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• How can I force a ListView with a custom panel to re-measure when the ListView width goes below the

  - by Scott Whitlock

  Sorry for the long winded question (I'm including background here). If you just want the question, go to the end. I have a ListView with a custom Panel implementation that I'm using to implement something similar to a WrapPanel, but not quite. I'm overriding the MeasureOverride and ArrangeOverride methods in the custom panel. If I do the naive implementation of a WrapPanel in the MeasureOverride method it doesn't work when the ListView is resized. Let's say the custom panel does a measure and the constraint is a width of 100 and let's say I have 3 items that are 40 wide each. The naive approach is to return a size of 80,80 but when I resize the window that the ListView is in, down to say 75, it just turns on the horizontal scrollbar and never calls measure or arrange again (it does keep measuring and arranging if the width is greater than 80). To get around this, I hard coded the measurement to only have a width of the widest item. Then in the arrange, it gives me more space than I asked for and I use as much horizontal space as I can before wrapping. If I resize the window smaller than the smallest item in the ListView, then it turns on the scrollbar, which is great. Unfortunately this is causing a big problem when I have one of these ListViews with a custom panel nested inside of another one. The outside one works ok, but I can't get the inside one to "take as much as it needs". It always sizes to the smallest item, and the only way around it is to set the MinWidth to be something greater than zero. Anyway, stepping back for a second, I think the real way to fix this is to go back to the Naive implementation of the WrapPanel but force it to re-measure when the ListView width goes below the Size I previously returned as a measurement. That should solve my problem with the nested one. So, that's my question: I have a ListView with a custom panel If I return a measurement width on the panel and the ListView is resized to less than that width, it stops calling MeasureOverride How can I get it to continue calling MeasureOverride?

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• Helpful advice on developing a professional MS Word add-on

  - by Dan Tao

  A few months back I put together a simple proof-of-concept piece of software for a small firm with an idea for a document editing tool. The company wanted this tool to be integrated into Microsoft Word, understandably, to maximize its accessibility to the average user. I essentially wrote the underlying library with all of the core functionality as a C# project, and then used VSTO to get it running inside of Word. It felt like a bit of a duct tape solution, really; but then, I have (practically) zero experience developing tools for integration with MS Office, and it was only a proof of concept anyway. Well, the firm was quite pleased with my work overall, and they're looking to move from "proof of concept" to the real deal. Fortunately, as I said, the core functionality is all there and will only need to be somewhat tweaked and enhanced. My main concern is figuring out how to put together an application that will integrate with MS Word in a clean and polished way, and which can be deployed easily in accordance with a regular user's expectations (i.e., simply running an install program and voila, it's there in Word). I seem to remember reading somewhere that nobody uses VSTO for real professional projects. Is this true? False? What are the alternatives? And what are the tips and gotchas that I should be aware of before getting started on this issue of MS Word integration?

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• MySQL Gurus: How to pull a complex grid of data from MySQL database with one query?

  - by iopener

  Hopefully this is less complex than I think. I have one table of companies, and another table of jobs, and a third table with that contains a single entry for each employee in each job from each company. NOTE: Some companies won't have employees in some jobs, and some companies will have more than one employee in some jobs. The company table has a companyid and companyname field, the job table has a jobid and jobtitle field, and the employee table has employeeid, companyid, jobid and employeename fields. I want to build a table like this: +-----------+-----------+-----------+ | Company A | Company B | Company C | ------+-----------+-----------+-----------+ Job A | Emp 1 | Emp 2 | | ------+-----------+-----------+-----------+ Job B | Emp 3 | | Emp 4 | | | | Emp 5 | ------+-----------+-----------+-----------+ Job C | | Emp 6 | | | | Emp 7 | | | | Emp 8 | | ------+-----------+-----------+-----------+ I had previously been looping through a result set of jobs, and for each job, looping through a result set of each company, and for each company, looping through each employee and printing it in a table (gross, but performance was not supposed to be a consideration). The app has grown in popularity, and now we have 100 companies and hundreds of jobs, and the server is crapping out (all the id fields are indexed). Any suggestions on how to write a single query to get this data? I don't need the company names or job titles (obviously), but I do need some way to identify where each row from the result should be printed. I'm imagining a result set that just contained a long list of joined employees, and I could write a loop to use the companyid and employeeid values to tell me when to create a new cell or table row. This works as long as there aren't ZERO employees; I would need a NULL employee name for that I think? Am I completely on the wrong track? Thanks in advance for any ideas!

