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• Why do Java/C# edge out C++ as the recommended language to learn OOP on S.O?

  - by viksit

  I noticed after reading the answers/discussion to this question (What is the best language to learn OOP on?) - that more and more people are recommending C# or Java over C++ to learn OOP on. A simple term search on that answer page results in 10 hits for C++, 21 for C# and 27 for Java. Now, I understand that these 2 languages fix a lot of quirks and issues with C++, and looked up these resources that relate mostly to performance, JVM vs native implementation, systems focus vs applications, manual memory management vs automated et al. My question is - are there any fundamental differences in the OO capabilities of Java/C# vs C++? Or are the former recommended purely due to their generic ease of use/improvements over the latter? Thanks. PS, I'm aware of Java interface inheritance vs C++ multiple inheritance as a difference. I would consider that an implementational one rather than functional.

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• System::IDisposable woes

  - by shadeMe

  public ref class ScriptEditor : public Form { public: typedef map<UInt32, ScriptEditor^> AlMap; static AlMap AllocationMap; Form^ EditorForm; RichTextBox^ EditorBox; StatusBar^ EditorStatusBar; StatusBarPanel^ StatusBarLineNo; void Destroy() { EditorForm->Close(); } ScriptEditor(unsigned int PosX, unsigned int PosY); }; The above code throws an Error C2039: '{dtor}' : is not a member of 'System::IDisposable'. I'm quite lost after having looked into articles that explain how the CLR manages memory. Any advice on getting rid of it would be appreciated. My first dabble in C+++/CLI isn't going too well.

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• How to mark empty in a single element in a float array

  - by Vineeth Mohan

  I have a large float (primitive) array and not every element in the array is filled. How can i mark a particular element as EMPTY. I understand this can be achieved by some special symbols but still i would like to know the standard way. Even if i am using some special symbol , how will i handle a situation where the actual data item is the value of special symbol. In short my question is how to implement the NULL feature in a primitive type array in java. PS - The reason why i am not using Float object is to achieve a high memory and speed performance. Thanks Vineeth

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• What libraries are available for manipulating super large images in .Net

  - by tpower

  I have some really large files for example 320 MB tif file with 14000 X 9000 pixels. The operations I need to perform are basically scaling the images to get smaller versions of it and breaking the image into tiles. My code works fine with small files and I use the .Net Bitmap objects but I will occasionally get Out of Memory exceptions for larger files. I've tried using the FreeImage libraries FreeImageBitmap but have the same problems. I'm using something like the following to scale the image: using (Graphics g = Graphics.FromImage((Image)result)) { g.DrawImage( source, xOffset, yOffset, source.Width * scale, source.Height * scale ); } Ideally I'd like a third party library to do all the hardwork, but if you have any tips or resources with more information I would appreciate it.

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• Where should I catch WM_HIBERNATE and WM_CLOSE in Windows Mobile/WinCE?

  - by afriza

  I have read about Windows Mobile's X button's behaviour, WM_HIBERNATE, and WM_CLOSE on Low Memory Situation. MSDN on WM_HIBERNATE: This message is sent to an application when system resources are running low. An application should attempt to release as many resources as possible when sent this message by unloading dialog boxes, destroying windows, or freeing up as much local storage as possible without changing the internal state. MSDN on WM_CLOSE: This message is sent as a signal that a window or an application should terminate. Where should I catch the message? in the main message pump? in every window? or only some windows? If I am using MFC, where should I catch it?

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• How to implement arrays in an interpreter?

  - by Ray

  I have managed to write several interpreters including Tokenizing Parsing, including more complicated expressions such as ((x+y)*z)/2 Building bytecode from syntax trees Actual bytecode execution What I didn't manage: Implementation of dictionaries/lists/arrays. I always got stuck with getting multiple values into one variable. My value structure (used for all values passed around, including variables) looks like this, for example: class Value { public: ValueType type; int integerValue; string stringValue; } Works fine with integers and strings, but how could I implement arrays? (From now on with array I mean arrays in my experimental language, not in C++) How can I fit the array concept into the Value class above? Is it possible? How should I make arrays able to be passed around just as you could pass around integers and strings in my language, using the class above? Accessing array elements or memory allocation wouldn't be the problem, I just don't know how to store them.

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• Keeping a large volume of data in Session - Suggestions / alternatives?

  - by Fishcake

  I'm developing a web app for which the client wants us to query their data as little as possible. The data will be coming from a Microsoft CRM instance. So we've agreed that data will only be queried as and when it is needed, therefore if a web user wants to see a list of contacts (for example) that list is fetched into a local DataTable. Then if a new contact is created on the website the new contact is sent to CRM and added to the local DataTable at the same time. Likewise for edits. If the user then looks at their contacts again the data will just come from the local DataTable. At the moment local data is being kept in Session but my concern is that too much memory will start being used up. However traffic is expected to be pretty small, perhaps no more than 20 concurrent users so am I worrying about nothing or is there a better way you can suggest to handle this?

