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• database design - empty fields

  - by imanc

  Hey, I am currently debating an issue with a guy on my dev team. He believes that empty fields are bad news. For instance, if we have a customer details table that stores data for customers from different countries, and each country has a slightly different address configuration - plus 1-2 extra fields, e.g. French customer details may also store details for entry code, and floor/level plus title fields (madamme, etc.). South Africa would have a security number. And so on. Given that we're talking about minor variances my idea is to put all of the fields into the table and use what is needed on each form. My colleague believes we should have a separate table with extra data. E.g. customer_info_fr. But this seams to totally defeat the purpose of a combined table in the first place. His argument is that empty fields / columns is bad - but I'm struggling to find justification in terms of database design principles for or against this argument and preferred solutions. Another option is a separate mini EAV table that stores extra data with parent_id, key, val fields. Or to serialise extra data into an extra_data column in the main customer_data table. I think I am confused because what I'm discussing is not covered by 3NF which is what I would typically use as a reference for how to structure data. So my question specifically: - if you have slight variances in data for each record (1-2 different fields for instance) what is the best way to proceed?

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• Java, Massive message processing with queue manager (trading)

  - by Ronny

  Hello, I would like to design a simple application (without j2ee and jms) that can process massive amount of messages (like in trading systems) I have created a service that can receive messages and place them in a queue to so that the system won't stuck when overloaded. Then I created a service (QueueService) that wraps the queue and has a pop method that pops out a message from the queue and if there is no messages returns null, this method is marked as "synchronized" for the next step. I have created a class that knows how process the message (MessageHandler) and another class that can "listen" for messages in a new thread (MessageListener). The thread has a "while(true)" and all the time tries to pop a message. If a message was returned, the thread calls the MessageHandler class and when it's done, he will ask for another message. Now, I have configured the application to open 10 MessageListener to allow multi message processing. I have now 10 threads that all time are in a loop. Is that a good design?? Can anyone reference me to some books or sites how to handle such scenario?? Thanks, Ronny

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• Serializability of enum-like class

  - by callisto

  I need to access an enum through a webservice. As a webservice allocates 0 based integers to an enumeration (ignoring preset values in enum definition), I built the following: public class StatusType { public StatusVal Pending { get { return new StatusVal( 1, "Pending"); } } public StatusVal Authorised { get { return new StatusVal(2, "Authorised"); } } public StatusVal Rejected { get { return new StatusVal(3, "Rejected"); } } public StatusVal Sent { get { return new StatusVal(4, "Sent"); } } public StatusVal InActive { get { return new StatusVal(5, "InActive"); } } public List<StatusVal> StatusList() { List<StatusVal> returnVal = new List<StatusVal>(); StatusType sv = new StatusType(); returnVal.Add(sv.Pending); returnVal.Add(sv.Authorised); returnVal.Add(sv.Rejected); returnVal.Add(sv.Sent); returnVal.Add(sv.InActive); return returnVal; } } public class StatusVal { public StatusVal(int a, string b) { this.ID = a; this.Name = b; } public int ID { get; set; } public string Name { get; set; } } I then get the list of StatusVal with the following webmethod: [WebMethod] public List<ATBusiness.StatusVal> GetStatus() { ATBusiness.StatusType a = new ATBusiness.StatusType(); return a.StatusList(); } I cannot however use this webmethod as referring it, I get the error: StatusVal cannot be serialized because it does not have a parameterless constructor. I don't quite understand: should I pass params into the StatusValue type defined as the WebMethod's return Type? I need this to return a list of StatusVals as per the StatusList() method.

