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• What are the original reasons for ToString() in Java and .NET?

  - by d.

  I've used ToString() modestly in the past and I've found it very useful in many circumstances. However, my usage of this method would hardly justify to put this method in none other than System.Object. My wild guess is that, at some point during the work carried out and meetings held to come up with the initial design of the .NET framework, it was decided that it was necessary - or at least extremely useful - to include a ToString() method that would be implemented by everything in the .NET framework. Does anyone know what the exact reasons were? Am I missing a ton of situations where ToString() proves useful enough as to be part of System.Object? What were the original reasons for ToString()? Thanks a lot! PS - Again: I'm not questioning the method or implying that it's not useful, I'm just curious to know what makes it SO useful as to be placed in System.Object. Side note - Imagine this: AnyDotNetNativeClass someInitialObject = new AnyDotNetNativeClass([some constructor parameters]); AnyDotNetNativeClass initialObjectFullCopy = AnyDotNetNativeClass.FromString(someInitialObject.ToString()); Wouldn't this be cool? EDIT(1): (A) - Based on some answers, it seems that .NET languages inherited this from Java. So, I'm adding "Java" to the subject and to the tags as well. If someone knows the reasons why this was implemented in Java then please shed some light! (B) - Static hypothetical FromString vs Serialization: sure, but that's quite a different story, right?

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• Activator.CreateInstance uses a huge amount of memory

  - by Marco

  I have been playing a bit with Silverlight and try to port my Silverlight 3.0 application to Silverlight 4.0. My application loads different XAP files and upon a user request create an instance of a Xaml user control and adds it to the main container, in a sort of MEF approach in order I can have an extensible and pluggable application. The application is pretty huge and to keep acceptable the performances and the initial loading I have built up some helper classes to load in the background all pages and user controls that might be used later on. On Silverlight 3.0 everything was running smoothly without any problem so far. Switching to SL 4.0 I have noticed that when the process approaches to create the instances of the user controls using Activator.CreateInstance, the layout freezes unexpectedly for a minute and sometimes for more. Looking at the task manager the memory usage of IE jumps from 50MB to 400MB and sometimes to 1.5 GB. If the process won't take that much the layout is rendered properly and the memory falls back to 50 MB. Otherwise everything crashes due to out of memory exeption. Does anybody encountered the same problem? Or has anybody a solution about this tricky issue?

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• What's the cleanest way to do byte-level manipulation?

  - by Jurily

  I have the following C struct from the source code of a server, and many similar: // preprocessing magic: 1-byte alignment typedef struct AUTH_LOGON_CHALLENGE_C { // 4 byte header uint8 cmd; uint8 error; uint16 size; // 30 bytes uint8 gamename[4]; uint8 version1; uint8 version2; uint8 version3; uint16 build; uint8 platform[4]; uint8 os[4]; uint8 country[4]; uint32 timezone_bias; uint32 ip; uint8 I_len; // I_len bytes uint8 I[1]; } sAuthLogonChallenge_C; // usage (the actual code that will read my packets): sAuthLogonChallenge_C *ch = (sAuthLogonChallenge_C*)&buf[0]; // where buf is a raw byte array These are TCP packets, and I need to implement something that emits and reads them in C#. What's the cleanest way to do this? My current approach involves [StructLayout(LayoutKind.Sequential, Pack = 1)] unsafe struct foo { ... } and a lot of fixed statements to read and write it, but it feels really clunky, and since the packet itself is not fixed length, I don't feel comfortable using it. Also, it's a lot of work. However, it does describe the data structure nicely, and the protocol may change over time, so this may be ideal for maintenance. What are my options? Would it be easier to just write it in C++ and use some .NET magic to use that?