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• Returning references while using shared_ptrs

  - by Goose Bumper

  Suppose I have a rather large class Matrix, and I've overloaded operator== to check for equality like so: bool operator==(Matrix &a, Matrix &b); Of course I'm passing the Matrix objects by reference because they are so large. Now i have a method Matrix::inverse() that returns a new Matrix object. Now I want to use the inverse directly in a comparison, like so: if (a.inverse()==b) { ... }` The problem is, this means the inverse method needs to return a reference to a Matrix object. Two questions: Since I'm just using that reference in this once comparison, is this a memory leak? What happens if the object-to-be-returned in the inverse() method belongs to a boost::shared_ptr? As soon as the method exits, the shared_ptr is destroyed and the object is no longer valid. Is there a way to return a reference to an object that belongs to a shared_ptr?

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• Java threadpool functionality

  - by cpf

  Hi stackoverflow, I need to make a program with a limited amount of threads (currently using newFixedThreadPool) but I have the problem that all threads get created from start, filling up memory at alarming rate. I wish to prevent this. Threads should only be created shortly before they are executed. e.g.: I call the program and instruct it to use 2 threads in the pool. The program should create & launch the first 2 Threads immediately (obviously), create the next 2 to wait for the previous 2, and at that point wait until one or both of the first 2 ended executing. I thought about extending executor or FixedThreadPool or such. However I have no clue on how to start there and doubt it is the best solution. Easiest would have my main Thread sleeping on intervals, which is not really good either... Thanks in advance!

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• How does multiple implementing multiple COM interfaces work in C++?

  - by Martin

  I am trying to understand this example code regarding Browser Helper Objects. Inside, the author implements a single class which exposes multiple interfaces (IObjectWithSite, IDispatch). His QueryInterface function performs the following: if(riid == IID_IUnknown) *ppv = static_cast<BHO*>(this); else if(riid == IID_IObjectWithSite) *ppv = static_cast<IObjectWithSite*>(this); else if (riid == IID_IDispatch) *ppv = static_cast<IDispatch*>(this); I have learned that from a C perspective, interface pointers are just pointers to VTables. So I take it to mean that C++ is capable of returning the VTable of any implemented interface using static_cast. Does this mean that a class constructed in this way has a bunch of VTables in memory (IObjectWithSite, IDispatch, etc)? What does C++ do with the name collisions on the different interfaces (they each have a QueryInterface, AddRef and Release function), can I implement different methods for each of these?

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• Large ResultSet on postgresql query

  - by tuler

  I'm running a query against a table in a postgresql database. The database is on a remote machine. The table has around 30 sub-tables using postgresql partitioning capability. The query will return a large result set, something around 1.8 million rows. In my code I use spring jdbc support, method JdbcTemplate.query, but my RowCallbackHandler is not being called. My best guess is that the postgresql jdbc driver (I use version 8.3-603.jdbc4) is accumulating the result in memory before calling my code. I thought the fetchSize configuration could control this, but I tried it and nothing changes. I did this as postgresql manual recomended. This query worked fine when I used Oracle XE. But I'm trying to migrate to postgresql because of the partitioning feature, which is not available in Oracle XE. My environment: Postgresql 8.3 Windows Server 2008 Enterprise 64-bit JRE 1.6 64-bit Spring 2.5.6 Postgresql JDBC Driver 8.3-603

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• Object sent -autorelease too many times

  - by mongeta

  I have this code that simple returns Today's date as a string formatted: +(NSString*) getTodayString_YYYY_MM_DD { NSDate * today = [NSDate date]; NSDateFormatter *formatter = [[NSDateFormatter alloc] init]; [formatter setDateFormat:@"yyyy-MM-dd"]; return [[formatter stringFromDate:today] autorelease]; } With instruments I'm not getting a memory leak, but when I Analyze, XCode says: Object sent -autorelease too many times If I understand correctly, I have to release manually the formatter as I'm creating it using 'alloc', but I can't release here because I have to return the value, so I add the autorelease. How I can do it better to improve it ? thanks, r.

