount == money.amount) && (Currency().Equals(money.Currency())); } public new int GetHashCode() { return (string.Format("{0}{1}", amount, currency)).GetHashCode(); } public static Money Dollar(int amount) { return new Money(amount, "USD"); } public static Money Franc(int amount) { return new Money(amount, "CHF"); } public Money Times(int multiplier) { return new Money(amount * multiplier, currency); } public string Currency() { return currency; } } And the test method itself: [TestFixture] public class DollarTest { [Test] public void TestMultiplication() { Money five = Money.Dollar(5); Assert.True(Money.Dollar(10).Equals(five.Times(2))); // ok Assert.AreEqual(Money.Dollar(10), five.Times(2)); // fails } } Thanks.

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  • Licensing for the undecided

    - by Jasper
    I am creating a game in C++. Now I am not sure on how I will distribute it yet - though I am pretty sure that I won't be asking money for it. And I am looking into a licensing and I wondered if there is a license that is suited for the undecided like me. My current releases (which are really really early versions of the game, with far from full functionality) are executable only. However, I am actually thinking that I might release the source on an open source license. For now, I am the only contributor, so that would be no problem as I only need my own permission to move to a less restrictive license. However, when I allow other people to contribute, I would need all their permissions to do so (right?). So I was wondering if there is a license that let's me distribute the game executable only for now, but will let me switch to a less restrictive license if I want. Basically I need a license in which contributors give permission to switch to a less restrictive license up front. Does anybody know of license (or other construction) that would allow me to do so?

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  • Random forests for short texts

    - by Jasie
    Hi all, I've been reading about Random Forests (1,2) because I think it'd be really cool to be able to classify a set of 1,000 sentences into pre-defined categories. I'm wondering if someone can explain to me the algorithm better, I think the papers are a bit dense. Here's the gist from 1: Overview We assume that the user knows about the construction of single classification trees. Random Forests grows many classification trees. To classify a new object from an input vector, put the input vector down each of the trees in the forest. Each tree gives a classification, and we say the tree "votes" for that class. The forest chooses the classification having the most votes (over all the trees in the forest). Each tree is grown as follows: If the number of cases in the training set is N, sample N cases at random - but with replacement, from the original data. This sample will be the training set for growing the tree. If there are M input variables, a number m « M is specified such that at each node, m variables are selected at random out of the M and the best split on these m is used to split the node. The value of m is held constant during the forest growing. Each tree is grown to the largest extent possible. There is no pruning. So, does this look right? I'd have N = 1,000 training cases (sentences), M = 100 variables (let's say, there are only 100 unique words across all sentences), so the input vector is a bit vector of length 100 corresponding to each word. I randomly sample N = 1000 cases at random (with replacement) to build trees from. I pick some small number of input variables m « M, let's say 10, to build a tree off of. Do I build tree nodes randomly, using all m input variables? How many classification trees do I build? Thanks for the help!

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  • Generic Class Vb.net

    - by KoolKabin
    hi guys, I am stuck with a problem about generic classes. I am confused how I call the constructor with parameters. My interface: Public Interface IDBObject Sub [Get](ByRef DataRow As DataRow) Property UIN() As Integer End Interface My Child Class: Public Class User Implements IDBObject Public Sub [Get](ByRef DataRow As System.Data.DataRow) Implements IDBObject.Get End Sub Public Property UIN() As Integer Implements IDBObject.UIN Get End Get Set(ByVal value As Integer) End Set End Property End Class My Next Class: Public Class Users Inherits DBLayer(Of User) #Region " Standard Methods " #End Region End Class My DBObject Class: Public Class DBLayer(Of DBObject As {New, IDBObject}) Public Shared Function GetData() As List(Of DBObject) Dim QueryString As String = "SELECT * ***;" Dim Dataset As DataSet = New DataSet() Dim DataList As List(Of DBObject) = New List(Of DBObject) Try Dataset = Query(QueryString) For Each DataRow As DataRow In Dataset.Tables(0).Rows **DataList.Add(New DBObject(DataRow))** Next Catch ex As Exception DataList = Nothing End Try Return DataList End Function End Class I get error in the starred area of the DBLayer Object. What might be the possible reason? what can I do to fix it? I even want to add New(byval someval as datatype) in IDBObject interface for overloading construction. but it also gives an error? how can i do it? Adding Sub New(ByVal DataRow As DataRow) in IDBObject producess following error 'Sub New' cannot be declared in an interface. Error Produced in DBLayer Object line: DataList.Add(New DBObject(DataRow)) Msg: Arguments cannot be passed to a 'New' used on a type parameter.

