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  • C++ CRTP(template pattern) question

    - by aaa
    following piece of code does not compile, the problem is in T::rank not be inaccessible (I think) or uninitialized in parent template. Can you tell me exactly what the problem is? is passing rank explicitly the only way? or is there a way to query tensor class directly? Thank you #include <boost/utility/enable_if.hpp> template<class T, // size_t N, class enable = void> struct tensor_operator; // template<class T, size_t N> template<class T> struct tensor_operator<T, typename boost::enable_if_c< T::rank == 4>::type > { tensor_operator(T &tensor) : tensor_(tensor) {} T& operator()(int i,int j,int k,int l) { return tensor_.layout.element_at(i, j, k, l); } T &tensor_; }; template<size_t N, typename T = double> // struct tensor : tensor_operator<tensor<N,T>, N> { struct tensor : tensor_operator<tensor<N,T> > { static const size_t rank = N; }; I know the workaround, however am interested in mechanics of template instantiation for self-education

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  • Link compatibility between C++ and D

    - by Caspin
    D easily interfaces with C. D just as easily interfaces with C++, but (and it's a big but) the C++ needs to be extremely trivial. The code cannot use: namespaces templates multiple inheritance mix virtual with non-virtual methods more? I completely understand the inheritance restriction. The rest however, feel like artificial limitations. Now I don't want to be able to use std::vector<T> directly, but I would really like to be able to link with std::vector<int> as an externed template. The C++ interfacing page has this particularly depressing comment. D templates have little in common with C++ templates, and it is very unlikely that any sort of reasonable method could be found to express C++ templates in a link-compatible way with D. This means that the C++ STL, and C++ Boost, likely will never be accessible from D. Admittedly I'll probably never need std::vector while coding in D, but I'd love to use QT or boost. So what's the deal. Why is it so hard to express non-trivial C++ classes in D? Would it not be worth it to add some special annotations or something to express at least namespaces?

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  • Creating Binary Block from struct

    - by MOnsDaR
    I hope the title is describing the problem, i'll change it if anyone has a better idea. I'm storing information in a struct like this: struct AnyStruct { AnyStruct : testInt(20), testDouble(100.01), testBool1(true), testBool2(false), testBool3(true), testChar('x') {} int testInt; double testDouble; bool testBool1; bool testBool2; bool testBool3; char testChar; std::vector<char> getBinaryBlock() { //how to build that? } } The struct should be sent via network in a binary byte-buffer with the following structure: Bit 00- 31: testInt Bit 32- 61: testDouble most significant portion Bit 62- 93: testDouble least significant portion Bit 94: testBool1 Bit 95: testBool2 Bit 96: testBool3 Bit 97-104: testChar According to this definition the resulting std::vector should have a size of 13 bytes (char == byte) My question now is how I can form such a packet out of the different datatypes I've got. I've already read through a lot of pages and found datatypes like std::bitset or boost::dynamic_bitset, but neither seems to solve my problem. I think it is easy to see, that the above code is just an example, the original standard is far more complex and contains more different datatypes. Solving the above example should solve my problems with the complex structures too i think. One last point: The problem should be solved just by using standard, portable language-features of C++ like STL or Boost (

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  • SQLite DB open time really long Problem

    - by sxingfeng
    I am using sqlite in c++ windows, And I have a db size about 60M, When I open the sqlite db, It takes about 13 second. sqlite3* mpDB; nRet = sqlite3_open16(szFile, &mpDB); And if I closed my application and reopen it again. It takse only less then 1 second. First, I thought It is because of disk cache. So I preload the 60M db file before sqlite open, and read the file using CFile, However, after preloading, the first time is still very slow. BOOL CQFilePro::PreLoad(const CString& strPath) { boost::shared_array<BYTE> temp = boost::shared_array<BYTE>(new BYTE[PRE_LOAD_BUFFER_LENGTH]); int nReadLength; try { CFile file; if (file.Open(strPath, CFile::modeRead) == FALSE) { return FALSE; } do { nReadLength = file.Read(temp.get(), PRE_LOAD_BUFFER_LENGTH); } while (nReadLength == PRE_LOAD_BUFFER_LENGTH); file.Close(); } catch(...) { } return TRUE; } My question is what is the difference between first open and second open. How can I accelerate the sqlite open-process.

