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• How to populate List<string> with Datarow values from single columns...

  - by James

  Hi, I'm still learning (baby steps). Messing about with a function and hoping to find a tidier way to deal with my datatables. For the more commonly used tables throughout the life of the program, I'll dump them to datatables and query those instead. What I'm hoping to do is query the datatables for say column x = "this", and convert the values of column "y" directly to a List to return to the caller: private List<string> LookupColumnY(string hex) { List<string> stringlist = new List<string>(); DataRow[] rows = tblDataTable.Select("Columnx = '" + hex + "'", "Columny ASC"); foreach (DataRow row in rows) { stringlist.Add(row["Columny"].ToString()); } return stringlist; } Anyone know a slightly simpler method? I guess this is easy enough, but I'm wondering if I do enough of these if iterating via foreach loop won't be a performance hit. TIA!

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• Exception handling in Iterable

  - by Maas

  Is there any way of handling -- and continuing from -- an exception in an iterator while maintaining the foreach syntactic sugar? I've got a parser that iterates over lines in a file, handing back a class-per-line. Occasionally lines will be syntactically bogus, but that doesn't necessarily mean that we shouldn't keep reading the file. My parser implements Iterable, but dealing with the potential exceptions means writing for (Iterator iter = myParser.iterator(); iter.hasNext(); ) { try { MyClass myClass = iter.next(); // .. do stuff .. } catch (Exception e) { // .. do exception stuff .. } } .. nothing wrong with that, but is there any way of getting exception handling on the implicit individual iter.next() calls in the foreach construct?

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• Grabbing Just The Top Entry From A LINQ Query

  - by Soo

  I basically have a lot of poorly designed code to do something that, I'm sure, can be done far more elegantly. What I'm trying to do is grab the last date from a database table. var Result = from a in DB.Table orderby a.Date descending select new {Date = a}; foreach(var Row in Result) { LastDate = Row.Date.Date; break; } Basically, there's a foreach loop that is designed to run only once. Crappy code! What's a "best practice" way to accomplish the same thing?

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• ForEach with EditorFor

  - by hermiod

  I have got an Entity model which contains a collection of Message objects which are of the type Message which has several properties, including content, MessageID, from, and to. I have created an EditorTemplate for type Message, however, I cannot get it to display the contents of the Messages collection. There are no errors, but nothing is output. Please note that the view code is from an EditorTemplate for the parent Talkback class. Can you have an EditorTemplate calling another EditorTemplate for a child collection? Both the Talkback and Message class are generated by Entity framework from an existing database. View code: <% foreach (TalkbackEntityTest.Message msg in Model.Messages) { Html.EditorFor(x=> msg, "Message"); } %> This is my template code. It is the standard auto-generated view code with some minor changes. <%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<TalkbackEntityTest.Message>" %> <%: Html.ValidationSummary(true) %> <fieldset> <legend>Fields</legend> <div class="editor-label"> <%: Html.LabelFor(model => model.MessageID) %> </div> <div class="editor-field"> <%: Html.TextBoxFor(model => model.MessageID) %> <%: Html.ValidationMessageFor(model => model.MessageID) %> </div> <div class="editor-label"> <%: Html.LabelFor(model => model.acad_period) %> </div> <div class="editor-field"> <%: Html.TextBoxFor(model => model.acad_period) %> <%: Html.ValidationMessageFor(model => model.acad_period) %> </div> <div class="editor-label"> <%: Html.LabelFor(model => model.talkback_id) %> </div> <div class="editor-field"> <%: Html.TextBoxFor(model => model.talkback_id) %> <%: Html.ValidationMessageFor(model => model.talkback_id) %> </div> <div class="editor-label"> <%: Html.LabelFor(model => model.From) %> </div> <div class="editor-field"> <%: Html.TextBoxFor(model => model.From) %> <%: Html.ValidationMessageFor(model => model.From) %> </div> <div class="editor-label"> <%: Html.LabelFor(model => model.To) %> </div> <div class="editor-field"> <%: Html.TextBoxFor(model => model.To) %> <%: Html.ValidationMessageFor(model => model.To) %> </div> <div class="editor-label"> <%: Html.LabelFor(model => model.SentDatetime) %> </div> <div class="editor-field"> <%: Html.TextBoxFor(model => model.SentDatetime, String.Format("{0:g}", Model.SentDatetime)) %> <%: Html.ValidationMessageFor(model => model.SentDatetime) %> </div> <div class="editor-label"> <%: Html.LabelFor(model => model.content) %> </div> <div class="editor-field"> <%: Html.TextBoxFor(model => model.content) %> <%: Html.ValidationMessageFor(model => model.content) %> </div> <div class="editor-label"> <%: Html.LabelFor(model => model.MessageTypeID) %> </div> <div class="editor-field"> <%: Html.TextBoxFor(model => model.MessageTypeID) %> <%: Html.ValidationMessageFor(model => model.MessageTypeID) %> </div> <p> <input type="submit" value="Save" /> </p> </fieldset> There is definitely content in the Message collection as, if I remove EditorFor and put in response.write on the content property of the Message class, I get the content field for 3 Message objects on the page, which is exactly as expected.

