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• Linux network stack : adding protocols with an LKM and dev_add_pack

  - by agent0range

  Hello, I have recently been trying to familiarize myself with the Linux Networking stack and device drivers (have both similarly named O'Reilly books) with the eventual goal of offloading UDP. I have already implemented UDP on the NIC but now the hard part... Rather than ask for assistance on this larger goal I was hoping someone could clarify for me a particular snippet I found that is part of a LKM which registeres a new protocol (OTP) that acts as a filter between the device driver and network stack. http://www.phrack.org/archives/55/p55_0x0c_Building%20Into%20The%20Linux%20Network%20Layer_by_lifeline%20&%20kossak.txt (Note: this Phrack article contains three different modules, code for the OTP is at the bottom of the page) In the init function of his example he has: otp_proto.type = htons(ETH_P_ALL); otp_proto.func = otp_func; dev_add_pack(&otp_proto); which (if I understand correctly) should register otp_proto as a packet sniffer and put it into the ptype_all data structure. My question is about the dev_add_pack. Is it the case that the protocol being registered as a filter will always be placed at this layer between L2 and the device driver? Or, for instance could I make such a filtering occur between the application and transport layers (analyze socket parameters) using the same process? I apologize if this is confusing - I am having some trouble wrapping my head around the bigger picture when it comes to modules altering kernel stack functionality. Thanks

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• How to check if two records have a self-referencing relation?

  - by Machine

  Consider the following schema with users and their collegues (friends): Users User: columns: user_id: name: user_id as userId type: integer(8) unsigned: 1 primary: true autoincrement: true first_name: name: first_name as firstName type: string(45) notnull: true last_name: name: last_name as lastName type: string(45) notnull: true email: type: string(45) notnull: true unique: true relations: Collegues: class: User local: invitor foreign: invitee refClass: CollegueStatus equal: true onDelete: CASCADE onUpdate: CASCADE Join table: CollegueStatus: columns: invitor: type: integer(8) unsigned: 1 primary: true invitee: type: integer(8) unsigned: 1 primary: true status: type: enum(8) values: [pending, accepted, denied] default: pending notnull: true Now, let's say I two records, one for the user making a HTTP request (the logged in user), and one record for a user he wants to send a message to. I want to check if these users are collegues. Questions: Does Doctrine have any pre-build functionality to check if two records with with self-relations are related? If not, how would you write a method to check this? Where would you put said method? (In the User-class, UserTable-class etc) I could probably do something like this: public function (User $user1, User $user2) { // Ensure we load collegues if $user1 was fetched with DQL that // doesn't load this relation $collegues = $user1->get('Collegues'); $areCollegues = false; foreach($collegues as $collegue) { if($collegue['userId'] === $user2['userId']) { $areCollegues = true; break; } } return $areCollegues; } But this looks a neither efficient nor pretty. I just feel that it should be solved already for self-referencing relations to be nice to use.

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• Force sending a user to custom QuerySet.

  - by Jack M.

  I'm trying to secure an application so that users can only see objects which are assigned to them. I've got a custom QuerySet which works for this, but I'm trying to find a way to force the use of this additional functionality. Here is my Model: class Inquiry(models.Model): ts = models.DateTimeField(auto_now_add=True) assigned_to_user = models.ForeignKey(User, blank=True, null=True, related_name="assigned_inquiries") objects = CustomQuerySetManager() class QuerySet(QuerySet): def for_user(self, user): return self.filter(assigned_to_user=user) (The CustomQuerySetManager is documented over here, if it is important.) I'm trying to force everything to use this filtering, so that other methods will raise an exception. For example: Inquiry.objects.all() ## Should raise an exception. Inquiry.objects.filter(pk=69) ## Should raise an exception. Inquiry.objects.for_user(request.user).filter(pk=69) ## Should work. inqs = Inquiry.objects.for_user(request.user) ## Should work. inqs.filter(pk=69) ## Should work. It seems to me that there should be a way to force the security of these objects by allowing only certain users to access them. I am not concerned with how this might impact the admin interface.

