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• A regex I have working in Ruby doesn't in PHP; what could the cause be?

  - by Alex R

  I do not know ruby. I am trying to use the following regex that was generated by ruby (namely by http://www.a-k-r.org/abnf/ running on the grammar given rfc1738) in php. It is failing to match in php, but it is successfully matching in ruby. Does anyone see what differences between php's and ruby's handling of regexes that might explain this discrepancy? http:\/\/(?:(?:(?:(?:[0-9a-z]|[0-9a-z](?:[\x2d0-9a-z]?)*[0-9a-z])\x2e)?)*(?:[a-z]|[a-z](?:[\x2d0-9a-z]?)*[0-9a-z])|\d+\x2e\d+\x2e\d+\x2e\d+)(?::\d+)?(?:\/(?:(?:[!\x24'-\x2e0-9_a-z]|%[0-9a-f][0-9a-f]|[&:;=@])?)*(?:(?:\/(?:(?:[!\x24'-\x2e0-9_a-z]|%[0-9a-f][0-9a-f]|[&:;=@])?)*)?)*(?:\x3f(?:(?:[!\x24'-\x2e0-9_a-z]|%[0-9a-f][0-9a-f]|[&:;=@])?)*)?)?/i Since you all love regexes so much, how about an alternate solution. Given the ABNF in an rfc, I want a way (in php) to check if an arbitrary string is in the grammar. APG fails to compile on a 64-bit system, VTC is not Free, and I have not found any other such tools. I would also prefer not to use a regex, but it's the closest I've come to success.

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• Python, Ruby, and C#: Use cases?

  - by thaorius

  Hi everyone. For as long as I can remember, I've always had a "favorite" language, which I use for most projects, until, for some particular reason, there is no way/point on using it for project XYZ. At that point, I find myself rusty (and sometimes outdated) on other languages+libraries+toolchains. So I decided, I would just use some languages/libs/tools for some things, and some for other, effectively keeping them fresh (there would obviously be exceptions, I'm not looking for an arbitrary rule set, but some guidelines). I wanted an opinion on what would be your standard use cases (new projects) for Python, Ruby, and C# (Mono). At the moment, I have time like this:Languages: C#: Mid-Large Sized Projects (mainly server-side daemons) High Performance (I hardly ever need C's performance, but Python just doesn't cut it) Relatively Low Footprint (vs the JVM, for example) Ruby: Web Applications Python: General Use Scripts (automation, system config, etc) Small-Mid Sized Projects Prototyping Web Applications About Ruby, I have no idea what to use it for that I can't use Python for (specially considering Python is more easily found installed by default). And I like both languages (though I'm really new to Ruby), which makes things even worse. As for C#, I have not used a Windows powered computer in a few years, I don't make things for Windows computers, and I don't mind waiting for Mono to implement some new features. That being said, I haven't found many people on the internet using it for server-sided *nix programming (not web related). I would appreciate some insight on this too. Thanks for your time.

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• Android - attach data to views

  - by Leonti

  Hi! In my application I create dynamic rows in table much as in this tutorial: http://en.androidwiki.com/wiki/Dynamically_adding_rows_to_TableLayout for(int i = startDay; i < startDay + 7; i++){ /* Create a TextView to be the row-content. */ TextView day = new TextView(this); day.setText(Integer.toString(i)); day.setLayoutParams(new LayoutParams( LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT)); day.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { Log.i("Listener: ", "Click"); } So now when I click on a TextView I can register click event, but how do I determine which TextView was clicked? Not just an object which I get with an event but data like which day number was clicked? Ideally I would want to have data attached to every view I create dynamically. Something like data() method in Javascript jQuery. Right now I can see only 1 way to solve this - while creating TextView add id with data and when clicked - get id back and parse it to get my data. But it strikes me as ugly approach. Is there a way to attach arbitrary data to android views?

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• KeyStore, HttpClient, and HTTPS: Can someone explain this code to me?