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• `enable_shared_from_this` has a non-virtual destructor

  - by Shtééf

  I have a pet project with which I experiment with new features of the upcoming C++0x standard. While I have experience with C, I'm fairly new to C++. To train myself into best practices, (besides reading a lot), I have enabled some strict compiler parameters (using GCC 4.4.1): -std=c++0x -Werror -Wall -Winline -Weffc++ -pedantic-errors This has worked fine for me. Until now, I have been able to resolve all obstacles. However, I have a need for enable_shared_from_this, and this is causing me problems. I get the following warning (error, in my case) when compiling my code (probably triggered by -Weffc++): base class ‘class std::enable_shared_from_this<Package>’ has a non-virtual destructor So basically, I'm a bit bugged by this implementation of enable_shared_from_this, because: A destructor of a class that is intended for subclassing should always be virtual, IMHO. The destructor is empty, why have it at all? I can't imagine anyone would want to delete their instance by reference to enable_shared_from_this. But I'm looking for ways to deal with this, so my question is really, is there a proper way to deal with this? And: am I correct in thinking that this destructor is bogus, or is there a real purpose to it?

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• Bizzare results when running two Visual Studio Express C++ 2008 solutions

  - by Jamie Keeling

  This is a follow on from my previous question although this is about something else. I've been having a problem where for some reason my message that I pass from one process to another only displays the first letter, in this case "M". My application based on a MSDN sample so to make sure I hadn't missed something I create a seperate solution, added the MSDN sample (Without any changes for my needs) and unsuprisingly it works fine. Now for the weird bit, when I run the MSDN sample running (As in debugging) and have my own application running, the text prints out fine without any problems. The second I run my on it's own without the original MSDN sample being open it fails to work and only shows an "M". I've looked in the debugger and don't seem to notice anything suspicious (It's a slightly dated picture, I've fixed the data type inconsistency). Can anyone provide a solution as to this? I've never encountered anything like this before. To look at my source code it's easier to just look at the link I posted at the top of the question, there's no point in me posting it twice. Thank you for any help.

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• Square Brackets in Python Regular Expressions (re.sub)

  - by user1479984

  I'm migrating wiki pages from the FlexWiki engine to the FOSwiki engine using Python regular expressions to handle the differences between the two engines' markup languages. The FlexWiki markup and the FOSwiki markup, for reference. Most of the conversion works very well, except when I try to convert the renamed links. Both wikis support renamed links in their markup. For example, Flexwiki uses: "Link To Wikipedia":[http://www.wikipedia.org/] FOSwiki uses: [[http://www.wikipedia.org/][Link To Wikipedia]] both of which produce something that looks like I'm using the regular expression renameLink = re.compile ("\"(?P<linkName>[^\"]+)\":\[(?P<linkTarget>[^\[\]]+)\]") to parse out the link elements from the FlexWiki markup, which after running through something like "Link Name":[LinkTarget] is reliably producing groups <linkName> = Link Name <linkTarget = LinkTarget My issue occurs when I try to use re.sub to insert the parsed content into the FOSwiki markup. My experience with regular expressions isn't anything to write home about, but I'm under the impression that, given the groups <linkName> = Link Name <linkTarget = LinkTarget a line like line = renameLink.sub ( "[[\g<linkTarget>][\g<linkName>]]" , line ) should produce [[LinkTarget][Link Name]] However, in the output to the text files I'm getting [[LinkTarget [[Link Name]] which breaks the renamed links. After a little bit of fiddling I managed a workaround, where line = renameLink.sub ( "[[\g<linkTarget>][ [\g<linkName>]]" , line ) produces [[LinkTarget][ [[Link Name]] which, when displayed in FOSwiki looks like <[[Link Name> <--- Which WORKS, but isn't very pretty. I've also tried line = renameLink.sub ( "[[\g<linkTarget>]" + "[\g<linkName>]]" , line ) which is producing [[linkTarget [[linkName]] There are probably thousands of instances of these renamed links in the pages I'm trying to convert, so fixing it by hand isn't any good. For the record I've run the script under Python 2.5.4 and Python 2.7.3, and gotten the same results. Am I missing something really obvious with the syntax? Or is there an easy workaround?