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• Android NDK import-module / code reuse

  - by Graeme

  Morning! I've created a small NDK project which allows dynamic serialisation of objects between Java and C++ through JNI. The logic works like this: Bean - JavaCInterface.Java - JavaCInterface.cpp - JavaCInterface.java - Bean The problem is I want to use this functionality in other projects. I separated out the test code from the project and created a "Tester" project. The tester project sends a Java object through to C++ which then echo's it back to the Java layer. I thought linking would be pretty simple - ("Simple" in terms of NDK/JNI is usually a day of frustration) I added the JNIBridge project as a source project and including the following lines to Android.mk: NDK_MODULE_PATH=.../JNIBridge/jni/" JNIBridge/jni/JavaCInterface/Android.mk: ... include $(BUILD_STATIC_LIBRARY) JNITester/jni/Android.mk: ... include $(BUILD_SHARED_LIBRARY) $(call import-module, JavaCInterface) This all works fine. The C++ files which rely on headers from JavaCInterface module work fine. Also the Java classes can happily use interfaces from JNIBridge project. All the linking is happy. Unfortunately JavaCInterface.java which contains the native method calls cannot see the JNI method located in the static library. (Logically they are in the same project but both are imported into the project where you wish to use them through the above mechanism). My current solutions are are follows. I'm hoping someone can suggest something that will preserve the modular nature of what I'm trying to achieve: My current solution would be to include the JavaCInterface cpp files in the calling project like so: LOCAL_SRC_FILES := FunctionTable.cpp $(PATH_TO_SHARED_PROJECT)/JavaCInterface.cpp But I'd rather not do this as it would lead to me needing to update each depending project if I changed the JavaCInterface architecture. I could create a new set of JNI method signatures in each local project which then link to the imported modules. Again, this binds the implementations too tightly.

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• Real time embeddable http server library required

  - by Howard May

  Having looked at several available http server libraries I have not yet found what I am looking for and am sure I can't be the first to have this set of requirements. I need a library which presents an API which is 'pipelined'. Pipelining is used to describe an HTTP feature where multiple HTTP requests can be sent across a TCP link at a time without waiting for a response. I want a similar feature on the library API where my application can receive all of those request without having to send a response (I will respond but want the ability to process multiple requests at a time to reduce the impact of internal latency). So the web server library will need to support the following flow 1) HTTP Client transmits http request 1 2) HTTP Client transmits http request 2 ... 3) Web Server Library receives request 1 and passes it to My Web Server App 4) My Web Server App receives request 1 and dispatches it to My System 5) Web Server receives request 2 and passes it to My Web Server App 6) My Web Server App receives request 2 and dispatches it to My System 7) My Web Server App receives response to request 1 from My System and passes it to Web Server 8) Web Server transmits HTTP response 1 to HTTP Client 9) My Web Server App receives response to request 2 from My System and passes it to Web Server 10) Web Server transmits HTTP response 2 to HTTP Client Hopefully this illustrates my requirement. There are two key points to recognise. Responses to the Web Server Library are asynchronous and there may be several HTTP requests passed to My Web Server App with responses outstanding. Additional requirements are Embeddable into an existing 'C' application Small footprint; I don't need all the functionality available in Apache etc. Efficient; will need to support thousands of requests a second Allows asynchronous responses to requests; their is a small latency to responses and given the required request throughput a synchronous architecture is not going to work for me. Support persistent TCP connections Support use with Server-Push Comet connections Open Source / GPL support for HTTPS Portable across linux, windows; preferably more. I will be very grateful for any recommendation Best Regards

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• Implementing MEF with ASP.NET MVC?

