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• Building a dll with .lib files

  - by Manish Shukla

  I have a C++ project which is build via bjam. With 'install' rule in Jamroot i am able to create statically linked libraries (.lib files) for my project. My question is, how i can build a load-time DLL (or run-time DLL is also fine) with these .lib files? More Info: I am building my project with bjam in windows using msvc. When i tried compiling my project under visual C++ 2008, it complied and linked just fine but when i used bjam with msvc for compilation, it started giving linking errors and showing dependency from other project folders. Why was this behavior via bjam but not shown in vc++ UI.

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• C++ auto function return type implementation

  - by aaa

  hello. Is there macro, something like BOOST_AUTO, which would allow to emulate automatic return type deduction of function in C++? I mean something like trailing-return-type, http://en.wikipedia.org/wiki/C%2B%2B0x#Alternative_function_syntax thank you

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• Is it a good idea to use only a key to encrypt an entire (small) filesystem?

  - by Fernando Miguélez

  This question comes as part of my doubts presented on a broader question about ideas implementing a small encrypted filesystem on Java Mobile phones (J2ME, BlackBerry, Android). Provided the litte feedback received, considering the density of the question, I decided to divide those doubts into small questions. So to sum up I plan to "create" an encrypted filesystem for for mobile phones (with the help of BoucyCastle or a subset of JCE), providing an API that let access to them in a transparent way. Encryption would be carried out on a file basis (not blocks). My question is this: Is it a good idea to use only a simmetric key (maybe AES-256) to encrypt all the files (they wouldn't be that many, maybe tens of them) and store this key in a keystore (protected by a pin) or would you rather encrypt each file with an on-the-fly generated key stored alongside each file, encrypting that key with the "master" key stored on the keystore? What are the benefits/drawbacks of each approach?

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• `enable_shared_from_this` has a non-virtual destructor

  - by Shtééf

  I have a pet project with which I experiment with new features of the upcoming C++0x standard. While I have experience with C, I'm fairly new to C++. To train myself into best practices, (besides reading a lot), I have enabled some strict compiler parameters (using GCC 4.4.1): -std=c++0x -Werror -Wall -Winline -Weffc++ -pedantic-errors This has worked fine for me. Until now, I have been able to resolve all obstacles. However, I have a need for enable_shared_from_this, and this is causing me problems. I get the following warning (error, in my case) when compiling my code (probably triggered by -Weffc++): base class ‘class std::enable_shared_from_this<Package>’ has a non-virtual destructor So basically, I'm a bit bugged by this implementation of enable_shared_from_this, because: A destructor of a class that is intended for subclassing should always be virtual, IMHO. The destructor is empty, why have it at all? I can't imagine anyone would want to delete their instance by reference to enable_shared_from_this. But I'm looking for ways to deal with this, so my question is really, is there a proper way to deal with this? And: am I correct in thinking that this destructor is bogus, or is there a real purpose to it?

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• How does one create a shared_ptr to pass to a function that takes a void *

  - by shaz

  That's pretty much it. I need to allocate memory and pass it to a function that takes a void *. I'd like to use a shared_ptr but I don't know how to do it.

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• C++: Binding to a base class

  - by Helltone

  The following code works, but I'm not sure it is correct/portable. #include <iostream> #include <tr1/functional> class base { public: base(int v) : x(v) {} protected: int x; }; class derived : public base { public: bool test() { return (x == 42); } }; int main(int argc, char* argv[]) { base b(42); if(std::tr1::bind((bool (base::*)()) &derived::test, b)()) { std::cout << "ok\n"; } return 0; }

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• Change Target of Edge in BGL

  - by Sunny

  If my BGL graph contain edge from node x to node y, and I want to change the target of this edge, so that now it's pointing from x to z, how it can be done? Are there any functions in BGL for that?

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• shared_ptr as class member

  - by idimba

  It's common to declared contained objects as a pointers to that class, while "forward declarating" them in header file. This in order to reduce physical dependencies in code. For example class B; // forward declaration class A { private: B* pB; }; Would it be good idea to declare such a member as shared_ptr, instead of naked pointer? I would prefer scoped_ptr, but AFAIKit it won't be in standard.

