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• Karmic iptables missing kernel moduyles on OpenVZ container

  - by luison

  After an unsuccessful p2v migration of my Ubuntu server to an OpenVZ container which I am stack with I thought I would give a try to a reinstall based on a clean OpenVZ template for Ubuntu 9.10 (from the OpenVZ wiki) When I try to load my iptables rules on the VM machine I've been getting errors which I believe are related to kernel modules not being loaded on the VM from the /vz/XXX.conf template model. I've been testing with a few post I've found but I was stack with the error: WARNING: Deprecated config file /etc/modprobe.conf, all config files belong into /etc/modprobe.d/. FATAL: Could not load /lib/modules/2.6.24-10-pve/modules.dep: No such file or directory iptables-restore v1.4.4: iptables-restore: unable to initialize table 'raw' Error occurred at line: 2 Try `iptables-restore -h' or 'iptables-restore --help' for more information. I read about the template not loading all iptables modules so I added modules to the XXX.conf of the VZ virtual machine like this: IPTABLES="ip_tables iptable_filter iptable_mangle ipt_limit ipt_multiport ipt_tos ipt_TOS ipt_REJECT ipt_TCPMSS ipt_tcpmss ipt_ttl ipt_LOG ipt_length ip_conntrack ip_conntrack_ftp ip_conntrack_irc ipt_conntrack ipt_state ipt_helper iptable_nat ip_nat_ftp ip_nat_irc" As the error remained I read that I should build dependencies again on the virtual machine: depmod -a but this returned an error: WARNING: Couldn't open directory /lib/modules/2.6.24-10-pve: No such file or directory FATAL: Could not open /lib/modules/2.6.24-10-pve/modules.dep.temp for writing: No such file or directory So I read again about creating the directory empty and redoing "depmod -a" it. I now don't get the dependancies error but get this and I don't have a clue how to proceed: WARNING: Deprecated config file /etc/modprobe.conf, all config files belong into /etc/modprobe.d/. FATAL: Module ip_tables not found. iptables-restore v1.4.4: iptables-restore: unable to initialize table 'raw' Error occurred at line: 2 Try `iptables-restore -h' or 'iptables-restore --help' for more information. I understand that iptables rules have to be different on the VM machine and perhaps some of the rules we are trying to apply (from our physical server) are not compatible but these are just source IP and destination port checks that I would like to be able to have available . I've heard that on the CentOS template there are no issues with this, so I understand is to do with VM config. Any help would be greatly appreciated.

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• linux container bridge filters ARP reply

  - by Dani Camps

  I am using kernel 3.0, and I have configured a linux container that is bridged to a tap interface in my host computer. This is the bridge configuration: :~$ brctl show bridge-1 bridge name bridge id STP enabled interfaces bridge-1 8000.9249c78a510b no ns3-mesh-tap-1 vethjUErij My problem is that this bridge is dropping ARP replies that come from the ns3-mesh-tap-1 interface. Instead, if I statically populate the ARP tables and ping directly everything works, so it has to be something related to ARP. I have read about similar problems in related posts, and I have tried with the solutions explained therein but nothing seems to work. Specifically: ~$ grep net.bridge /etc/sysctl.conf net.bridge.bridge-nf-call-arptables = 0 net.bridge.bridge-nf-call-iptables = 0 net.bridge.bridge-nf-call-ip6tables = 0 net.bridge.bridge-nf-filter-vlan-tagged = 0 net.bridge.bridge-nf-filter-pppoe-tagged = 0 arptables and ebtables are not installed. iptables FORWARD is all set to accept: Chain FORWARD (policy ACCEPT) target prot opt source destination The bridged interfaces are set to PROMISC: ~$ ifconfig ns3-mesh-tap-1 Link encap:Ethernet HWaddr 1a:c7:24:ef:36:1a ... UP BROADCAST PROMISC MULTICAST MTU:1500 Metric:1 vethjUErij Link encap:Ethernet HWaddr aa:b0:d1:3b:9a:0a .... UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1 The macs learned by the bridge are correct (checked with brctl showmacs). Any insight on what I am doing wrong would be greatly appreciated. Best Regards Daniel

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• Extracting pair member in lambda expressions and template typedef idiom