  - by mark smith

  I am trying to find out if anyone has any experience or ideas of using MEF (Managed Extensible Framework (Microsoft's new plugin framework) with ASP.NET MVC. I need to create a standard ASP.NET MVC, which I have. But I need to offer additional functionality i.e. Views and Controllers, etc, depending on if I add a plugin. It doesn't need to be dynamically compiled i.e. source code... but a DLL that i put into the system.. Is there any way to dynamically load a DLL when the app starts, and then MERGE a VIEWS and CONTROLLERS with the main system? I don't know if i am on the right track here. Then, I suppose in the "STANDARD" views that come with the app, I can use an "IF THEN" to find out if a plugin is loaded and MERGE in a user control. Well, I'm talking out loud here, but I think you understand what I am getting at. Any ideas?

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• What OOP pattern to use when only adding new methods, not data?

  - by Jonathon Reinhart

  Hello eveyone... In my app, I have deal with several different "parameters", which derive from IParameter interface, and also ParamBase abstract base class. I currently have two different parameter types, call them FooParameter and BarParameter, which both derive from ParamBase. Obviously, I can treat them both as IParameters when I need to deal with them generically, or detect their specific type when I need to handle their specific functionality. My question lies in specific FooParameters. I currently have a few specific ones with their own classes which derive from FooParameter, we'll call them FP12, FP13, FP14, etc. These all have certain characteristics, which make me treat them differently in the UI. (Most have names associated with the individual bits, or ranges of bits). Note that these specific, derived FP's have no additional data associated with them, only properties (which refer to the same data in different ways) or methods. Now, I'd like to keep all of these parameters in a Dictionary<String, IParameter> for easy generic access. The problem is, if I want to refer to a specific one with the special GUI functions, I can't write: FP12 fp12 = (FP12)paramList["FP12"] because you can't downcast to a derived type (rightfully so). But in my case, I didn't add any data, so the cast would theoretically work. What type of programming model should I be using instead? Thanks!

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• Are there more secure alternatives to the .Net SQLConnection class?

  - by KeyboardMonkey

  Hi SO people, I'm very surprised this issue hasn't been discussed in-depth: This article tells us how to use windbg to dump a running .Net process strings in memory. I spent much time researching the SecureString class, which uses unmanaged pinned memory blocks, and keeps the data encrypted too. Great stuff. The problem comes in when you use it's value, and assign it to the SQLConnection.ConnectionString property, which is of the System.String type. What does this mean? Well... It's stored in plain text Garbage Collection moves it around, leaving copies in memory It can be read with windbg memory dumps That totally negates the SecureString functionality! On top of that, the SQLConnection class is non-inheritable, I can't even roll my own with a SecureString property instead; Yay for closed-source. Yay. A new DAL layer is in progress, but for a new major version and for so many users it will be at least 2 years before every user is upgraded, others might stay on the old version indefinitely, for whatever reason. Because of the frequency the connection is used, marshalling from a SecureString won't help, since the immutable old copies stick in memory until GC comes around. Integrated Windows security isn't an option, since some clients don't work on domains, and other roam and connect over the net. How can I secure the connection string, in memory, so it can't be viewed with windbg?

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• Qt/PyQt dialog with togglable fullscreen mode - problem on Windows