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  • Should I pass a SqlDataReader by reference or not when passing it out to multiple threads.

    - by deroby
    Hi all, being new to c# I've run into this 'conundrum' when passing around a SqlDataReader between different threads. Without going into too much detail, the idea is to have a main thread fetching data from the database (a large recordset) and then have a helper-task run through this record by record and doing some stuff based upon the contents of this. There is no feedback to the recordset, it simply wades through until no records are left. This works fine, but given the nature of the job at hand it should be possible to have this job spread over different threads (CPUs) to maximize throughput (the order of execution is of no significance). The question then becomes, when I pass this recordset in a SqlDataReader, do I have to use ref or not ? It kind of boils down to the question : if I pass the object around without specifying ref, won't it create new copies in memory and have records processed n times ? Or, don't I risk having the record-position being moved forward while not all fields have been fully read yet ? The latter seems more like a 'data racing' issue and probably is covered by the lock()ing mechanism (or not?). My initial take on the problem was that it doesn't really hurt passing the variable using ref, yet as a colleague put it : "you only need ref when you're doing something wrong" =) Additionally using ref restricts me from applying a Using() construction too which isn't very nice either. I thus create a "basic" project that tackles the same approach but without the ref notation. Tests so far show that it works flawlessly on a Core2Duo (2cpu) using any number of threads, yet I'm still a bit wary... What do you experts think about this ? Use ref or not ? You can find the test-project here as it seems I can't upload it to this question directly ?!? ps: it's just a test-project and I'm new to c#, so please be gentle on me when breaking down the code =P

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  • Dealing with infinite loops when constructing states for LR(1) parsing

    - by Bruce
    I'm currently constructing LR(1) states from the following grammar. S->AS S->c A->aA A->b where A,S are nonterminals and a,b,c are terminals. This is the construction of I0 I0: S' -> .S, epsilon --------------- S -> .AS, epsilon S -> .c, epsilon --------------- S -> .AS, a S -> .c, c A -> .aA, a A -> .b, b And I1. From S, I1: S' -> S., epsilon //DONE And so on. But when I get to constructing I4... From a, I4: A -> a.A, a ----------- A -> .aA, a A -> .b, b The problem is A - .aA When I attempt to construct the next state from a, I'm going to once again get the exact same content of I4, and this continues infinitely. A similar loop occurs with S -> .AS So, what am I doing wrong? There has to be some detail that I'm missing, but I've browsed my notes and my book and either can't find or just don't understand what's wrong here. Any help?

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  • Add a value to an element in a list of sets

    - by Kapelson
    Hello. I'm using python, and I have a list of sets, constructed like this: list = [set([])]*n ...where n is the number of sets I want in the list. I want to add a value to a specific set in the list. Say, the second set. I tried list[1].add(value) But this instead adds the value to each set in the list. This behaviour is pretty non-intuitive to me. Through further tests, I think I've found the problem: the list apparently contains 10 instances of the same set, or ten pointers to the same set, or something. Constructing the list through repeated calls of list.append(set([])) allowed me to use the syntax above to add elements to single sets. So my question is this: what exactly is going on in my first list-construction technique? It is clear I don't understand the syntax so well. Also, is there a better way to intialize an n-element list? I've been using this syntax for a while and this is my first problem with it.

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  • What are salesforce.com and Apex like as an application development platform?

    - by mhollers
    I have recently discovered that salesforce.com is much more than an online CRM after coming across a Morrison's Case Study in which they develop a works management application. I've been trying it out with a view to recreating our own Works Management system on the platform. My background is in Microsoft and .Net, and the obvious 1st choice would be asp.net. However, there's only really myself with .net experience and my manager with a more legacy Synergy programming background, and I am self taught and am looking at evaluating other RAD options (eg Ironspeed). the nature of the business is in the main 2-5 concurrent construction type contracts that run for 3-5 yrs each, each requiring 15-50 system users. Traditionally we have used our character based Works Mangement system for everything and tweaked it for each contract. The Salesforce licensing model on the face of it suits this sort of flexibilty, but I'm worried about the development flexibilty/learning curve and all the issues that surround lock-in. There doesn't seem to be much neutral sober analysis of the platform on the web that isn't salesforce's own material/blogs Has anyone any experience of developing an application on salesforce as compared to the more 'traditional' .Net route?