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• "|" pipe operator not working in command line in C++

  - by user332024

  I am having a windows application interacting with DB2 database. In my application i have code to execute some DB2 commands through command line interface. I have used windowsAPI "ShellExecuteEx()" to execute those DB2 commands through command line. Following is the code written to execute DB2 command through command line. string command = "/c /w /i DB2 UNCATALOG NODE DB_DATABASE "" test.log | echo %date% %time% test.log SHELLEXECUTEINFO shellInfo; ZeroMemory(&shellInfo, sizeof(shellInfo)); shellInfo.cbSize = sizeof(shellInfo); shellInfo.fMask = SEE_MASK_FLAG_NO_UI | SEE_MASK_NOCLOSEPROCESS; //shellInfo.lpFile = "db2cmd"; shellInfo.lpFile = "db2cmd"; shellInfo.lpParameters = command.c_str(); The code is executed successfully , however if test.log is observered i only get result of DB2 command and not date and time. If you see the above command there is "|" pipe operator and echo command to log date and time in test.log Please note that if I execute above DB2 command through separately command line i.e. not through code. I am able to view date and time log along with DB2 command result in test.log. Following is the full command which i executed through command line. DB2CMD /c /i /w DB2 UNCATALOG NODE DB_DATABASE "" test.log | echo %date% %time% test.log According to me since DB2 command is executed successfully through code, there is problem with only usage of "|" pipe operator or echo command.

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• An Erroneous SQL Query makes browser hang until script timeout exceeded

  - by Jimbo

  I have an admin page in a Classic ASP web application that allows the admin user to run queries against the database (SQL Server 2000) Whats really strange is that if the query you send has an error in it (an invalid table join, a column you've forgotten to group by etc) the BROWSER hangs (CPU usage goes to maximum) until the SERVER script timeout is exceeded and then spits out a timeout exceeded error (server and browser are on different machines, so not sure how this happens!) I have tried this in IE 8 and FF 3 with the same result. If you run that same query (with errors) directly from SQL Enterprise Manager, it returns the real error immediately. Is this a security feature? Does anyone know how to turn it off? It even happens when the connection to the database is using 'sa' credentials so I dont think its a security setting :( Dim oRS Set oRS = Server.CreateObject("ADODB.Recordset") oRS.ActiveConnection = sConnectionString // run the query - this is for the admin only so doesnt check for sql safe commands etc. oRS.Open Request.Form("txtSQL") If Not oRS.EOF Then // list the field names from the recordset For i = 0 to oRS.Fields.Count - 1 Response.Write oRS.Fields(i).name & "&nbsp;" Next // show the data for each record in the recordset While Not oRS.EOF For i = 0 to oRS.Fields.Count - 1 Response.Write oRS.Fields(i).value & "&nbsp;" Next Response.Write "<br />" oRS.Movenext() Wend End If

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• Recommendations for IPC between parent and child processes in .NET?

  - by Jeremy

  My .NET program needs to run an algorithm that makes heavy use of 3rd party libraries (32-bit), most of which are unmanaged code. I want to drive the CPU as hard as I can, so the code runs several threads in parallel to divide up the work. I find that running all these threads simultaneously results in temporary memory spikes, causing the process' virtual memory size to approach the 2 GB limit. This memory is released back pretty quickly, but occasionally if enough threads enter the wrong sections of code at once, the process crosses the "red line" and either the unmanaged code or the .NET code encounters an out of memory error. I can throttle back the number of threads but then my CPU usage is not as high as I would like. I am thinking of creating worker processes rather than worker threads to help avoid the out of memory errors, since doing so would give each thread of execution its own 2 GB of virtual address space (my box has lots of RAM). I am wondering what are the best/easiest methods to communicate the input and output between the processes in .NET? The file system is an obvious choice. I am used to shared memory, named pipes, and such from my UNIX background. Is there a Windows or .NET specific mechanism I should use?