  - by Guard

  I have a dialog created in PyQt. It's purpose and functionality don't matter. The init is: class MyDialog(QWidget, ui_module.Ui_Dialog): def __init__(self, parent=None): super(MyDialog, self).__init__(parent) self.setupUi(self) self.installEventFilter(self) self.setWindowFlags(Qt.Dialog | Qt.WindowTitleHint) self.showMaximized() Then I have event filtering method: def eventFilter(self, obj, event): if event.type() == QEvent.KeyPress: key = event.key() if key == Qt.Key_F11: if self.isFullScreen(): self.setWindowFlags(self._flags) if self._state == 'm': self.showMaximized() else: self.showNormal() self.setGeometry(self._geometry) else: self._state = 'm' if self.isMaximized() else 'n' self._flags = self.windowFlags() self._geometry = self.geometry() self.setWindowFlags(Qt.Tool | Qt.FramelessWindowHint) self.showFullScreen() return True elif key == Qt.Key_Escape: self.close() return QWidget.eventFilter(self, obj, event) As can be seen, Esc is used for dialog hiding, and F11 is used for toggling full-screen. In addition, if the user changed the dialog mode from the initial maximized to normal and possibly moved the dialog, it's state and position are restored after exiting the full-screen. Finally, the dialog is created on the MainWindow action triggered: d = MyDialog(self) d.show() It works fine on Linux (Ubuntu Lucid), but quite strange on Windows 7: if I go to the full-screen from the maximized mode, I can't exit full-screen (on F11 dialog disappears and appears in full-screen mode again). If I change the dialog's mode to Normal (by double-clicking its title), then go to full-screen and then return back, the dialog is shown in the normal mode, in the correct position, but without the title line. Most probably the reason for both cases is the same - the setWindowFlags doesn't work. But why? Is it also possible that it is the bug in the recent PyQt version? On Ubuntu I have 4.6.x from apt, and on Windows - the latest installer from the riverbank site.

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• How to learn a C++ GUI library effectively?

  - by Chan

  Hello everyone, I have many options for GUI in my head while searching in stackoverflow, but these are what I chose among others: Qt gtkmm GTK+ I used GTK+ couple years ago, and I felt so painful when using C API without string object and containers. I prefer C++ style, I then switched to C++ gtkmm, but the documentation was bad at that time. I found no help when encountering an issue. Now I want to give a hard try for Qt4, but I really want to know how to learn a GUI librarie effectively. With core C++, I usually pick up a problem and try to solve it in different ways using that particular technique, functionality. On the other hand, after skimming through the documentation from Qt site, I don't think this way of studying is applicable, since the GUI classes and APIs are so much bigger. Plus I'm still in school, so I won't have much time to play all the day long with it. How do you guys learn GUI before? Can anyone share some experiences how they learn thing, that would be an invaluable input for me! Best regards, Chan Nguyen

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• SystemStackError in Rails::ActiveSupport::Callbacks

  - by coreyward

  I'm building a Rails app that connects to Dropbox and syncs with a folder to update a personal site. I'm using Rails 3.0.3, Ruby 1.9.2, and the Dropbox gem. Right now I have a DropboxAccounts Controller, and two models: DropboxSession, which wraps calls to the gem with application-specific functionality, and DropboxAccount, which stores the session and settings in the database. After the user authorizes their account with Dropbox they're redirected back over and the DropboxAccount is saved with the authorized session. That all works just fine. My problem is that when I try to call Dropbox::API#create_folder(any path) I end up with a SystemStackError in lib/activesupport/callbacks.rb:421 which refers to the code below. If I remove the call to create the folder, it works. If I call create folder from another request, it works. I doubled the stack size to 16K to no avail. # This is called the first time a callback is called with a particular # key. It creates a new callback method for the key, calculating # which callbacks can be omitted because of per_key conditions. # def __create_keyed_callback(name, kind, object, &blk) #:nodoc: @_keyed_callbacks ||= {} @_keyed_callbacks[name] ||= begin str = send("_#{kind}_callbacks").compile(name, object) class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1 def #{name}() #{str} end # THIS IS LINE 421 protected :#{name} RUBY_EVAL true end end I'm not very familiar with Rails yet, and I'm not sure what the intention of the code above is or why it would cause a stack overflow. I'm not using any method_missing/ghost method magic in my code. I suspected it was something with a callback serialize :files but commenting it out did nothing. My DropboxAccount model contains only a call to belongs_to :user, and DropboxSession is just a handful of methods, none of which contain callbacks. Bypassing them and using the Dropbox::Session methods directly doesn't help. I hope someone on StackOverflow can help me with this stack overflow. ;)

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• Unity 1.2 Dependency injection of internal types