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• Losing URI segments when paginating with CodeIgniter

  - by Danny Herran

  I have a /payments interface where the user should be able to filter via price range, bank, and other stuff. Those filters are standard select boxes. When I submit the filter form, all the post data goes to another method called payments/search. That method performs the validation, saves the post values into a session flashdata and redirects the user back to /payments passing the flashdata name via URL. So my standard pagination links with no filters are exactly like this: payments/index/20/ payments/index/40/ payments/index/60/ And if you submit the filter form, the returning URL is: payments/index/0/b48c7cbd5489129a337b0a24f830fd93 This works just great. If I change the zero for something else, it paginates just fine. The only issue however is that the << 1 2 3 4 page links wont keep the hash after the pagination offset. CodeIgniter is generating the page links ignoring that additional uri segment. My uri_segment config is already set to 3: $config['uri_segment'] = 3; I cannot set the page offset to 4 because that hash may or may not exists. Any ideas of how can I solve this? Is it mandatory for CI to have the offset as the last segment in the uri? Maybe I am trying an incorrect approach, so I am all ears. Thank you folks.

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• Why doesn't this simple regex match what I think it should?

  - by Kevin Stargel

  I have a data file that looks like the following example. I've added '%' in lieu of \t, the tab control character. 1234:56% Alice Worthington alicew% Jan 1, 2010 10:20:30 AM% Closed% Development Digg: Reddit: Update%% file-one.txt% 1.1% c:/foo/bar/quux Add%% file-two.txt% 2.5.2% c:/foo/bar/quux Remove%% file-three.txt% 3.4% c:/bar/quux Update%% file-four.txt% 4.6.5.3% c:/zzz ... many more records of the above form The records I'm interested in are the lines beginning with "Update", "Add", "Remove", and so on. I won't know what the lines begin with ahead of time, or how many lines precede them. I do know that they always begin with a string of letters followed by two tabs. So I wrote this regex: generate-report-for 1234:56 | egrep "^[[:alpha:]]+\t\t.+" But this matches zero lines. Where did I go wrong? Edit: I get the same results whether I use '...' or "..." for the egrep expression, so I'm not sure it's a shell thing.

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• Tell me SQL Server Full-Text searcher is crazy, not me.

  - by Ian Boyd

  i have some customers with a particular address that the user is searching for: 123 generic way There are 5 rows in the database that match: ResidentialAddress1 ============================= 123 GENERIC WAY 123 GENERIC WAY 123 GENERIC WAY 123 GENERIC WAY 123 GENERIC WAY i run a FT query to look for these rows. i'll show you each step as i add more criteria to the search: SELECT ResidentialAddress1 FROM Patrons WHERE CONTAINS(Patrons.ResidentialAddress1, '"123*"') ResidentialAddress1 ========================= 123 MAPLE STREET 12345 TEST 123 MINE STREET 123 GENERIC WAY 123 FAKE STREET ... (30 row(s) affected) Okay, so far so good, now adding the word "generic": SELECT ResidentialAddress1 FROM Patrons WHERE CONTAINS(Patrons.ResidentialAddress1, '"123*"') AND CONTAINS(Patrons.ResidentialAddress1, '"generic*"') ResidentialAddress1 ============================= 123 GENERIC WAY 123 GENERIC WAY 123 GENERIC WAY 123 GENERIC WAY 123 GENERIC WAY (5 row(s) affected) Excellent. And now i'l add the final keyword that the user wants to make sure exists: SELECT ResidentialAddress1 FROM Patrons WHERE CONTAINS(Patrons.ResidentialAddress1, '"123*"') AND CONTAINS(Patrons.ResidentialAddress1, '"generic*"') AND CONTAINS(Patrons.ResidentialAddress1, '"way*"') ResidentialAddress1 ------------------------------ (0 row(s) affected) Huh? No rows? What if i query for just "way*": SELECT ResidentialAddress1 FROM Patrons WHERE CONTAINS(Patrons.ResidentialAddress1, '"way*"') ResidentialAddress1 ------------------------------ (0 row(s) affected) At first i thought that perhaps it's because of the *, and it's requiring that the root way have more characters after it. But that's not true: Searching for "123*" matches "123" Searching for "generic*" matches "generic" Books online says, The asterisk matches zero, one, or more characters What if i remove the * just for s&g: SELECT ResidentialAddress1 FROM Patrons WHERE CONTAINS(Patrons.ResidentialAddress1, '"way"') Server: Msg 7619, Level 16, State 1, Line 1 A clause of the query contained only ignored words. So one might think that you are just not allowed to even search for way, either alone, or as a root. But this isn't true either: SELECT * FROM Patrons WHERE CONTAINS(Patrons.*, '"way*"') AccountNumber FirstName Lastname ------------- --------- -------- 33589 JOHN WAYNE So sum up, the user is searching for rows that contain all the words: 123 generic way Which i, correctly, translate into the WHERE clauses: SELECT * FROM Patrons WHERE CONTAINS(Patrons.*, '"123*"') AND CONTAINS(Patrons.*, '"generic*"') AND CONTAINS(Patrons.*, '"way*"') which returns no rows. Tell me this just isn't going to work, that it's not my fault, and SQL Server is crazy. Note: i've emptied the FT index and rebuilt it.