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  • Flash Player: Any remedy for the stale video image data problem (in a reused NetStream object)?

    - by amn
    Has anyone experienced stale stills of a previous playback for a reused NetStream object? If so, what are the workarounds for this, except re-creating the object (which eats performance and time)? It is hard to reuse NetStream objects because of a (in my opinion) fundamental issue with NetStream objects - when you 'close' a playing stream and at a later point issue a 'play' call on it again with a different name, the stream appears to still contain a stale image lingering from previous playback, and this is of course displayed in the Video object for a moment - the moment I assume it takes for new stream data to become available from server. Because of this behavior, to improve my users' visual experience, I simply discard a NetStream object after a playback session, and assign a new NetStream object to the same variable, set it up, and play something else. It appears to work - no stale image - but what bugs me is that it's a work around and costs performance (construction and setting up the object again - event listeners and 'client' delegates and more memory usage - NetStream objects are not garbage collected immediately, it takes some time). It would be really nice to REALLY be able to reuse a stream. I am thinking of something akin to Video.clear method, but for the NetStream class. Am I missing something?

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  • Split node list to parts.

    - by Kalinin
    xml: <mode>1</mode> <mode>2</mode> <mode>3</mode> <mode>4</mode> <mode>5</mode> <mode>6</mode> <mode>7</mode> <mode>8</mode> <mode>9</mode> <mode>10</mode> <mode>11</mode> <mode>12</mode> i need to separate it on parts (for ex. on 4): xslt: <xsl:variable name="vNodes" select="mode"/> <xsl:variable name="vNumParts" select="4"/> <xsl:variable name="vNumCols" select="ceiling(count($vNodes) div $vNumParts)"/> <xsl:for-each select="$vNodes[position() mod $vNumCols = 1]"> <xsl:variable name="vCurPos" select="(position()-1)*$vNumCols +1"/> <ul> <xsl:for-each select="$vNodes[position() >= $vCurPos and not(position() > $vCurPos + $vNumCols -1)]"> <li><xsl:value-of select="."/></li> </xsl:for-each> </ul> </xsl:for-each> this code is written by Dimitre Novatchev - great coder)) but for the number of nodes less then number of parts (for ex. i have 2 modes) this code does not work - it outputs nothing. How it upgrade for that case (without choose construction)?

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  • Memory optimization while downloading

    - by lboregard
    hello all i have the following piece of code, that im looking forward to optimize, since i'm consuming gobs of memory this routine is heavily used first optimization would be to move the stringbuilder construction out of the download routine and make it a field of the class, then i would clear it inside the routine can you please suggest any other optimization or point me in the direction of some resources that could help me with this (web articles, books, etc). i'm thinking about replacing the stringbuilder by a fixed (much larger) size buffer ... or perhaps create a larger sized stringbuilder thanks in advance. StreamWriter _writer; StreamReader _reader; public string Download(string msgId) { _writer.WriteLine("BODY <" + msgId + ">"); string response = _reader.ReadLine(); if (!response.StartsWith("222")) return null; bool done = false; StringBuilder body = new StringBuilder(256* 1024); do { response = _reader.ReadLine(); if (OnProgress != null) OnProgress(response.Length); if (response == ".") { done = true; } else { if (response.StartsWith("..")) response = response.Remove(0, 1); body.Append(response); body.Append("\r\n"); } } while (!done); return body.ToString(); }

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  • WPF app startup problems