  - by qvin

  I have a facade in a library that exposes some complex functionality through a simple interface. My question is how do I do dependency injection for the internal types used in the facade. Let's say my C# library code looks like - public class XYZfacade:IFacade { [Dependency] internal IType1 type1 { get; set; } [Dependency] internal IType2 type2 { get; set; } public string SomeFunction() { return type1.someString(); } } internal class TypeA { .... } internal class TypeB { .... } And my website code is like - IUnityContainer container = new UnityContainer(); container.RegisterType<IType1, TypeA>(); container.RegisterType<IType2, TypeB>(); container.RegisterType<IFacade, XYZFacade>(); ... ... IFacade facade = container.Resolve<IFacade>(); Here facade.SomeFunction() throws an exception because facade.type1 and facade.type2 are null. Any help is appreciated.

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• Remove application entry from switch-app menu

  - by bdhar

  What am I trying to achieve? I am writing a windows-form based application in C# .NET 2.0. The application should behave like this: No form should be visible; just a system tray icon is the entire application. So, I have to hide the form during startup and make a NotifyIcon available in the system tray with a ContextMenuStrip attached to it. What have I done so far? I have created a Windows application with the default form's properties WindowState-Minimized and ShowInTaskbar-false. Added a NotifyIcon and attached a ContextMenuStrip to it. What's happening? The application starts as a system tray icon and the form is hidden. So far so good. But when I am working with other applications and when I switch between other application using the Alt-Tab combination in Windows, the application icon appears in the switch-application menu; and when I select my application, the form appears. What's expected? The application should not be available in the switch-application menu; because, the form is empty and there is no functionality attached to it. All that is needed is the system-tray icon. How to hide the application entry from the switch-application menu? Thanks.

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• Function pointers in Objective-C

  - by Stefan Klumpp

  I have the following scenario: Class_A - method_U - method_V - method_X - method_Y Class_B - method_M - method_N HttpClass - startRequest - didReceiveResponse // is a callback Now I want to realize these three flows (actually there are many more, but these are enough to demonstrate my question): Class_A :: method_X -> HttpClass :: startRequest:params -> ... wait, wait, wait ... -> HttpClass :: didReceiveResponse -> Class_A :: method_Y:result and: Class_A :: method_U -> HttpClass :: startRequest:params -> ... wait, wait, wait ... -> HttpClass :: didReceiveResponse -> Class_A :: method_V:result and the last one: Class_B :: method_M -> HttpClass :: startRequest:params -> ... wait, wait, wait ... -> HttpClass :: didReceiveResponse -> Class_B :: method_N:result Please note, that the methods in Class_A and Class_B have different names and functionality, they just make us of the same HttpClass. My solution now would be to pass a C function pointer to startRequest, store it in the HttpClass and when didReceiveResponse gets called I invoke the function pointer and pass the result (which will always be a JSON Dictionary). Now I'm wondering if there can be any problems using plain C or if there are better solutions doing it in a more Objective-C way. Any ideas?

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• Rails: creating a custom data type, to use with generator classes and a bunch of questions related t

  - by Shyam

  Hi, After being productive with Rails for some weeks, I learned some tricks and got some experience with the framework. About 10 days ago, I figured out it is possible to build a custom data type for migrations by adding some code in the Table definition. Also, after learning a bit about floating points (and how evil they are) vs integers, the money gem and other possible solutions, I decided I didn't WANT to use the money gem, but instead try to learn more about programming and finding a solution myself. Some suggestions said that I should be using integers, one for the whole numbers and one for the cents. When playing in script/console, I discovered how easy it is to work with calculations and arrays. But, I am talking to much (and the reason I am, is to give some sufficient background). Right now, while playing with the scaffold generator (yes, I use it, because I like they way I can quickly set up a prototype while I am still researching my objectives), I like to use a DRY method. In my opinion, I should build a custom "object", that can hold two variables (Fixnum), one for the whole, one for the cents. In my big dream, I would be able to do the following: script/generate scaffold Cake name:string description:text cost:mycustom Where mycustom should create two integer columns (one for wholes, one for cents). Right now I could do this by doing: script/generate scaffold Cake name:string description:text cost_w:integer cost_c:integer I had also had an idea that would be creating a "cost model", which would hold two columns of integers and create a cost_id column to my scaffold. But wouldn't that be an extra table that would cause some kind of performance penalty? And wouldn't that be defy the purpose of the Cake model in the first place, because the costs are an attribute of individual Cake entries? The reason why I would want to have such a functionality because I am thinking of having multiple "costs" inside my rails application. Thank you for your feedback, comments and answers! I hope my message got through as understandable, my apologies for incorrect grammar or weird sentences as English is not my native language.