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• recvfrom returns invalid argument when *from* is passed

  - by Aditya Sehgal

  I am currently writing a small UDP server program in linux. The UDP server will receive packets from two different peers and will perform different operations based on from which peer it received the packet. I am trying to determine the source from where I receive the packet. However, when select returns and recvfrom is called, it returns with an error of Invalid Argument. If I pass NULL as the second last arguments, recvfrom succeeds. I have tried declaring fromAddr as struct sockaddr_storage, struct sockaddr_in, struct sockaddr without any success. Is their something wrong with this code? Is this the correct way to determine the source of the packet? The code snippet follows. ` /*TODO : update for TCP. use recv */ if((pkInfo->rcvLen=recvfrom(psInfo->sockFd, pkInfo->buffer, MAX_PKTSZ, 0, /* (struct sockaddr*)&fromAddr,*/ NULL, &(addrLen) )) < 0) { perror("RecvFrom failed\n"); } else { /*Apply Filter */ #if 0 struct sockaddr_in* tmpAddr; tmpAddr = (struct sockaddr_in* )&fromAddr; printf("Received Msg From %s\n",inet_ntoa(tmpAddr->sin_addr)); #endif printf("Packet Received of len = %d\n",pkInfo->rcvLen); } `

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• Help dealing with data dependency between two registration forms

  - by franko75

  I have a tricky issue here with a registration of both a user and his/her pet. Both the user and the pet are treated as separate entities and both require separate registration forms. However, the user's pet has to be linked to the user via a foreign key in the database. The process is basically that when a new user joins the site, firstly they register their pet, then they register themselves. The reason for this order is to check their pet's eligibility for the site (there are some criteria to be met) first, instead of getting the user to sign up only to then find out their pet is ineligible. It is this ordering of the form submissions which is causing me a bit of a headache, as follows... The site is being developed with an MVC framework, and the User registration process is managed via a method in a User_form controller, while the pet registration process is managed via a method in the Pet_form controller. The pet registration form happens first, and the pet data can be saved without the owner_id at this stage, with the user id possibly being added (e.g by retrieving pet's id from session) following user registration. However, doing it this way could potentially result in redundant data, where pet records would be created in the database, but if the user doesn't actually register themselves too, then the pets will be ownerless records in the DB. Other option is to serialize the new pet's data at the pet registration stage, don't save it to the DB until the user fills out their registration form. Once the user is created, i can pass serialised data AND the owner_id to a method in the Pet Model which can update the DB. However, I also need to set the newly created $pet to $this-pet which I then access for a sequence of other related forms. Should I just set the session variable in the model method? Then in the Pet controller constructor, do a check for pet stored in session, if yes, assign to $this-pet... If this makes any sense to anybody and you have some advice, i'd be grateful to hear it!

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• What library can I use to do simple, lightweight message passing?

  - by Mike

  I will be starting a project which requires communication between distributed nodes(the project is in C++). I need a lightweight message passing library to pass very simple messages(basically just strings of text) between nodes. The library must have the following characteristics: No external setup required. I need to be able to get everything up-and-running in my code - I don't want to require the user to install any packages or edit any configuration files(other than a list of IP addresses and ports to connect to). The underlying protocol which the library uses must be TCP(or if it is UDP, the library must guarantee the eventual receipt of the message). The library must be able to send and receive arbitrarily large strings(think up to 3GB+). The library needn't support any security mechanisms, fault tolerance, or encryption - I just need it to be fast, simple, and easy to use. I've considered MPI, but concluded it would require too much setup on the user's machine for my project. What library would you recommend for such a project? I would roll my own, but due to time constraints, I don't think that will be feasible.