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  • C++ CRTP question

    - by aaa
    following piece of code does not compile, the problem is in T::rank not be inaccessible (I think) or uninitialized in parent template. Can you tell me exactly what the problem is? is passing rank explicitly the only way? or is there a way to query tensor class directly? Thank you #include <boost/utility/enable_if.hpp> template<class T, // size_t N, class enable = void> struct tensor_operator; // template<class T, size_t N> template<class T> struct tensor_operator<T, typename boost::enable_if_c< T::rank == 4>::type > { tensor_operator(T &tensor) : tensor_(tensor) {} T& operator()(int i,int j,int k,int l) { return tensor_.layout.element_at(i, j, k, l); } T &tensor_; }; template<size_t N, typename T = double> // struct tensor : tensor_operator<tensor<N,T>, N> { struct tensor : tensor_operator<tensor<N,T> > { static const size_t rank = N; }; I know the workaround, however am interested in mechanics of template instantiation for self-education

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  • Reversing strings in a vector using for_each and bind

    - by fmuecke
    Hi! I was wandering how it's possible to reverese strings that are contained in a vector using a single for_each command just in one "simple" line. Yea, I know it is easy with a custom functor, but I can't accept, that it can't be done using bind (at least I couldn't do it). #include <vector> #include <string> #include <algorithm> std::vector<std::string> v; v.push_back("abc"); v.push_back("12345"); std::for_each(v.begin(), v.end(), /*call std::reverse for each element*/); Edit: Thanks a lot for those funtastic solutions. However, the solution for me was not to use the tr1::bind that comes with the Visual Studio 2008 feature pack/SP1. I don't know why it does not work like expected but that's the way it is (even MS admits that it's buggy). Maybe some hotfixes will help. With boost::bind everything works like desired and is so easy (but sometimes relly messy:)). I really should have tried boost::bind in the first place...

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  • Resource allocation and automatic deallocation

    - by nabulke
    In my application I got many instances of class CDbaOciNotifier. They all share a pointer to only one instance of class OCIEnv. What I like to achieve is that allocation and deallocation of the resource class OCIEnv will be handled automatically inside class CDbaOciNotifier. The desired behaviour is, with the first instance of class CDbaOciNotifier the environment will be created, after that all following notifiers use that same environment. With the destruction of the last notifier, the environment will be destroyed too (call to custom deleter). What I've got so far (using a static factory method to create notifiers): #pragma once #include <string> #include <memory> #include "boost\noncopyable.hpp" class CDbaOciNotifier : private boost::noncopyable { public: virtual ~CDbaOciNotifier(void); static std::auto_ptr<CDbaOciNotifier> createNotifier(const std::string &tnsName, const std::string &user, const std::string &password); private: CDbaOciNotifier(OCIEnv* envhp); // All notifiers share one environment static OCIEnv* m_ENVHP; // Custom deleter static void freeEnvironment(OCIEnv *env); OCIEnv* m_envhp; }; CPP: #include "DbaOciNotifier.h" using namespace std; OCIEnv* CDbaOciNotifier::m_ENVHP = 0; CDbaOciNotifier::~CDbaOciNotifier(void) { } CDbaOciNotifier::CDbaOciNotifier(OCIEnv* envhp) :m_envhp(envhp) { } void CDbaOciNotifier::freeEnvironment(OCIEnv *env) { OCIHandleFree((dvoid *) env, (ub4) OCI_HTYPE_ENV); *env = null; } auto_ptr<CDbaOciNotifier> CDbaOciNotifier::createNotifier(const string &tnsName, const string &user, const string &password) { if(!m_ENVHP) { OCIEnvCreate( (OCIEnv **) &m_ENVHP, OCI_EVENTS|OCI_OBJECT, (dvoid *)0, (dvoid * (*)(dvoid *, size_t)) 0, (dvoid * (*)(dvoid *, dvoid *, size_t))0, (void (*)(dvoid *, dvoid *)) 0, (size_t) 0, (dvoid **) 0 ); } //shared_ptr<OCIEnv> spEnvhp(m_ENVHP, freeEnvironment); ...got so far... return auto_ptr<CDbaOciNotifier>(new CDbaOciNotifier(m_ENVHP)); } I'd like to avoid counting references (notifiers) myself, and use something like shared_ptr. Do you see an easy solution to my problem?