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• How should backbone.js handle a GET request that returns no results?

  - by Nyxynyx

  I have a number of text input elements that when its values are changed, will trigger a fetch on listingListView's collection listingCollection, which then updates listingListView with the new data via the function listingListView.refreshList as shown below. I am using PHP/Codeigniter to expose a RESTful API. Problem: Everything works fine if there are results retrieved from the fetch(). However, when the filters results in no result being returned, how should the server side and the client side handle it? Currently Chrome's javascript console displays a 404 error and in the Network tab, the XHR request is highlighted in red. All I want to do in the event of zero results returned, is to blank the listingListView and show a message like (No results returned) and not throw any errors in the javascript console. Thanks! PHP Code function listings_get() { // Get filters $price_min = $this->get('price_min'); $this->load->model('app_model'); $results = $this->app_model->get_listings($price_min); if($results) $this->response($results); else $this->response(NULL); } JS Code window.ListingListView = Backbone.View.extend({ tagName: 'table', initialize: function() { this.model.bind('reset', this.refreshList, this); this.model.bind('add', function(listing) { $(this.el).append(new ListingListItemView({ model: listing }).render().el); }, this); }, render: function() { _.each(this.model.models, function(listing) { $(this.el).append(new ListingListItemView({ model: listing }).render().el); }, this); return this; }, close: function() { $(this.el).unbind(); $(this.el).empty(); }, refreshList: function() { $(this.el).empty(); this.render(); } });

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• What most efficient method to find a that triangle which contains the given point?

  - by Christo

  Given the triangle with vertices (a,b,c): c / \ / \ / \ a - - - b Which is then subdivided into four triangles by halving each of the edges: c / \ / \ ca / \ bc /\ - - - /\ / \ / \ / \ / \ a- - - - ab - - - -b Wich results in four triangles (a, ab, ca), (b, bc, ab), (c, ca, bc), (ab, bc, ca). Now given a point p. How do I determine in which triangle p lies, given that p is within the outer triangle (a, b, c)? Currently I intend to use ab as the origin. Check whether it is to the left of right of the line "ca - ab" using the perp of "ca - ab" and checking the sign against the dot product of "ab - a" and the perp vector and the vector "p - ab". If it is the same or the dot product is zero then it must be in (a, ab, ca)... Continue with this procedure with the other outer triangles (b, ba, ab) & (c, ca, ba). In the end if it didn't match with these it must be contained within the inner triangle (ab, bc, ca). Is there a better way to do it?

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• Explaining the forecasts from an ARIMA model

  - by Samik R.

  I am trying to explain to myself the forecasting result from applying an ARIMA model to a time-series dataset. The data is from the M1-Competition, the series is MNB65. For quick reference, I have a google doc spreadsheet with the data. I am trying to fit the data to an ARIMA(1,0,0) model and get the forecasts. I am using R. Here are some output snippets: > arima(x, order = c(1,0,0)) Series: x ARIMA(1,0,0) with non-zero mean Call: arima(x = x, order = c(1, 0, 0)) Coefficients: ar1 intercept 0.9421 12260.298 s.e. 0.0474 202.717 > predict(arima(x, order = c(1,0,0)), n.ahead=12) $pred Time Series: Start = 53 End = 64 Frequency = 1 [1] 11757.39 11786.50 11813.92 11839.75 11864.09 11887.02 11908.62 11928.97 11948.15 11966.21 11983.23 11999.27 I have a few questions: (1) How do I explain that although the dataset shows a clear downward trend, the forecast from this model trends upward. This also happens for ARIMA(2,0,0), which is the best ARIMA fit for the data using auto.arima (forecast package) and for an ARIMA(1,0,1) model. (2) The intercept value for the ARIMA(1,0,0) model is 12260.298. Shouldn't the intercept satisfy the equation: C = mean * (1 - sum(AR coeffs)), in which case, the value should be 715.52. I must be missing something basic here. (3) This is clearly a series with non-stationary mean. Why is an AR(2) model still selected as the best model by auto.arima? Could there be an intuitive explanation? Thanks.