  - by Nazgob

  Hi, I have some complex types here so I decided to use nifty trick to have typedef on templated types. Then I have a class some_container that has a container as a member. Container is a vector of pairs composed of element and vector. I want to write std::find_if algorithm with lambda expression to find element that have certain value. To get the value I have to call first on pair and then get value from element. Below my std::find_if there is normal loop that does the trick. My lambda fails to compile. How to access value inside element which is inside pair? I use g++ 4.4+ and VS 2010 and I want to stick to boost lambda for now. #include <vector> #include <algorithm> #include <boost\lambda\lambda.hpp> #include <boost\lambda\bind.hpp> template<typename T> class element { public: T value; }; template<typename T> class element_vector_pair // idiom to have templated typedef { public: typedef std::pair<element<T>, std::vector<T> > type; }; template<typename T> class vector_containter // idiom to have templated typedef { public: typedef std::vector<typename element_vector_pair<T>::type > type; }; template<typename T> bool operator==(const typename element_vector_pair<T>::type & lhs, const typename element_vector_pair<T>::type & rhs) { return lhs.first.value == rhs.first.value; } template<typename T> class some_container { public: element<T> get_element(const T& value) const { std::find_if(container.begin(), container.end(), bind(&typename vector_containter<T>::type::value_type::first::value, boost::lambda::_1) == value); /*for(size_t i = 0; i < container.size(); ++i) { if(container.at(i).first.value == value) { return container.at(i); } }*/ return element<T>(); //whatever } protected: typename vector_containter<T>::type container; }; int main() { some_container<int> s; s.get_element(5); return 0; }

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• Need help revolving a 2D array

  - by Brett

  Pretty much all I'm trying to do is revolve my 2D Array by its container. I'm using this array for a background and I seem to be having problems with it revolving. public class TileTransformer : GridConstants { public Tile[,] Tiles; ContentManager Content; public TileTransformer(ContentManager content) { Content = content; } public Tile[,] Wraping(Tile[,] tiles,Point shift) { Tiles = tiles; for (int x = shift.X; x < 0; x++)//Left shift { for (int X = 0; X < GridWidth; X++) { for (int Y = 0; Y < GridHeight; Y++) { if (X + 1 >GridWidth-1) { Tiles[0, Y].Container =tiles[X, Y].Container; } else { Tiles[X+1, Y].Container =tiles[X, Y].Container; } } } } for (int x = shift.X; x > 0; x--)//right shift { for (int X = 0; X < GridWidth; X++) { for (int Y = 0; Y< GridHeight; Y++) { if (X-1==-1) { Tiles[GridWidth-1, Y].Container =tiles[0, Y].Container; } else { Tiles[X - 1, Y].Container =tiles[X, Y].Container; } } } } for (int y = shift.Y; y > 0; y--)//shift up { for (int X = 0; X < GridWidth; X++) { for (int Y = 0; Y < GridHeight; Y++) { if (Y - 1 == -1) { Tiles[X, GridHeight-1].Container = tiles[X, Y].Container; } else { Tiles[X, Y - 1].Container = tiles[X, Y].Container; } } } } for (int y = shift.Y; y < 0; y++)//shift down { for (int X = 0; X < GridWidth; X++) { for (int Y = 0; Y < GridHeight; Y++) { if (Y + 1 == GridHeight) { Tiles[X, 0].Container = tiles[X, Y].Container; } else { Tiles[X, Y + 1].Container = tiles[X, Y].Container; } } } } return Tiles; } Now the Problems that I'm having is either when I shift up or left it seems the whole array is cleared back to the default state. Also when I'm revolving the array it appears to stretch it upon the sides of the screen that it is shifting towards.

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• Problem resolving a generic Repository with Entity Framework and Castle Windsor Container

  - by user368776

  Hi, im working in a generic repository implementarion with EF v4, the repository must be resolved by Windsor Container. First the interface public interface IRepository<T> { void Add(T entity); void Delete(T entity); T Find(int key) } Then a concrete class implements the interface public class Repository<T> : IRepository<T> where T: class { private IObjectSet<T> _objectSet; } So i need _objectSet to do stuff like this in the previous class public void Add(T entity) { _objectSet.AddObject(entity); } And now the problem, as you can see im using a EF interface like IObjectSet to do the work, but this type requires a constraint for the T generic type "where T: class". That constrait is causing an exception when Windsor tries to resolve its concrete type. Windsor configuration look like this. <castle> <components> <component id="LVRepository" service="Repository.Infraestructure.IRepository`1, Repository" type="Repository.Infraestructure.Repository`1, Repository" lifestyle="transient"> </component> </components> The container resolve code IRepository<Product> productsRep =_container.Resolve<IRepository<Product>>(); Now the exception im gettin System.ArgumentException: GenericArguments[0], 'T', on 'Repository.Infraestructure.Repository`1[T]' violates the constraint of type 'T'. ---> System.TypeLoadException: GenericArguments[0], 'T', on 'Repository.Infraestructure.Repository`1[T]' violates the constraint of type parameter 'T'. If i remove the constraint in the concrete class and the depedency on IObjectSet (if i dont do it get a compile error) everything works FINE, so i dont think is a container issue, but IObjectSet is a MUST in the implementation. Some help with this, please.