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• Memory Leakage using datatables

  - by Vix

  Hi, I have situation in which i'm compelled to retrieve 30,000 records each to 2 datatables.I need to do some manipulations and insert into records into the SQL server in Manipulate(dt1,dt2) function.I have to do this in 15 times as you can see in the for loop.Now I want to know what would be the effective way in terms of memory usage.I've used the first approach.Please suggest me the best approach. (1) for (int i = 0; i < 15; i++) { DataTable dt1 = GetInfo(i); DataTable dt2 = GetData(i); Manipulate(dt1,dt2); } (OR) (2) DataTable dt1 = new DataTable(); DataTable dt2 = new DataTable(); for (int i = 0; i < 15; i++) { dt1=null; dt2=null; dt1 = GetInfo(); dt2 = GetData(); Manipulate(dt1, dt2); } Thanks, Vix.

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• Flash Player: Any remedy for the stale video image data problem (in a reused NetStream object)?

  - by amn

  Has anyone experienced stale stills of a previous playback for a reused NetStream object? If so, what are the workarounds for this, except re-creating the object (which eats performance and time)? It is hard to reuse NetStream objects because of a (in my opinion) fundamental issue with NetStream objects - when you 'close' a playing stream and at a later point issue a 'play' call on it again with a different name, the stream appears to still contain a stale image lingering from previous playback, and this is of course displayed in the Video object for a moment - the moment I assume it takes for new stream data to become available from server. Because of this behavior, to improve my users' visual experience, I simply discard a NetStream object after a playback session, and assign a new NetStream object to the same variable, set it up, and play something else. It appears to work - no stale image - but what bugs me is that it's a work around and costs performance (construction and setting up the object again - event listeners and 'client' delegates and more memory usage - NetStream objects are not garbage collected immediately, it takes some time). It would be really nice to REALLY be able to reuse a stream. I am thinking of something akin to Video.clear method, but for the NetStream class. Am I missing something?

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• Implement a threading to prevent UI block on a bug in an async function

  - by Marcx

  I think I ran up againt a bug in an async function... Precisely the getDirectoryListingAsync() of the File class... This method is supposted to return an object containing the lists of files in a specified folder. I found that calling this method on a direcory with a lot of files (in my tests more than 20k files), after few seconds there is a block on the UI until the process is completed... I think that this method is separated in two main block: 1) get the list of files 2) create the array with the details of the files The point 1 seems to be async (for a few second the ui is responsive), then when the process pass from point 1 to point 2 the block of the UI occurs until the complete event is dispathed... Here's some (simple) code: private function checkFiles(dir:File):void { if (dir.exists) { dir.addEventListener( FileListEvent.DIRECTORY_LISTING, listaImmaginiLocale); dir.getDirectoryListingAsync(); // after this point, for the firsts seconds the UI respond well (point 1), // few seconds later (point 2) the UI is frozen } } private function listaImmaginiLocale( event:FileListEvent ):void { // from this point on the UI is responsive again... } Actually in my projects there are some function that perform an heavy cpu usage and to prevent the UI block I implemented a simple function that after some iteration will wait giving time to UI to be refreshed. private var maxIteration:int = 150000; private function sampleFunct(offset:int = 0) :void { if (offset < maxIteration) { // do something // call the recursive function using a timeout.. // if the offset in multiple by 1000 the function will wait 15 millisec, // otherwise it will be called immediately // 1000 is a random number for the pourpose of this example, but I usually change the // value based on how much heavy is the function itself... setTimeout(function():void{aaa(++offset);}, (offset%1000?15:0)); } } Using this method I got a good responsive UI without afflicting performance... I'd like to implement it into the getDirectoryListingAsync method but I don't know if it's possibile how can I do it where is the file to edit or extend.. Any suggestion???

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• Compact data structure for storing a large set of integral values

  - by Odrade

  I'm working on an application that needs to pass around large sets of Int32 values. The sets are expected to contain ~1,000,000-50,000,000 items, where each item is a database key in the range 0-50,000,000. I expect distribution of ids in any given set to be effectively random over this range. The operations I need on the set are dirt simple: Add a new value Iterate over all of the values. There is a serious concern about the memory usage of these sets, so I'm looking for a data structure that can store the ids more efficiently than a simple List<int>or HashSet<int>. I've looked at BitArray, but that can be wasteful depending on how sparse the ids are. I've also considered a bitwise trie, but I'm unsure how to calculate the space efficiency of that solution for the expected data. A Bloom Filter would be great, if only I could tolerate the false negatives. I would appreciate any suggestions of data structures suitable for this purpose. I'm interested in both out-of-the-box and custom solutions. EDIT: To answer your questions: No, the items don't need to be sorted By "pass around" I mean both pass between methods and serialize and send over the wire. I clearly should have mentioned this. There could be a decent number of these sets in memory at once (~100).