  - by stormin986

  I'm trying to understand what's going on in this code. KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType()); FileInputStream instream = new FileInputStream(new File("my.keystore")); try { trustStore.load(instream, "nopassword".toCharArray()); } finally { instream.close(); } SSLSocketFactory socketFactory = new SSLSocketFactory(trustStore); Scheme sch = new Scheme("https", socketFactory, 443); httpclient.getConnectionManager().getSchemeRegistry().register(sch); My Questions: trustStore.load(instream, "nopassword".toCharArray()); is doing what exactly? From reading the documentation load() will load KeyStore data from an input stream (which is just an empty file we just created), using some arbitrary "nopassword". Why not just load it with null as the InputStream parameter and an empty string as the password field? And then what is happening when this empty KeyStore is being passed to the SSLSocketFactory constructor? What's the result of such an operation? Or -- is this simply an example where in a real application you would have to actually put a reference to an existing keystore file / password?

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• File based caching under PHP

  - by azatoth

  I've been using http://code.google.com/p/phpbrowscap/ for a project, and it usually works nice. But a few times it's cache, which is plain php-files (see http://code.google.com/p/phpbrowscap/source/browse/trunk/browscap/Browscap.php#372 et. al.), has been "zeroed", i.e. the whole cache file has become large blob of NULLs. Instead of trying to find out why the files become NULL, I though perhaps it might be better to change the caching strategy to something more resilient. So I do wonder if you has any good ideas what would be a good solution; I've been looking at http://www.jongales.com/blog/2009/02/18/simple-file-based-php-cache-class/ and http://www.phpclasses.org/package/313-PHP-Cache-arbitrary-data-in-files-.html and I also though of just saving an serialized array to the file instead of pure php as it's been doing now; But I'm uncertain what approach I should target here. I'm grateful for any insight into this area of technology, as I know it's complex from a performance point of view.

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• C++ Exception Handling

  - by user1413793

  So I was writing some code and I noticed that apart from syntactical, type, and other compile-time errors, C++ does not throw any other exceptions. So I decided to test this out with a very trivial program: #include<iostream> int main() { std::count<<5/0<<std::endl; return 1 } When I compiled it using g++, g++ gave me a warning saying I was dividing by 0. But it still compiled the code. Then when I ran it, it printed some really large arbitrary number. When I want to know is, how does C++ deal with exceptions? Integer division by 0 should be a very trivial example of when an exception should be thrown and the program should terminate. Do I have to essentially enclose my entire program in a huge try block and then catch certain exceptions? I know in Python when an exception is thrown, the program will immediately terminate and print out the error. What does C++ do? Are there even runtime exceptions which stop execution and kill the program?

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• Are there pitfalls to using static class/event as an application message bus

  - by Doug Clutter

  I have a static generic class that helps me move events around with very little overhead: public static class MessageBus<T> where T : EventArgs { public static event EventHandler<T> MessageReceived; public static void SendMessage(object sender, T message) { if (MessageReceived != null) MessageReceived(sender, message); } } To create a system-wide message bus, I simply need to define an EventArgs class to pass around any arbitrary bits of information: class MyEventArgs : EventArgs { public string Message { get; set; } } Anywhere I'm interested in this event, I just wire up a handler: MessageBus<MyEventArgs>.MessageReceived += (s,e) => DoSomething(); Likewise, triggering the event is just as easy: MessageBus<MyEventArgs>.SendMessage(this, new MyEventArgs() {Message="hi mom"}); Using MessageBus and a custom EventArgs class lets me have an application wide message sink for a specific type of message. This comes in handy when you have several forms that, for example, display customer information and maybe a couple forms that update that information. None of the forms know about each other and none of them need to be wired to a static "super class". I have a couple questions: fxCop complains about using static methods with generics, but this is exactly what I'm after here. I want there to be exactly one MessageBus for each type of message handled. Using a static with a generic saves me from writing all the code that would maintain the list of MessageBus objects. Are the listening objects being kept "alive" via the MessageReceived event? For instance, perhaps I have this code in a Form.Load event: MessageBus<CustomerChangedEventArgs>.MessageReceived += (s,e) => DoReload(); When the Form is Closed, is the Form being retained in memory because MessageReceived has a reference to its DoReload method? Should I be removing the reference when the form closes: MessageBus<CustomerChangedEventArgs>.MessageReceived -= (s,e) => DoReload();

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• How to syntax-highlight XML in CDATA elements in Vim?