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• Modifying bundled properties from visitor

  - by ravenspoint

  How should I modify the bundled properties of a vertex from inside a visitor? I would like to use the simple method of sub-scripting the graph, but the graph parameter passed into the visitor is const, so compiler disallows changes. I can store a reference to the graph in the visitor, but this seems weird. /** A visitor which identifies vertices as leafs or trees */ class bfs_vis_leaf_finder:public default_bfs_visitor { public: /** Constructor @param[in] total reference to int variable to store total number of leaves @param[in] g reference to graph ( used to modify bundled properties ) */ bfs_vis_leaf_finder( int& total, graph_t& g ) : myTotal( total ), myGraph( g ) { myTotal = 0; } /** Called when the search finds a new vertex If the vertex has no children, it is a leaf and the total leaf count is incremented */ template <typename Vertex, typename Graph> void discover_vertex( Vertex u, Graph& g) { if( out_edges( u, g ).first == out_edges( u, g ).second ) { myTotal++; //g[u].myLevel = s3d::cV::leaf; myGraph[u].myLevel = s3d::cV::leaf; } else { //g[u].myLevel = s3d::cV::tree; myGraph[u].myLevel = s3d::cV::tree; } } int& myTotal; graph_t& myGraph; };

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• Serializing struct containing char*

  - by Dave18

  I'm getting an error with serializing a char* string error C2228: left of '.serialize' must have class/struct/union I could use a std::string and then get a const char* from it. but I require the char* string.

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• C++ associative array with arbitrary types for values

  - by Gerald Kaszuba

  What is the best way to have an associative array with arbitrary value types for each key in C++? Currently my plan is to create a "value" class with member variables of the types I will be expecting. For example: class Value { int iValue; Value(int v) { iValue = v; } std::string sValue; Value(std::string v) { sValue = v; } SomeClass *cValue; Value(SomeClass *v) { cValue = c; } }; std::map<std::string, Value> table; A downside with this is you have to know the type when accessing the "Value". i.e.: table["something"] = Value(5); SomeClass *s = table["something"].cValue; // broken pointer Also the more types that are put in Value, the more bloated the array will be. Any better suggestions?

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• Why timed lock doesnt throws a timeout exception in C++0x?

  - by Vicente Botet Escriba

  C++0x allows to lock on a mutex until a given time is reached, and return a boolean stating if the mutex has been locked or not. template <class Clock, class Duration> bool try_lock_until(const chrono::time_point<Clock, Duration>& abs_time); In some contexts, I consider an exceptional situation that the locking fails because of timeout. In this case an exception should be more appropriated. To make the difference a function lock_until could be used to get a timeout exception when the time is reached before locking. template <class Clock, class Duration> void lock_until(const chrono::time_point<Clock, Duration>& abs_time); Do you think that lock_until should be more adequate in some contexts? if yes, on which ones? If no, why try_lock_until will always be a better choice?

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• Disallow taking pointer/reference to const to a temporary object in C++ (no C++0X)

  - by KRao

  Hi, I am faced with the following issue. Consider the following class: //Will be similar to bost::reference_wrapper template<class T> class Ref { public: explicit Ref(T& t) : m_ptr(&t) {} private: T* m_ptr; }; and this function returning a double double fun() {return 1.0;} If we now have double x = 1.0; const double xc = 1.0; Ref<double> ref1(x); //OK Ref<const double> refc1(cx); //OK good so far, however: //Ref<double> ref2( fun() ); //Fails as I want it to Ref<const double> refc2( fun() ); //Works but I would like it not to Is there a way to modify Ref (the way you prefer) but not the function fun, so that the last line returns a compile-time error? Please notice you can modify the constructor signature (as long as I am able to initialise the Ref as intended). Thank you in advance for your help!

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• Can a trait state if a C++ class has a default constructor?

  - by Vicente Botet Escriba

  Traits classes can be defined to check if a C++ class has a member variable, function or a type (see here). Curiously, the ConceptTraits do not include traits to check if a C++ class defines a default constructor or given constructor? Can traits be used to check the constructor presence? If yes, how? If not, why it is not possible?

