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• C++'s unordered_map / hash_map / Google's dense_hash - how to input binary data (buf+len) and insert

  - by shlomif

  Hi all, I have two questions about Google's dense_hash_map, which can be used instead of the more standard unordered_map or hash_map: How do I use an arbitrary binary data memory segment as a key: I want a buffer+length pair, which may still contain some NUL (\0) characters. I can see how I use a NUL-terminated char * string , but that's not what I want. How do I implement an operation where I look if a key exists, and if not - insert it and if it does return the pointer to the existing key and let me know what actually happened. I'd appreciate it if anyone can shed any light on this subject. Regards, -- Shlomi Fish

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• Processing large recordsets in Rails

  - by japancheese

  Hello, I'm trying to perform a daily operation on a larger than normal dataset (2m+ records). However, Rails seems to take a very long time performing operations on such a dataset. Operations like Dataset.all.each do |data| ... end take a very long time to complete (I assume this is because it can't fit all the items into memory at once, right?). Does anyone have any strategies on how I could handle this situation? I know SQL would probably speed up the process, but I'm looking to use the Rails environment as I can do many more complicated things to the data than I can with just SQL statements.

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• Windows equivalent of inb(), outb(), low level i/o

  - by Sebastian Dwornik

  I have some Linux code that monitors our hardware by collecting temperatures, voltages, and fan speeds, from the motherboard using inb(), outb(), inl(), etc. low level i/o functions. My challenge is to port that code over to run under Windows as a simple console app. But am puzzled in what functions Win32 (or .NET) provide that allow me permission to access direct memory mapped ports. I don't want to code a system driver either. My Windows tool preference is VS2008. (fyi) Is this possible?

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• Modify input stream data on the fly

  - by Frizi

  I would like to implement a std::stream modifier/parser, that is doing data manipulation on the fly. Is it possible to create it in form of stream manipulator? For example, i want to strip all the line comments (from any // to the end of line) out of the stdin and pass it to stdout. string str; istream strippingCin = cin >> stripcomments; while(strippingCin.good()) { strippingCin >> str; cout << str; } There may be also a large file input instead of cin, so i don't want to load full stream data into memory at once. Is it possible without writing my own stream class? Maybe is there another route i should take instead?

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• whats wrong with this piece of code for saving contacts

  - by Shadow

  Hi, i am using the latest Nokia Qt SDK. i have tried to add the contacts, its not getting added.. what is missing here.. // Construct contact manager for default contact backend QContactManager* cm = new QContactManager("simulator"); // QContactManager* cm = new QContactManager("memory"); // i tried this, its also not working // Create example contact QContact example; // Add contact name QContactName name; name.setFirstName("John"); name.setLastName("Doe"); example.saveDetail(&name); // Add contact email address //QContactEmailAddress email; // email.setContexts(QContactDetail::ContextHome); //email.setEmailAddress(“[email protected]”); // example.saveDetail(&email); // Finally, save the contact details cm->saveContact(&example); delete cm; Thanks

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• Program visible to Linux as normal directory

  - by Xam

  I'm trying to write program to work as programmable directory, in other words: User, or other systems open that directory and read/write files or dirs. I try to create program to cache most used files in memory (less I/O to HDD), but right now I don't know how to achive that. There are probably some docs about this but I can't find them. I know that there is FUSE, NFS and others, but reading their source is quite difficult. If any one has info about implementation in C lang I'll be very grateful. Sorry for my English..

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• Microsoft Enterprise Logging Application Block - Reading Log File

  - by Or A

  Hi, I'm using MS log application block for logging my application event into a file called app-trace.log which located on the c:\temp folder. I'm trying to find the best way to read this file at runtime and display it when the user asks for it. now i have 2 issues: it seems that this kind of feature is not supported by the framework, hence i have to write this reader myself. am i missing something here? is there any better way of getting this data (w/o buffering it in the memory or saving it into another file). if i'm taking the only alternative that left for me, and implementing the reader myself, when i'm tring to do: System.IO.FileStream fs = new System.IO.FileStream(@"c:\temp\app-trace.log", FileMode.Open, FileAccess.Read); i'm getting "File being used by another process c#", probably the file is locked by the application block. is there any way to access and read it anyhow? Thank

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• iphone best practice, how to load multiple high quality images

  - by bennythemink

  Hi guys and girls, I have about 20-ish high quality images (~3840x5800 px) that I need to load in a simple gallery type app. The user clicks a button and the next image is loaded into the UIImageView. I currently use [UIImage imageWithContentsOfFile:] which takes about 6 seconds to load each image in the simulator :( if I use [UIImage imageNamed:] it takes even longer to load but caches the images which means its quicker if the user wishes to see the same images again. But it may cause memory problems later with all that caching crashing my app. I want to know whats the best practice for loading these? I'm experimenting with reducing image file size as much as is possible but I really need them to be high quality image for the purpose of the app (zoomable, etc.). Thanks for any advice

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• Undefined behaviour with non-virtual destructors - is it a real-world issue?