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• PHP Array issue - not looping through foreach...

  - by Homer_J

  Ok, Here is the code: function fetch_questions($page) { global $link; $proc = mysqli_prepare($link, "SELECT * FROM tquestions_cwh WHERE page = ?"); mysqli_stmt_bind_param($proc, "i", $page); mysqli_stmt_execute($proc); $rows = array(); stmt_bind_assoc($proc, $rowq); // loop through all result rows while ($proc->fetch()) { // print_r($rowq); $rows[]=$rowq; } mysqli_stmt_close($proc); mysqli_clean_connection($link); return($rows); } I then add this to a php variable, like so: $qs = fetch_questions($page); I then loop through is, like so: foreach($qs as $value){ echo "<tr>".$value['qnum']." is the questions number and the question text is ".$value['qtext'].". The page and q values are ".$value['page']." and ".$value['questions']." respectively.</tr>"; The output, however is this: 8 is the questions number and the question text is I know how what I do fits into my team's objectives. The page and q values are 1 and q8 respectively.8 is the questions number and the question text is I know how what I do fits into my team's objectives. The page and q values are 1 and q8 respectively.8 is the questions number and the question text is I know how what I do fits into my team's objectives. The page and q values are 1 and q8 respectively.8 is the questions number and the question text is I know how what I do fits into my team's objectives. The page and q values are 1 and q8 respectively.8 is the questions number and the question text is I know how what I do fits into my team's objectives. The page and q values are 1 and q8 respectively.8 is the questions number and the question text is I know how what I do fits into my team's objectives. The page and q values are 1 and q8 respectively.8 is the questions number and the question text is I know how what I do fits into my team's objectives. The page and q values are 1 and q8 respectively.8 is the questions number and the question text is I know how what I do fits into my team's objectives. The page and q values are 1 and q8 respectively. Which is not what I want, for information purposes, the array using the print function looks like this: Array ( [0] => Array ( [questions] => q8 [qnum] => 8 [qtext] => I know how what I do fits into my team's objectives [page] => 1 ) [1] => Array ( [questions] => q8 [qnum] => 8 [qtext] => I know how what I do fits into my team's objectives [page] => 1 ) [2] => Array ( [questions] => q8 [qnum] => 8 [qtext] => I know how what I do fits into my team's objectives [page] => 1 ) [3] => Array ( [questions] => q8 [qnum] => 8 [qtext] => I know how what I do fits into my team's objectives [page] => 1 ) [4] => Array ( [questions] => q8 [qnum] => 8 [qtext] => I know how what I do fits into my team's objectives [page] => 1 ) [5] => Array ( [questions] => q8 [qnum] => 8 [qtext] => I know how what I do fits into my team's objectives [page] => 1 ) [6] => Array ( [questions] => q8 [qnum] => 8 [qtext] => I know how what I do fits into my team's objectives [page] => 1 ) [7] => Array ( [questions] => q8 [qnum] => 8 [qtext] => I know how what I do fits into my team's objectives [page] => 1 ) ) Clearly it's not looping through and displaying each row as it should...any advice? Homer.