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• Vertically center a fluid image in a fluid container

  - by Ferdy

  I certainly do not want to add to the pile of vertical alignments CSS questions, but I've spent hours trying to find a solution to no avail yet. Here's the situation: I am building a slideshow gallery of images. I want the images to be displayed as large as the user's window allows. So I have this outer placeholder: <section class="photo full"> (Yes, I'm using HTML5 elements). Which has the following CSS: section.photo.full { display:inline-block; width:100%; height:100%; position:absolute; overflow:hidden; text-align:center; } Next, the image is placed inside it. Depending on the orientation of the image, I set either the width or height to 75%, and the other axis to auto: $wide = $bigimage['width'] >= $bigimage['height'] ? true: false; ?> <img src="<?= $bigimage['url'] ?>" width="<?= $wide? "75%" : "auto"?>" height="<?= $wide? "auto" : "75%"?>"/> So, we have a fluid outer container, with inside a fluid image. The horizontal centering of the image works, yet I cannot seem to find a way to vertically center the image within it's container. I have researched centering methods but most assume either the container or image has a known width or height. Then there is the display:table-cell method, which does not seem to work for me either. I'm stuck. I'm looking for a CSS solution, but am open to js solutions too.

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• How to store a public key in a machine-level RSA key container

  - by Andrew Kimball

  I'm having a problem using a machine level RSA key container when storing only the public key of a public/private key pair. The following code creates a public/private pair and extracts the public key from that pair. The pair and the public key are stored in separate key containers. The keys are then obtained from those key containers at which point they should be the same as the keys going into the containers. The code works when CspProviderFlags.UseDefaultKeyContainer is specified for CspParameters.Flags (i.e. the key read back out from the PublicKey container is the same), but when CspProviderFlags.UseMachineKeyStore is specified for CspParameters.Flags the key read back from PublicKey is different. Why is the behaviour different, and what do I need to do differently to retrieve the public key from a machine-level RSA key container? var publicPrivateRsa = new RSACryptoServiceProvider(new CspParameters() { KeyContainerName = "PublicPrivateKey", Flags = CspProviderFlags.UseMachineKeyStore //Flags = CspProviderFlags.UseDefaultKeyContainer } ) { PersistKeyInCsp = true, }; var publicRsa = new RSACryptoServiceProvider(new CspParameters() { KeyContainerName = "PublicKey", Flags = CspProviderFlags.UseMachineKeyStore //Flags = CspProviderFlags.UseDefaultKeyContainer } ) { PersistKeyInCsp = true }; //Export the key. publicRsa.ImportParameters(publicPrivateRsa.ExportParameters(false)); Console.WriteLine(publicRsa.ToXmlString(false)); Console.WriteLine(publicPrivateRsa.ToXmlString(false)); //Dispose those two CSPs. using (publicRsa) { publicRsa.Clear(); } using (publicPrivateRsa) { publicRsa.Clear(); } publicPrivateRsa = new RSACryptoServiceProvider(new CspParameters() { KeyContainerName = "PublicPrivateKey", Flags = CspProviderFlags.UseMachineKeyStore //Flags = CspProviderFlags.UseDefaultKeyContainer } ); publicRsa = new RSACryptoServiceProvider(new CspParameters() { KeyContainerName = "PublicKey", Flags = CspProviderFlags.UseMachineKeyStore //Flags = CspProviderFlags.UseDefaultKeyContainer } ); Console.WriteLine(publicRsa.ToXmlString(false)); Console.WriteLine(publicPrivateRsa.ToXmlString(false)); using (publicRsa) { publicRsa.Clear(); } using (publicPrivateRsa) { publicRsa.Clear(); }

