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• Could Grand Central Dispatch (`libdispatch`) ever be made available on Windows?

  - by elliottcable

  I’m looking into multithreading, and GCD seems like a much better option than manually writing a solution using pthread.h and pthreads-win32. However, although it looks like libdispatch is either working on, or soon going to be working on, most newer POSIX-compatible systems… I have to ask, what about Windows? What are the chances of libdispatch being ported to Windows? What are the barriers preventing that from happening? If it came down to it, what would I need to do to preform that portage? Edit: Some things I already know, to get the discussion started: We need a blocks-compatible compiler that will compile on Windows, no? Will PLBlocks handle that? Can we use the LLVM blocks runtime? Can’t we replace all the pthread.h dependencies in userspace libdispatch with APR calls, for portability? Or, alternatively, use pthreads-win32 I suppose…

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• How many instructions to access pointer in C?

  - by Derek

  Hi All, I am trying to figure out how many clock cycles or total instructions it takes to access a pointer in C. I dont think I know how to figure out for example, p-x = d-a + f-b i would assume two loads per pointer, just guessing that there would be a load for the pointer, and a load for the value. So in this operations, the pointer resolution would be a much larger factor than the actual addition, as far as trying to speed this code up, right? This may depend on the compiler and architecture implemented, but am I on the right track? I have seen some code where each value used in say, 3 additions, came from a f2->sum = p1->p2->p3->x + p1->p2->p3->a + p1->p2->p3->m type of structure, and I am trying to define how bad this is

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• Are returned locals automatically xvalues

  - by mark

  Following on from a comment I made on this: passing std::vector to constructor and move semantics Is the std::move necessary in the following code, to ensure that the returned value is a xvalue? std::vector<string> buildVector() { std::vector<string> local; // .... build a vector return std::move(local); } It is my understanding that this is required. I have often seen this used when returning a std::unique_ptr from a function, however GManNickG made the following comment: It is my understanding that in a return statement all local variables are automatically xvalues (expiring values) and will be moved, but I'm unsure if that only applies to the returned object itself. So OP should go ahead and put that in there until I'm more confident it shouldn't have to be. :) Can anyone clarify if the std::move is necessary? Is the behaviour compiler dependent?

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• Recursive compilation using gcc

  - by curiousexplorer

  I am using the gcc compiler. My project source tree looks like somewhat like this test$~: tree . . |-- folder | |-- hello.cpp | `-- hello.h `-- main.cpp 1 directory, 3 files test$~: The file main.cpp contains the main() function and all the functions invoked by main.cpp lie in the directory named folder So far in all my little projects I never had to put some source code under a sub-directory. What I am looking for, in short, is some gcc command for recursive compilation in sub-directories and their subdirectories and so on... This command should be invoked from the home directory of the code project.

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• C# huge size 2-dim arrays

  - by 4eburek

  I need to declare square matrices in C# WinForms with more than 20000 items in a row. I read about 2GB .Net object size limit in 32bit and also the same case in 64bit OS. So as I understood the single answer - is using unsafe code or separate library built withing C++ compiler. The problem for me is worth because ushort[20000,20000] is smaller then 2GB but actually I cannot allocate even 700MB of memory. My limit is 650MB and I don't understand why - I have 32bit WinXP with 3GB of memory. I tried to use Marshal.AllocHGlobal(700<<20) but it throws OutOfMemoryException, GC.GetTotalMemory returns 4.5MB before trying to allocate memory. I found only that many people say use unsafe code but I cannot find example of how to declare 2-dim array in heap (any stack can't keep so huge amount of data) and how to work with it using pointers. Is it pure C++ code inside of unsafe{} brackets? Could you please provide a small example of working with matrices using pointers in unsafe code.

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• F# - This code isn't compiling for me

  - by stacker

  This code isn't compiling for me: let countDown = [5L .. -1L .. 0L];; I have a book that says it should return this: val countDown : int list = [5L; 4L; 3L; 2L; 1L; 0L] Compiler Error: Program.fs(42,24): error FS0010: Unexpected character '-' in expression > > let countDown = [5L .. -1L .. 0L];; let countDown = [5L .. -1L .. 0L];; -----------------------^

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• Do I have to create a static library to test my application?