    - by Dave
    My brain is all over the map trying to fully understand Unity right now. So I decided to just dive in and start adding it in a branch to see where it takes me. Surprisingly enough (or maybe not), I am stuck just getting my darn Application to load properly. It seems like the right way to do this is to override OnStartup in App.cs. I've removed my StartupUri from App.xaml so it doesn't create my GUI XAML. My App.cs now looks something like this: public partial class App : Application { private IUnityContainer container { get; set; } protected override void OnStartup(StartupEventArgs e) { container = new UnityContainer(); GUI gui = new GUI(); gui.Show(); } protected override void OnExit(ExitEventArgs e) { container.Dispose(); base.OnExit(e); } } The problem is that nothing happens when I start the app! I put a breakpoint at the container assignment, and it never gets hit. What am I missing? App.xaml is currently set to ApplicationDefinition, but I'd expect this to work because some sample Unity + WPF code I'm looking at (from Codeplex) does the exact same thing, except that it works! I've also started the app by single-stepping, and it eventually hits the first line in App.xaml. When I step into this line, that's when the app just starts "running", but I don't see anything (and my breakpoint isn't hit). If I do the exact same thing in the sample application, stepping into App.xaml puts me right into OnStartup, which is what I'd expect to happen. Argh! Is it a Bad Thing to just put the Unity construction in my GUI's Window_Loaded event handler? Does it really need to be at the App level?

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  • Get type of the parameter from list of objects, templates, C++

    - by CrocodileDundee
    This question follows to my previous question Get type of the parameter, templates, C++ There is the following data structure: Object1.h template <class T> class Object1 { private: T a1; T a2; public: T getA1() {return a1;} typedef T type; }; Object2.h template <class T> class Object2: public Object1 <T> { private: T b1; T b2; public: T getB1() {return b1;} } List.h template <typename Item> struct TList { typedef std::vector <Item> Type; }; template <typename Item> class List { private: typename TList <Item>::Type items; }; Is there any way how to get type T of an object from the list of objects (i.e. Object is not a direct parameter of the function but a template parameter)? template <class Object> void process (List <Object> *objects) { typename Object::type a1 = objects[0].getA1(); // g++ error: 'Object1<double>*' is not a class, struct, or union type } But his construction works (i.e. Object represents a parameter of the function) template <class Object> void process (Object *o1) { typename Object::type a1 = o1.getA1(); // OK }

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  • How can one enforce calling a base class function after derived class constructor?

    - by Mike Elkins
    I'm looking for a clean C++ idiom for the following situation: class SomeLibraryClass { public: SomeLibraryClass() { /* start initialization */ } void addFoo() { /* we are a collection of foos */ } void funcToCallAfterAllAddFoos() { /* Making sure this is called is the issue */ } }; class SomeUserClass : public SomeLibraryClass { public: SomeUserClass() { addFoo(); addFoo(); addFoo(); // SomeUserClass has three foos. } }; class SomeUserDerrivedClass : public SomeUserClass { public: SomeUserDerrivedClass() { addFoo(); // This one has four foos. } }; So, what I really want is for SomeLibraryClass to enforce the calling of funcToCallAfterAllAddFoos at the end of the construction process. The user can't put it at the end of SomeUserClass::SomeUserClass(), that would mess up SomeUserDerrivedClass. If he puts it at the end of SomeUserDerrivedClass, then it never gets called for SomeUserClass. To further clarify what I need, imagine that /* start initialization */ acquires a lock, and funcToCallAfterAllAddFoos() releases a lock. The compiler knows when all the initializations for an object are done, but can I get at that information by some nice trick?

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  • Quality questionnaire php mysql graphipcs

    - by Marcelo
    Hi, i'm making a questionnaire about a service quality, its contains the options (poor, regular, good, very good). It's contains 6 questions (radio button) and a suggestion box (textbox). In the table of the database i created 6 rows for questions, 1 for suggestion and 1 for date (a friend of mine tole me to use this but i didn't get why). q1) I'm going to atribute a value form 1 to 4 to the radio buttons options, and i'd like to sum every answer for each question, and then divide by the numbers of user that answered that question and give the mean. how am i supposed to to that? I'd also like generate reports of the month, of the year. q2) not only about the questionnaire but for registration too. I need all the fields to be completed, no blank options, if he don't complete all of fields it'll not be submitted and there will be a warning message to the user. q3) about the field type, i'd like it to be the same class that is in the database, i'm having a "problem". Ex: Name(varchar) : 1234(int), in the field 'name' of the table of the database 1234 will be shown as name, and i don't want this, i want only the type that i declared in the construction of the table. q4) i'd also like to know if it's possible to create pizza graphics, about the percentage of each question, is this possible? q5) I'm using phpmyadmin and some of my id's are auto_increment, but 'cause of my tests they at a high number, i'd like to restart to 0 the ids number, is this possible? Thanks for the attention.