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• Mobile Intel® GMA 4500MHD boost

  - by Andy Smith

  My machine has a Mobile Intel® GMA 4500MHD integrated graphics chipset. The machine is currently running 64 bit windows 7 premium with 3GB of ram (1x1gb and 1x2gb). I note that the Mobile Intel® GMA 4500MHD shares the physical memory to process the graphics. now, the total available graphics memory can be up to 1,340 MB with a 32-bit operating system and 3 GB system memory or 1,759 MB with a 64-bit operating system and 4 GB system memory. I am considering investing in a 4GB stick to replace the 1gb stick bringing the total up to 6gb, mainly for an increase in graphics processing ability. Can anyone let me know what sort of power (if any over the 4gb) I could expect by upgrading to 6GB?

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• Boost Audio Input on OS X?

  - by alanstorm

  I'm using my 13" Mac Book Pro's audio input functionality with an external microphone (recent vintage, bought around Thanksgiving). I've increased my input volume to the maximum in system preference, but the resulting recorded volume (using iShowU HD) is very low. Is there anyway to increase the input volume/sensitivity beyond Apple's default settings? I've found plenty on google about increasing the OUTPUT volume, but I want to increase the input volume.

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• Boost Up My Old Laptop Using a SSD

  - by Sina Bizbone

  I have an old laptop Lenovo SL400 (Core2Due T9550 2.66GHz / 4GB DDR2 Ram). Since I can't afford to buy a new laptop, I thought maybe I could throw an ADATA SP600 64GB SSD as primary drive and move my current HDD to DVD-ROM space by using HDDCADDY. I know that 64gb will come short after installing Visual Studio, SQL Server, etc. So is there anyway to just install the kernel part of windows on SSD and the rest on HDD. Doesn't windows have built-in support to do this? (ReadyBoost is out of picture since it's just simple caching)

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• What does the `forall` keyword in Haskell/GHC do?

  - by JUST MY correct OPINION

  I've been banging my head on this one for (quite literally) years now. I'm beginning to kinda/sorta understand how the foreach keyword is used in so-called "existential types" like this: data ShowBox = forall s. Show s => SB s (This despite the confusingly-worded explanations of it in the fragments found all around the web.) This is only a subset, however, of how foreach is used and I simply cannot wrap my mind around its use in things like this: runST :: forall a. (forall s. ST s a) -> a Or explaining why these are different: foo :: (forall a. a -> a) -> (Char,Bool) bar :: forall a. ((a -> a) -> (Char, Bool)) Or the whole RankNTypes stuff that breaks my brain when "explained" in a way that makes me want to do that Samuel L. Jackson thing from Pulp Fiction. (Don't follow that link if you're easily offended by strong language.) The problem, really, is that I'm a dullard. I can't fathom the chicken scratchings (some call them "formulae") of the elite mathematicians that created this language seeing as my university years are over two decades behind me and I never actually had to put what I learnt into use in practice. I also tend to prefer clear, jargon-free English rather than the kinds of language which are normal in academic environments. Most of the explanations I attempt to read on this (the ones I can find through search engines) have these problems: They're incomplete. They explain one part of the use of this keyword (like "existential types") which makes me feel happy until I read code that uses it in a completely different way (like runST, foo and bar above). They're densely packed with assumptions that I've read the latest in whatever branch of discrete math, category theory or abstract algebra is popular this week. (If I never read the words "consult the paper whatever for details of implementation" again, it will be too soon.) They're written in ways that frequently turn even simple concepts into tortuously twisted and fractured grammar and semantics. (I suspect that the last two items are the biggest problem. I wouldn't know, though, since I'm too much a dullard to comprehend them.) It's been asked why Haskell never really caught on in industry. I suspect, in my own humble, unintelligent way, that my experience in figuring out one stupid little keyword -- a keyword that is increasingly ubiquitous in the libraries being written these days -- are also part of the answer to that question. It's hard for a language to catch on when even its individual keywords cause years-long quests to comprehend. Years-long quests which end in failure. So... On to the actual question. Can anybody completely explain the foreach keyword in clear, plain English (or, if it exists somewhere, point to such a clear explanation which I've missed) that doesn't assume I'm a mathematician steeped in the jargon?