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• ASP.net MVC Linq-To-SQL Many-To-Many Field Binding

  - by user336858

  Hi there, The short version of this question is "Is there a way to gracefully handle database insertion for an object that has a many-to-many field that has been set up in a partial class?" Apologies if it's been asked before. Example Suppose I have a typical MVC setup with the tables: Posts {PostID, ...} Categories {CategoryID, ...} A post can have more than one category, and a category can identify more than one post. Thus suppose further that I need an extra table: PostCategories {PostID, CategoryID, ...} This handles the many-to-many relationship between posts and categories. As far as I know, there's no way to do this in Linq-to-SQL right now so I have to shoehorn it in by adding a partial Post class to the project to add that functionality. Something like: public partial class Post { public IEnumerable<Category> Categories{ get { ... } set { ... } } } So I can now create a "Create" view that automatically populates a "Categories" UI item. This is where the trouble starts. So here's my question: How do you get automatic object model binding to work cleanly with an object that has a many-to-many relationship to control? The workaround that makes many-to-many relationships possible relies on the Post object having a PostID in order to be associated with CategoryID(s), which is only issued after the Post object has been submitted for validation and insertion. Bit of a Catch22 here. Any terminology, links, or tips you can provide would be tremendously helpful!

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• Do you know a date picker to quickly pick one day of the current week?

  - by Murmelschlurmel

  Most date pickers allow you to pick the date from a tine calendar or enter the date by hand. For example http://jqueryui.com/demos/datepicker/ This requires - two clicks (one to display the calendar and one to select the correct date) - good eyesight (usually the pop-up calendar is very small) - and good hand-eye coordination to pick the correct date in the tiny calendar with your mouse. That's no problem for power users, but a hassle for older people and computer beginners. I found a website with a different approach. It seems like their users mostly select dates of the current week. So they listed all the days of the week in a bar together with the weekday. The current day is marked in another color. There is a tiny calender icon on the right hand that opens up a regular date picker. That gives you access to all regular date picker functionality. Here is a screenshot: http://mite.yo.lk/assets/img/tour/de/zeiten-erfassen.png Do you know of any jquery plugin which has a similar feature? If not, do you any other plugin or widget which would help me speed up development ? Thank you!

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• Compiling a Windows C++ program in g++

