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• Designing a state machine in C++

  - by skyeagle

  I have a little problem that involves modelling a state machine. I have managed to do a little bit of knowledge engineering and 'reverse engineer' a set of primitive deterministic rules that determine state as well as state transitions. I would like to know what the best practises are regarding: How to rigorously test my states and state transitions to make sure that the system cannot end up in an undeetermined state. How to enforce state transition requirements (for example, it should be impossible to go directly from stateFoo to StateFooBar, i.e. to embue each state with 'knowlege' about the states it can transition to. Ideally, I would like to use clean, pattern based design, with templates wherever possible. I do need somewhere to start though and I would be grateful for any pointers (no pun intended), that are sent my way.

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• How do chains work in Rainbow tables?

  - by James Moore

  Hello, I was wondering if should one could explain in detail how chains work in rainbow tables as though you would a complete novice but with relevance to programming. I understand that a chain is 16 bytes long. 8 bytes mark the starting point and 8 mark the end. I also understand that in the filename we have the chain length i.e. 2400. Which means that between our starting point and end point in just 16 bytes we have 2400 possible clear texts? What? How does that work? in those 16 bytes how do i get my 2400 hashes and clear texts or am i miss understanding this? Your help is greatly appreciated. Thanks P.s. I have read the related papers and googled this topic a fair bit. I think im just missing something important to make these gears turn.

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• Is there a Java API for creating a XHTML document?

  - by Bedwyr Humphreys

  I want to provide a simple XHTML representation of each of the resources in a REST web service. At the moment i'm using a StringBuilder to generate these which is both tedious and error prone. I don't see these changing after I publish the service but the process of coding each is a bit painful. Is there a XHTML document writer api? Should I just use an XML writer? Which one? Should I just roll my own basic HTML document class - doctype is the same each time, i just need to set the title, metatags and body content, most of which (but not all content) is already in HTML for the GETs. Or should I just use StringBuilder and stop whining? ;) Thanks.

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• Propertygrid changes not picked up when using menu shortcut for saving

  - by Ebbe

  I am trying to implement a simple windows forms application, where the user can edit instances of a simple Person class. The application makes use of the standard propertygrid, assigning instances of the Person class to the SelectedObject property of the propertygrid. When the user clicks the menu item Save, the application gets the selected item from the propertygrid and saves it. This works fine. However, if a shortcut such as ctrl+S, assigned to the menu item, is used for saving the SelectedObject of the propertygrid, then the changes are not picked up. It appears to be related to the fact that the properties of the Person object are not updated unless the field in the propertygrid looses focus, and the ctrl+S shortcut doesn’t take away focus from fields in the propertygrid. Other developers, such as Mark Gilbert, have solved this issue by forcing away focus from the propertygrid, but this seems to be a bit of a hack, especially since it would be nice to keep the focus at the field. The Visual Studio developers apparently got it right, but I haven’t figured out how.

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• PHP: require_once library -> failed to open stream

  - by matt

  I might be a bit confused and may need your help with this. I'm inside inc/newsletter.php and want to include a library that is inside lib/mailchimp-api-class How do I refer to this class file? I thought it should be … require_once '../lib/mailchimp-api-class/MCAPI.class.php'; However, this doesn't work …  Warning: require_once(../lib/mailchimp-api-class/MCAPI.class.php) [function.require- once]: failed to open stream: No such file or directory in /Users/myname/htdocs/wr/ wp-content/themes/mytheme/inc/newsletter.php on line 6

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• Efficiency of checking for null varbinary(max) column ?

  - by Moe Sisko

  Using SQL Server 2008. Example table : CREATE table dbo.blobtest (id int primary key not null, name nvarchar(200) not null, data varbinary(max) null) Example query : select id, name, cast((case when data is null then 0 else 1 end) as bit) as DataExists from dbo.blobtest Now, the query needs to return a "DataExists" column, that returns 0 if the blob is null, else 1. This all works fine, but I'm wondering how efficient it is. i.e. does SQL server need to read in the whole blob to its memory, or is there some optimization so that it just does enough reads to figure out if the blob is null or not ? (FWIW, the sp_tableoption "large value types out of row" option is set to OFF for this example).

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• Are we asking too much of transactional memory?