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  • Implementing comparision operators via 'tuple' and 'tie', a good idea?

    - by Xeo
    (Note: tuple and tie can be taken from Boost or C++11.) When writing small structs with only two elements, I sometimes tend to choose a std::pair, as all important stuff is already done for that datatype, like operator< for strict-weak-ordering. The downsides though are the pretty much useless variable names. Even if I myself created that typedef, I won't remember 2 days later what first and what second exactly was, especially if they are both of the same type. This gets even worse for more than two members, as nesting pairs pretty much sucks. The other option for that is a tuple, either from Boost or C++11, but that doesn't really look any nicer and clearer. So I go back to writing the structs myself, including any needed comparision operators. Since especially the operator< can be quite cumbersome, I thought of circumventing this whole mess by just relying on the operations defined for tuple: Example of operator<, e.g. for strict-weak-ordering: bool operator<(MyStruct const& lhs, MyStruct const& rhs){ return std::tie(lhs.one_member, lhs.another, lhs.yet_more) < std::tie(rhs.one_member, rhs.another, rhs.yet_more); } (tie makes a tuple of T& references from the passed arguments.) Edit: The suggestion from @DeadMG to privately inherit from tuple isn't a bad one, but it got quite some drawbacks: If the operators are free-standing (possibly friends), I need to inherit publicly With casting, my functions / operators (operator= specifically) can be easily bypassed With the tie solution, I can leave out certain members if they don't matter for the ordering Are there any drawbacks in this implementation that I need to consider?

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  • How recovery zip password using CUDA (GPU) ?

    - by marc
    Welcome, How can i recovery zip password on linux using CUDA (GPU). From 2 day's i'm trying using "fcrackzip" but it's too slow. Few months back i saw some application that can use GPU / CUDA and get large performance boost in compare to CPU. If brute-force using cuda is not possible, please tell me what's the best application for dictionary attack, and where can i find best (largest) dictionary. Regards

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  • Any reason not to disable Windows kernel paging?

    - by Nathaniel
    So I'm planning on eventually going to 2 GB (mobo max) RAM from 1 GB, and I want to disable kernel paging once I do, because I've heard it can give a performance boost (and that I believe). Any reason not to do it or any general thoughts about it? Edit: for clarification, this is not disabling general RAM paging. This is disabling having kernel memory paged (or at least parts of it, as Charlls noted).

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  • How practical is using a Wireless-N router together with a B and G router?

    - by Jian Lin
    I hope to use a Wireless N router to boost up the speed of wireless Internet, but there are some device that probably only supports B or G, such as iPhone, iPad, Wii, so if it is to replace the existing Wireless-B/G router, then some device won't work. Is it practical to buy a Wireless-N router, and then just plug the existing wireless router to it, or if I am using AT&T's u-verse, which has a central Wireless-B/G router, then plug in a new Wireless-N router into it?

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  • How can i recover a zip password using CUDA (GPU) ?

    - by marc
    How can i recover a zip password on linux using CUDA (GPU). For the past two days i tried using "fcrackzip" but it's too slow Few months back i saw some application that can use GPU / CUDA and get large performance boost in comparison to CPU. If brute-force using cuda is not possible, please tell me what's the best application for performing a dictionary attack, and where can i find best (largest) dictionary. Regards

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  • varnish3, mod_geoip with apache2 using mod_rewrite and mod_rpaf