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• ListView - Index and Position Behavior upon restart()

  - by tunneling

  I am using a ListView with an ArrayAdapter that holds objects. When I select an item, I am capturing the position and index of the selected item. If I scroll down prior to selection, the position and index represent the location of the item in the list. Selecting that items takes me to another activity. When I use the back button to return to the list, it seems that the ListView get's a new position and index for the visible items. As a result, I can't figure out how to reference the selected item during the restart() of the ListView Activity. I have tried to caputure position and index, but as I've said, they change upon returning to the Activity. Is my understanding of the ListView "redraw" correct? Does it renumber my items based on what's visible? -When in the life cycle is getView() called? Is there a way to force an update to the ListView so that my caputured index still points to the same object? Thanks, Jason

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• php array split

  - by Rahul Mehta

  I am passing the space separated value to in input and split this in operation and make an array. givecard 442 ashutosh2 Y But i want to pass the message in this string and want to split as complete message in operation or output. givecard 442 ashutosh2 Y hi how are you if i split this line than i get the result is Array ( [0] => givecard [1] => 442 [2] => ashutosh2 [3] => Y [4] => hi [5] => how [6] => are [7] => you ) But i want like this Array ( [0] => givecard [1] => 442 [2] => ashutosh2 [3] => Y [4] => hi how are you ) as here hi how are you i want to extract as complete one message in a variable . How can i achieve this

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• Handling Apache Thrift list/map Return Types in C++

  - by initzero

  First off, I'll say I'm not the most competent C++ programmer, but I'm learning, and enjoying the power of Thrift. I've implemented a Thrift Service with some basic functions that return void, i32, and list. I'm using a Python client controlled by a Django web app to make RPC calls and it works pretty well. The generated code is pretty straight forward, except for list returns: namespace cpp Remote enum N_PROTO { N_TCP, N_UDP, N_ANY } service Rcon { i32 ping() i32 KillFlows() i32 RestartDispatch() i32 PrintActiveFlows() i32 PrintActiveListeners(1:i32 proto) list<string> ListAllFlows() } The generated signatures from Rcon.h: int32_t ping(); int32_t KillFlows(); int32_t RestartDispatch(); int32_t PrintActiveFlows(); int32_t PrintActiveListeners(const int32_t proto); int64_t ListenerBytesReceived(const int32_t id); void ListAllFlows(std::vector<std::string> & _return); As you see, the ListAllFlows() function generated takes a reference to a vector of strings. I guess I expect it to return a vector of strings as laid out in the .thrift description. I'm wondering if I am meant to provide the function a vector of strings to modify and then Thrift will handle returning it to my client despite the function returning void. I can find absolutely no resources or example usages of Thrift list< types in C++. Any guidance would be appreciated.

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• Specifying SOAP Headers for a Zend_Soap Service

  - by Stephen

  I have a generally straight forward web service that I've written (converting code to ZF from a Java implementation of the same service and trying to maintain the same wsdl structure as much as possible). The service loads a PHP class, rather than individual functions. The PHP class contains three different functions within it. Everything seems to be working just fine, except that I can't seem to figure out how to specify that a given function parameter should be passed as a SOAP header. I've not seen any mention of SOAP headers in the Server context, only how to pass header parameters with a client to a server. In addition to the standard parameters for the function that would be sent in the SOAP body and detailed in the docblock, I would like to specify two parameters (a username and password) that would be sent in a SOAP header. I have to assume this is possible, but haven't been able to find anything online, nor have I had any responses to a similar post on Zend's forum. Is there something that can be added in the docblock area to specify a parameter as a header (maybe in a similar fashion to using WebParam?)? Any suggestions/examples on how to get this accomplished would be greatly appreciated!