  - by Jim Hurne

  Vim's syntax highlighting for XML/XSL is great, except it turns off all syntax highlighting in CDATA regions. Is there a way to turn on syntax highlighting on in CDATA regions? At work, we have a lot of XSL code embedded within other XML documents. It would be great if I could get all of the goodness of XML editing for the embedded XSL code as well without having to temporarily remove the CDATA tags, or copy the CDATA content into a temporary file. Example: <root> <someTag><![CDATA[ <xsl:template match="/"> <!-- XSL content here --> </xsl:template> ]]> </someTag> </root> Note that the name of the tag (in the example, someTag) containing the content could be anything. We also sometimes embed Javascript inside CDATA regions as well, and again, it would be nice to turn on Javascript syntax highlighting for those regions. Again, the tag the data is embedded in is usually arbitrary and can be anything.

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• How to bind data from a view of type List<List<MyViewModelClass>>?

  - by Robert Koritnik

  I have a strong type view of type List<List<MyViewModelClass>> The outer list will always have two lists of List<MyViewModelClass>. For each of the two outer lists I want to display a group of checkboxes. Each set can have an arbitrary number of choices. My view model class looks similar to this: public class MyViewModelClass { public Area Area { get; set; } public bool IsGeneric { get; set; } public string Code { get; set; } public bool IsChecked { get; set; } } So the final view will look something like: Please select those that apply: First set of choices: x Option 1 x Option 2 x Option 3 etc. Second set of choices: x Second Option 1 x Second Option 2 x Second Option 3 x Second Option 4 etc. Checkboxes should display MyViewModelClass.Area.Name, and their value should be related to MyViewModelClass.Area.Id. Checked state is of course related to MyViewModel.IsChecked. Question I wonder how should I use Html.CheckBox() or Html.CheckBoxFor() helper to display my checkboxes? I have to get these values back to the server on a postback of course. If it makes things simpler, I could make a separate view model type like: public class Options { public List<MyViewModelClass> General { get; set; } public List<MyViewModelClass> Others { get; set; } }

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• Writing a VM - well formed bytecode?

  - by David Titarenco

  Hi, I'm writing a virtual machine in C just for fun. Lame, I know, but luckily I'm on SO so hopefully no one will make fun :) I wrote a really quick'n'dirty VM that reads lines of (my own) ASM and does stuff. Right now, I only have 3 instructions: add, jmp, end. All is well and it's actually pretty cool being able to feed lines (doing it something like write_line(&prog[1], "jmp", regA, regB, 0); and then running the program: while (machine.code_pointer <= BOUNDS && DONE != true) { run_line(&prog[machine.cp]); } I'm using an opcode lookup table (which may not be efficient but it's elegant) in C and everything seems to be working OK. My question is more of a "best practices" question but I do think there's a correct answer to it. I'm making the VM able to read binary files (storing bytes in unsigned char[]) and execute bytecode. My question is: is it the VM's job to make sure the bytecode is well formed or is it just the compiler's job to make sure the binary file it spits out is well formed? I only ask this because what would happen if someone would edit a binary file and screw stuff up (delete arbitrary parts of it, etc). Clearly, the program would be buggy and probably not functional. Is this even the VM's problem? I'm sure that people much smarter than me have figured out solutions to these problems, I'm just curious what they are!

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• Posting forms to a 404 + HttpHandler in IIS7: why has all POST data gone missing?

  - by Rahul

  OK, this might sound a bit confusing and complicated, so bear with me. We've written a framework that allows us to define friendly URLs. If you surf to any arbitrary URL, IIS tries to display a 404 error (or, in some cases, 403;14 or 405). However, IIS is set up so that anything directed to those specific errors is sent to an .aspx file. This allows us to implement an HttpHandler to handle the request and do stuff, which involves finding the an associated template and then executing whatever's associated with it. Now, this all works in IIS 5 and 6 and, to an extent, on IIS7 - but for one catch, which happens when you post a form. See, when you post a form to a non-existent URL, IIS says "ah, but that url doesn't exist" and throws a 405 "method not allowed" error. Since we're telling IIS to redirect those errors to our .aspx page and therefore handling it with our HttpHandler, this normally isn't a problem. But as of IIS7, all POST information has gone missing after being redirected to the 405. And so you can no longer do the most trivial of things involving forms. To solve this we've tried using a HttpModule, which preserves POST data but appears to not have an initialized Session at the right time (when it's needed). We also tried using a HttpModule for all requests, not just the missing requests that hit 404/403;14/405, but that means stuff like images, css, js etc are being handled by .NET code, which is terribly inefficient. Which brings me to the actual question: has anyone ever encountered this, and does anyone have any advice or know what to do to get things working again? So far someone has suggested using Microsoft's own URL Rewriting module. Would this help solve our problem? Thanks.