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• Is there a better way to keep track of session variable creation/access throughout different pages?

  - by Brandon

  Here's what I am working on. At my website I have multiple processes with each one containing multiple steps. Now in one of the processes, there is an error checking routine executed before proceeding to the next step of that process. A session var is set indicating the error status and it will either redirect back to the referrer or display the next page's contents. Now this kind of functionality, I believe, is common throughout web development. The issue that is occurring is that session vars are left around and are not being cleaned up properly. At times this introduces undesired behavior. My website is growing and I find that I am requiring more and more session vars to keep track of different system and error states. So I was thinking about creating a kind of "session variable keeper" to keep track of session var usage. The idea is fairly simple. It will have the notion of a context (e.g. registration process) and allow access to a predefined set of session vars within that context. In addition, the var and context will be paired with an action to proceed to some form of event handling. So if you haven't noticed I'm new to web development. Any thoughts or comments on the idea that I am proposing would be greatly appreciated. The back-end is written in PHP/MySQL.

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• Disabling browser print options (headers, footers, margins) from page?

  - by Anthony

  I have seen this question asked in a couple of different ways on SO and several other websites, but most of them are either too specific or out-of-date. I'm hoping someone can provide a definitive answer here without pandering to speculation. Is there a way, either with CSS or javascript, to change the default printer settings when someone prints within their browser? And of course by "prints from their browser" I mean some form of HTML, not PDF or some other plug-in reliant mime-type. Please note: If some browsers offer this and others don't (or if you only know how to do it for some browsers) I welcome browser-specific solutions. Similarly, if you know of a mainstream browser that has specific restrictions against EVER doing this, that is also helpful, but some fairly up-to-date documentation would be appreciated. (simply saying "that goes against XYZ's security policy" isn't very convincing when XYZ has made significant changes in said policy in the last three years). Finally, when I say "change default print settings" I don't mean forever, just for my page, and I am referring specifically to print margins, headers, and footers. I am very aware that CSS offers the option of changing the page orientation as well as the page margins. One of the many struggles is with Firefox. If I set the page margins to 1 inch, it ADDS this to the half inch it already puts into place. I very much want to reduce the usage of PDFs on my client's site, but the infringement on presentation (as well as the lack of reliability) are their main concern.

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• Shaping EF LINQ Query Results Using Multi-Table Includes

  - by sisdog

  I have a simple LINQ EF query below using the method syntax. I'm using my Include statement to join four tables: Event and Doc are the two main tables, EventDoc is a many-to-many link table, and DocUsage is a lookup table. My challenge is that I'd like to shape my results by only selecting specific columns from each of the four tables. But, the compiler is giving a compiler is giving me the following error: 'System.Data.Objects.DataClasses.EntityCollection does not contain a definition for "Doc' and no extension method 'Doc' accepting a first argument of type 'System.Data.Objects.DataClasses.EntityCollection' could be found. I'm sure this is something easy but I'm not figuring it out. I haven't been able to find an example of someone using the multi-table include but also shaping the projection. Thx,Mark var qry= context.Event .Include("EventDoc.Doc.DocUsage") .Select(n => new { n.EventDate, n.EventDoc.Doc.Filename, //<=COMPILER ERROR HERE n.EventDoc.Doc.DocUsage.Usage }) .ToList(); EventDoc ed; Doc d = ed.Doc; //<=NO COMPILER ERROR SO I KNOW MY MODEL'S CORRECT DocUsage du = d.DocUsage;

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• programs hangs during socket interaction