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• Saving tags into a database table in CakePHP

  - by Cameron

  I have the following setup for my CakePHP app: Posts id title content Topics id title Topic_Posts id topic_id post_id So basically I have a table of Topics (tags) that are all unique and have an id. And then they can be attached to post using the Topic_Posts join table. When a user creates a new post they will fill in the topics by typing them in to a textarea separated by a comma which will then save these into the Topics table if they do not already exist and then save the references into the Topic_posts table. I have the models set up like so: Post model: class Post extends AppModel { public $name = 'Post'; public $hasAndBelongsToMany = array( 'Topic' => array('with' => 'TopicPost') ); } Topic model: class Topic extends AppModel { public $hasMany = array( 'TopicPost' ); } TopicPost model: class TopicPost extends AppModel { public $belongsTo = array( 'Topic', 'Post' ); } And for the New post method I have this so far: public function add() { if ($this->request->is('post')) { //$this->Post->create(); if ($this->Post->saveAll($this->request->data)) { // Redirect the user to the newly created post (pass the slug for performance) $this->redirect(array('controller'=>'posts','action'=>'view','id'=>$this->Post->id)); } else { $this->Session->setFlash('Server broke!'); } } } As you can see I have used saveAll but how do I go about dealing with the Topic data?

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• SIlverlight Navigate: how does it work? How would you implement in f# w/o VS wizards and helpers?

  - by akaphenom

  After a nights sleep the problem can be stated more accurately as I have a 100% f# / silverlight implementation and am looking to use the built in Navigation components. C# creates page.xaml and page.xaml.cs um - ok; but what is the relationship at a fundamental level? How would I go about doing this in f#? The applcuation is loaded in the default module, and I pull the XAML in and reference it from the application object. Do I need to create instances / references to the pages from within the application object? Or set up some other page management object with the proper name value pairs? When all the Help of VS is stripped away - what are we left with? original post (for those who may be reading replies) I have a 100% silverlight 3.0 / f# 2.0 application I am wrapping my brain around. I have the base application loading correctly - and now I want to add the naigation controls to it. My page is stored as an embedded resource - but the Frame.Navigate takes a URI. I know what I have is wrong but here it is: let nav : Frame = mainGrid ? mainFrame let url = "/page1.xaml" let uri = new System.Uri(url, System.UriKind.Relative) ; nav.Navigate uri Any thoughts?

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• Task Queue stopped working

  - by pocoa

  I was playing with Goole App Engine Task Queue API to learn how to use it. But I couldn't make it trigger locally. My application is working like a charm when I upload to Google servers. But it doesn't trigger locally. All I see from the admin is the list of the tasks. But when their ETA comes, they just pass it. It's like they runs but they fails and waiting for the retries. But I can't see these events on command line. When I try to click "Run" on admin panel, it runs successfuly and I can see these requests from the command line. I'm using App Engine SDK 1.3.4 on Linux with google-app-engine-django. I'm trying to find the problem from 3 hours now and I couldn't find it. It's also very hard to debug GAE applications. Because debug messages do not appear on console screen. Thanks.

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• Not getting key value from Identity column back after inserting new row with SubSonic ActiveRecord

  - by mikedevenney

  I'm sure I'm missing the obvious answer here, but could use a hand. I'm new to SubSonic and using version 3. I've got myself to the point of being able to query and insert, but I'm stuck with how I would get the value of the identity column back after my insert. I saw another post that mentioned Linq Templates. I'm not using those (at least I don't think I am...?) TIA ... UPDATE ... So I've been debugging through my code watching how the SubSonic code works and I found where the indentity column is being ignored. I use int as the datatype for my ID columns in the database and set them as identity. Since int is a non-nullable data type in c# the logical test in the Add method (public void Add(IDataProvider provider)) that checks if there is a value in the key column by doing a (key==null) could be the issue. The code that gets the new value for the identity field is in the 'true path', since an int can't be null and I use ints as my identity column data types this test will never pass. The ID field for my object has a 0 in it that I didn't put there. I assume it's set during the initialization of the object. Am I off base here? Is the answer to change my data types in the database? Another question (more a curiosity). I noticed that some of the properties in the generated classes are declared with a ? after the datatype. I'm not familiar with this declaration construct... what gives? There are some declared as an int (non key fields) and others that are declared as int? (key fields). Does this have something to do with how they're treated at initialization? Any help is appreciated! --BUMP--