  - by Carl Seleborg

  I've been reading up a lot about transactional memory lately. There is a bit of hype around TM, so a lot of people are enthusiastic about it, and it does provide solutions for painful problems with locking, but you regularly also see complaints: You can't do I/O You have to write your atomic sections so they can run several times (be careful with your local variables!) Software transactional memory offers poor performance [Insert your pet peeve here] I understand these concerns: more often than not, you find articles about STMs that only run on some particular hardware that supports some really nifty atomic operation (like LL/SC), or it has to be supported by some imaginary compiler, or it requires that all accesses to memory be transactional, it introduces type constraints monad-style, etc. And above all: these are real problems. This has lead me to ask myself: what speaks against local use of transactional memory as a replacement for locks? Would this already bring enough value, or must transactional memory be used all over the place if used at all?

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• arbitrary typed data in django model

  - by Dmitry Shevchenko

  I have a model, say, Item. I want to store arbitrary amount of attributes on it, like title, description, release_date. And i want them to be not just strings but have python type, so string, boolean, datetime etc. What are my options here? EAV pattern with separate name-value table won't work because of the same DB type across all values. JSONField can probably help, but it doesn't know about datetime, for example. Also i was looking at PickeField, it fits perfectly, but i'm a bit concerned about performance.

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• What happens to date-times and booleans when using DbLinq with SQLite?

  - by DanM

  I've been thinking about using SQLite for my next project, but I'm concerned that it seems to lack proper datetime and bit data types. If I use DbLinq (or some other ORM) to generate C# classes, will the data types of the properties be "dumbed down"? Will date-time data be placed in properties of type string or double? Will boolean data be placed in properties of type int? If yes, what are the implications? I'm imaging a scenario where I need to write a whole second layer of classes with more specific data types and do a bunch of transformations and casts, but maybe it's not so bad. If you have any experience with this or a similar scenario, what are your "lessons learned"?

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• Memory footprint of a parsed XML file in Classic ASP?

  - by Pete Duncanson

  Anyone know of a way to find out the amount of memory/size of a XMLDocument once it has parsed a XML file? I've been doing "beer mat" calculations so far but have been asked to come up with some more legit numbers through monitoring some how. I need to create about 1500 XML files (via FreeThreadedXMl-DOM object), which verge between 3-9K in size and store them in Application vars but our SysAdmin is worried about us gobbling up too much memory. Other than the crude method of booting up a fresh IIS instance and then loading everything in and monitoring before and after memory usage in Task Manager I can't think of a way of doing it with a bit more accuracy.

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• Efficiently storing a list of prime numbers

  - by eSKay

  This article says: Every prime number can be expressed as 30k±1, 30k±7, 30k±11, or 30k±13 for some k. That means we can use eight bits per thirty numbers to store all the primes; a million primes can be compressed to 33,334 bytes "That means we can use eight bits per thirty numbers to store all the primes" This "eight bits per thirty numbers" would be for k, correct? But each k value will not necessarily take-up just one bit. Shouldn't it be eight k values instead? "a million primes can be compressed to 33,334 bytes" I am not sure how this is true. We need to indicate two things: VALUE of k (can be arbitrarily large) STATE from one of the eight states (-13,-11,-7,-1,1,7,11,13) I am not following how 33,334 bytes was arrived at, but I can say one thing: as the prime numbers become larger and larger in value, we will need more space to store the value of k. How, then can we fix it at 33,334 bytes?

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• What is your longest-held programming assumption that turned out to be incorrect?

  - by Demi

  I am doing some research into common errors and poor assumptions made by junior (and perhaps senior) software engineers. What was your longest-held poor assumption that was eventually corrected? For example: I at one point failed to understand that the size of an integer was not a standard (depends on the language and target). A bit embarrassing to state, but there it is. Be frank: what hard-held belief did you have, and roughly how long did you maintain the assumption? It can be about an algorithm, a language, a programming concept, testing, anything under the computer science domain.

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• C: How come an array's address is equal to its value?