  - by Christopher Gateley

  I'm just getting started with TDD and am curious as to what approaches others take to run their tests. For reference, I am using the google testing framework, but I believe the question is applicable to most other testing frameworks and to languages other than C/C++. My general approach so far has been to do either one of three things: Write the majority of the application in a static library, then create two executables. One executable is the application itself, while the other is the test runner with all of the tests. Both link to the static library. Embed the testing code directly into the application itself, and enable or disable the testing code using compiler flags. This is probably the best approach I've used so far, but clutters up the code a bit. Embed the testing code directly into the application itself, and, given certain command-line switches either run the application itself or run the tests embedded in the application. None of these solutions are particularly elegant... How do you do it?

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• Memory section handling error

  - by Basilevs

  I'm getting a link time error: WARNING: /home/gulevich/development/camac-fedorov/camac/linux/k0607-lsi6/camac-k0607-lsi6.o (.ctors): unexpected non-allocatable section. Did you forget to use "ax"/"aw" in a .S file? Note that for example <linux/init.h> contains section definitions for use in .S files. The code causing the error (assembly in C source): # if defined(__ELF__) # define __SECTION_FLAGS ", \"aw\" , @progbits" /* writable flag needed for ld ".[cd]tors" sections bug workaround) */ # elif defined(__COFF__) # define __SECTION_FLAGS ", \"dr\"" /* untested, may be writable flag needed */ # endif asm ( ".section .ctors" __SECTION_FLAGS "\n" ".globl __ctors_begin__\n" "__ctors_begin__:\n" ".previous\n" ); Is there any way to fix this? The idea is to put a varaible __ctors_begin__ at the beginning of a certain memory section. This code is a legacy that worked fine using a different build system and older compiler. Meaning of this assembly code explained in an answer to my previous question.

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• C++ class is not being included properly.

  - by ravloony

  Hello all, I have a problem which is either something I have completely failed to understand, or very strange. It's probably the first one, but I have spent the whole afternoon googling with no success, so here goes... I have a class called Schedule, which has as a member a vector of Room. However, when I compile using cmake, or even by hand, I get the following: In file included from schedule.cpp:1: schedule.h:13: error: ‘Room’ was not declared in this scope schedule.h:13: error: template argument 1 is invalid schedule.h:13: error: template argument 2 is invalid schedule.cpp: In constructor ‘Schedule::Schedule(int, int, int)’: schedule.cpp:12: error: ‘Room’ was not declared in this scope schedule.cpp:12: error: expected ‘;’ before ‘r’ schedule.cpp:13: error: request for member ‘push_back’ in ‘((Schedule*)this)->Schedule::_sched’, which is of non-class type ‘int’ schedule.cpp:13: error: ‘r’ was not declared in this scope Here are the relevant bits of code: #include <vector> #include "room.h" class Schedule { private: std::vector<Room> _sched; //line 13 int _ndays; int _nrooms; int _ntslots; public: Schedule(); ~Schedule(); Schedule(int nrooms, int ndays, int ntslots); }; Schedule::Schedule(int nrooms, int ndays, int ntslots):_ndays(ndays), _nrooms(nrooms),_ntslots(ntslots) { for (int i=0; i<nrooms;i++) { Room r(ndays,ntslots); _sched.push_back(r); } } In theory, g++ should compile a class before the one that includes it. There are no circular dependencies here, it's all straightforward stuff. I am completely stumped on this one, which is what leads me to believe that I must be missing something. :-D

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• Technology and language for a stable Digital Audio Workstation development

  - by Kill KRT

  Hi, I'm designing a cross platform (Windows/Linux/OS X) application, something like a digital audio workstation. I'd like to create a software where users have a fully featured sequencer (multiple tracks with automation) and where it is possible to create instruments using a visual language (as Pure Data/Max MSP). Ehm... I know that I've already posted a question about a related issue... But in order to decide which technology I should use, I think I'd better to make more investigation. I'm a quite experted user of audio trackers (Renoise, Protracker,...) and sequencers (FL Studio, Cubase 5), but I didn't ever try to develop even a basic audio tracker. I know just the basic theory of mixing sound and know how basically a DSP works. My questions are: Where I can find a good tutorial/guide/book about this issue? Do you think using C# (with NAudio) could dramatically reduce performance? I know C++ would be the best choice, but I find C# so elegant and easy to build and port, while C++ is so powerful and fast, but there are too #define and bad things for my taste! ;-) Thank you.

