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• Using C++, why can `throw` cause `terminate()`, and when are the stack variables to be freed?

  - by nbolton

  I'm pondering a question on Brainbench. I actually realised that I could answer my question easily by compiling the code, but it's an interesting question nonetheless, so I'll ask the question anyway and answer it myself shortly. Take a look at this snippet: The question considers what happens when we throw from a destructor (which causes terminate() to be called). It's become clear to me by asking the question that the memory is indeed freed and the destructor is called, but, is this before or after throw is called from foo? Perhaps the issue here is that throw is used while the stack is unwinding that is the problem... Actually this is slightly confusing.

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• C++ smart pointer for a non-object type?

  - by Brian

  Hi, I'm trying to use smart pointers such as auto_ptr, shared_ptr. However, I don't know how to use it in this situation. CvMemStorage *storage = cvCreateMemStorage(); ... use the pointer ... cvReleaseMemStorage(&storage); I'm not sure, but I think that the storage variable is just a malloc'ed memory, not a C++ class object. Is there a way to use the smart pointers for the storage variable? Thank you.

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• Delphi VirtualStringTree - Check for Duplicates?

  - by Jeff

  Hello S.O! Yeah, I know I post a lot of questions, but thats because I either need assurance that I am doing it right, what I am doing wrong, or if I am totally clueless, and cant find anything in the documentation. Anyways, I am trying to check for duplicate nodes. Here is how I would want to do it: Loop thru my nodes, and compare each single node's text (record), but if I got many nodes, wouldnt that be too time and memory consuming? Would there be a better approach for this? Thanks! - Jeff.

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• What is the difference between a 32-bit and 64-bit processor?

  - by JJG

  I have been trying to read up on 32-bit and 64-bit processors (http://en.wikipedia.org/wiki/32-bit_processing). My understanding is that a 32-bit processor (like x86) has registers 32-bits wide. I'm not sure what that means. So it has special "memory spaces" that can store integer values up to 2^32? I don't want to sound stupid, but I have no idea about processors. I'm assuming 64-bits is, in general, better than 32-bits. Although my computer now (one year old, Win 7, Intel Atom) has a 32-bit processor.

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• How to calculate real-time stats?

  - by Diego Jancic

  I have a site with millions of users (well, actually it doesn't have any yet, but let's imagine), and I want to calculate some stats like "log-ins in the past hour". The problem is similar to the one described here: http://highscalability.com/blog/2008/4/19/how-to-build-a-real-time-analytics-system.html The simplest approach would be to do a select like this: select count(distinct user_id) from logs where date>='20120601 1200' and date <='20120601 1300' (of course other conditions could apply for the stats, like log-ins per country) Of course this would be really slow, mainly if it has millions (or even thousands) of rows, and I want to query this every time a page is displayed. How would you summarize the data? What should go to the (mem)cache? EDIT: I'm looking for a way to de-normalize the data, or to keep the cache up-to-date. For example I could increment an in-memory variable every time someone logs in, but that would help to know the total amount of logins, not the "logins in the last hour". Hope it's more clear now.

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• VS2010's "Public Property <PropertyName> As <DataType> vs. Public var

  - by Velika2

  In VS2008, I used to type Public Property <PropName> As <dataType> and hit the Enter key and the IDE editor would automatically expand it out to a full blown property block. Now, from what I understand, a new feature of 2010 is that the compiler automatically "expands" the short syntax above into the same IL code that you would get with the full property GET AND SET sub methods that were are accustomed to seeing before in the editor. But functionality, how the heck is this any different than just having a Public class level variable? If the only diff is what it compiles to and if otehrwise there is no functional difference, isn't the new way less efficient than the old since it involves more code than just having a class level memory variable? Public as I thought that if you weren't going to have code behind your properties that they were essentially the same. I guess the diffrenece is that they just added the keyword "Property" but functionality, their is no diff, eh?

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• What is your favourite Windbg tip/trick?

  - by user15071

  I have come to realize that Windbg is a very powerful debugger for the Windows platform & I learn something new about it once in a while. Can fellow Windbg users share some of their mad skills? ps: I am not looking for a nifty command, those can be found in the documentation. How about sharing tips on doing something that one couldn't otherwise imagine could be done with windbg? e.g. Some way to generate statistics about memory allocations when a process is run under windbg.