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• how to read in a list of custom configuration objects

  - by Johnny

  hi, I want to implement Craig Andera's custom XML configuration handler in a slightly different scenario. What I want to be able to do is to read in a list of arbitrary length of custom objects defined as: public class TextFileInfo { public string Name { get; set; } public string TextFilePath { get; set; } public string XmlFilePath { get; set; } } I managed to replicate Craig's solution for one custom object but what if I want several? Craig's deserialization code is: public class XmlSerializerSectionHandler : IConfigurationSectionHandler { public object Create(object parent, object configContext, XmlNode section) { XPathNavigator nav = section.CreateNavigator(); string typename = (string)nav.Evaluate("string(@type)"); Type t = Type.GetType(typename); XmlSerializer ser = new XmlSerializer(t); return ser.Deserialize(new XmlNodeReader(section)); } } I think I could do this if I could get Type t = Type.GetType("System.Collections.Generic.List<TextFileInfo>") to work but it throws Could not load type 'System.Collections.Generic.List<Test1.TextFileInfo>' from assembly 'Test1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.

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• Configuring an offscreen framebuffer fails the completeness test

  - by randallmeadows

  I'm trying to create an offscreen framebuffer into which I can do some OpenGL drawing, and then pull the bits out manually. I'm following the instructions here, but in step 4, status is 0 instead of GL_FRAMEBUFFER_COMPLETE_OES. If I insert a call go glGetError() after every gl call, it returns 0 (GL_NO_ERROR) every time. But, the values of variables do not change during the call. E.g., GLuint framebuffer; glGenFramebuffersOES(1, &framebuffer); glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer); the value of framebuffer does not get altered at all (even when I change it to some arbitrary value and re-execute). It's almost like the gl calls are not actually being made. I'm linking against OpenGLES framework, and get no compile, link, or run-time errors (or warnings). I'm at a loss as to what to do to fix this. I've tried continuing on with my drawing, but do not see the results I expect, but at this point I can't tell whether it's because of the above error, or the conversion to a UIImage.

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• using an alternative string quotation syntax in python

  - by Cawas

  Just wondering... I find using escape characters too distracting. I'd rather do something like this: print ^'Let's begin and end with sets of unlikely 2 chars and bingo!'^ Let's begin and end with sets of unlikely 2 chars and bingo! Note the ' inside the string, and how this syntax would have no issue with it, or whatever else inside for basically all cases. Too bad markdown can't properly colorize it (yet), so I decided to <pre> it. Sure, the ^ could be any other char, I'm not sure what would look/work better. That sounds good enough to me, tho. Probably some other language already have a similar solution. And, just maybe, Python already have such a feature and I overlooked it. I hope this is the case. But if it isn't, would it be too hard to, somehow, change Python's interpreter and be able to select an arbitrary (or even standardized) syntax for notating the strings? I realize there are many ways to change statements and the whole syntax in general by using pre-compilators, but this is far more specific. And going any of those routes is what I call "too hard". I'm not really needing to do this so, again, I'm just wondering.

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• What makes people think that NNs have more computational power than existing models?