    - by mursalat
    I am maintaining a website with 3 different versions of the site, with 3 different languages, handles with a single system written in php, which takes in environment variables based on the domain name that is being accessed. These are the three sites: myshop.com : english international version myshop.eu : european version of site myshop.ru : russian version of the site when myshop.com is accessed from russia it is to be redirected to myshop.ru, and any country from europe accesses myshop.com, is redirected to myshop.eu, and international visitors stay at myshop.com, although they can go to the country specific site. All these redirections for the country is done using GeoIP apache2 mod in order to determine the country code, which is used in a RewriteCondition to state a RewriteRule, there are some exceptions of IPs that do not do the rewrite for, basically the IPs of the developer's PCs. The site has been doing just fine, until we decided to setup varnish to give the site a boost, it really did give it a great boost, but the country specific rewrites has become buggy. What started to happen is that a russian visitor can go to myshop.com and won't be redirected, until he clicks a random link (perhaps a link not cached by varnish yet) and the user is redirected to their specific country. For that i setup mod_rpaf, and for exceptions to the rewrite rule (for the developer's ip), i used this RewriteCond %{HTTP:X-FORWARDED-FOR} !^43\.43\.43\.43, and i restarted varnish and apache2, it worked for a while, then it messed up again. And whole day i have been doing changes however i have little no clue as to what's going on, sometimes it works, and sometimes it doesn't, and sometimes it half works, etc... As for geoip, i used a php to check the $_SERVER variable, and here is the general idea of the output [HTTP_X_FORWARDED_FOR] => 43.43.43.44 [HTTP_X_VARNISH] => 1705675599 [SERVER_ADDR] => 127.0.0.1 [SERVER_PORT] => 80 [REMOTE_ADDR] => 43.43.43.44 [GEOIP_ADDR] => 43.43.43.44 [GEOIP_CONTINENT_CODE] => EU [GEOIP_COUNTRY_CODE] => FR [GEOIP_COUNTRY_NAME] => France Now, thanks to the "random" redirects, i hardly have a clue as to what is going on, so can you guys please give me some ideas as to what tools to use to debug this? I have tried to see the redirect logs, but they really dont show much, and varnishlog isn't helping much either - although i must admit i am no professional at varnish. I believe the problem is with varnish trying to cache the url, and thus apache redirects are not being done properly, however visits the site first has a redirect, and based on that other users are served the content, depending on from where the user was when the cache was last updated, is it correct? if so, how can i solve the problem? Also, i have the option of using geoip redirects on varnish3 instead of using apache2 to do the redirects, is that what the best practice is? Any suggestion as to debugging this or to fix this would be helpful! thnx!

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  • I/O intensive MySql server on Amazon AWS

    - by rhossi
    We recently moved from a traditional Data Center to cloud computing on AWS. We are developing a product in partnership with another company, and we need to create a database server for the product we'll release. I have been using Amazon Web Services for the past 3 years, but this is the first time I received a spec with this very specific hardware configuration. I know there are trade-offs and that real hardware will always be faster than virtual machines, and knowing that fact forehand, what would you recommend? 1) Amazon EC2? 2) Amazon RDS? 3) Something else? 4) Forget it baby, stick to the real hardware Here is the hardware requirements This server will be focused on I/O and MySQL for the statistics, memory size and disk space for the images hosting. Server 1 I/O The very main part on this server will be I/O processing, FusionIO cards have proven themselves extremely efficient, this is currently the best you can have in this domain. o Fusion ioDrive2 MLC 365GB (http://www.fusionio.com/load/-media-/1m66wu/docsLibrary/FIO_ioDrive2_Datasheet.pdf) CPU MySQL will use less CPU cores than Apache but it will use them very hard, the E7 family has 30M Cache L3 wichi provide boost performance : o 1x Intel E7-2870 will be ok. Storage SAS will be good enough in terms of performance, especially considering the space required. o RAID 10 of 4 x SAS 10k or 15k for a total available space of 512 GB. Memory o 64 GB minimum is required on this server considering the size of the statistics database. Warning: the statistics database will grow quickly, if possible consider starting with 128 GB directly, it will help. This server will be focused on I/O and MySQL for the statistics, memory size and disk space for the images hosting. Server 2 I/O The very main part on this server will be I/O processing, FusionIO cards have proven themselves extremely efficient, this is currently the best you can have in this domain. o Fusion ioDrive2 MLC 365GB (http://www.fusionio.com/load/-media-/1m66wu/docsLibrary/FIO_ioDrive2_Datasheet.pdf) CPU MySQL will use less CPU cores than Apache but it will use them very hard, the E7 family has 30M Cache L3 wichi provide boost performance : o 1x Intel E7-2870 will be ok. Storage SAS will be good enough in terms of performance, especially considering the space required. o RAID 10 of 4 x SAS 10k or 15k for a total available space of 512 GB. Memory o 64 GB minimum is required on this server considering the size of the statistics database. Warning: the statistics database will grow quickly, if possible consider starting with 128 GB directly, it will help. Thanks in advance. Best,