  - by herrturtur

  I have two programs, sendfile.py and recvfile.py that are supposed to interact to send a file across the network. They communicate over TCP sockets. The communication is supposed to go something like this: sender =====filename=====> receiver sender <===== 'ok' ======= receiver or sender <===== 'no' ======= receiver if ok: sender ====== file ======> receiver I've got The sender and receiver code is here: Sender: import sys from jmm_sockets import * if len(sys.argv) != 4: print "Usage:", sys.argv[0], "<host> <port> <filename>" sys.exit(1) s = getClientSocket(sys.argv[1], int(sys.argv[2])) try: f = open(sys.argv[3]) except IOError, msg: print "couldn't open file" sys.exit(1) # send filename s.send(sys.argv[3]) # receive 'ok' buffer = None response = str() while 1: buffer = s.recv(1) if buffer == '': break else: response = response + buffer if response == 'ok': print 'receiver acknowledged receipt of filename' # send file s.send(f.read()) elif response == 'no': print "receiver doesn't want the file" # cleanup f.close() s.close() Receiver: from jmm_sockets import * s = getServerSocket(None, 16001) conn, addr = s.accept() buffer = None filename = str() # receive filename while 1: buffer = conn.recv(1) if buffer == '': break else: filename = filename + buffer print "sender wants to send", filename, "is that ok?" user_choice = raw_input("ok/no: ") if user_choice == 'ok': # send ok conn.send('ok') #receive file data = str() while 1: buffer = conn.recv(1) if buffer=='': break else: data = data + buffer print data else: conn.send('no') conn.close() I'm sure I'm missing something here in the sorts of a deadlock, but don't know what it is.

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• Application that depends heavily on stored procedures

  - by PieterG

  We currently have an application that depends largely on stored procedures. There is a heavy use of temp tables. It's an extremely large application. Facing this situation, I would like to use Entity Framework or Linq2Sql for a rewrite. I might consider using Fluent Hibernate or Subsonic, as i've used them quite extensively in the past. I've had problems with Linq2Sql generating the return types for the stored procedures because of the usage of the temp tables, and I think it's cumbersome to go and change all the stored procedures from temp tables to in-memory tables. Considering the 2 choices that I want to make, which one of the 2 is the best route to go and why? If my choices are extremely idiotic, please provide alternatives. Edit: The reason for the question and the change is that the data access layer is non-existent and was built 10 years ago. We currently still run into a lot of issues with it. I don't want to divulge too much, but if you saw it, your eyes would start bleeding :)

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• Android - Memory leak when dynamically building UI with image resource backgrounds

  - by Rich

  I have an Activity that I swear is leaking memory. The app I'm working on does a lot with images, so I've had to be pretty stingy with memory when working directly with Bitmaps. I added an Activity, and now if you use this new Activity it basically puts me over the edge with mem usage and I end up throwing the "Bitmap exceeds VM budget" exception. If you never launch this Activity, everything is smooth as it was previously. I started reading about memory leaks, and I think that I have a similar situation to what is described in the article in the Android docs. I'm dynamically creating a bunch of image views and adding a BackgroundDrawable from the resources and adding an OnClickListener as well. I imagine I have to do some cleanup when the Activity hits onPause in its life cycle, but I'd like to know specifically what is the correct way. Here is the code that should demonstrate the objects I'm working with... LinearLayout templateContainer; . . . ImageView imgTemplatePreview = (ImageView) item.findViewById(R.id.imgTemplatePreview); . . . imgTemplatePreview.setBackgroundDrawable(getResources().getDrawable(previewId)); imgTemplatePreview.setOnClickListener(imgClick); templateContainer.addView(item);

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• Inline function v. Macro in C -- What's the Overhead (Memory/Speed)?