  - by Bubba88

  I've read in Wikipedia that neural-network functions defined on a field of arbitrary real/rational numbers (along with algorithmic schemas, and the speculative `transrecursive' models) have more computational power than the computers we use today. Of course it was a page of russian wikipedia (ru.wikipedia.org) and that may be not properly proven, but that's not the only source of such.. rumors Now, the thing that I really do not understand is: How can a string-rewriting machine (NNs are exactly string-rewriting machines just as Turing machines are; only programming language is different) be more powerful than a universally capable U-machine? Yes, the descriptive instrument is really different, but the fact is that any function of such class can be (easily or not) turned to be a legal Turing-machine. Am I wrong? Do I miss something important? What is the cause of people saying that? I do know that the fenomenum of undecidability is widely accepted today (though not consistently proven according to what I've read), but I do not really see a smallest chance of NNs being able to solve that particular problem. Add-in: Not consistently proven according to what I've read - I meant that you might want to take a look at A. Zenkin's (russian mathematician) papers after mid-90-s where he persuasively postulates the wrongness of G. Cantor's concepts, including transfinite sets, uncountable sets, diagonalization method (method used in the proof of undecidability by Turing) and maybe others. Even Goedel's incompletness theorems were proven in right way in only 21-st century.. That's all just to plug Zenkin's work to the post cause I don't know how widespread that knowledge is in CS community so forgive me if that did look stupid. Thank you!

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• Which JavaScript or ASP.NET Charting Component/Tool/Library Will Work For This?

  - by Jason Bunting

  [Update]: Forgot to include ComponentArt... Hi, An interaction designer employed by the client I am currently working for produced some mock-ups, and now it is my job to determine the best way of implementing the charts included therein. After looking at the options I am aware of and was able to find doing some simple Google searches, I have narrowed it down to using either ComponentArt, Dundas Charts or Infragistics, simply because from what I can see of their demos, they have certain features I believe I will need to get things done. Here are the pictures from the mock-ups - ideally I need one piece of software that will cover all of these: This chart seems to be simple enough. Notice the arbitrary spacing between the years - not yet sure if this will be a sticking-point for the client or not. I don't know that I have ever seen a chart like this one - it combines the previous chart with some additional data. Here is the same chart, only this time illustrating what happens when a user mouses-over or clicks on an annotation within the chart. They want the nice styling within the pop-up, so the pop-up needs to be something like an iframe or similar. Any ideas or recommendations would be appreciated, I haven't used charting controls in years, so I am at a bit of a loss and the client wants an estimate soon. Thank you!

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• How do I programmatically insert rows into a Silverlight DataGrid without binding?

  - by j0rd4n

  I am using a common Silverlight DataGrid to display results from a search. The "schema" of the search can vary from query to query. To accommodate this, I am trying to dynamically populate the DataGrid. I can set explicitly set the columns, but I am having trouble setting the ItemSource. All of the MSDN examples set the ItemSource to a collection with a strong type (e.g. a Custom type with public properties matching the schema). The DataGrid then uses reflection to scour the strong type for public properties that will match the columns. Since my search results are dynamic, I cannot create a strong type to represent what comes back. Can I not just give the DataGrid an arbitrary list of objects so long as the number of objects in each list matches the number of columns? Anyone know if this is possible? I would like to do something similar to this: List<List<object>> myResults = <voodoo that populates the result list> myDataGrid.ItemsSource = myResults;

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• Is there a safe / standard way to manage unstructured memory in C++?

  - by andand

  I'm building a toy VM that requires a block of memory for storing and accessing data elements of different types and of different sizes. I've done this by writing a wrapper class around a uint8_t[] data block of the needed size. That class has some template methods to write / read typed data elements to / from arbitrary locations in the memory block, both of which check to make certain the bounds aren't violated. These methods use memmove in what I hope is a more or less safe manner. That said, while I am willing to press on in this direction, I've got to believe that other with more expertise have been here before and might be willing to share their wisdom. In particular: 1) Is there a class in one of the C++ standards (past, present, future) that has been defined to perform a function similar to what I have outlined above? 2) If not, is there a (preferably free as in beer) library out there that does? 3) Short of that, besides bounds checking and the inevitable issue of writing one type to a memory location and reading a different from that location, are there other issues I should be aware of? Thanks.-&&

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• Hibernate Query for a List of Objects that matches a List of Objects' ids