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• Is this GetEnumAsStrings<T>() method reinventing the wheel?

  - by Edward Tanguay

  I have a number of enums and need to get them as List<string> objects in order to enumerate through them and hence made the GetEnumAsStrings<T>() method. But it seems to me there would be an easier way. Is there not a built-in method to get an enum like this into a List<string>? using System; using System.Collections.Generic; namespace TestEnumForeach2312 { class Program { static void Main(string[] args) { List<string> testModes = StringHelpers.GetEnumAsStrings<TestModes>(); testModes.ForEach(s => Console.WriteLine(s)); Console.ReadLine(); } } public static class StringHelpers { public static List<string> GetEnumAsStrings<T>() { List<string> enumNames = new List<string>(); foreach (T item in Enum.GetValues(typeof(TestModes))) { enumNames.Add(item.ToString()); } return enumNames; } } public enum TestModes { Test, Show, Wait, Stop } }

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• Why won't this loop normalize my Vector2 list?

  - by ssb

  See the following code: List<Vector2> axes = new List<Vector2>(); axes.Add(TopRight() - TopLeft()); axes.Add(BottomLeft() - TopLeft()); axes.Add(otherRectangle.TopRight() - otherRectangle.TopLeft()); axes.Add(otherRectangle.BottomLeft() - otherRectangle.TopLeft()); // Try normalizing vectors? foreach (Vector2 axis in axes) { axis.Normalize(); } the Vector2.Normalize() method is a void method that normalizes the vector it's called on. Yet for some reason when I do this loop it doesn't normalize the vectors. Am I just unable to modify a list this way? Some oddities: Iterating with a for loop, i.e. axis[i].Normalize() doesn't work. Iterating with the built-in List<T>.ForEach iterator does not work. Creating a normalizing the vector before adding it to the list rather than iterating over the list does work. Why does iteration not work?

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• Floating point comparison in STL, BOOST

  - by Paul

  Is there in the STL or in Boost a set of generic simple comparison functions? The one I found are always requiring template parameters, and/or instantiation of a struct template. I'm looking for something with a syntax like : if ( is_greater(x,y) ) { ... } Which could be implemented as : template <typename T> bool is_greater(const T& x, const T& y) { return x > y + Precision<T>::eps; }

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• compiling boost based application using cron

  - by user303544

  Hi All, I am building some boost based application for various embedded targets. I have developed a script which can build my application with different toolchain for several targets. This script works fine when I run it from command line but if it is invoked from cron it always fails to link the object files. My application has dependency on openssl. Can anyone please give some idea? What would be the root cause of this kind of behavior? Thanks in advance.

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• Adapting Map Iterators Using STL/Boost/Lambdas

  - by John Dibling

  Consider the following non-working code: typedef map<int, unsigned> mymap; mymap m; for( int i = 1; i < 5; ++i ) m[i] = i; // 'remove' all elements from map where .second < 3 remove(m.begin(), m.end(), bind2nd(less<int>(), 3)); I'm trying to remove elements from this map where .second < 3. This obviously isn't written correctly. How do I write this correctly using: Standard STL function objects & techniques Boost.Bind C++0x Lambdas I know I'm not eraseing the elements. Don't worry about that; I'm just simplifying the problem to solve.

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• converting a timestring to a duration

  - by radman

  Hi, At the moment I am trying to read in a timestring formatted and create a duration from that. I am currently trying to use the boost date_time time_duration class to read and store the value. boost date_time provides a method time_duration duration_from_string(std::string) that allows a time_duration to be created from a time string and it accepts strings formatted appropriately ("[-]h[h][:mm][:ss][.fff]".). Now this method works fine if you use a correctly formatted time string. However if you submit something invalid like "ham_sandwich" or "100" then you will still be returned a time_duration that is not valid. Specifically if you try to pass it to a standard output stream then an assertion will occur. My question is: Does anyone know how to test the validity of the boost time_duration? and failing that can you suggest another method of reading a timestring and getting a duration from it? Note: I have tried the obvious testing methods that time_duration provides; is_not_a_date_time(), is_special() etc and they don't pick up that there is an issue. Using boost 1.38.0

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• How to write a custom predicate for multi_index_containder with composite_key?