  - by Jason R. Mick

  I searched Stack Overflow for the pros/cons of function-like macros v. inline functions. I found the following discussion: Pros and Cons of Different macro function / inline methods in C ...but it didn't answer my primary burning question. Namely, what is the overhead in c of using a macro function (with variables, possibly other function calls) v. an inline function, in terms of memory usage and execution speed? Are there any compiler-dependent differences in overhead? I have both icc and gcc at my disposal. My code snippet I'm modularizing is: double AttractiveTerm = pow(SigmaSquared/RadialDistanceSquared,3); double RepulsiveTerm = AttractiveTerm * AttractiveTerm; EnergyContribution += 4 * Epsilon * (RepulsiveTerm - AttractiveTerm); My reason for turning it into an inline function/macro is so I can drop it into a c file and then conditionally compile other similar, but slightly different functions/macros. e.g.: double AttractiveTerm = pow(SigmaSquared/RadialDistanceSquared,3); double RepulsiveTerm = pow(SigmaSquared/RadialDistanceSquared,9); EnergyContribution += 4 * Epsilon * (RepulsiveTerm - AttractiveTerm); (note the difference in the second line...) This function is a central one to my code and gets called thousands of times per step in my program and my program performs millions of steps. Thus I want to have the LEAST overhead possible, hence why I'm wasting time worrying about the overhead of inlining v. transforming the code into a macro. Based on the prior discussion I already realize other pros/cons (type independence and resulting errors from that) of macros... but what I want to know most, and don't currently know is the PERFORMANCE. I know some of you C veterans will have some great insight for me!!

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• Namespace scoped aliases for generic types in C#

  - by TN

  Let's have a following example: public class X { } public class Y { } public class Z { } public delegate IDictionary<Y, IList<Z>> Bar(IList<X> x, int i); public interface IFoo { // ... Bar Bar { get; } } public class Foo : IFoo { // ... public Bar Bar { get { return null; //... } } } void Main() { IFoo foo; //= ... IEnumerable<IList<X>> source; //= ... var results = source.Select(foo.Bar); } The compiler says: The type arguments for method 'System.Linq.Enumerable.Select(System.Collections.Generic.IEnumerable, System.Func)' cannot be inferred from the usage. Try specifying the type arguments explicitly. It's because, it cannot convert Bar to Func<IList<X>, int, IDictionary<Y, IList<Z>>>. It would be great if I could create type namespace scoped type aliases for generic types in C#. Then I would define Bar not as a delegate, but rather I would define it as an namespace scoped alias for Func<IList<X>, int, IDictionary<Y, IList<Z>>>. public alias Bar = Func<IList<X>, int, IDictionary<Y, IList<Z>>>; I could then also define namespace scoped alias for e.g. IDictionary<Y, IList<Z>>. And if used appropriately:), it will make the code more readable. Now I have inline the generic types and the real code is not well readable:( Have you find the same trouble:)? Is there any good reason why it is not in C# 3.0? Or there is no good reason, it's just matter of money and/or time? EDIT: I know that I can use using, but it is not namespace based - not so convenient for my case.

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• Transparently surround a component with a link in Wicket

  - by Toni Menzel

  I want to be able to add links on certain items in an ListView. If an items is surrounded by the link or not is up to the code, so its not in the normal page markup. Say i have a markup like this: <div class="column" wicket:id="columnRepeater"> <span wicket:id="column"></span> </div> So essentially, while filling the repeater with a ListView i am able to find a custom renderer for the column component. (not my playingfield). What i want is to add a Link/Ajax Link around the column component. I learned using wicket:border lets you surround additional stuff. Now, the border markup looks like this: <wicket:border> <a wicket:id="link"><wicket:body/></a> </wicket:border> Now, i am a bit puzzled what the Border implementation looks like. Anyone there who can suggest a working java part? I have a couple of "work in progress" solutions but none works. Most questions have to do with usage of component ids. Is the border id = column ? Whats the id of the inner (border body) id then?

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• Could someone explain gtk2hs drag and drop to me, the listDND.hs demo just isn't doing it for me?