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• DOS Batch file to echo a specific line number

  - by Lee

  So for the second part of my current dilemma, I have a list of folders in "c:\file_list.txt". I need to be able to extract them (well, echo them with some mods) based on the line number because this batch script is being called by an iterative macro process. I'm passing the line number as a parameter. @echo off setlocal enabledelayedexpansion set /a counter=0 set /a %%a = "" for /f "usebackq delims=" %%a in (c:\file_list.txt) do (if "!counter!"=="%1" goto :printme & set /a counter+=1) :printme echo %%a which gives me an output of "%a". Doh! So, I've tried echoing !a! (result: "ECHO is off."); I've tried echoing %a (result: a) I figured the easy thing to do would be to modify the "head.bat" code found here: http://stackoverflow.com/questions/130116/dos-batch-commands-to-read-first-line-from-text-file except rather than echoing every line - I'd just echo the last line found. Not as simple as one might think. I've noticed that my counter is staying at zero for some reason; I'm wondering if the "set /a counter+=1" is doing what I think it's doing.

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• Singleton Pattern combine with a Decorator

  - by Mike

  Attached is a classic Decorator pattern. My question is how would you modify the below code so that you can wrap zero or one of each topping on to the Pizza Right now I can have a Pepporini - Sausage -- Pepporini -- Pizza class driving the total cost up to $10, charging twice for Pepporini. I don't think I want to use the Chain of Responsibility pattern as order does not matter and not all toppings are used? Thank you namespace PizzaDecorator { public interface IPizza { double CalculateCost(); } public class Pizza: IPizza { public Pizza() { } public double CalculateCost() { return 8.00; } } public abstract class Topping : IPizza { protected IPizza _pizzaItem; public Topping(IPizza pizzaItem) { this._pizzaItem = pizzaItem; } public abstract double CalculateCost(); } public class Pepporini : Topping { public Pepporini(IPizza pizzaItem) : base(pizzaItem) { } public override double CalculateCost() { return this._pizzaItem.CalculateCost() + 0.50; } } public class Sausage : Topping { public Sausage(IPizza pizzaItem) : base(pizzaItem) { } public override double CalculateCost() { return this._pizzaItem.CalculateCost() + 1.00; } } public class Onions : Topping { public Onions(IPizza pizzaItem) : base(pizzaItem) { } public override double CalculateCost() { return this._pizzaItem.CalculateCost() + .25; } } }

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• Is there a limit for the number of files in a directory on an SD card?

  - by jamesh

  I have a project written for Android devices. It generates a large number of files, each day. These are all text files and images. The app uses a database to reference these files. The app is supposed to clear up these files after a little use (perhaps after a few days), but this process may or may not be working. This is not the subject of this question. Due to a historic accident, the organization of the files are somewhat naive: everything is in the same directory; a .hidden directory which contains a zero byte .nomedia file to prevent the MediaScanner indexing it. Today, I am seeing an error reported: java.io.IOException: Cannot create: /sdcard/.hidden/file-4200.html at java.io.File.createNewFile(File.java:1263) Regarding the sdcard, I see it has plenty of storage left, but counting $ cd /Volumes/NO_NAME/.hidden $ ls | wc -w 9058 Deleting a number of files seems to have allowed the file creation for today to proceed. Regrettably, I did not try touching a new file to try and reproduce the error on a commandline; I also deleted several hundred files rather than a handful. However, my question is: are there hard limits on filesize or number of files in a directory? am I even on the right track here? Nota Bene: The SD card is as-is - i.e. I haven't formatted it, so I would guess it would be a FAT-* format. The FAT-32 format has hard limits of filesize of 2GB (well above the filesizes I am dealing with) and a limit of number of files in the root directory. I am definitely not writing files in the root directory.

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• xsd.exe creating invalid constraints in dataset from xsd file

  - by Dan Neely

  I have a sequence with an allowed minimum length of zero in my xsd. When I try and load an xml file which doesn't have any elements of the sequence into the DataSet that xsd.exe created I get an exception indicating that my file violated one of the DataSet's constraints. The xml file validates against the schema so I know it's valid. Is there anything I can do to make the tool generate a valid dataset? <xs:sequence minOccurs="0" maxOccurs="unbounded"> <xs:element name="Numbers" type="xs:double"/> </xs:sequence> Edit: if I change my schema to this the generated code works properly. It looks wrong to me though since it appears to be implying that I could have sequence items with nothing in them, which doesn't make any sense. <xs:sequence minOccurs="0" maxOccurs="unbounded"> <xs:element name="Numbers" type="xs:double" minOccurs="0"/> </xs:sequence>