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• SQLAlchemy automatically converts str to unicode on commit

  - by Victor Stanciu

  Hello, When inserting an object into a database with SQLAlchemy, all it's properties that correspond to String() columns are automatically transformed from <type 'str'> to <type 'unicode'>. Is there a way to prevent this behavior? Here is the code: from sqlalchemy import create_engine, Table, Column, Integer, String, MetaData from sqlalchemy.orm import mapper, sessionmaker engine = create_engine('sqlite:///:memory:', echo=False) metadata = MetaData() table = Table('projects', metadata, Column('id', Integer, primary_key=True), Column('name', String(50)) ) class Project(object): def __init__(self, name): self.name = name mapper(Project, table) metadata.create_all(engine) session = sessionmaker(bind=engine)() project = Project("Lorem ipsum") print(type(project.name)) session.add(project) session.commit() print(type(project.name)) And here is the output: <type 'str'> <type 'unicode'> I know I should probably just work with unicode, but this would involve digging through some third-party code and I don't have the Python skills for that yet :)

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• STL Vectors, pointers and classes

  - by anubis9

  Hey! Let's say i have 2 classes: class Class1 { public: std::vector<CustomClass3*> mVec; public: Class1(); ~Class1() { //iterate over all the members of the vector and delete the objects } }; class InitializerClass2 { private: Class1 * mPtrToClass1; public: InitializerClass2(); void Initialize() { mPtrToClass1->mVec.push_back(new CustomClass3(bla bla parameters)); } }; Will this work? Or the memory allocated in the InitializerClass2::Initialize() method might get corrupted after the method terminates? Thanks!

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• Javascript clears a variable after there is no further reference it

  - by Praveen Prasad

  It is said, javascript clears a variable from memory after its being referenced last. just for the sake of this question i created a JS file with only one variable; //file start //variable defined var a=["Hello"] //refenence to that variable alert(a[0]); // //file end no further reference to that variable, so i expect javascript to clear varaible 'a' Now i just ran this page and then opened firebug and ran this code alert(a[0]); Now this alerts the value of variable, If the statement "Javascript clears a variable after there is no further reference it" is true how come alert() shows its value. Is it because all variable defined in global context become properties of window object, and since even after the execution file window objects exist so does it properties.

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• How is a new programming language actually formed/created ?

  - by hory.incpp

  Fortran-Algol-Cpl-Bcpl-C-C++-Java ..... Seems like every language is built upon an ancestor language. My question : New languages extend parent ones or there is some kind of a trick? e.g. System.out.print() in Java ; is it actually printf() in C, and so on (printf is actually .. in Cpl)? If so, doesn't this make every further language be slower and need more memory? What separates a new language from a framework?

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• Find the closest vector

  - by Alexey Lebedev

  Hello! Recently I wrote the algorithm to quantize an RGB image. Every pixel is represented by an (R,G,B) vector, and quantization codebook is a couple of 3-dimensional vectors. Every pixel of the image needs to be mapped to (say, "replaced by") the codebook pixel closest in terms of euclidean distance (more exactly, squared euclidean). I did it as follows: class EuclideanMetric(DistanceMetric): def __call__(self, x, y): d = x - y return sqrt(sum(d * d, -1)) class Quantizer(object): def __init__(self, codebook, distanceMetric = EuclideanMetric()): self._codebook = codebook self._distMetric = distanceMetric def quantize(self, imageArray): quantizedRaster = zeros(imageArray.shape) X = quantizedRaster.shape[0] Y = quantizedRaster.shape[1] for i in xrange(0, X): print i for j in xrange(0, Y): dist = self._distMetric(imageArray[i,j], self._codebook) code = argmin(dist) quantizedRaster[i,j] = self._codebook[code] return quantizedRaster ...and it works awfully, almost 800 seconds on my Pentium Core Duo 2.2 GHz, 4 Gigs of memory and an image of 2600*2700 pixels:( Is there a way to somewhat optimize this? Maybe the other algorithm or some Python-specific optimizations.