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• Using game of life or other virtual environment for artificial (intelligence) life simulation? [clos

  - by Berlin Brown

  One of my interests in AI focuses not so much on data but more on biologic computing. This includes neural networks, mapping the brain, cellular-automata, virtual life and environments. Described below is an exciting project that includes develop a virtual environment for bots to evolve in. "Polyworld is a cross-platform (Linux, Mac OS X) program written by Larry Yaeger to evolve Artificial Intelligence through natural selection and evolutionary algorithms." http://en.wikipedia.org/wiki/Polyworld " Polyworld is a promising project for studying virtual life but it still is far from creating an "intelligent autonomous" agent. Here is my question, in theory, what parameters would you use create an AI environment? Possibly a brain environment? Possibly multiple self contained life organisms that have their own "brain" or life structures. I would like a create a spin on the game of life simulation. What if you have a 64x64 game of life grid. But instead of one grid, you might have N number of grids. The N number of grids are your "life force" If all of the game of life entities die in a particular grid then that entire grid dies. A group of "grids" makes up a life form. I don't have an immediate goal. First, I want to simulate an environment and visualize what is going on in the environment with OpenGL and see if there are any interesting properties to the environment. I then want to add "scarce resources" and see if the AI environment can manage resources adequately.

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• SubSonic 3.0 - Save method with all columns as parameters?

  - by Todd Menier

  Hi, Just getting started with SubSonic. I'm using the Repository pattern, so my domain objects are totally seperate, and SubSonic-generated classes are used only in my data access layer. I'm wondering if a template exists that will give me a Save method (Insert/Update) that requires all table column values as parameters. My thinking is that since I need to do the mapping work manually, at least if my database schema changes (ie, a new column is added), I won't forget to add a corresponding mapping, since the auto-generated method signature would change and the compiler would catch it. I've considered messing with the T4 templates to add this feature, but thought I'd check if this already exists somewhere before I head down that path. Thanks in advance.

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• How well does Scala Perform Comapred to Java?

  - by Teja Kantamneni

  The Question actually says it all. The reason behind this question is I am about to start a small side project and want to do it in Scala. I am learning scala for the past one month and now I am comfortable working with it. The scala compiler itself is pretty slow (unless you use fsc). So how well does it perform on JVM? I previously worked on groovy and I had seen sometimes over performed than java. My Question is how well scala perform on JVM compared to Java. I know scala has some very good features(FP, dynamic lang, statically typed...) but end of the day we need the performance...

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• Use WM_COPYDATA to send data between processes

  - by Charles Gargent

  I wish to send text between processes. I have found lots of examples of this but none that I can get working. Here is what I have so far: for the sending part: COPYDATASTRUCT CDS; CDS.dwData = 1; CDS.cbData = 8; CDS.lpData = NULL; SendMessage(hwnd, WM_COPYDATA , (WPARAM)hwnd, (LPARAM) (LPVOID) &CDS); the receiving part: case WM_COPYDATA: COPYDATASTRUCT* cds = (COPYDATASTRUCT*) lParam; I dont know how to construct the COPYDATASTRUCT, I have just put something in that seems to work. When debugging the WM_COPYDATA case is executed, but again I dont know what to do with the COPYDATASTRUCT. I would like to send text between the two processes. As you can probably tell I am just starting out, I am using GNU GCC Compiler in Code::Blocks, I am trying to avoid MFC and dependencies.

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• Webforms vs. MVC. Once you start using MVC.. Do you ever go back to webforms?