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• How to read a file with variable multi-row data in Python

  - by dr.bunsen

  I have a file that is about 100Mb that looks like this: #meta data 1 skadjflaskdjfasljdfalskdjfl sdkfjhasdlkgjhsdlkjghlaskdj asdhfk #meta data 2 jflaksdjflaksjdflkjasdlfjas ldaksjflkdsajlkdfj #meta data 3 alsdkjflasdjkfglalaskdjf This file contains one row of meta data that corresponds to several, variable length data containing only alpha-numeric characters. What is the best way to read this data into a simple list like this: data = [[#meta data 1, skadjflaskdjfasljdfalskdjflsdkfjhasdlkgjhsdlkjghlaskdjasdhfk], [#meta data 2, jflaksdjflaksjdflkjasdlfjasldaksjflkdsajlkdfj], [#meta data 3, alsdkjflasdjkfglalaskdjf]] My initial idea was to use the read() method to read the whole file into memory and then use regular expressions to parse the data into the desired format. Is there a better more pythonic way? All metadata lines start with an octothorpe and all data lines are all alpha-numeric. Thanks!

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• SQLserver multithreaded locking with TABLOCKX

  - by WilfriedVS

  I have a table "tbluser" with 2 fields: userid = integer (autoincrement) user = nvarchar(100) I have a multithreaded/multi server application that uses this table. I want to accomplish the following: Guarantee that field user is unique in my table Guarantee that combination userid/user is unique in each server's memory I have the following stored procedure: CREATE PROCEDURE uniqueuser @user nvarchar(100) AS BEGIN BEGIN TRAN DECLARE @userID int SET nocount ON SET @userID = (SELECT @userID FROM tbluser WITH (TABLOCKX) WHERE [user] = @user) IF @userID <> '' BEGIN SELECT userID = @userID END ELSE BEGIN INSERT INTO tbluser([user]) VALUES (@user) SELECT userID = SCOPE_IDENTITY() END COMMIT TRAN END Basically the application calls the stored procedure and provides a username as parameter. The stored procedure either gets the userid or insert the user if it is a new user. Am I correct to assume that the table is locked (only one server can insert/query)?

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• Plugin architecture in .net: unloading

  - by henchman

  Hello everybody, I need to implement a plugin architecture within c#/.net in order to load custom user defined actions data type handling code for a custom data grid / conversion / ... from non-static linked assembly files. Because the application has to handle many custom user defined actions, Iam in need for unloading them once executed in order to reduce memory usage. I found several good articles about plugin architectures, eg: ExtensionManager PluginArchitecture ... but none of them gave me enough sausage for properly unloading an assembly. As the program is to be distributed and the user defined actions are (as the name states) user defined: how to i prevent the assembly from executing malicious code (eg. closing my progra, deleting files)? Are there any other pitfalls one of you has encountered?

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• How to index a string like "aaa.bbb.ddd-fff" in Lucene?

  - by user46703

  Hi, I have to index a lot documents that contain reference numbers like "aaa.bbb.ddd-fff". The structure can change but it's always some arbitrary numbers or characters combined with "/","-","_" or some other delimiter. The users want to be able to search for any of the substrings like "aaa" or "ddd" and also for combinations like "aaa.bbb" or "ddd-fff". The best I have been able to come up with is to create my own token filter modeled after the synonym filter in "Lucene in action" which spits out multiple terms for each input. In my case I return "aaa.bbb", "bbb.ddd","bbb.ddd-fff" and all other combinations of the substrings. This works pretty well but when I index large documents (100MB) that contain lots of such strings I tend to get out of memory exceptions because my filter returns multiple terms for each input string. Is there a better way to index these strings?

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• How to reduce java concurrent mode failure and excessive gc

  - by jimx

  In Java, the concurrent mode failure means that the concurrent collector failed to free up enough memory space form tenured and permanent gen and has to give up and let the full stop-the-world gc kicks in. The end result could be very expensive. I understand this concept but never had a good comprehensive understanding of A) what could cause a concurrent mode failure and B) what's the solution?. This sort of unclearness leads me to write/debug code without much of hints in mind and often has to shop around those performance flags from Foo to Bar without particular reasons, just have to try. I'd like to learn from developers here how your experience is. If you had previous encountered such performance issue, what was the cause and how you addressed it? If you have coding recommendations, please don't be too general. Thanks!

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• Converting MS Word Documents to PDF in ASP.NET

  - by glaxaco

  Similar questions have been asked, but nothing exactly like mine, so here goes. We have a collection of Microsoft Word documents on an ASP.NET web server with merge fields whose values are filled in as a result of user form submissions. After the field merge, the server must convert the document to PDF and stream it down to the browser. Our first inclination was to use the Visual Studio Tools for Office API; however, we ran into this warning from Microsoft: Microsoft does not currently recommend, and does not support, Automation of Microsoft Office applications from any unattended, non-interactive client application or component (including ASP, ASP.NET, DCOM, and NT Services), because Office may exhibit unstable behavior and/or deadlock when Office is run in this environment. It looks like the field manipulation can be done using the Open XML SDK, but what's the best way to convert Word 2007 documents to PDF without opening Word? The optimal solution would be low-cost, scalable, have a low memory footprint, be easy to deploy, and have a .NET API.