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  • Any reason not to disable Windows kernel paging?

    - by Nathaniel
    So I'm planning on eventually going to 2 GB (mobo max) RAM from 1 GB, and I want to disable kernel paging once I do, because I've heard it can give a performance boost (and that I believe). Any reason not to do it or any general thoughts about it? Edit: for clarification, this is not disabling general RAM paging. This is disabling having kernel memory paged (or at least parts of it, as Charlls noted).

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  • Using SSD as disk cache

    - by casualcoder
    Is there software for Linux to use an SSD as disk cache? I believe that Sun does something like this with ZFS, though not sure. A quick search provides nothing suitable. The goal would be to put frequently requested files on the SSD on-the-fly. Since the SSD has more capacity than RAM for less money and better performance than hard disk, this should provide an efficient performance boost.

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  • USB Drive is Very Slow

    - by Luminose
    I recently bought a Patriot Xporter XT Boost 8GB Flash Drive whish is supposed to be one of the faster flash drives but it seems extremelly slow. For isntance Firefox takes several minutes to load. Are there any tips or tricks to making it run faster? NTFS vs FAT32? Any registry settings or options in device manager?

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  • Does software RAID 1 in Windows 7 improve read speeds?

    - by Rich
    As the title says, does software RAID 1 (mirroring) in Windows 7 improve read speeds? I'd like to set up RAID 1 to help protect my important documents (yes, yes, I know it's not a backup), but performance is also important to me. As I understand it, RAID 1 should theoretically be able to improve my read speeds by n times, where n is the number of disks. Is Windows 7 able to get this boost? I haven't been able to find out this information anywhere.

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  • How to throttle bandwidth speed from VPS

    - by Burning the Codeigniter
    I was wondering if you can throttle/boost the download speed from my VPS to me, because now and often I download a database which is quite big, typically 5-7GB. My side is quite slow (typically I have max speeds of 100Kb/s) so I was wondering if it's possible to throttle the bandwidth speed from my server to me that it could make the download much faster. If this is possible, how can I do this? My server is running Ubuntu 11.04 with a 100Mbps line.

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  • Annoying sound from microphone in headphone

    - by Paul
    I recently bought a Plantronics bluetooth headset for VOIP in Skype. But I am facing an annoying problem. The microphone is really sensitive and I could hear all the background noises and my sound though the headphone (of blutooth headset). I tried to disable the bluetooth headset in Playback devices and I could hear the amplified background noise through speakers! I checked if there is a microphone boost option enabled, but couldn't find it in the properties of the headset recording device

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  • Anyone tried boosting Windows performance by putting Swap File on a Flash drive?

    - by Clay Nichols
    Windows Vista introduced ReadyBoost which lets you use a Flash drive as a third (after RAM and HD) type of memory. It occurred to me that I could boost peformance on an old PC here w/ Win XP (32 bit, max'd at 4GB RAM) by putting it's swap file (page file) on a flash drive. (Now, before anyone comments: apparently Flash drives (10-30MB/s transfer rates) are slower than HDD (100+ MB/s) (I'm asking that as a separate question on this forum).

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  • "Raid 0 SAS" versus "2nd generation SSD"

    - by Stefano
    Hi everybody, i was planning to buy a SAS system made of two 15k RPM disks in Raid 0 configuration to give a boost to my s.o. and my apps... but after i saw that article on Coding Horror, i've started to thinking if a new 2nd generation SSD could do the same job, or even better... Does anybody have any information to help me decide?

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