  - by punkouter

  I checked out MVC months ago and didn't really get it.. but recently as I have become a better programmer I think it is making sense.. Here is my theory.. tell me if I got it Right In the 90s for Microsoft Devs we had Classic ASP. This mixed VBscript and HTML on the same page. So you needed to create all the HTML yourself and mix HTML and VBScript. This was not considered Ideal. Then .NET came along and everyone liked it because it was similiar to event driven VB 6 style programming. It created this abstraction of binding data to ASP Servier controls. It made getting Enumerated data easy to get on the screen with one line. Then recently Jquery and SOA concepts are mixed together.. Now people think.. Why create this extra layer of abstraction when I can just directly use .NET as a data provider and use jquery AJAX calls to get the data and create the HTML with it directly .. no need for the Webforms abstraction layer.. Sowe are back to creating HTML directly like we did in 1999. So MVC is all about saying Stop pretending like WEb programming is a VB6 app! Generate HTML directly! Am I missing anything? So I wonder.. for you people out there using MVC... is it the sort of things that once you get used to it you never want to go back to webforms??

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• Should I return an NSMutableString in a method that returns NSString

  - by Casey Marshall

  Ok, so I have a method that takes an NSString as input, does an operation on the contents of this string, and returns the processed string. So the declaration is: - (NSString *) processString: (NSString *) str; The question: should I just return the NSMutableString instance that I used as my "work" buffer, or should I create a new NSString around the mutable one, and return that? So should I do this: - (NSString *) processString: (NSString *) str { NSMutableString *work = [NSMutableString stringWithString: str]; // process 'work' return work; } Or this: - (NSString *) processString: (NSString *) str { NSMutableString *work = [NSMutableString stringWithString: str]; // process 'work' return [NSString stringWithString: work]; // or [work stringValue]? } The second one makes another copy of the string I'm returning, unless NSString does smart things like copy-on-modify. But the first one is returning something the caller could, in theory, go and modify later. I don't care if they do that, since the string is theirs. But are there valid reasons for preferring the latter form over the former? And, is either stringWithString or stringValue preferred over the other?

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• Custom class object in Initialization list

  - by Michael

  I have a class Bar: class Bar { public: Bar(void); ~Bar(void); }; And a class Foo that gets a reference to Bar object as a constructor parameter and needs to save it in a private member bar_ : class Foo { private: Bar& bar_; public: Foo(Bar& bar) : bar_(bar) {} ~Foo(void) {} }; This doesn't compile : overloaded member function not found in 'Parser' missing type specifier - int assumed. Note: C++ does not support default-int Now i suspect couple of things that i need to assure, the second error is for Bar& bar_; declaration in Foo. Do i need to use an explicit constructor when declaring bar_ ? I am interested in learning how the compiler works regarding this matter, so a detailed explanation would be highly appreciated. Thanks.

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• How to learn to program C the right way

  - by sfactor

  i have been programming in C/C++ for my academic courses a lot and was under the impression i had a pretty good grasp of it. but lately i had to work in a bluetooth application that had a server and client implementation in a Linux box and an embedded system. i learned bluez bluetooth API, socket/network programming and coded it. however i ran into a lot of problems with memory leaks and segmentation faults and other memory related errors along the way.as the code grew more complex i all but lost control of the pointers and threads and sockets. this got me wondering that i had a lot to learn that they didn't say in the basic C/C++ books. so i wanted to ask for the resources that are available that'll help be code better in a professional way in C/C++ .especially for the Linux/Mac environment (gcc compiler).

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• How can I find a package?

  - by Roman

  In my code I have the following statement import com.apple.dnssd.*; and compiler (javac) complains about this line. It writes that the package does not exist. But I think that it could be that "javac" search the package in a wrong place (directory). In this respect I have two questions: How can I know where javac search for the packages? I think that it is very likely that I have the above mentioned package but I do not know where it is located. What are the typical place to look for the packages?

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• vector<vector<largeObject>> vs. vector<vector<largeObject>*> in c++

  - by Leif Andersen

  Obviously it will vary depending on the compiler you use, but I'm curious as to the performance issues when doing vector<vector<largeObject>> vs. vector<vector<largeObject>*>, especially in c++. In specific: let's say that you have the outer vector full, and you want to start inserting elements into first inner vector. How will that be stored in memory if the outer vector is just storing pointers, as apposed to storing the whole inner vector. Will the whole outer vector have to be moved to gain more space, or will the inner vector be moved (assuming that space wasn't pre-allocated), causing problems with the outer vector? Thank you

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• How can I compare market data feed sources for quality and latency improvement?