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• Override absolute position on child container (modal window)

  - by Shawn Mclean

  I have a modal window that is pulled from the server and inserted into a container that is absolute positioned. When that window is triggered to open, it does not display properly, it positions itself inside the container and most of it is hidden. Is there a specific css to be written for the container of the modal window (MyModalWindow). My code is as follows: <div style="position:relative;"> <div style="position: absolute;"> <div id="MyModalWindow"> </div> </div> </div> This is a jquery tools window and attaches the following style to MyModalWindow when it shows.: element.style { display:block; left:183.5px position:absolute; top:468.4px; z-index:9999; } I basically need the div to not be a child of the parent, since as jquery calculates it to be positioned at the center of the webpage no matter where the div is.

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• Resizing a container when child's visibility is changed?

  - by deux11

  When I set the visible property to false for a child in a container, how can I get the container to resize? In the example bellow, when clicking on "Toggle", "containerB" is hidden, but the main container's scrollable area is not resized. (I do not want to scroll through a lot of empty space.) <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"> <mx:Script> <![CDATA[ public function toggle():void { containerB.visible = !containerB.visible; } ]]> </mx:Script> <mx:VBox height="300" width="200" horizontalAlign="center"> <mx:Button label="Toggle" click="toggle()" width="200"/> <mx:VBox id="containerA" height="400" width="150" horizontalAlign="center"> <mx:Button label="A" height="400" width="100"/> </mx:VBox> <mx:VBox id="containerB" height="400" width="150" horizontalAlign="center"> <mx:Button label="B" height="400" width="100"/> </mx:VBox> </mx:VBox>

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• C++ iterator and const_iterator problem for own container class

  - by BaCh

  Hi there, I'm writing an own container class and have run into a problem I can't get my head around. Here's the bare-bone sample that shows the problem. It consists of a container class and two test classes: one test class using a std:vector which compiles nicely and the second test class which tries to use my own container class in exact the same way but fails miserably to compile. #include <vector> #include <algorithm> #include <iterator> using namespace std; template <typename T> class MyContainer { public: class iterator { public: typedef iterator self_type; inline iterator() { } }; class const_iterator { public: typedef const_iterator self_type; inline const_iterator() { } }; iterator begin() { return iterator(); } const_iterator begin() const { return const_iterator(); } }; // This one compiles ok, using std::vector class TestClassVector { public: void test() { vector<int>::const_iterator I=myc.begin(); } private: vector<int> myc; }; // this one fails to compile. Why? class TestClassMyContainer { public: void test(){ MyContainer<int>::const_iterator I=myc.begin(); } private: MyContainer<int> myc; }; int main(int argc, char ** argv) { return 0; } gcc tells me: test2.C: In member function ‘void TestClassMyContainer::test()’: test2.C:51: error: conversion from ‘MyContainer::iterator’ to non-scalar type ‘MyContainer::const_iterator’ requested I'm not sure where and why the compiler wants to convert an iterator to a const_iterator for my own class but not for the STL vector class. What am I doing wrong?

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• Pointers into elements in a container

  - by Pillsy

  Say I have an object: struct Foo { int bar_; Foo(int bar) bar_(bar) {} }; and I have an STL container that contains Foos, perhaps a vector, and I take // Elsewhere... vector<Foo> vec; vec.push_back(Foo(4)); int *p = &(vec[0].bar_) This is a terrible idea, right? The reason is that vector is going to be storing its elements in a dynamically allocated array somewhere, and eventually, if you add enough elements, it will have to allocate another array, copy over all the elements of the original array, and delete the old array. After that happens, p points to garbage. This is why many operations on a vector will invalidate iterators. It seems like it would be reasonable to assume that an operation that would invalidate iterators from a container will also invalidate pointers to data members of container elements, and that if an operation doesn't invalidate iterators, those pointers will still be safe. However, many reasonable assumptions are false. Is this one of them?

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• CSS Container DIV Not Expanding

  - by rsmith84

  I've been researching this for hours now and it seems to be an IE thing but my issue is that I have a container DIV that, in IE9, doesn't expand and cuts everything off after about 400px. Chrome and FF work perfectly, of course. Container DIV #main_container{ font-family: arial, verdana; width: 920px; top: 0; margin-left: auto; margin-right: auto; background-color: #fff; overflow-x: hidden; } Page Container DIV #page_container{ font-family: arial, verdana; font-size: 14px; width: 900px; color: #000; border: 0px solid; overflow: hidden; } And the standard markup of page block looks like this <div id="main_container"> <div id="page_container"> Variable page data goes here </div> </div> Is there an issue with my CSS that I'm missing or is there an IE hack that I need to apply?