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• C++ struct, public data members and inheritance

  - by Marius

  Is it ok to have public data members in a C++ class/struct in certain particular situations? How would that go along with inheritance? I've read opinions on the matter, some stated already here http://stackoverflow.com/questions/952907/practices-on-when-to-implement-accessors-on-private-member-variables-rather-than http://stackoverflow.com/questions/670958/accessors-vs-public-members or in books/articles (Stroustrup, Meyers) but I'm still a little bit in the shade. I have some configuration blocks that I read from a file (integers, bools, floats) and I need to place them into a structure for later use. I don't want to expose these externally just use them inside another class (I actually do want to pass these config parameters to another class but don't want to expose them through a public API). The fact is that I have many such config parameters (15 or so) and writing getters and setters seems an unnecessary overhead. Also I have more than one configuration block and these are sharing some of the parameters. Making a struct with all the data members public and then subclassing does not feel right. What's the best way to tackle that situation? Does making a big struct to cover all parameters provide an acceptable compromise (I would have to leave some of these set to their default values for blocks that do not use them)?

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• UIDocumentInteractionController & ARC: [UIPopoverController dealloc] reached while popover is still visible

  - by muffel

  This issue or similar issues have been discussed here before, but I didn't find any working solution for me. I am using the following code to display a UIDocumentInteractionController on an ARC-enabled iOS 7 project: - (void) exportDoc{ // [...] docController = [UIDocumentInteractionController interactionControllerWithURL:[NSURL fileURLWithPath:path]]; docController.delegate = self; [docController presentOpenInMenuFromBarButtonItem:mainMenuButton animated:YES]; } First I didn't want to create a property that holds the controller reference, but as many people said that there are not alternatives to it. It is defined as @property (strong) UIDocumentInteractionController* docController; exportDoc is run in the main thread using NSOperationQueue. Whenever it is executed, I get the following error message: Terminating app due to uncaught exception 'NSGenericException', reason: '-[UIPopoverController dealloc] reached while popover is still visible.' This is what the backtrace says: (lldb) bt * thread #1: tid = 0x1c97d9, 0x000000019a23c1c0 libobjc.A.dylibobjc_exception_throw, queue = 'com.apple.main-thread', stop reason = breakpoint 2.1 frame #0: 0x000000019a23c1c0 libobjc.A.dylibobjc_exception_throw frame #1: 0x000000018d982e90 CoreFoundation+[NSException raise:format:] + 128 frame #2: 0x0000000190bc348c UIKit-[UIPopoverController dealloc] + 96 frame #3: 0x0000000190e18fc8 UIKit-[UIDocumentInteractionController dealloc] + 168 frame #4: 0x000000019a255474 libobjc.A.dylib(anonymous namespace)::AutoreleasePoolPage::pop(void*) + 524 frame #5: 0x000000018d881988 CoreFoundation_CFAutoreleasePoolPop + 28 frame #6: 0x000000018e42cb18 Foundation-[NSOperationInternal _start:] + 892 frame #7: 0x000000018e4eea38 Foundation__NSOQSchedule_f + 76 frame #8: 0x000000019a813fd4 libdispatch.dylib_dispatch_client_callout + 16 frame #9: 0x000000019a8171dc libdispatch.dylib_dispatch_main_queue_callback_4CF + 336 frame #10: 0x000000018d942c2c CoreFoundation__CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE + 12 frame #11: 0x000000018d940f6c CoreFoundation__CFRunLoopRun + 1452 frame #12: 0x000000018d881c20 CoreFoundationCFRunLoopRunSpecific + 452 frame #13: 0x0000000193511c0c GraphicsServicesGSEventRunModal + 168 frame #14: 0x00000001909b2fdc UIKitUIApplicationMain + 1156 * frame #15: 0x000000010000947c MyApplicationmain(argc=1, argv=0x000000016fdfbc80) + 108 at main.m:16 frame #16: 0x000000019a82faa0 libdyld.dylibstart + 4 As far as I understand the autoreleasepool just releases the controller. Shouldn't this be prevented by using a strong property just as I did? Do you have any idea what the problem can be and how I can solve it?