  - by Roddy

  Consider the following code: class A { public: A() {} ~A() {} }; class B: public A { B() {} ~B() {} }; A* b = new B; delete b; // undefined behaviour My understanding is that the C++ standard says that deleting b is undefined behaviour - ie, anything could happen. But, in the real world, my experience is that ~A() is always invoked, and the memory is correctly freed. if B introduces any class members with their own destructors, they won't get invoked, but I'm only interested in the simple kind of case above, where inheritance is used maybe to fix a bug in one class method for which source code is unavailable. Obviously this isn't going to be what you want in non-trivial cases, but it is at least consistent. Are you aware of any C++ implementation where the above does NOT happen, for the code shown?

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• delete & new in c++

  - by singh

  Hi This may be very simple question,But please help me. i wanted to know what exactly happens when i call new & delete , For example in below code char * ptr=new char [10]; delete [] ptr; call to new returns me memory address. Does it allocate exact 10 bytes on heap, Where information about size is stored.When i call delete on same pointer,i see in debugger that there are a lot of byte get changed before and after the 10 Bytes. Is there any header for each new which contain information about number of byte allocated by new. Thanks a lot

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• Reset JPA generated value between tests

  - by Rythmic

  I'm running spring + hibernate + JUnit with springJunit4runner and transactional set to default rollback I'm using in-memory derbydb as Database. Hibernate is used as a JPA Provider and I am successfully testing CRUD kinds of stuff. However, I have a problem with JPA and the behaviour of @GeneratedValue If I run one of my tests in isolation, two entitys are persisted with id 1 and 2. If i run the whole test suite the ids are instead 6 and 7. Spring does rollbacks just fine so there are only these two entitys in the database after addition and of course zero before. But behaviour of @GeneratedValue doesn't allow me to reliable findById unless I would return the Id from the dao.add(Entity e) //method I don't feel like doing that for the sake of testing, or is it a good practise to return the entity that was persisted so I should be doing it anyway?

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• Is there an automatic way to remove debugging methods for a release build?

  - by Lewis

  Note: This is an extension of an earlier question I asked here: Do additional function/method definitions increase a program's memory footprint? When I write a class, I usually end up writing several testing/debugging methods, used to make sure the class works as it should, or for printing data to help with debugging, or for unit testing, etc. Is there an easy/automatic way to make a release without these methods, or do I need to manually delete the extra code any time I want to compile a release version? I ask this question both from a C++ and a Java perspective. I'm using Code::Blocks and Eclipse as IDEs, if that plays into the answer somehow.

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• What is the best way to declare a property?

  - by Simon

  Hi. We declare properties using the @property keyword and synthesize it in the implementation file. My question is, What if I declare a property using the @property keyword and also declare a variable in the interface block with the same name? For example, consider the following code, Interface: @interface myClass : NSObject { NSString *myClass_name; // LINE 1 } @property(nonatomic, retain) NSString *myClass_name; // LINE 2 @end Implementation: @implementation myClass @synthesize myClass_name // LINE 3 @end Declaring myClass_name in LINE 1 will make any problem? Like any reference problem or any unnecessary memory consumption problem?

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• Is there a way to cause a new C++ class instance to fail, if certain conditions in the contructor ar

  - by Jim Fell

  As I understand it, when a new class is instantiated in C++, a pointer to the new class is returned, or NULL, if there is insufficient memory. I am writing a class that initializes a linked list in the constructor. If there is an error while initializing the list, I would like the class instantiator to return NULL. For example: MyClass * pRags = new MyClass; If the linked list in the MyClass constructor fails to initialize properly, I would like pRags to equal NULL. I know that I can use flags and additional checks to do this, but I would like to avoid that, if possible. Does anyone know of a way to do this? Thanks.

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• Is there any conflict between NFS and calling getFD().sync()?

  - by Dr.Dredel

  My boss is worried that our NFS file system will not be happy with the jboss run java process calling getFD().sync on the files we are writing. We have noticed that frequently the time stamp on the created file is minutes (sometimes as many as 15 minutes) after the log claims the file was finished writing. My only guess is that the NFS is hanging on to the file in memory and not writing it till it feels like it. sync should solve that probelm, right? I also noticed that there is never a close() called on the file. Wondering if that could have been the cause as well? any thoughts appreciated.

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• Less Mathematical Approaches to Machine Learning?

  - by Ed

  Out of curiosity, I've been reading up a bit on the field of Machine Learning, and I'm surprised at the amount of computation and mathematics involved. One book I'm reading through uses advanced concepts such as Ring Theory and PDEs (note: the only thing I know about PDEs is that they use that funny looking character). This strikes me as odd considering that mathematics itself is a hard thing to "learn." Are there any branches of Machine Learning that use different approaches? I would think that a approaches relying more on logic, memory, construction of unfounded assumptions, and over-generalizations would be a better way to go, since that seems more like the way animals think. Animals don't (explicitly) calculate probabilities and statistics; at least as far as I know.