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• Pointers to structs

  - by Bobby

  I have the following struct: struct Datastore_T { Partition_Datastores_T cmtDatastores; // bytes 0 to 499 Partition_Datastores_T cdhDatastores; // bytes 500 to 999 Partition_Datastores_T gncDatastores; // bytes 1000 to 1499 Partition_Datastores_T inpDatastores; // bytes 1500 1999 Partition_Datastores_T outDatastores; // bytes 2000 to 2499 Partition_Datastores_T tmlDatastores; // bytes 2500 to 2999 Partition_Datastores_T sm_Datastores; // bytes 3000 to 3499 }; I want to set a char* to struct of this type like so: struct Datastore_T datastores; // Elided: datastores is initialized with data here char* DatastoreStartAddr = (char*)&datastores; memset(DatastoreStartAddr, 0, sizeof(Datastore_T)); The problem I have is that the value that DatastoreStartAddr points to always has a value of zero when it should point to the struct that has been initialized with data. Meaning if I change the values in the struct using the struct directly, the values pointed to by DatastoreStartAddr should also change b/c they are pointing to the same address. But this is not happening. What am I doing wrong?

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• Using PLINQ to calculate and update values within the enclosure does not work

  - by Keith

  I recently needed to do a running total on a report. Where for each group, I order the rows and then calculate the running total based on the previous rows within the group. Aha! I thought, a perfect use case for PLINQ! However, when I wrote up the code, I got some strange behavior. The values I was modifying showed as being modified when stepping through the debugger, but when they were accessed they were always zero. Sample Code: class Item { public int PortfolioID; public int TAAccountID; public DateTime TradeDate; public decimal Shares; public decimal RunningTotal; } List<Item> itemList = new List<Item> { new Item { PortfolioID = 1, TAAccountID = 1, TradeDate = new DateTime(2010, 5, 1), Shares = 5.335m, }, new Item { PortfolioID = 1, TAAccountID = 1, TradeDate = new DateTime(2010, 5, 2), Shares = -2.335m, }, new Item { PortfolioID = 2, TAAccountID = 1, TradeDate = new DateTime(2010, 5, 1), Shares = 7.335m, }, new Item { PortfolioID = 2, TAAccountID = 1, TradeDate = new DateTime(2010, 5, 2), Shares = -3.335m, }, }; var found = (from i in itemList where i.TAAccountID == 1 select new Item { TAAccountID = i.TAAccountID, PortfolioID = i.PortfolioID, Shares = i.Shares, TradeDate = i.TradeDate, RunningTotal = 0 }); found.AsParallel().ForAll(x => { var prevItems = found.Where(i => i.PortfolioID == x.PortfolioID && i.TAAccountID == x.TAAccountID && i.TradeDate <= x.TradeDate); x.RunningTotal = prevItems.Sum(s => s.Shares); }); foreach (Item i in found) { Console.WriteLine("Running total: {0}", i.RunningTotal); } Console.ReadLine(); If I change the select for found to be .ToArray(), then it works fine and I get calculated reuslts. Any ideas what I am doing wrong?

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• What is the best approach to 2D collision detection on the iPhone?

  - by Magic Bullet Dave

  Been working on this problem of collision detection and there appears to be 3 main approaches I could take: Sprite and mask approach. (AND the overlap of the sprites and check for a non-zero number in the resulting sprite pixel data). Bounding circles, rectangles or polygons. (Create one or more shapes that enclose the sprites and do the basic maths to check for overlaps). Use an existing sprite library. The first approach, even though it would have been the way I would have done it in the old days of 16x16 sprite blocks, it appears that there just isn’t an easy way of getting at the individual image pixel data and/or alpha channel within Quartz (or OPENGL for that matter). Detecting the overlap of the bounding box is easy, but then creating a 3rd image from the overlap and then testing it for pixels is complicated and my gut feel is that even if we could get it to work would be slow. Am I missing something neat here? The second approach involves dividing up our sprites into several polygons and testing them for overlaps. The more polygons the more accurate the collision detection. The benefit is that it is fast, and can be accurate. The downside is it makes the sprite creation more complicated. i.e., we have to create the polygons for each sprite. For speed the best approach is to create a tree of polygons. The 3rd approach I’m not sure about as it involves buying code (or using an open source licence). I am not sure what the best library to use is or whether this would make life easier or give us a problem integrating this into our app. So in short I am favouring the polygon and tree approach and would appreciate you views on this before I go and write lots of code. Best regards Dave

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• Flag bit computation and detection

  - by Majid

  Hi all, In some code I'm working on I should take care of ten independent parameters which can take one of two values (0 or 1). This creates 2^10 distinct conditions. Some of the conditions never occur and can be left out, but those which do occur are still A LOT and making a switch to handle all cases is insane. I want to use 10 if statements instead of a huge switch. For this I know I should use flag bits, or rather flag bytes as the language is javascript and its easier to work with a 10 byte string with to represent a 10-bit binary. Now, my problem is, I don't know how to implement this. I have seen this used in APIs where multiple-selectable options are exposed with numbers 1, 2, 4, 8, ... , n^(n-1) which are decimal equivalents of 1, 10, 100, 1000, etc. in binary. So if we make call like bar = foo(7), bar will be an object with whatever options the three rightmost flags enable. I can convert the decimal number into binary and in each if statement check to see if the corresponding digit is set or not. But I wonder, is there a way to determine the n-th digit of a decimal number is zero or one in binary form, without actually doing the conversion?