  - by Tom Carstens

  As the title says, I just don't get DND (or rather I understand the concept and I understand the order of callbacks, I just don't understand how to setup DND for actual usage.) I'd like to say that I've done DND stuff before in C, but considering I never really got that working... So I'm trying (and mostly succeeding, save DND) to write a text editor (using gtksourceview, because it has built in code highlighting.) Reasons are below if you want them. Anyways, there's not really a good DND demo or tutorial available for gtk2hs (listDND.hs just doesn't translate well in my head.) So what I'm asking is for code that demonstrates simple DND on a window widget (for example.) Ideally, it should accept drops from other windows (such as Thunar) and print out the information in string form. I think I can take it from there... Reasons: I'm running a fairly light weight setup, dwm and a few gtk+2 programs. I really don't want to have to pull in gtk+3 to get the current gedit from the repos (Arch Linux.) Currently, I'm using geany for all of my text editing needs, however, geany is a bit heavy for editing config files. Further, geany doesn't care for my terminal of choice (st;) so I don't even get the benefit of using it as an IDE. Meaning I'd like a lightweight text editor with syntax highlighting. I could configure emacs or vim or something, but that seems to me to be more of a hack then a proper solution. Thus my project was born. It's mostly working (aside from DND, all that's left is proper multi-tab support.) Admittedly, I could probably work this out if I wrote it in C, but there isn't that much state in a text editor so Haskell's been working fine with almost no need for mutable variables.

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• How do you hide a Swing Popup when you click somewhere else.

  - by Casey Watson

  I have a Popup that is shown when a user clicks on a button. I would like to hide the popup when any of the following events occur: The user clicks somewhere else in the application. (The background panel for example) The user minimizes the application. The JPopupMenu has this behavior, but I need more than just JMenuItems. The following code block is a simplified illustration to demonstrate the current usage. import java.awt.*; import java.awt.event.ActionEvent; import javax.swing.*; public class PopupTester extends JFrame { public static void main(String[] args) { final PopupTester popupTester = new PopupTester(); popupTester.setLayout(new FlowLayout()); popupTester.setSize(300, 100); popupTester.add(new JButton("Click Me") { @Override protected void fireActionPerformed(ActionEvent event) { Point location = getLocationOnScreen(); int y = (int) (location.getY() + getHeight()); int x = (int) location.getX(); JLabel myComponent = new JLabel("Howdy"); Popup popup = PopupFactory.getSharedInstance().getPopup(popupTester, myComponent, x, y); popup.show(); } }); popupTester.add(new JButton("No Click Me")); popupTester.setVisible(true); popupTester.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); } }

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• Do the 'up to date' guarantees provided by final field in Java's memory model extend to indirect ref

  - by mattbh

  The Java language spec defines semantics of final fields in section 17.5: The usage model for final fields is a simple one. Set the final fields for an object in that object's constructor. Do not write a reference to the object being constructed in a place where another thread can see it before the object's constructor is finished. If this is followed, then when the object is seen by another thread, that thread will always see the correctly constructed version of that object's final fields. It will also see versions of any object or array referenced by those final fields that are at least as up-to-date as the final fields are. My question is - does the 'up-to-date' guarantee extend to the contents of nested arrays, and nested objects? An example scenario: Thread A constructs a HashMap of ArrayLists, then assigns the HashMap to final field 'myFinal' in an instance of class 'MyClass' Thread B sees a (non-synchronized) reference to the MyClass instance and reads 'myFinal', and accesses and reads the contents of one of the ArrayLists In this scenario, are the members of the ArrayList as seen by Thread B guaranteed to be at least as up to date as they were when MyClass's constructor completed?

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• Using an embedded DB (SQLite / SQL Compact) for Message Passing within an app?