  - by Alexandre

  In the following bit of code, pointer values and pointer addresses differ as expected. But array values and addresses don't! How can this be? Output my_array = 0022FF00 &my_array = 0022FF00 pointer_to_array = 0022FF00 &pointer_to_array = 0022FEFC ... #include <stdio.h> int main() { char my_array[100] = "some cool string"; printf("my_array = %p\n", my_array); printf("&my_array = %p\n", &my_array); char *pointer_to_array = my_array; printf("pointer_to_array = %p\n", pointer_to_array); printf("&pointer_to_array = %p\n", &pointer_to_array); printf("Press ENTER to continue...\n"); getchar(); return 0; }

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• How are vector patterns used in syntax-rules?

  - by Jay

  Hi, I have been writing Common Lisp macros, so Scheme's R5Rs macros are a bit unnatural to me. I think I got the idea, except that I don't understand how one would use vector patterns in syntax-rules: (define-syntax mac (syntax-rules () ((mac #(a b c d)) (let () (display a) (newline) (display d) (newline))))) (expand '(mac #(1 2 3 4))) ;; Chicken's expand-full extension shows macroexpansion => (let746 () (display747 1) (newline748) (display747 4) (newline748)) I don't see how I'd use a macro that requires its arguments to be written as a vector: (mac #(1 2 3 4)) => 1 4 Is there some kind of technique that uses those patterns? Thank you!

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• Embedding a YouTube Video Based on a PHP Variable

  - by jeffpm

  I have a website that I am creating for a class project. The website shows information about bands (which is stored in a mysql database). I am trying to spruce up the site a bit, and I would like to embed a YouTube video based on the band's name. Say, for instance, I have "Led Zeppelin" stored in my database. How can I take a PHP variable containing "Led Zeppelin", search YouTube using that variable, find a random video, and then embed that in the website? From the research I've done, it seems you can only embed YouTube videos if you know the exact address of the video. Thanks!

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• ::LookupAccountSid API Extremely Slow When Targetting x64 Platform (Windows 7)

  - by Chris

  During our application startup, we are making a call to ::LookupAccountSid(). When I build targetting the x86 architecture, this call is nearly instantaneous. However, when I target x64 (debug or release), the call generally takes over 40s to complete. Since this is occurring during application startup, the result is fairly unpleasant as it will appear to the user that the application is not launching. I am running Windows 7 Professional 64-bit on a Dell Studio XPS 16 (Intel Core i7 Q 720). Our application is a native Windows application written in C++. My compiler options (CCOPTS) and linker options (LINKOPTS) are as follows: CCOPTS = "/nologo /Gz /W3 /EHs /c /DWIN32 /D_MBCS /Ob1 /vmg /vmv /Zi /MD /DNDEBUG /DDV_BUILD_DLL /DIV_BUILD_DLL /DDVASSERT_EXCEPTION /Zc:wchar_t-" LINKOPTS = "/manifest:no /nologo /machine:X64 kernel32.lib user32.lib gdi32.lib winspool.lib comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib uuid.lib odbc32.lib odbccp32.lib /DEBUG /subsystem:windows /DLL" Any help would be greatly appreciated :D Thanks, --Chris

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• using BOSH/similar technique for existing application/system

  - by SnapConfig.com

  We've an existing system which connects to the the back end via http (apache/ssl) and polls the server for new messages, needless to say we have scalability issues. I'm researching on removing this polling and have come across BOSH/XMPP but I'm not sure how we should take the BOSH technique (using long lived http connection). I've seen there are few libraries available but the entire thing seems bloaty since we do not need buddy lists etc and simply want to notify the clients of available messages. The client is written in C/C++ and works across most OS so that is an important factor. The server is in Java. does bosh result in huge number of httpd processes? since it has to keep all the clients connected, what would be the limit on that. we are also planning to move to 64 bit JVM/apache what would be the max limit of clients in that case. any hints?

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• Garbage collecting at ColdFusion CFC

  - by Sergii

  Hello. I have a CFC as singletone object in Application scope. One of the methods is used for massive data processing and periodically causes the "Java heap space" errors. EDIT All variables inside the method are VAR-scoped, so they should not be kept in the object scope when invokation ended. It can be a bit dumb question for Java people, but I'd like to know how Java garbage collector cleans up the CFC methods memory: only when whole request ends, or maybe right after each method/function invokation? Second option is interesting because it can allow me to split my large method into the few, as one of the possible optimizations.