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• Detect how many times the users have click the button...

  - by Jerry

  Hello guys. Just want to know if there is a way to detect how many times a user has clicked a button by using Jquery. My main application has a button that can add input fields depend on the users. He/She can adds as many input fields as they need. When they submit the form, The add page will add the data to my database. My current idea is to create a hidden input field and set the value to zero. Every time a user clicks the button, jquery would update the attribute of the hidden input field value. Then the "add page" can detect the loop time. See the example below. I just want to know if there are better practices to do this. Thanks for the helps. main page <form method='post' action='add.php'> //omit <input type="hidden" id="add" name="add" value="0"/> <input type="button" id="addMatch" value="Add a match"/> //omit </form> jquery $(document).ready(function(){ var a =0; $("#addMatch").live('click', function(){ $('#table').append("<input name='match"+a+"Name' />") //the input field will append //as many as the user wants. a++; $('#add').attr('value', 'a'); //pass the a value to hidden input field return false; }); Add Page $a=$_POST['a']; // for($k=0;$k<$a;$k++){ //get all matchName input field $matchName=$_POST['match'.$k.'Name']; //insert the match $updateQuery=mysql_query("INSERT INTO game (team) values('$matchName')",$connection); if(!$updateQuery){ DIE('mysql Error:'+mysql_error()); }

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• Avoiding a fork()/SIGCHLD race condition

  - by larry

  Please consider the following fork()/SIGCHLD pseudo-code. // main program excerpt for (;;) { if ( is_time_to_make_babies ) { pid = fork(); if (pid == -1) { /* fail */ } else if (pid == 0) { /* child stuff */ print "child started" exit } else { /* parent stuff */ print "parent forked new child ", pid children.add(pid); } } } // SIGCHLD handler sigchld_handler(signo) { while ( (pid = wait(status, WNOHANG)) > 0 ) { print "parent caught SIGCHLD from ", pid children.remove(pid); } } In the above example there's a race-condition. It's possible for "/* child stuff */" to finish before "/* parent stuff */" starts which can result in a child's pid being added to the list of children after it's exited, and never being removed. When the time comes for the app to close down, the parent will wait endlessly for the already-finished child to finish. One solution I can think of to counter this is to have two lists: started_children and finished_children. I'd add to started_children in the same place I'm adding to children now. But in the signal handler, instead of removing from children I'd add to finished_children. When the app closes down, the parent can simply wait until the difference between started_children and finished_children is zero. Another possible solution I can think of is using shared-memory, e.g. share the parent's list of children and let the children .add and .remove themselves? But I don't know too much about this. EDIT: Another possible solution, which was the first thing that came to mind, is to simply add a sleep(1) at the start of /* child stuff */ but that smells funny to me, which is why I left it out. I'm also not even sure it's a 100% fix. So, how would you correct this race-condition? And if there's a well-established recommended pattern for this, please let me know! Thanks.

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• What is the preferred way in C++ for converting a builtin type (int) to bool?

  - by Martin

  When programming with Visual C++, I think every developer is used to see the warning warning C4800: 'BOOL' : forcing value to bool 'true' or 'false' from time to time. The reason obviously is that BOOL is defined as int and directly assigning any of the built-in numerical types to bool is considered a bad idea. So my question is now, given any built-in numerical type (int, short, ...) that is to be interpreted as a boolean value, what is the/your preferred way of actually storing that value into a variable of type bool? Note: While mixing BOOL and bool is probably a bad idea, I think the problem will inevitably pop up whether on Windows or somewhere else, so I think this question is neither Visual-C++ nor Windows specific. Given int nBoolean; I prefer this style: bool b = nBoolean?true:false; The following might be alternatives: bool b = !!nBoolean; bool b = (nBoolean != 0); Is there a generally preferred way? Rationale? I should add: Since I only work with Visual-C++ I cannot really say if this is a VC++ specific question or if the same problem pops up with other compilers. So it would be interesting to specifically hear from g++ or users how they handle the int-bool case. Regarding Standard C++: As David Thornley notes in a comment, the C++ Standard does not require this behavior. In fact it seems to explicitly allow this, so one might consider this a VC++ weirdness. To quote the N3029 draft (which is what I have around atm.): 4.12 Boolean conversions [conv.bool] A prvalue of arithmetic, unscoped enumeration, pointer, or pointer to member type can be converted to a prvalue of type bool. A zero value, null pointer value, or null member pointer value is converted to false; any other value is converted to true. (...)