  - by sal

  Given a classes Foo, Bar which have hibernate mappings to tables Foo, A, B and C public class Foo { Integer aid; Integer bid; Integer cid; ...; } public class Bar { A a; B b; C c; ...; } I build a List fooList of an arbitrary size and I would like to use hibernate to fetch List where the resulting list will look something like this: Bar[1] = [X1,Y2,ZA,...] Bar[2] = [X1,Y2,ZB,...] Bar[3] = [X1,Y2,ZC,...] Bar[4] = [X1,Y3,ZD,...] Bar[5] = [X2,Y4,ZE,...] Bar[6] = [X2,Y4,ZF,...] Bar[7] = [X2,Y5,ZG,...] Bar[8] = ... Where each Xi, Yi and Zi represents a unique object. I know I can iterate fooList and fetch each List and call barList.addAll(...) to build the result list with something like this: List<bar> barList.addAll(s.createQuery("from Bar bar where bar.aid = :aid and ... ") .setEntity("aid", foo.getAid()) .setEntity("bid", foo.getBid()) .setEntity("cid", foo.getCid()) .list(); ); Is there any easier way, ideally one that makes better use of hibernate and make a minimal number of database calls? Am I missing something? Is hibernate not the right tool for this?

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• Most efficient way to update attribute of one instance

  - by Begbie00

  Hi all - I'm creating an arbitrary number of instances (using for loops and ranges). At some event in the future, I need to change an attribute for only one of the instances. What's the best way to do this? Right now, I'm doing the following: 1) Manage the instances in a list. 2) Iterate through the list to find a key value. 3) Once I find the right object within the list (i.e. key value = value I'm looking for), change whatever attribute I need to change. for Instance within ListofInstances: if Instance.KeyValue == SearchValue: Instance.AttributeToChange = 10 This feels really inefficient: I'm basically iterating over the entire list of instances, even through I only need to change an attribute in one of them. Should I be storing the Instance references in a structure more suitable for random access (e.g. dictionary with KeyValue as the dictionary key?) Is a dictionary any more efficient in this case? Should I be using something else? Thanks, Mike

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• How can I get the rank of rows relative to total number of rows based on a field?

  - by Arms

  I have a scores table that has two fields: user_id score I'm fetching specific rows that match a list of user_id's. How can I determine a rank for each row relative to the total number of rows, based on score? The rows in the result set are not necessarily sequential (the scores will vary widely from one row to the next). I'm not sure if this matters, but user_id is a unique field. Edit @Greelmo I'm already ordering the rows. If I fetch 15 rows, I don't want the rank to be 1-15. I need it to be the position of that row compared against the entire table by the score property. So if I have 200 rows, one row's rank may be 3 and another may be 179 (these are arbitrary #'s for example only). Edit 2 I'm having some luck with this query, but I actually want to avoid ties SELECT s.score , s.created_at , u.name , u.location , u.icon_id , u.photo , (SELECT COUNT(*) + 1 FROM scores WHERE score > s.score) AS rank FROM scores s LEFT JOIN users u ON u.uID = s.user_id ORDER BY s.score DESC , s.created_at DESC LIMIT 15 If two or more rows have the same score, I want the latest one (or earliest - I don't care) to be ranked higher. I tried modifying the subquery with AND id > s.id but that ended up giving me an unexpected result set and different ties.

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• Hashing the state of a complex object in .NET

  - by Jan

  Some background information: I am working on a C#/WPF application, which basically is about creating, editing, saving and loading some data model. The data model contains of a hierarchy of various objects. There is a "root" object of class A, which has a list of objects of class B, which each has a list of objects of class C, etc. Around 30 classes involved in total. Now my problem is that I want to prompt the user with the usual "you have unsaved changes, save?" dialog, if he tries to exit the program. But how do I know if the data in current loaded model is actually changed? There is of course ways to solve this, like e.g. reloading the model from file and compare against the one in memory value by value or make every UI control set a flag indicating the model has been changed. Now instead, I want to create a hash value based on the model state on load and generate a new value when the user tries to exit, and compare those two. Now the question: So inspired of that, I was wondering if there exist some way to generate a hash value from the (value)state of some arbitrary complex object? Preferably in a generic way, e.g. no need to apply attributes to each involved class/field. One idea could be to use some of .NET's serialization functionality (assuming it will work out-of-the-box in this case) and apply a hash function to the content of the resulting file. However, I guess there exist some more suitable approach. Thanks in advance.

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• Why can't decimal numbers be represented exactly in binary?