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• Tracking Viewing Habits of Website Visitors

  - by Leland

  Hello everyone! First time using this service for a question. I hope I am not asking something that has already been answered. I attempted to find an answer to my question with the search engine but i was unable to. My question is as follows: Using php, javascript, or anything actually, is it possible for me to track how my users are viewing the pages on my blog/website? Specifically, I want to track the time the user's browser spends reading specific sections of my content on the same page. For example, it would answer questions such as: How much time did someone spend reading the introduction to my article vs the conclusion? (located on the same page) Basically, tracking the "eyes" of a web visitor by looking at where the browser is currently scrolled down the page too. I'm sorry if i'm a bit noob! Thanks for any help with my problem you can provide to me! ^_^

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• Model-Controller cyclic reference/design problem

  - by jasamer

  I have a CoreData entity X, and controllers for this entity, XController. Now there's another entity, XGroup, containing a collection of X entities, and a XGroupController. Now the problem is that XGroupController needs to interact with XController, and it would be nice to just pass XGroupController a XGroup to observe, and then get the XControllers from the X entities. So the question is: is it a good idea to store a (weak, to avoid retain cycles) reference to a controller in an entity? It just feels a bit "wrong". Is there another design pattern for this?

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• set Image to Button

  - by Ivan

  Hello all, Could somebody help me a little bit with my issue below? When I call the myFunction, images which I want to set to buttons appear after 2 sec simultaneously, not one by one with delay of 0.5 sec. More info: generatedNumbers is array with four elements of NSNumber (4,1,3,2) buttons are set in UIView via IB and are tagged (1,2,3,4) -(IBAction) myFunction:(id) sender { int i, value; for (i = 0; i<[generatedNumbers count]; i++) { value = [[generatedNumbers objectAtIndex:i] intValue]; UIButton *button = (UIButton *)[self.view viewWithTag:i+1]; UIImage *img = [UIImage imageNamed:[NSString stringWithFormat:@"%d.png",value]]; [button setImage:img forState:UIControlStateNormal]; [img release]; usleep(500000); } }

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• What is resource-ref in web.xml used for?

  - by Denise

  Hi everyone, I'm just wondering when/why you would define a resource-ref element in your web.xml file? I would have thought that it would be defined in your web/app server using JNDI and then look up the JNDI reference in your Java code? The resource-ref definition seems a bit redundant to me and I can't think of when it might be useful. Example: <resource-ref> <description>Primary database</description> <res-ref-name>jdbc/primaryDB</res-ref-name> <res-type>javax.sql.DataSource</res-type> <res-auth>CONTAINER</res-auth> </resource-ref> Thanks!

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• Checking that all libs and dlls are from the same build?

  - by unknownthreat

  I am developing a program in VS C++ 2008. Right now, I have a huge list of dll and lib dependencies and I am adding some more. I worry that when I need to update a dependency by building from source (where I have to manually replace built dlls and libs in the correct place), if I accidently forgot to replace something or vice versa, I may run into a compile and/or runtime problem. And finding which place goes wrong can be a bit difficult. So is there some sort of program or method out there that can suit this task to ease building a program with many updating dependencies?

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• Convert svn repository to hg - authentication fails

  - by Kim L

  I'm trying to convert an existing svn repository to a mercurial repo with the following command hg convert <repository> <folder> My problem is that the svn repository's authentication is done with p12 certificates. I'm a bit lost on how to configure the certificate for the hg client so that I can pull the svn repo and convert it. Currently, if I try to run the above command, I get initializing destination hg-client repository abort: error: _ssl.c:480: error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure In other words, it cannot find the required certificate. The question is, how do I configure my hg client so that it can use my certificate? I'm using the command line hg client on linux.

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• Managing string resources in a Java application - singleton?

  - by Joe Attardi

  I seek a solution to the age-old problem of managing string resources. My current implementation seems to work well, but it depends on using singletons, and I know how often singletons can be maligned. The resource manager class has a singleton instance that handles lookups in the ResourceBundle, and you use it like so: MessageResources mr = MessageResources.getMessageResources(); // returns singleton instance ... JLabel helloLabel = new JLabel(mr.getString("label.hello")); Is this an appropriate use of a singleton? Is there some better, more universally used approach that I'm not aware of? I understand that this is probably a bit subjective, but any feedback I can get would be appreciated. I'd rather find out early on that I'm doing it wrong than later on in the process. Thanks!

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