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• What is the best possible technology for pulling huge data from 4 remote servers

  - by Habib Ullah Bahar

  Hello, For one of our project, we need to pull huge real time stock data from 4 remote servers across two countries. The trivial process here, check the sources for a regular interval and save the update to database. But as these are real time stock data of more than 1000 companies, I have to pull every second, which isn't good in case of memory, bandwidth I think. Please give me suggestion on which technology/platform [We are flexible here. PHP, Python, Java, PERL - anyone of them will be OK for us] we should choose, it can be achieved easily and with better performance.

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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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• Java appliction design question

  - by ring bearer

  Hi I have a hobby project, which is basically to maintain 'todo' tasks in the way I like. One task can be described as: public class TodoItem { private String subject; private Date dueBy; private Date startBy; private Priority priority; private String category; private Status status; private String notes; } as you can imagine I would have 1000 todo items at a given time. What is the best strategy to store a todo item? (currently on an XML file) such that all the items are loaded quickly up on app start up(the application shows kind of a dashboard of all the items at start up) What is the best way to design its back-end so that it can be ported to android/or a J2ME based phone Currently this is done using java swing. What should be the concerns so that it works efficiently on a device where memory is limited? Thanks!

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• Passing arguments to java vm from NSIS script

  - by CodeBuddy

  I'm developing my first java application using Eclipse. I've recently needed to adjust the amount of memory allocated by passing -Xmx256M to the JVM. The application is currently package up as a runnable jar and installed using the NSIS. I'm having a problem passing arguments to the jar file once its installed. What is the common practice for doing this? Here is what I'm currently doing in my nsi file: CreateShortcut "$SMPROGRAMS\$StartMenuGroup\$(^Name).lnk" "$SYSDIR\javaw.exe" "-jar -Xmx256M $INSTDIR\Foo.jar" This results in the following being created as the shortcut Target on windows: C:\WINDOWS\system32\javaw.exe -jar -Xmx256M C:\Program Files\Foo\Foo.jar Unfortunately this does not work due to the space in C:\Program Files, If I change the link created manually to include quotes all is well: C:\WINDOWS\system32\javaw.exe -jar -Xmx256M "C:\Program Files\Foo\Foo.jar"

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• Does MATLAB perform tail call optimization?

  - by Shea Levy

  I've recently learned Haskell, and am trying to carry the pure functional style over to my other code when possible. An important aspect of this is treating all variables as immutable, i.e. constants. In order to do so, many computations that would be implemented using loops in an imperative style have to be performed using recursion, which typically incurs a memory penalty due to the allocation a new stack frame for each function call. In the special case of a tail call (where the return value of a called function is immediately returned to the callee's caller), however, this penalty can be bypassed by a process called tail call optimization (in one method, this can be done by essentially replacing a call with a jmp after setting up the stack properly). Does MATLAB perform TCO by default, or is there a way to tell it to?

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• How to diganose an unlogged Error 500 on Apache?

  - by samuel morhaim

  We are running a very simple Symfony script, that randomly returns an Error 500. The system administrator says he can't find any trace of an Error 500 on the error logs, however using Curl or Firebug, it is obvious that an Error 500 is being returned. The script simply parses a POST request submitted to an URL on our server. We already checked for performance, memory etc but nothing seems to be the problem. How is this possible? We already enabled all debugging, logging, on Apache, PHP, etc and nothing.

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• Socket ping-pong performance

  - by Kamil_H

  I have written two simple programs (tried it in C++ and C#). This is pseudo code: -------- Client --------------- for(int i = 0; i < 200.000; i++) { socket_send("ping") socket_receive(buff) } --------- Server ------------- while(1) { socket_receive(buff) socket_send("pong") } I tried it on Windows. Execution time of client is about 45 seconds. Can somebody explain me why this takes so long? I understand that if there were real network connection between client and server the time of one 'ping-pong' would be: generate_ping + send_via_network + generate_pong + send_via_network but here everything is done in 'local' mode. Is there any way to make this inter process ping-pong faster using network sockets (I'm not asking about shared memory for example :) )

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• What is the largest file size we can transfer through air application?