  - by Titan

  I googled and searched in the boost's man, but didn't find any examples. May be it's a stupid question...anyway. So we have the famous phonebook from the man: typedef multi_index_container< phonebook_entry, indexed_by< ordered_non_unique< composite_key< phonebook_entry, member<phonebook_entry,std::string,&phonebook_entry::family_name>, member<phonebook_entry,std::string,&phonebook_entry::given_name> >, composite_key_compare< std::less<std::string>, // family names sorted as by default std::greater<std::string> // given names reversed > >, ordered_unique< member<phonebook_entry,std::string,&phonebook_entry::phone_number> > > > phonebook; phonebook pb; ... // look for all Whites std::pair<phonebook::iterator,phonebook::iterator> p= pb.equal_range(boost::make_tuple("White"), my_custom_comp()); How should my_custom_comp() look like? I mean it's clear for me then it takes boost::multi_index::composite_key_result<CompositeKey> as an argumen (due to compilation errors :) ), but what is CompositeKey in that particular case? struct my_custom_comp { bool operator()( ?? boost::multi_index::composite_key_result<CompositeKey> ?? ) const { return blah_blah_blah; } }; Thanks in advance.

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• Convert enumeration to string

  - by emptyheaded

  I am trying to build a function that converts an item from an enum to its corresponding string. The enums I use are fairly long, so I didn't want to use a switch-case. I found a method using boost::unordered_map very convenient, but I don't know how to make a default return (when there is no item matching the enum). const boost::unordered_map<enum_type, const std::string> enumToString = boost::assign::map_list_of (data_1, "data_1") (data_2, "data_2"); I tried to create an additional function: std::string convert(enum_type entry) { if (enumToString.find(entry)) // not sure what test to place here, return enumToString.at(entry); //because the find method returns an iter else return "invalid_value"; } I even tried something exceedingly wrong: std::string convert(enum_type entry) { try{ return enumToString.at(entry); } catch(...){ return "invalid_value"; } } Result: evil "Debug" runtime error. Can somebody give me a suggestion on how to either 1) find an easier method to convert enum to a string with the same name as the enum item 2) find a way to use already built boost methods to get a default value from a hash map (best option) 3) find what to place in the test to use a function that returns either the pair of the key-value, or a different string if the key is not found in the map. Thank you very much.

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• Work with function references

  - by Ockonal

  Hello, I have another one question about functions reference. For example, I have such definition: typedef boost::function<bool (Entity &handle)> behaviorRef; std::map< std::string, ptr_vector<behaviorRef> > eventAssociation; The first question is: how to insert values into such map object? I tried: eventAssociation.insert(std::pair< std::string, ptr_vector<behaviorRef> >(eventType, ptr_vector<behaviorRef>(callback))); But the error: no matching function for call to ‘boost::ptr_vector<boost::function<bool(Entity&)> >::push_back(Entity::behaviorRef&)’ And I undersatnd it, but can't make workable code. The second question is how to call such functions? For example, I have one object of behaviorRef, how to call it with boost::bind with passing my own values?

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• is there a simple timed lock algorithm avoiding deadlock on multiple mutexes?

  - by Vicente Botet Escriba

  C++0x thread library or Boost.thread define a non-member variadic template function that locks all mutex at once that helps to avoid deadlock. template <class L1, class L2, class... L3> void lock(L1&, L2&, L3&...); The same can be applied to a non-member variadic template function try_lock_until, which locks all the mutex until a given time is reached that helps to avoid deadlock like lock(...). template <class Clock, class Duration, class L1, class L2, class... L3> void try_lock_until( const chrono::time_point<Clock,Duration>& abs_time, L1&, L2&, L3&...); I have an implementation that follows the same design as the Boost function boost::lock(...). But this is quite complex. As I can be missing something evident I wanted to know if: is there a simple timed lock algorithm avoiding deadlock on multiple mutexes? If no simple implementation exists, can this justify a proposal to Boost? P.S. Please avoid posting complex solutions.