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• Castle Windsor in ASP.NET MVC projet

  - by Kris-I

  Hello, In an ASP.NET MVC project, using Castle Windsor as IoC container. I'd like use the Logger facilities of this package. I read several article about the configuration but I'd find the right configuration to add the logger to the container. Do you have an idea ? Thanks,

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• How can I resolve circular dependencies in Funq IoC?

  - by Rickard

  I have two classes which I need to reference each other. class Foo { public Foo(IBar bar) {} } class Bar { public Bar(IFoo foo) {} } When I do: container.RegisterAutoWiredAs<Foo, IFoo>(); container.RegisterAutoWiredAs<Bar, IBar>(); and when I try to resolve either interface I get a circular dependency graph which results in an eternal loop. Is there an easy way to solve this in Funq or do you know of a workaround?

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• Active Directory Services: PrincipalContext -- What is the DN of a "container" object?

  - by Ranger Pretzel

  I'm currently trying to authenticate via Active Directory Services using the PrincipalContext class. I would like to have my application authenticate to the Domain using Sealed and SSL contexts. In order to do this, I have to use the following constructor of PrincipalContext (link to MSDN page): public PrincipalContext( ContextType contextType, string name, string container, ContextOptions options ) Specifically, I'm using the constructor as so: PrincipalContext domainContext = new PrincipalContext( ContextType.Domain, domain, container, ContextOptions.Sealing | ContextOptions.SecureSocketLayer); MSDN says about "container": The container on the store to use as the root of the context. All queries are performed under this root, and all inserts are performed into this container. For Domain and ApplicationDirectory context types, this parameter is the distinguished name (DN) of a container object. What is the DN of a container object? How do I find out what my container object is? Can I query the Active Directory (or LDAP) server for this?

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• fatal error LNK1104: cannot open file 'libboost_system-vc90-mt-gd-1_43.lib'

  - by Poni

  Made a new project, added main.cpp and wrote the code at this URL: http://www.boost.org/doc/libs/1_43_0/doc/html/boost_asio/example/echo/async_tcp_echo_server.cpp Also, added the appropriate include path. What's next?!?!! It seems like a darn mystery to build a boost code! Been digging on it for more than 10 hours. Can anyone give a straightforward answer on how to build the boost library from the code under windows, VC9? God bless you all.

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• Class member functions instantiated by traits [policies, actually]