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• What's the reason why core data takes care of the life-cycle of modeled properties?

  - by mystify

  The docs say that I should not release any modeled property in -dealloc. For me, that feels like violating the big memory management rules. I see a big retain in the header and no -release, because Core Data seems to do it at any other time. Is it because Core Data may drop the value of a property dynamically, at any time when needed? And what's Core Data doing when dropping an managed object? If there's no -dealloc, then how and when are the properties getting freed up?

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• Windows XP: Have my program run in kernel mode?

  - by Kalamari

  I'm currently learning about the different modes the Windows operating system runs in (kernel mode vs. user mode), device drivers, their respective advantages and disadvantages and computer security in general. I would like to create a practical example of what a faulty device driver that runs in kernel mode can do to the system, by for example corrupting memory used for critical OS-processes. How can I execute my code in kernel mode instead of user mode, directly? Do I have to write a dummy device driver and install it to do this? Where can I read more about kernel and user mode in Windows? I know the dangers of this and will do all of the experiments on a virtual machine running Windows XP only

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• Firefox: how to apply XSLT from plugin to opened XML document? (how to replace document with another

  - by aloispaulin

  Hi! I've developed a plug-in for Firefox, that can read and manipulate the content of the currently opened document. I would like to apply a XLST to the document in case it is XML. I have no problem to read the XML document and apply a XSLT to it in memory, however, I have no idea of how to replace the existing document with the newly created one. Thus, I see two possible scenarios: a) I replace the document with the result of the transformation b) I apply the XSLT directly to the XML All my attempts to realize one of both possible solutions have failed... Hoping the community can provide help! Many tnx in advance! Alois

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• NULL In a Class Destructor

  - by Hyper-DarkStar

  Simple question; Is it pointless to set a pointer( which allocates heap memory ) to NULL in the destructor? class SampleClass { public: SampleClass( int Init = 0 ) { Value = new int( Init ); } ~SampleClass( void ) { delete Value; Value = NULL; // Is this pointless? } int *Value; }; While on the subject of classes, when should I use the explicit keyword? Thanks.

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• How to deal with callback to your UIController after your UIController unloads?

  - by erotsppa

  Suppose your controller is a table view and one of the cells you are going off to do a length task (say download a thumbnail) to be viewed in the cell. Typically you would have the network call do a callback to your controller when it is done downloading. The callback can then reload the table or do some other form of UI update (hides a spinner etc). However, what if the controller is unloaded? Say the user navigated away from this controller and it got released? What happens? Will the callback still work despite the controller now not in memory? Also, if the callback operates on some objects (say the UITableView) what happens when the controller is deallocated? I suppose the controller can release all the objects and the callback would just be calling methods on nil to prevent crash. But is this the convention?

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• UITableView with contact image problems.

  - by prathumca

  As par my app requirement, I'm showing the contact images in a UITableView as shown below. ABRecordRef contact = [self getContact]; if(contact && ABPersonHasImageData(contact)) { UIImage *contactImage = [UIImage imageWithData:(NSData*)ABPersonCopyImageData(contact)]; callImage.image = contactImage; } I've two problems if I use the above code segment. Table Scrolling is too slow. If comment the above code, then UITable responds very fast. Memory Management. My app started using 25 - 30 MB of RAM. Is there any better way to avoid the above two problems?

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• Table Variables in SSIS

  - by aceinthehole

  In one SQL Task can I create a table variable DELCARE @TableVar TABLE (...) Then in another SQL Task or DataSource destination and select or insert into the table variable? The other option I have considered is using a Temp Table. CREATE TABLE #TempTable (...) I would prefer to use Table Variable so that it remains in memory. But can use temp table if it is not possible to use table variable. Also I cannot use the record set destination as I need to preform straight SQL tasks on it later on.

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• Would vector of vectors be contiguous?

  - by user1150989

  I need to allocate a vector of rows where row contains a vector of rows. I know that a vector would be contiguous. I wanted to know whether a vector of vectors would also be contiguous. Example code is given below vector<long> firstRow; firstRow.push_back(0); firstRow.push_back(1); vector<long> secondRow; secondRow.push_back(0); secondRow.push_back(1); vector< vector < long> > data; data.push_back(firstRow); data.push_back(secondRow); Would the sequence in memory be 0 1 0 1?

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• Intercommunication between Java Chat Servers

  - by Pravingate

  I have a application in which I am using socket programming , having this(image) scenario. Where number of clients will try to connect Broadcast server. Now here I am managing load through LVS(Load balancer). so as a example shown in image, suppose 200 clients will wish to login for broadcast they will be distributed as 100 users on server 1 and another 100 users on server 2.clients will get connected to servers using TCP connection. Now I am maintaining user information on server side in arraylist which will be stored in heap memory,Now the problem is if client wish to broadcast to all logged in users, but that particular client is logged in server 1. and so client will not be able to broadcast another 100 users from server 2. Because both ther servers are unaware about each others state. please suggest to solve this scenario by whatever means you want.

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