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• Module not found

  - by TMP

  Hi There! I've been working on this one quite a bit and haven't gotten any closer to a solution. I juut dug up my old copy of the WindowsHookLib again - It's available with source at http://www.codeproject.com/KB/DLL/WindowsHookLib.aspx. This library allows Global Windows Mouse/Keyboard/Clipboard Hooks, which is very useful. I'm trying to use the Mouse Hook in here to Capture Mouse-Motion (I could use a Timer that always polls Cursor.Position, but I plan on using more features of WindowsHookLib later). Code as follows: MouseHook mh = new MouseHook(); mh.InstallHook(); mh.MouseMove += new EventHandler<WindowsHookLib.MouseEventArgs>(mh_MouseMove); But on the call to InstallHook(), I get an Exception: "The specified Module could not be found". Strange. Searching, I found that someone thought this occurs because a DLL is not in a place included in the Windows PATH variable, and because placing it in system32 didn't help I went the whole hog and translated the thing to C# for inclusion directly in my project (I was curious how it works). However the error was obstinately persistent, so I dug a bit on this, and found the Code in the Library that is responsible: In InstallHook(), we have IntPtr hinstDLL = Marshal.GetHINSTANCE(Assembly.GetExecutingAssembly().GetModules()[0]); this._hMouseHook = UnsafeNativeMethods.SetWindowsHookEx(14, this._mouseProc, hinstDLL, 0); if (this._hMouseHook == IntPtr.Zero) { throw new MouseHookException(new Win32Exception(Marshal.GetLastWin32Error()).Message); } And this (after modification and recompile) tells me that what I'm really getting is a Windows error "ERROR_MOD_NOT_FOUND"! Now, Here I'm stumped. Didn't I just compile the Hook Library directly into my project? (UnsafeMethods.SetWindowsHookEx is just a DllImported Method from user32) Any Answers, or Prods in the right direction, or any hints, pointers or similar are very much appreciated!

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• Box2dx: Cancel force on a body?

  - by Rosarch

  I'm doing pathfinding where I use force to push body to waypoints. However, once they get close enough to the waypoint, I want to cancel out the force. How can I do this? Do I need to maintain separately all the forces I've applied to the body in question? I'm using Box2dx (C#/XNA). Here is my attempt, but it doesn't work at all: internal PathProgressionStatus MoveAlongPath(PositionUpdater posUpdater) { Vector2 nextGoal = posUpdater.Goals.Peek(); Vector2 currPos = posUpdater.Model.Body.Position; float distanceToNextGoal = Vector2.Distance(currPos, nextGoal); bool isAtGoal = distanceToNextGoal < PROXIMITY_THRESHOLD; Vector2 forceToApply = new Vector2(); double angleToGoal = Math.Atan2(nextGoal.Y - currPos.Y, nextGoal.X - currPos.X); forceToApply.X = (float)Math.Cos(angleToGoal) * posUpdater.Speed; forceToApply.Y = (float)Math.Sin(angleToGoal) * posUpdater.Speed; float rotation = (float)(angleToGoal + Math.PI / 2); posUpdater.Model.Body.Rotation = rotation; if (!isAtGoal) { posUpdater.Model.Body.ApplyForce(forceToApply, posUpdater.Model.Body.Position); posUpdater.forcedTowardsGoal = true; } if (isAtGoal) { // how can the body be stopped? posUpdater.forcedTowardsGoal = false; //posUpdater.Model.Body.SetLinearVelocity(new Vector2(0, 0)); //posUpdater.Model.Body.ApplyForce(-forceToApply, posUpdater.Model.Body.GetPosition()); posUpdater.Goals.Dequeue(); if (posUpdater.Goals.Count == 0) { return PathProgressionStatus.COMPLETE; } } UPDATE If I do keep track of how much force I've applied, it fails to account for other forces that may act on it. I could use reflection and set _force to zero directly, but that feels dirty.

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• Trouble with Unions in C program.