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• MySQL SELECT MAX multiple tables : foreach parent return eldest son's picture

  - by Guillermo

  **Table parent** parentId | name **Table children** childId | parentId | pictureId | age **Table childrenPictures** pictureId | imgUrl no i would like to return all parent names with their eldest son's picture (only return parents that have children, and only consider children that have pictures) so i thought of something like : SELECT c.childId AS childId, p.name AS parentName, cp.imgUrl AS imgUrl, MAX(c.age) AS age FROM parent AS p RIGHT JOIN children AS c ON (p.parentId = c.parentId) RIGHT JOIN childrenPictures AS cp ON (c.pictureId = cp.pictureId)) GROUP BY p.name This query will return each parent's eldest son's age, but the childId will not correspond to the eldest sons id, so the output does not show the right sons picture. Well if anyone has a hint i'd appreciate very much Thank you very much, G

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• Java List use through use of JSTL <c:forEach>

  - by Mark Lewis

  Hello If I have a JSF backing bean return an object of type ArrayList, I should be able to use to iterate over the elements in the list. Each element contains a map and although the question of how to access the map content through JSTL has been answered here, if I pass an array of such maps, I can't find how to iterate over them and still access the map content using JSTL. There's documentation which refers to simple iterators but not to those whose items are themselves maps. BalusC, I'm not trying to force the issue, just that I've been looking at this all day, and still cannot seem to be able to output the contents of my data structure through jsp (only on the console). This as a separate question still has merit. If anyone can give me a simple example of how a java List is iterated over in JSP I'd be massively appreciative. Mark

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• foreach loop a java creation?

  - by abson

  Why was this loop introduced in java?Is it a java creation? What is its purpose(increases memory/cpu utilisation efficiency)?

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• Java: using foreach over strings from arrayList does not print anything

  - by HH

  $ javac ArrayListTest.java $ java ArrayListTest $ cat ArrayListTest.java import java.io.*; import java.util.*; public class ArrayListTest{ public static void main(String[] args) { try { String hello ="oeoaseu oeu hsoae sthoaust hoaeut hoasntu"; ArrayList<String> appendMe = null; for(String s : hello.split(" ")) appendMe.add(s+" "); for(String s : appendMe) System.out.println(s); //WHY DOES IT NOT PRINT? }catch(Exception e){ } } }

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• Code doesn't work in foreach

  - by Arlen Beiler

  Here is my code: var divarray = document.getElementById("yui-main").getElementsByTagName("div"); var articleHTML; var absHTML; var keyHTML; var bodyHTML = []; for( var i in divarray) { if(divarray[i].className == "articleBody"){ articleHTML = divarray[i]; for( var j in articleHTML ){ bodyHTML[i] = ''; if(articleHTML[j].className == "issueMiniFeature"){continue;} if(articleHTML[j].className == "abstract"){absHTML = articleHTML[i]; continue;} if(articleHTML[j].className == "journalKeywords"){keyHTML = articleHTML[i]; continue;} bodyHTML[i] = articleHTML[i]; } break; } i++; } The error I am getting is: SyntaxError: Unexpected token var I am using Google Chrome

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• odd nullreference error at foreach when rendering view

  - by giddy

  This error is so weird I Just can't really figure out what is really wrong! In UserController I have public virtual ActionResult Index() { var usersmdl = from u in RepositoryFactory.GetUserRepo().GetAll() select new UserViewModel { ID = u.ID, UserName = u.Username, UserGroupName = u.UserGroupMain.GroupName, BranchName = u.Branch.BranchName, Password = u.Password, Ace = u.ACE, CIF = u.CIF, PF = u.PF }; if (usersmdl != null) { return View(usersmdl.AsEnumerable()); } return View(); } My view is of type @model IEnumerable<UserViewModel> on the top. This is what happens: Where and what exactly IS null!? I create the users from a fake repository with moq. I also wrote unit tests, which pass, to ensure the right amount of mocked users are returned. Maybe someone can point me in the right direction here? Top of the stack trace is : at lambda_method(Closure , User ) at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext() at ASP.Index_cshtml.Execute() Is it something to do with linq here? Tell me If I should include the full stack trace.

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