  - by wk1989

  Hello, Just out of curiosity, for applications that have a fairly complicated module tree, would something like sqlite/sql compact edition work well for message passing? So if I have modules containing data such as: \SubsystemA\SubSubSysB\ModuleB\ModuleDataC, \SubSystemB\SubSubSystemC\ModuleA\ModuleDataX Using traditional message passing/routing, you have to go through intermediate modules in order to pass a message to ModuleB to request say ModuleDataC. Instead of doing that, if we we simply store "\SubsystemA\SubSubSysB\ModuleB\ModuleDataC" in a sqlite database, getting that data is as simple as a sql query and needs no routing and passing stuff around. Has anyone done this before? Even if you haven't, do you foresee any issues & performance impact? The only concern I have right now would be the passing of custom types, e.g. if ModuleDataC is a custom data structure or a pointer, I'll need some way of storing the data structure into the DB or storing the pointer into the DB. Thanks, JW EDIT One usage case I haven't thought about is when you want to send a message from ModuleA to ModuleB to get ModuleB to do something rather than just getting/setting data. Is it possible to do this using an embedded DB? I believe callback from the DB would be needed, how feasible is this?

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• Need advice on C++ coding pattern

  - by Kotti

  Hi! I have a working prototype of a game engine and right now I'm doing some refactoring. What I'm asking for is your opinion on usage of the following C++ coding patterns. I have implemented some trivial algorithms for collision detection and they are implemented the following way: Not shown here - class constructor is made private and using algorithms looks like Algorithm::HandleInnerCollision(...) struct Algorithm { // Private routines static bool is_inside(Point& p, Object& object) { // (...) } public: /** * Handle collision where the moving object should be always * located inside the static object * * @param MovingObject & mobject * @param const StaticObject & sobject * @return void * @see */ static void HandleInnerCollision(MovingObject& mobject, const StaticObject& sobject) { // (...) } So, my question is - somebody advised me to do it "the C++" way - so that all functions are wrapped in a namespace, but not in a class. Is there some good way to preserve privating if I will wrap them into a namespace as adviced? What I want to have is a simple interface and ability to call functions as Algorithm::HandleInnerCollision(...) while not polluting the namespace with other functions such as is_inside(...) Of, if you can advise any alternative design pattern for such kind of logics, I would really appreciate that...

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• power and modulo on the fly for big numbers

  - by user unknown

  I raise some basis b to the power p and take the modulo m of that. Let's assume b=55170 or 55172 and m=3043839241 (which happens to be the square of 55171). The linux-calculator bc gives the results (we need this for control): echo "p=5606;b=55171;m=b*b;((b-1)^p)%m;((b+1)^p)%m" | bc 2734550616 309288627 Now calculating 55170^5606 gives a somewhat large number, but since I have to do a modulooperation, I can circumvent the usage of BigInt, I thought, because of: (a*b) % c == ((a%c) * (b%c))%c i.e. (9*7) % 5 == ((9%5) * (7%5))%5 => 63 % 5 == (4 * 2) %5 => 3 == 8 % 5 ... and a^d = a^(b+c) = a^b * a^c, therefore I can divide b+c by 2, which gives, for even or odd ds d/2 and d-(d/2), so for 8^5 I can calculate 8^2 * 8^3. So my (defective) method, which always cut's off the divisor on the fly looks like that: def powMod (b: Long, pot: Int, mod: Long) : Long = { if (pot == 1) b % mod else { val pot2 = pot/2 val pm1 = powMod (b, pot, mod) val pm2 = powMod (b, pot-pot2, mod) (pm1 * pm2) % mod } } and feeded with some values, powMod (55170, 5606, 3043839241L) res2: Long = 1885539617 powMod (55172, 5606, 3043839241L) res4: Long = 309288627 As we can see, the second result is exactly the same as the one above, but the first one looks quiet different. I'm doing a lot of such calculations, and they seem to be accurate as long as they stay in the range of Int, but I can't see any error. Using a BigInt works as well, but is way too slow: def calc2 (n: Int, pri: Long) = { val p: BigInt = pri val p3 = p * p val p1 = (p-1).pow (n) % (p3) val p2 = (p+1).pow (n) % (p3) print ("p1: " + p1 + " p2: " + p2) } calc2 (5606, 55171) p1: 2734550616 p2: 309288627 (same result as with bc) Can somebody see the error in powMod?

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