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• PHP: Use a string as an array index path to retreive a value.

  - by Charles

  Say I have an array like: Array ( [0] => Array ( [Data] => Array ( [id] => 1 [title] => Manager [name] => John Smith ) ) [1] => Array ( [Data] => Array ( [id] => 1 [title] => Clerk [name] => ( [first] => Jane [last] => Smith ) ) ) ) I want to be able to build a function that I can pass a string to that will act as the array index path and return the appropriate array value without using eval(). Is that possible? function($indexPath, $arrayToAccess) { //$indexPath would be something like [0]['Data']['name'] which would return //"Manager" or it could be [1]['Data']['name']['first'] which would return //"Jane" but the amount of array indexs that will be in the index path can //change, so there might be 3 like the first example, or 4 like the second. return $arrayToAccess[$indexPath] <-obviously wont work }

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• Designing a chain of states

  - by devoured elysium

  I want to model a kind of FSM(Finite State Machine). I have a sequence of states (let's say, from StateA to StateZ). This sequence is called a Chain and is implemented internally as a List. I will add states by the order I want them to run. My purpose is to be able to make a sequence of actions in my computer (for example, mouse clicks). (I know this has been done a zillion times). So a state is defined as a: boolean Precondition() <- Checks to see if for this state, some condition is true. For example, if I want to click in the Record button of a program, in this method I would check if the program's process is running or not. If it is, go to the next state in the chain list, otherwise, go to what was defined as the fail state (generally is the first state of them all). IState GetNextState() <- Returns the next state to evaluate. If Precondition() was sucessful, it should yield the next state in the chain otherwise it should yield the fail state. Run() Simply checks the Precondition() and sets the internal data so GetNextState() works as expected. So, a naive approach to this would be something like this: Chain chain = new Chain(); //chain.AddState(new State(Precondition, FailState, NextState) <- Method structure chain.AddState(new State(new WinampIsOpenCondition(), null, new <problem here, I want to referr to a state that still wasn't defined!>); The big problem is that I want to make a reference to a State that at this point still wasn't defined. I could circumvent the problem by using strings when refrering to states and using an internal hashtable, but isn't there a clearer alternative? I could just pass only the pre-condition and failure states in the constructor, having the chain just before execution put in each state the correct next state in a public property but that seems kind of awkward.

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• C++ socket protocol design issue (ring inclusion)

  - by Martin Lauridsen

  So I have these two classes, mpqs_client and client_protocol. The mpqs_client class handles a Boost socket connection to a server (sending and receiving messages with some specific format. Upon receiving a message, it calls a static method, parse_message(..), in the class client_protocol, and this method should analyse the message received and perform some corresponding action. Given some specific input, the parse_message method needs to send some data back to the server. As mentioned, this happens through the class mpqs_client. So I could, from mpqs_client, pass "this" to parse_message(..) in client_protocol. However, this leads to a two-way association relationship between the two classes. Something which I reckon is not desireable. Also, to implement this, I would need to include the other in each one, and this gives me a terrible pain. I am thinking this is more of a design issue. What is the best solution here? Code is posted below. Class mpqs_client: #include "mpqs_client.h" mpqs_client::mpqs_client(boost::asio::io_service& io_service, tcp::resolver::iterator endpoint_iterator) : io_service_(io_service), socket_(io_service) { ... } ... void mpqs_client::write(const network_message& msg) { io_service_.post(boost::bind(&mpqs_client::do_write, this, msg)); } Class client_protocol: #include "../network_message.hpp" #include "../protocol_consts.h" class client_protocol { public: static void parse_message(network_message& msg, mpqs_sieve **instance_, mpqs_client &client_) { ... switch (type) { case MPQS_DATA: ... break; case POLYNOMIAL_DATA: ... break; default: break; } }