  - by yves Baumes

  I am in the very first stages of implementing a tool to compare 2 market data feed sources in order to prove the quality of new developed sources to my boss ( meaning there are no regressions, no missed updates, or wrong ), and to prove latencies improvement. So the tool I need must be able to check updates differences as well as to tell which source is the best (in term of latency). Concrectly, reference source could be Reuters while the other one is a Feed handler we develop internally. People warned me that updates might not arrive in the same order as Reuters implementation could differs totally from ours. Therefore a simple algorithm based on the fact that updates could arrive in the same order is likely not to work. My very first idea would be to use fingerprint to compare feed sources, as Shazaam application does to find the title of the tube you are submitting. Google told me it is based on FFT. And I was wondering if signal processing theory could behaves well with market access applications. I wanted to know your own experience in that field, is that possible to develop a quite accurate algorithm to meet the needs? What was your own idea? What do you think about fingerprint based comparison?

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• Should non-English member names be changed to English?

  - by M.A. Hanin

  Situation: Automatically generated memebers, such as MenuStrip items, have their (automatically generated) names based on the text entered when the item was created. My most common situation is creating a menu-strip and adding menu-items by entering their text (using the graphical designer). Since my GUI is in Hebrew, all these members have a name which contains a Hebrew string. Something like "(hebrew-text)ToolStripItem". When I create event handlers, the event handlers "inherit" the hebrew text: "(hebrew-text)ToolStripMenuItem_Click". This actually works well, IntelliSense has no problem with Hebrew text, and so does the compiler. The question is: should I change these names (or prevent them from being created in the first place)? What are the possible consequences of keeping those names?

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• Dependency Injection with @Inject in Weld (JSR-299 RI). How is the corresponding @Produces found?

  - by Thorbjørn Ravn Andersen

  I have played with the JSR-299 Reference Implementation "Weld" with the purpose of using it in a stand-alone application, and I have had a look at the documentation, and marveled at the magic. My question is how the producer of a given object to be @Inject'ed is found? Either the java compiler produces hints for annotations which is easily found by the classloader, or the complete classpath must be traversed loading all classes to see what they do which sounds highly inefficient to me, or it is a completely different approach. What is the trick?

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• Is it possible to use Dependency Injection/IoC on an ASP.NET MVC FilterAttribute ?

  - by Pure.Krome

  Hi folks, I've got a simple custom FilterAttribute which I use decorate various ActionMethods. eg. [AcceptVerbs(HttpVerbs.Get)] [MyCustomFilter] public ActionResult Bar(...) { ... } Now, I wish to add some logging to this CustomFilter Action .. so being a good boy, I'm using DI/IoC ... and as such wish to use this pattern for my custom FilterAttribute. So if i have the following... ILoggingService and wish to add this my custom FilterAttribute .. i'm not sure how. Like, it's easy for me to do the following... public class MyCustomFilterAttribute : FilterAttribute { public MyCustomFilterAttribute(ILoggingService loggingService) { ... } } But the compiler errors saying the attribute which decorates my ActionMethod (listed above...) requires 1 arg .. so i'm just not sure what to do :(

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• Hierarchical/Nested Database Structure for Comments

  - by Stephen Melrose

  Hi, I'm trying to figure out the best approach for a database schema for comments. The problem I'm having is that the comments system will need to allow nested/hierarchical comments, and I'm not sure how to design this out properly. My requirements are, Comments can be made on comments, so I need to store the tree hierarchy I need to be able to query the comments in the tree hierarchy order, but efficiently, preferably in a fast single query, but I don't know if this is possible I'd need to make some wierd queries, e.g. pull out the latest 5 root comments, and a maximum of 3 children for each one of those I read an article on the MySQL website on this very subject, http://dev.mysql.com/tech-resources/articles/hierarchical-data.html The "Nested Set Model" in theory sounds like it will do what I need, except I'm worried about querying the thing, and also inserting. If this is the right approach, How would I do my 3rd requirement above? If I have 2000 comments, and I add a new sub-comment on the first comment, that will be a LOT of updating to do. This doesn't seem right to me? Or is there a better approach for the type of data I'm wanting to store and query? Thank you

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