  - by Jive Dadson

  I am reluctant to say I can't figure this out, but I can't figure this out. I've googled and searched Stack Overflow, and come up empty. The abstract, and possibly overly vague form of the question is, how can I use the traits-pattern to instantiate member functions? [Update: I used the wrong term here. It should be "policies" rather than "traits." Traits describe existing classes. Policies prescribe synthetic classes.] The question came up while modernizing a set of multivariate function optimizers that I wrote more than 10 years ago. The optimizers all operate by selecting a straight-line path through the parameter space away from the current best point (the "update"), then finding a better point on that line (the "line search"), then testing for the "done" condition, and if not done, iterating. There are different methods for doing the update, the line-search, and conceivably for the done test, and other things. Mix and match. Different update formulae require different state-variable data. For example, the LMQN update requires a vector, and the BFGS update requires a matrix. If evaluating gradients is cheap, the line-search should do so. If not, it should use function evaluations only. Some methods require more accurate line-searches than others. Those are just some examples. The original version instantiates several of the combinations by means of virtual functions. Some traits are selected by setting mode bits that are tested at runtime. Yuck. It would be trivial to define the traits with #define's and the member functions with #ifdef's and macros. But that's so twenty years ago. It bugs me that I cannot figure out a whiz-bang modern way. If there were only one trait that varied, I could use the curiously recurring template pattern. But I see no way to extend that to arbitrary combinations of traits. I tried doing it using boost::enable_if, etc.. The specialized state information was easy. I managed to get the functions done, but only by resorting to non-friend external functions that have the this-pointer as a parameter. I never even figured out how to make the functions friends, much less member functions. The compiler (VC++ 2008) always complained that things didn't match. I would yell, "SFINAE, you moron!" but the moron is probably me. Perhaps tag-dispatch is the key. I haven't gotten very deeply into that. Surely it's possible, right? If so, what is best practice? UPDATE: Here's another try at explaining it. I want the user to be able to fill out an order (manifest) for a custom optimizer, something like ordering off of a Chinese menu - one from column A, one from column B, etc.. Waiter, from column A (updaters), I'll have the BFGS update with Cholesky-decompositon sauce. From column B (line-searchers), I'll have the cubic interpolation line-search with an eta of 0.4 and a rho of 1e-4, please. Etc... UPDATE: Okay, okay. Here's the playing-around that I've done. I offer it reluctantly, because I suspect it's a completely wrong-headed approach. It runs okay under vc++ 2008. #include <boost/utility.hpp> #include <boost/type_traits/integral_constant.hpp> namespace dj { struct CBFGS { void bar() {printf("CBFGS::bar %d\n", data);} CBFGS(): data(1234){} int data; }; template<class T> struct is_CBFGS: boost::false_type{}; template<> struct is_CBFGS<CBFGS>: boost::true_type{}; struct LMQN {LMQN(): data(54.321){} void bar() {printf("LMQN::bar %lf\n", data);} double data; }; template<class T> struct is_LMQN: boost::false_type{}; template<> struct is_LMQN<LMQN> : boost::true_type{}; // "Order form" struct default_optimizer_traits { typedef CBFGS update_type; // Selection from column A - updaters }; template<class traits> class Optimizer; template<class traits> void foo(typename boost::enable_if<is_LMQN<typename traits::update_type>, Optimizer<traits> >::type& self) { printf(" LMQN %lf\n", self.data); } template<class traits> void foo(typename boost::enable_if<is_CBFGS<typename traits::update_type>, Optimizer<traits> >::type& self) { printf("CBFGS %d\n", self.data); } template<class traits = default_optimizer_traits> class Optimizer{ friend typename traits::update_type; //friend void dj::foo<traits>(typename Optimizer<traits> & self); // How? public: //void foo(void); // How??? void foo() { dj::foo<traits>(*this); } void bar() { data.bar(); } //protected: // How? typedef typename traits::update_type update_type; update_type data; }; } // namespace dj int main() { dj::Optimizer<> opt; opt.foo(); opt.bar(); std::getchar(); return 0; }

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• Libtool versioning of a library that depends on other libraries.

  - by Artyom

  Hello, I have a framework that uses Boost and CgiCC in the core application and in its interface. How should I version the library binary interface (a.k.a. libtool -version-info)? I have no problems tracking the changes in library itself when I make various changes. As it is clear for me how should I version. But... Both Boost and CgiCC libraries do not provide any backward compatible API/ABI and my library may be linked with quite arbitrary versions Boost and CgiCC so I can't provide any promise about the interfaces, so I can't really specify -version-info because even the same library compiled against different versions of Boost and CgiCC would not be compatible. So... What should I do? How should I version library? I know that I should not depend on Boost and CgiCC interfaces in first place, but this is what I get so far for existing stable version. This issue is addressed in next major release but I still have and want to maintain current release as it is very valuable.

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• Recommendations for a C++ polymorphic, seekable, binary I/O interface

  - by Trevor Robinson

  I've been using std::istream and ostream as a polymorphic interface for random-access binary I/O in C++, but it seems suboptimal in numerous ways: 64-bit seeks are non-portable and error-prone due to streampos/streamoff limitations; currently using boost/iostreams/positioning.hpp as a workaround, but it requires vigilance Missing operations such as truncating or extending a file (ala POSIX ftruncate) Inconsistency between concrete implementations; e.g. stringstream has independent get/put positions whereas filestream does not Inconsistency between platform implementations; e.g. behavior of seeking pass the end of a file or usage of failbit/badbit on errors Don't need all the formatting facilities of stream or possibly even the buffering of streambuf streambuf error reporting (i.e. exceptions vs. returning an error indicator) is supposedly implementation-dependent in practice I like the simplified interface provided by the Boost.Iostreams Device concept, but it's provided as function templates rather than a polymorphic class. (There is a device class, but it's not polymorphic and is just an implementation helper class not necessarily used by the supplied device implementations.) I'm primarily using large disk files, but I really want polymorphism so I can easily substitute alternate implementations (e.g. use stringstream instead of fstream for unit tests) without all the complexity and compile-time coupling of deep template instantiation. Does anyone have any recommendations of a standard approach to this? It seems like a common situation, so I don't want to invent my own interfaces unnecessarily. As an example, something like java.nio.FileChannel seems ideal. My best solution so far is to put a thin polymorphic layer on top of Boost.Iostreams devices. For example: class my_istream { public: virtual std::streampos seek(stream_offset off, std::ios_base::seekdir way) = 0; virtual std::streamsize read(char* s, std::streamsize n) = 0; virtual void close() = 0; }; template <class T> class boost_istream : public my_istream { public: boost_istream(const T& device) : m_device(device) { } virtual std::streampos seek(stream_offset off, std::ios_base::seekdir way) { return boost::iostreams::seek(m_device, off, way); } virtual std::streamsize read(char* s, std::streamsize n) { return boost::iostreams::read(m_device, s, n); } virtual void close() { boost::iostreams::close(m_device); } private: T m_device; };