  - by Phenom

  I'm trying to compile a Windows C++ program in g++. This is what I get. /usr/include/c++/4.4/backward/backward_warning.h:28:2: warning: #warning This file includes at least one deprecated or antiquated header which may be removed without further notice at a future date. Please use a non-deprecated interface with equivalent functionality instead. For a listing of replacement headers and interfaces, consult the file backward_warning.h. To disable this warning use -Wno-deprecated. btree.cpp:1204: error: ‘_TCHAR’ has not been declared btree.cpp: In function ‘int _tmain(int, int**)’: btree.cpp:1218: error: ‘__int64’ was not declared in this scope btree.cpp:1218: error: expected ‘;’ before ‘frequency’ btree.cpp:1220: error: ‘LARGE_INTEGER’ was not declared in this scope btree.cpp:1220: error: expected primary-expression before ‘)’ token btree.cpp:1220: error: ‘frequency’ was not declared in this scope btree.cpp:1220: error: ‘QueryPerformanceFrequency’ was not declared in this scope btree.cpp:1262: error: expected primary-expression before ‘)’ token btree.cpp:1262: error: ‘start’ was not declared in this scope btree.cpp:1262: error: ‘QueryPerformanceCounter’ was not declared in this scope btree.cpp:1264: error: name lookup of ‘i’ changed for ISO ‘for’ scoping btree.cpp:1264: note: (if you use ‘-fpermissive’ G++ will accept your code) btree.cpp:1304: error: expected primary-expression before ‘)’ token btree.cpp:1304: error: ‘end’ was not declared in this scope btree.cpp:1306: error: ‘total’ was not declared in this scope btree.cpp:1316: error: ‘getchar’ was not declared in this scope The first thing I noticed is that there are these variable types called _TCHAR, _int64, and LARGE_INTEGER, which is probably a Windows thing. What can these be changed to so that they will work in g++? Also, if there's anything else in here that you know can be converted to g++, that would be helpful. I got the code from here: http://touc.org/btree.html

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• How to specialize a type parameterized argument to multiple different types for in Scala?

  - by jmount

  I need a back-check (please). In an article ( http://www.win-vector.com/blog/2010/06/automatic-differentiation-with-scala/ ) I just wrote I stated that it is my belief in Scala that you can not specify a function that takes an argument that is itself a function with an unbound type parameter. What I mean is you can write: def g(f:Array[Double]=>Double,Array[Double]):Double but you can not write something like: def g(f[Y]:Array[Y]=>Double,Array[Double]):Double because Y is not known. The intended use is that inside g() I will specialize fY to multiple different types at different times. You can write: def g[Y](f:Array[Y]=>Double,Array[Double]):Double but then f() is of a single type per call to g() (which is exactly what we do not want). However, you can get all of the equivalent functionality by using a trait extension instead insisting on passing around a function. What I advocated in my article was: 1) Creating a trait that imitates the structure of Scala's Function1 trait. Something like: abstract trait VectorFN { def apply[Y](x:Array[Y]):Y } 2) declaring def g(f:VectorFN,Double):Double (using the trait is the type). This works (people here on StackOverflow helped me find it, and I am happy with it)- but am I mis-representing Scala by missing an even better solution?

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• Multiple Inheritence with same Base Classes in Python

  - by Jordan Reiter

  I'm trying to wrap my head around multiple inheritance in python. Suppose I have the following base class: class Structure(object): def build(self, *args): print "I am building a structure!" self.components = args And let's say I have two classes that inherit from it: class House(Structure): def build(self, *args): print "I am building a house!" super(House, self).build(*args) class School(Structure): def build(self, type="Elementary", *args): print "I am building a school!" super(School, self).build(*args) Finally, a create a class that uses multiple inheritance: class SchoolHouse(School, House): def build(self, *args): print "I am building a schoolhouse!" super(School, self).build(*args) Then, I create a SchoolHouse object and run build on it: >>> sh = SchoolHouse() >>> sh.build("roof", "walls") I am building a schoolhouse! I am building a house! I am building a structure! So I'm wondering -- what happened to the School class? Is there any way to get Python to run both somehow? I'm wondering specifically because there are a fair number of Django packages out there that provide custom Managers for models. But there doesn't appear to be a way to combine them without writing one or the other of the Managers as inheriting from the other one. It'd be nice to just import both and use both somehow, but looks like it can't be done? Also I guess it'd just help to be pointed to a good primer on multiple inheritance in Python. I have done some work with Mixins before and really enjoy using them. I guess I just wonder if there is any elegant way to combine functionality from two different classes when they inherit from the same base class.