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  • Passing C++ object to C++ code through Python?

    - by cornail
    Hi all, I have written some physics simulation code in C++ and parsing the input text files is a bottleneck of it. As one of the input parameters, the user has to specify a math function which will be evaluated many times at run-time. The C++ code has some pre-defined function classes for this (they are actually quite complex on the math side) and some limited parsing capability but I am not satisfied with this construction at all. What I need is that both the algorithm and the function evaluation remain speedy, so it is advantageous to keep them both as compiled code (and preferrably, the math functions as C++ function objects). However I thought of glueing the whole simulation together with Python: the user could specify the input parameters in a Python script, while also implementing storage, visualization of the results (matplotlib) and GUI, too, in Python. I know that most of the time, exposing C++ classes can be done, e.g. with SWIG but I still have a question concerning the parsing of the user defined math function in Python: Is it possible to somehow to construct a C++ function object in Python and pass it to the C++ algorithm? E.g. when I call f = WrappedCPPGaussianFunctionClass(sigma=0.5) WrappedCPPAlgorithm(f) in Python, it would return a pointer to a C++ object which would then be passed to a C++ routine requiring such a pointer, or something similar... (don't ask me about memory management in this case, though :S) The point is that no callback should be made to Python code in the algorithm. Later I would like to extend this example to also do some simple expression parsing on the Python side, such as sum or product of functions, and return some compound, parse-tree like C++ object but let's stay at the basics for now. Sorry for the long post and thx for the suggestions in advance.

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  • How string accepting interface should look like?

    - by ybungalobill
    Hello, This is a follow up of this question. Suppose I write a C++ interface that accepts or returns a const string. I can use a const char* zero-terminated string: void f(const char* str); // (1) The other way would be to use an std::string: void f(const string& str); // (2) It's also possible to write an overload and accept both: void f(const char* str); // (3) void f(const string& str); Or even a template in conjunction with boost string algorithms: template<class Range> void f(const Range& str); // (4) My thoughts are: (1) is not C++ish and may be less efficient when subsequent operations may need to know the string length. (2) is bad because now f("long very long C string"); invokes a construction of std::string which involves a heap allocation. If f uses that string just to pass it to some low-level interface that expects a C-string (like fopen) then it is just a waste of resources. (3) causes code duplication. Although one f can call the other depending on what is the most efficient implementation. However we can't overload based on return type, like in case of std::exception::what() that returns a const char*. (4) doesn't work with separate compilation and may cause even larger code bloat. Choosing between (1) and (2) based on what's needed by the implementation is, well, leaking an implementation detail to the interface. The question is: what is the preffered way? Is there any single guideline I can follow? What's your experience?

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  • Looking for a book which teaches how to write applications (as opposed to writng code)

    - by rumtscho
    I am not a developer. I have coded for fun and for university projects in several languages, and during an internship, I have written code which is still in use by a department of Fortune Global 500 company. I also have extensive theoretical knowledge of software engineering - process models, architecture, project management, UI construction using Lauesen's virtual windows... you get the picture. But I am not involved with software development in my job. I recently decided to start coding for fun again, and now I have some free days to do it. But this time, I want to do it right. I want to write a real, useful application, install it on my devices and use it myself. Also I want to publish it for others to use, should they want to do so. I am vaguely aware that there is more to writing an application than to writing code. There is stuff like version control software, decision for the right IDE, having a suite of unit tests, producing an installation package - and probably lots of other things I never thought of but which must be taken care of in a proper application, as opposed to a bunch of classes I am running from my IDE. All this is stuff I should know before I start, but I have not learned it. Coding books touch on some of the subjects like IDE choice, but don't go into detail, and are not exhaustive. Theoretical software engineering textbooks are even less helpful. So is there a book which teaches exactly that? I know that I can find information on each of these topics on the Internet, but I'd rather have a systematic book exhaustively listing all the things I should take care of if I want to create a good application, and offering the currently accepted solutions for them. In the best case, it will be language- and platform independent, but if you know of a good book focusing on a specific platform, I would like to know about it too. I know I want a lot, but given how important such knowledge is and how many people need it, surely somebody must have written such a book?

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