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• What interprocess locking calls should I monitor?

  - by Matt Joiner

  I'm monitoring a process with strace/ltrace in the hope to find and intercept a call that checks, and potentially activates some kind of globally shared lock. While I've dealt with and read about several forms of interprocess locking on Linux before, I'm drawing a blank on what to calls to look for. Currently my only suspect is futex() which comes up very early on in the process' execution. Update0 There is some confusion about what I'm after. I'm monitoring an existing process for calls to persistent interprocess memory or equivalent. I'd like to know what system and library calls to look for. I have no intention call these myself, so naturally futex() will come up, I'm sure many libraries will implement their locking calls in terms of this, etc. Update1 I'd like a list of function names or a link to documentation, that I should monitor at the ltrace and strace levels (and specifying which). Any other good advice about how to track and locate the global lock in mind would be great.

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• addObjectsFromArray

  - by derek.lo

  I have a question about memory management when using the addObjectsFromArray method. Basically, I have 2 arrays defined in the appDelegate. I need these 2 arrays for the duration of my application's runtime. I therefore release them in my appDelegate's dealloc method. When I go to use these two arrays in a class, I want one array to store the values from the other, so that the other can have it's contents removed, but still stick around for use. Something like this: [appDelegate.arrayTwo addObjectsFromArray:appDelegate.arrayOne]; [appDelegate.arrayOne removeAllObjects]; I'm getting the compiler error: EXC_BAD_ACCESS because of a pointer issue? retaining issue? Any help would be greatly appreciated! Thanks

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• Chaning coding style due to Android GC performance, how far is too far?

  - by Benju

  I keep hearing that Android applications should try to limit the number of objects created in order to reduce the workload on the garbage collector. It makes sense that you may not want to created massive numbers of objects to track on a limited memory footprint, for example on a traditional server application created 100,000 objects within a few seconds would not be unheard of. The problem is how far should I take this? I've seen tons of examples of Android applications relying on static state in order supposedly "speed things up". Does increasing the number of instances that need to be garbage collected from dozens to hundreds really make that big of a difference? I can imagine changing my coding style to now created hundreds of thousands of objects like you might have on a full-blown Java-EE server but relying on a bunch of static state to (supposedly) reduce the number of objects to be garbage collected seems odd. How much is it really necessary to change your coding style in order to create performance Android apps?

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• Conseqences of assigning self

  - by Vegar

  Hi, Found a piece of code today, that I find a little smelly... TMyObject.LoadFromFile(const filename: String); begin if fileExists(filename) then self := TSomeObjectStreamer.ReadObjectFromFile(filename); end; If this code works, it will atleast leak some memory, but does it work? Is OK to assign to self in this manner? What if the streamed object is of a different subclass then the original self? What if the streamed object is of a different class with no common ancestore to the original self?

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• How can I catch runtime error in C++

  - by Yan Cheng CHEOK

  By referring to http://stackoverflow.com/questions/315948/c-catching-all-exceptions try { int i = 0; int j = 0/i; /* Division by 0 */ int *k = 0; std::cout << *k << std::endl; /* De-reference invalid memory location. */ } catch (...) { std::cout << "Opps!" << std::endl; } The above run-time error are unable to be detected. Or, am I having wrong expectation on C++ exception handling feature?

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• Parsing XML stream in ASP.NET 3.5

  - by Ranjit

  Hi All, I am trying to build an ASP.NET 3.5 application based on XML streams from a legacy systems. My issue is once I get the XML I have to built menus and sub menus from the XML as well filter data(XML stream) based on the menu selection without making roundtrip to the Data store(legacy system). Right now I have a DAL which will get the XML stream in the form of XDocument.I was able to built the first level Menu Items, but not the sub Menu Items based on the selection in the Main Menu and then the final content based on the sub menu selection, all this without making a round trip. Is there a way to do this in-memory. Please suggest. thank you. Ranjit

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• What is a .NET managed module?

  - by Abhijeet Patel

  I know it's a Windows PE32, but I also know that the unit of deployment in .NET is an assembly which in turn has a manifest and can be made up of multiple managed modules. My questions are : 1) How would you create multiple managed modules when building a project such as a class lib or a console app etc. 2) Is there a way to specify this to the compiler(via the project properties for example) to partition your source code files into multiple managed modules. If so what is the benefit of doing so? 3)Can managed modules span assemblies? 4)Are separate file created on disk when the source code is compiled or are these created in memory and directly embedded in an assembly?

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