  - by Jordan S

  I am working on a C program that uses a Union. The union definition is in FILE_A header file and looks like this... // FILE_A.h**************************************************** xdata union { long position; char bytes[4]; }CurrentPosition; If I set the value of CurrentPosition.position in FILE_A.c and then call a function in FILE_B.c that uses the union, the data in the union is back to Zero. This is demonstrated below. // FILE_A.c**************************************************** int main.c(void) { CurrentPosition.position = 12345; SomeFunctionInFileB(); } // FILE_B.c**************************************************** void SomeFunctionInFileB(void) { // After the following lines execute I see all zeros in the flash memory. WriteByteToFlash(CurrentPosition.bytes[0]; WriteByteToFlash(CurrentPosition.bytes[1]; WriteByteToFlash(CurrentPosition.bytes[2]; WriteByteToFlash(CurrentPosition.bytes[3]; } Now, If I pass a long to SomeFunctionInFileB(long temp) and then store it into CurrentPosition.bytes within that function, and finally call WriteBytesToFlash(CurrentPosition.bytes[n]... it works just fine. It appears as though the CurrentPosition Union is not global. So I tried changing the union definition in the header file to include the extern keyword like this... extern xdata union { long position; char bytes[4]; }CurrentPosition; and then putting this in the source (.c) file... xdata union { long position; char bytes[4]; }CurrentPosition; but this causes a compile error that says: C:\SiLabs\Optec Programs\AgosRot\MotionControl.c:76: error 91: extern definition for 'CurrentPosition' mismatches with declaration. C:\SiLabs\Optec Programs\AgosRot\/MotionControl.h:48: error 177: previously defined here So what am I doing wrong? How do I make the union global?

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• String Length Evaluating Incorrectly

  - by Justin R.

  My coworker and I are debugging an issue in a WCF service he's working on where a string's length isn't being evaluated correctly. He is running this method to unit test a method in his WCF service: // Unit test method public void RemoveAppGroupTest() { string addGroup = "TestGroup"; string status = string.Empty; string message = string.Empty; appActiveDirectoryServicesClient.RemoveAppGroup("AOD", addGroup, ref status, ref message); } // Inside the WCF service [OperationBehavior(Impersonation = ImpersonationOption.Required)] public void RemoveAppGroup(string AppName, string GroupName, ref string Status, ref string Message) { string accessOnDemandDomain = "MyDomain"; RemoveAppGroupFromDomain(AppName, accessOnDemandDomain, GroupName, ref Status, ref Message); } public AppActiveDirectoryDomain(string AppName, string DomainName) { if (string.IsNullOrEmpty(AppName)) { throw new ArgumentNullException("AppName", "You must specify an application name"); } } We tried to step into the .NET source code to see what value string.IsNullOrEmpty was receiving, but the IDE printed this message when we attempted to evaluate the variable: 'Cannot obtain value of local or argument 'value' as it is not available at this instruction pointer, possibly because it has been optimized away.' (None of the projects involved have optimizations enabled). So, we decided to try explicitly setting the value of the variable inside the method itself, immediately before the length check -- but that didn't help. // Lets try this again. public AppActiveDirectoryDomain(string AppName, string DomainName) { // Explicitly set the value for testing purposes. AppName = "AOD"; if (AppName == null) { throw new ArgumentNullException("AppName", "You must specify an application name"); } if (AppName.Length == 0) { // This exception gets thrown, even though it obviously isn't a zero length string. throw new ArgumentNullException("AppName", "You must specify an application name"); } } We're really pulling our hair out on this one. Has anyone else experienced behavior like this? Any tips on debugging it?

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• Correlate GROUP BY and LEFT JOIN on multiple criteria to show latest record?

  - by Sunbird

  In a simple stock management database, quantity of new stock is added and shipped until quantity reaches zero. Each stock movement is assigned a reference, only the latest reference is used. In the example provided, the latest references are never shown, the stock ID's 1,4 should have references charlie, foxtrot respectively, but instead show alpha, delta. How can a GROUP BY and LEFT JOIN on multiple criteria be correlated to show the latest record? http://sqlfiddle.com/#!2/6bf37/107 CREATE TABLE stock ( id tinyint PRIMARY KEY, quantity int, parent_id tinyint ); CREATE TABLE stock_reference ( id tinyint PRIMARY KEY, stock_id tinyint, stock_reference_type_id tinyint, reference varchar(50) ); CREATE TABLE stock_reference_type ( id tinyint PRIMARY KEY, name varchar(50) ); INSERT INTO stock VALUES (1, 10, 1), (2, -5, 1), (3, -5, 1), (4, 20, 4), (5, -10, 4), (6, -5, 4); INSERT INTO stock_reference VALUES (1, 1, 1, 'Alpha'), (2, 2, 1, 'Beta'), (3, 3, 1, 'Charlie'), (4, 4, 1, 'Delta'), (5, 5, 1, 'Echo'), (6, 6, 1, 'Foxtrot'); INSERT INTO stock_reference_type VALUES (1, 'Customer Reference'); SELECT stock.id, SUM(stock.quantity) as quantity, customer.reference FROM stock LEFT JOIN stock_reference AS customer ON stock.id = customer.stock_id AND stock_reference_type_id = 1 GROUP BY stock.parent_id

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