  - by Naveen kumar

  Hi all, I'm trying to transfer large file(1Gb+) using UDP(in packets) through air application. I'm transfering byteArray by taking chunks of packets from FileStream. But its giving 'Error #1000: The system is out of memory' at sender side after certain number of packets sent and by this time the downloaded file size at server side is 256 MB. I tried with other files but after downloading 256MB, sender is giving the same error. Is it because of the file stream size? How can I solve this problem so that I can transfer files of GB size.

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• Linux Kernel - Slab Allocator Question

  - by Drex

  I am playing around with the kernel and am looking at the kmem_cache files_cachep belonging to fork.c. It detects the sizeof(files_struct). My question is this: I have altered files_struct and added a rb_root (red/black tree root) using the built-in functionality in linux/rbtree.h. I can properly insert values into this tree. However, at some point, a segfault occurs and GDB backtraces the following information: (gdb) backtrace 0 0x08066ad7 in page_ok (page=) at arch/um/os-Linux/sys-i386/task_size.c:31 1 0x08066bdf in os_get_top_address () at arch/um/os-Linux/sys-i386/task_size.c:100 2 0x0804a216 in linux_main (argc=1, argv=0xbfb05f14) at arch/um/kernel/um_arch.c:277 3 0x0804acdc in main (argc=1, argv=0xbfb05f14, envp=0xbfb05f1c) at arch/um/os-Linux/main.c:150 I have spent many hours trying to figure out why there is a segfault given that the red/black tree inserts properly. I'm thinking it's a memory allocation issue with new processes made by fork() of a parent process. Could this be the case and could it have something to do with kmem_cache files_cachep?

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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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• Strange profiling results: definitely non-bottleneck method pops up

  - by jkff

  I'm profiling a program using sampling profiling in YourKit and JProfiler, and also "manually" (I launch it and press Ctrl-Break several times to get thread dumps). All three methods give me extremely strange results: some tens of percents of time spent in a 3-line method that does not even do any allocation or synchronization and doesn't have loops etc. Moreover, after I made this method into a NOP and even removed its invocation completely, the observable program performance didn't change at all (although it got a negligible memory leak, since it was a method for freeing a cheap resource). I'm thinking that this might be because of the constraints that JVM puts on the moments at which a thread's stacktrace may be taken, and it somehow turns out that in my program it is exactly the moments where this method is invoked, although there is absolutely nothing special about it or the context in which it is invoked. What can be the explanation for this phenomenon? What are the aforementioned constraints? What further measurements can I take to clarify the situation?

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• Puzzled with nib files...

  - by Michael

  I know nib files are serialized objects and they have owner, outlets to make connections. Using XCode Navigation window template I created application, which in its order created 2 nib files - MainWindow and SecondView. I can't understand how MainWindow is referring to SecondView, there is no connection between those two as far as I can see. SecondView's owner is UIViewController and in MainWindow there is a navigation tab which is also UIViewController. But how they are connected in IB I can't understand... Also I don't understand who is instanciating MainWindow's owner object and where that object is being kept, where is the variable which is UIApplication myApp = [[UIApplication alloc] init]. If I create 10 nib files with UIViewController owner, who will trigger their deserialization? If some class is nib file's owner, what is the essential responsibilities of that class? Is it deserializing nib file into memory? Sorry for unorganized questions, I've been reading numerous articles and docs about nib files, but it is still confusing.

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• How to use a dialog in an Excel shared addin

  - by user169867

  I'm writing a shared addin for Excel. It adds a CommandBarButton that when clicked opens a WPF window to collect some information from the user. I wanted to keep the same WPF dialog in memory and reuse it so that if the user clicks the CommandBarButton again their previous values would still be there. So I made a reference to my WPD as a private member of my addin object that implements Extensibility.IDTExtensibility2. I created the window during OnStartupComplete(), but for some reason when I run Excel the window immediately opens even though I never called ShowDialog() and when I do call ShowDialog() when the CommandBarButton is clicked to reOpen the window it fails to load. Does anyone know why this happens and what the correct way to handle this is? Thanks very much for any help.

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