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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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• Doing coding in Linux through a virtual machine on Windows VS partitioning

  - by ihaveitnow

  I already have experience with setting up virtual machines, running them and other minor tasks. Im a gamer, so I wont get rid of windows (for now at least...) but I do want to be a great programmer and to be involved with the Open-Source community. Id like to know if its a good idea to do my programming in linux through a virtual machine, vs giving it a partitioned section of the HDD. Id like to know about performance pros and cons and functionality. All responses are appreciated, thanks in advance. The type of programming I intend to dive into : Android Dev, Web Dev, Desktop Dev...More Android and Web right now though. So im looking at C#,C,C++,Java,PHP,HTML,MySQL...Off the top of the dome. I do web designing as well, so dreamweaver is added as an "essential". But im sure I can do dreamweaver files and upload them to the server after programming in Linux...Right? And any info on IDE's in Linux for the above mentioned are appreciated, but i would prefer going the coding route and understanding the essence of whats happening "under the covers" Thanks to all for reading, I appreciate it. Hope this isnt confusing :S

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• pdf external streams in Max OS X Preview

  - by olpa

  According to the specification, a part of a PDF document can reside in an external file. An example for an image: 2 0 obj << /Type /XObject /Subtype /Image /Width 117 /Height 117 /BitsPerComponent 8 /Length 0 /ColorSpace /DeviceRGB /FFilter /DCTDecode /F (pinguine.jpg) >> stream endstream endobj I found that this functionality does work in Adobe Acrobat 5.0 for Windows (sample PDF with the image), also I managed to view this file in Adobe Acrobat Reader 8.1.3 for Mac OS X after I found the setting "Allow external content". Unfortunately, it seems that non-Adobe tools ignore the external stream feature. I hope I'm wrong, therefore ask the question: How to enable external streams in Mac OS X? (I think that all the system Mac OS X tools use the same library, therefore say "Mac OS X" instead of "Preview".) Or maybe there could be a programming hook to emulate external streams? My task is: store a big set of images (total ˜300Mb) outside of a small PDF (˜1Mb). At some moment, I want to filter PDF through a quartz filter and get a PDF with the images embedded. Any suggestions are welcome.

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• Keeping sync in multiplayer RTS game that uses floating point arithmetic

  - by Calmarius

  I'm writing a 2D space RTS game in C#. Single player works. Now I want to add some multiplayer functionality. I googled for it and it seems there is only one way to have thousands of units continuously moving without a powerful net connection: send only the commands through the network while running the same simulation at every player. And now there is a problem the entire engine uses doubles everywhere. And floating point calculations are depends heavily on compiler optimalizations and cpu architecture so it is very hard to keep things syncronized. And it is not grid based at all, and have a simple phisics engine to move the space-ships (space ships have impulse and angular-momentum...). So recoding the entire stuff to use fixed point would be quite cumbersome (but probably the only solution). So I have 2 options so far: Say bye to the current code and restart from scratch using integers Make the game LAN only where there is enough bandwidth to have 8 players with thousands of units and sending the positions and orientation etc in (almost) every frame... So I looking for better opinions, (or even tips on migrating the code to fixed-point without messing everything up...)

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• Do you have health checks in your web app or web site?

  - by Pekka

  I have built PHP based "health check" scripts for several projects, but they were always custom-made for the occasion and not written for abstraction as an independent product. I would like to know whether such a solution exists. What I meam by "health check" is a protected web page that functions much like a suite of unit tests, but on a more operational level, showing red/yellow/green statuses for things like Are the cache directories writable? Is the PHP version correct, are required extensions installed? Is the configuration file protected from writing? Is the database server reachable? Do the key tables exist in the database? Is there enough disk space available? Is the site's front page reachable and renders fully ( = no PHP errors)? Do the project's libraries' MD5 checksums match the original ones? Do you do this - or parts of it - in your applications and web sites? Are there any standardized tools for this that bring along all the functionality to perform the tests (ideally as plugins), and just need to be configured accordingly? Is there a way to set this up using one of the Unit Testing frameworks available for PHP (preferably PHPUnit)? If so, do you know any resources / tutorials outlining how?

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