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• Javascript function objects, this keyword points to wrong object

  - by Rody van Sambeek

  I've got a problem concerning the javascript "this" keyword when used within a javascript functional object. I want to be able to create an object for handling a Modal popup (JQuery UI Dialog). The object is called CreateItemModal. Which i want to be able to instantiate and pass some config settings. One of the config settings. When the show method is called, the dialog will be shown, but the cancel button is not functioning because the this refers to the DOM object instead of the CreateItemModal object. How can I fix this, or is there a better approach to put seperate behaviour in seperate "classes" or "objects". I've tried several approaches, including passing the "this" object into the events, but this does not feel like a clean solution. See (simplified) code below: function CreateItemModal(config) { // initialize some variables including $wrapper }; CreateItemModal.prototype.show = function() { this.$wrapper.dialog({ buttons: { // this crashes because this is not the current object here Cancel: this.close } }); }; CreateItemModal.prototype.close = function() { this.config.$wrapper.dialog('close'); };

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• Javascript function with PHP throwing a "Illegally Formed XML Syntax" error

  - by Joe

  I'm trying to learn some javascript and i'm having trouble figuring out why my code is incorrect (i'm sure i'm doing something wrong lol), but anyways I am trying to create a login page so that when the form is submitted javascript will call a function that checks if the login is in a mysql database and then checks the validity of the password for the user if they exist. however I am getting an error (Illegally Formed XML Syntax) i cannot resolve. I'm really confused, mostly because netbeans is saying it is a xml syntax error and i'm not using xml. here is the code in question: function validateLogin(login){ login.addEventListener("input", function() { $value = login.value; if (<?php //connect to mysql mysql_connect(host, user, pass) or die(mysql_error()); echo("<script type='text/javascript'>"); echo("alert('MYSQL Connected.');"); echo("</script>"); //select db mysql_select_db() or die(mysql_error()); echo("<script type='text/javascript'>"); echo("alert('MYSQL Database Selected.');"); echo("</script>"); //query $result = mysql_query("SELECT * FROM logins") or die(mysql_error()); //check results against given login while($row = mysql_fetch_array($result)){ if($row[login] == $value){ echo("true"); exit(0); } } echo("false"); exit(0); ?>) { login.setCustomValidity("Invalid Login. Please Click 'Register' Below.") } else { login.setCustomValidity("") } }); } the code is in an external js file and the error throws on the last line. Also from reading i understand best practices is to not mix js and php so how would i got about separating them but maintaining the functionality i need? thanks!

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• calculating the index of an array C#

  - by Kerry G

  I want to display a list of the answers a student entered incorrectly. How do I identify the index of these questions? I am hoping to change the contents of a textbox to a list of the questions answered incorrectly, which would require calculating the index of each incorrect question. using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Threading.Tasks; using System.Windows.Forms; namespace WindowsFormsApplication5 { public partial class Form1 : Form { public Form1() { InitializeComponent(); } //return a pass/fail //return number of correct answers //return number of incorrect answers //return index figures of incorrect values public void examResults () { string[] correctAnswers = {B,D,A,A,C,A,B,A,C,D,B,C,D,A,D,C,C,B,D,A}; string[] studentResults = File.ReadAllLines("studentResults.txt"); var c = correctAnswers.Where((x, i) => x.Equals(studentResults[i])).Count(); if ( c <= 14) passFailBox.Text = "Student has failed the exam"; else passFailBox.Text = "Student has passed the exam"; numberCorrectBox.Text = "Student has answered" + c + "answers correctly"; int f; f= 21-c; numberIncorrectBox.Text = "Student has answered" + f + "answers incorrectly"; } } }

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