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• Using static mutex in a class

  - by Dmitry Yudakov

  I have a class that I can have many instances of. Inside it creates and initializes some members from a 3rd party library (that use some global variables) and is not thread-safe. I thought about using static boost::mutex, that would be locked in my class constructor and destructor. Thus creating and destroying instances among my threads would be safe for the 3rd party members. class MyClass { static boost::mutex mx; // 3rd party library members public: MyClass(); ~MyClass(); }; MyClass::MyClass() { boost::mutex::scoped_lock scoped_lock(mx); // create and init 3rd party library stuff } MyClass::~MyClass() { boost::mutex::scoped_lock scoped_lock(mx); // destroy 3rd party library stuff } I cannot link because I receive error: undefined reference to `MyClass::mx` Do I need some special initialization of such static member? Is the whole conception of static mutex wrong?

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• When to put C++ function in header file

  - by John Smith

  I've been looking at Boost and various other C++ libraries. The vast majority of Boost is implemented in header files. My question is: under what conditions do you do a head only implementation (like Boost) or also include a .cpp file?

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• C++: conjunction of binds?

  - by Helltone

  Suppose the following two functions: #include <iostream> #include <cstdlib> // atoi #include <cstring> // strcmp #include <boost/bind.hpp> bool match1(const char* a, const char* b) { return (strcmp(a, b) == 0); } bool match2(int a, const char* b) { return (atoi(b) == a); } Each of these functions takes two arguments, but can be transformed into a callable object that takes only one argument by using (std/boost)bind. Something along the lines of: boost::bind(match1, "a test"); boost::bind(match2, 42); I want to be able to obtain, from two functions like these that take one argument and return bool, a callable object that takes two arguments and returns the && of the bools. The type of the arguments is arbitrary. Something like an operator&& for functions that return bool.

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• Calculate rolling / moving average in c or c++

  - by Biohazard

  I know this is achievable with boost as per: Using boost::accumulators, how can I reset a rolling window size, does it keep extra history? But I really would like to avoid using boost. I have googled and not found any suitable or readable examples. Basically I want to track the moving average of an ongoing stream of a stream of floating point numbers using the most recent 1000 numbers as a data sample. What is the easiest way to achieve this?

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• What's the bug in the following code ?

  - by Johannes

  #include <iostream> #include <algorithm> #include <vector> #include <boost/array.hpp> #include <boost/bind.hpp> int main() { boost::array<int, 4> a = {45, 11, 67, 23}; std::vector<int> v(a.begin(), a.end()); std::vector<int> v2; std::transform(v.begin(), v.end(), v2.begin(), boost::bind(std::multiplies<int>(), _1, 2)); std::copy(v2.begin(), v2.end(), std::ostream_iterator<int>(std::cout, " ")); } When run, this gives a creepy segmentation fault. Please tell me where I'm going wrong.

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• How do I iterate over a tuple

  - by Caligo

  How can I iterate over a tuple starting from, say, index 1 to 2? The following doesn't work. using boost::fusion::cons; typedef cons<A, cons<B, cons<C, cons<D> > > > MyTuple; MyTuple tuple_; template <class T> struct DoSomething{ DoSomething(T& t) : t_(&t){ } template <class U> void operator()(U u){ boost::fusion::at<mpl::int_<u> >(*t_); } T* t_; }; boost::mpl::for_each< boost::mpl::range_c<int, 1, 3> >( DoSomething<MyTuple>(tuple_) );

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