  - by Barry Brown

  There have been several questions posted to SO about floating-point representation. For example, the decimal number 0.1 doesn't have an exact binary representation, so it's dangerous to use the == operator to compare it to another floating-point number. I understand the principles behind floating-point representation. What I don't understand is why, from a mathematical perspective, are the numbers to the right of the decimal point any more "special" that the ones to the left? For example, the number 61.0 has an exact binary representation because the integral portion of any number is always exact. But the number 6.10 is not exact. All I did was move the decimal one place and suddenly I've gone from Exactopia to Inexactville. Mathematically, there should be no intrinsic difference between the two numbers -- they're just numbers. By contrast, if I move the decimal one place in the other direction to produce the number 610, I'm still in Exactopia. I can keep going in that direction (6100, 610000000, 610000000000000) and they're still exact, exact, exact. But as soon as the decimal crosses some threshold, the numbers are no longer exact. What's going on? Edit: to clarify, I want to stay away from discussion about industry-standard representations, such as IEEE, and stick with what I believe is the mathematically "pure" way. In base 10, the positional values are: ... 1000 100 10 1 1/10 1/100 ... In binary, they would be: ... 8 4 2 1 1/2 1/4 1/8 ... There are also no arbitrary limits placed on these numbers. The positions increase indefinitely to the left and to the right.

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• Using PHP as template language

  - by Kunal

  I wrote up this quick class to do templating via PHP -- I was wondering if this is easily exploitable if I were ever to open up templating to users (not the immediate plan, but thinking down the road). class Template { private $allowed_methods = array( 'if', 'switch', 'foreach', 'for', 'while' ); private function secure_code($template_code) { $php_section_pattern = '/\<\?(.*?)\?\>/'; $php_method_pattern = '/([a-zA-Z0-9_]+)[\s]*\(/'; preg_match_all($php_section_pattern, $template_code, $matches); foreach (array_unique($matches[1]) as $index => $code_chunk) { preg_match_all($php_method_pattern, $code_chunk, $sub_matches); $code_allowed = true; foreach ($sub_matches[1] as $method_name) { if (!in_array($method_name, $this->allowed_methods)) { $code_allowed = false; break; } } if (!$code_allowed) { $template_code = str_replace($matches[0][$index], '', $template_code); } } return $template_code; } public function render($template_code, $params) { extract($params); ob_start(); eval('?>'.$this->secure_code($template_code).'<?php '); $result = ob_get_contents(); ob_end_clean(); return $result; } } Example usage: $template_code = '<?= $title ?><? foreach ($photos as $photo): ?><img src="<?= $photo ?>"><? endforeach ?>'; $params = array('title' => 'My Title', 'photos' => array('img1.jpg', 'img2.jpg')); $template = new Template; echo $template->render($template_code, $params); The idea here is that I'd store the templates (PHP code) in the database, and then run it through the class which uses regular expressions to only allow permitted methods (if, for, etc.). Anyone see an obvious way to exploit this and run arbitrary PHP? If so, I'll probably go the more standard route of a templating language such as Smarty...

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• Storing float numbers as strings in android database

  - by sandis

  So I have an app where I put arbitrary strings in a database and later extract them like this: Cursor DBresult = myDatabase.query(false, Constant.DATABASE_NOTES_TABLE_NAME, new String[] {"myStuff"}, where, null, null, null, null, null); DBresult.getString(0); This works fine in all cases except for when the string looks like a float number, for example "221.123123123". After saving it to the database I can extract the database to my computer and look inside it with a DB-viewer, and the saved number is correct. However, when using cursor.getString() the string "221.123" is returned. I cant for the life of me understand how I can prevent this. I guess I could do a cursor.getDouble() on every single string to see if this gives a better result, but that feels sooo ugly and inefficient. Any suggestions? Cheers, edit: I just made a small test program. This program prints "result: 123.123", when I would like it to print "result: 123.123123123" SQLiteDatabase database = openOrCreateDatabase("databas", Context.MODE_PRIVATE, null); database.execSQL("create table if not exists tabell (nyckel string primary key);"); ContentValues value = new ContentValues(); value.put("nyckel", "123.123123123"); database.insert("tabell", null, value); Cursor result = database.query("tabell", new String[]{"nyckel"}, null, null, null, null, null); result.moveToFirst(); Log.d("TAG","result: " + result.getString(0));

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