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• enable_shared_from_this and inheritance

  - by DeadMG

  I've got a type which inherits from enable_shared_from_this<type>, and another type that inherits from this type. Now I can't use the shared_from_this method because it returns the base type and in a specific derived class method I need the derived type. Is it valid to just construct a shared_ptr from this directly? Edit: In a related question, how can I move from an rvalue of type shared_ptr<base> to a type of shared_ptr<derived>? I used dynamic_cast to verify that it really was the correct type, but now I can't seem to accomplish the actual move.

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• How to see if turbo boost is working on I7 860 CPU?

  - by Jan Derk

  I just build myself a new system with a Intel I7 860 CPU. When loading it using a single threaded application like Super PI, CPU-Z shows 2.933Ghz as speed. Now I understood that the I7 goes into turbo boost mode up to 3.46GHz for a single core. How can I check that? Is there a utility to monitor CPU speed per core?

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• Hyper-V Ubuntu 10.04, Filesystem suddenly becomes Read-Only?

  - by Daniel Upton

  We are running a Ubuntu 10.04 VM on a Hyper-V system, The VM is dedicated to running one of our web applications. We have enabled the Hyper-V drivers in /etc/initramfs-tools/modules like so: hv_vmbus hv_storvsc hv_blkvsc hv_netvsc And updated the kernel image like so: $ update-initramfs -u And all was good... until.. This morning i got a support request that our web application was throwing an error 500, so i checked the logs and nothing was there. Then I remembered that I had seen this on another of our ubuntu servers so I... $ touch foo.txt And my suspicions were confirmed: touch: cannot touch `foo.txt': Read-only file system Why is the filesystem randomly becoming readonly? Is this only in Ubuntu on HV? Is it a problem on RedHat or Cent?

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• Best filesystem for an external drive? ExFAT?

  - by GiH

  What is the best filesystem for use with multiple OS's? I saw this question but its old and doesn't take into account ExFAT. Here is what I know from my findings: NTFS - Can't write from Mac FAT32 - Doesn't support files larger than 4GB HFS - Only mac ExFAT - ??? I don't know much about this but it seems like it got rid of the 4GB limit of FAT32 and can be read on Windows, Mac, and Linux. Is ExFAT the best bet? I tried formatting the drive in ExFAT just now, but on Windows XP SP3 it was showing up as not formatted... It seems to me like FAT32 is still the best, but I wanted to see what other people had to say.

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• A space-efficient guest filesystem for grow-as-needed virtual disks ?

  - by Steve Schnepp

  A common practice is to use non-preallocated virtual disks. Since they only grow as needed, it makes them perfect for fast backup, overallocation and creation speed. Since file systems are usually based on physical disks they have the tendency to use the whole area available1 in order to increase the speed2 or reliability3. I'm searching a filesystem that does the exact opposite : try to touch the minimum blocks need by an aggressive block reuse. I would happily trade some performance for space usage. There is already a similar question, but it is rather general. I have very specific goal : space-efficiency. 1. Like page caching uses all the free physical memory 2. Canonical example : online defragmentation 3. Canonical example : snapshotting

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• How can I audit a Linux filesystem for files which have been changed or added within a specific time

  - by Bcos

  We are a website design/hosting company running several sites on a Linux server using Joomla 1.5.14 and recently someone was able exploit a vulnerability in the RW Cards component to write arbitrary files/modify existing files on our filesystem enabling them to do some nasty things to our customers sites. We have removed vulnerable modules from all sites but are still seeing some problems. We suspect that they still have some scripts installed and need a way to audit anything that has been changed or added in the last 10 days. Is there a command or script we can run to do this?

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• What is the best filesystem for storing thousands of files in one dictionary-like id-blob structure?

  - by Ivan

  What filesystem best suits my needs? Thousands or even millions of files in one directory. Good (ext4 & ntfs level or close) reliability (incl. fault tolerance) and access speed. No directories actually needed, as well as descriptive names, just a dictionary-like structure of id-blob pairs is all I need. No links, attributes, and access control features needed. The purpose is a file storage where all the metadata (data describing all the facts about what the file actually contains and who can access it) is stored in a MySQL database. As far as I know common filesystems like NTFS and ext3/4 can go dead-slow if there are too many files placed in one directory - that's why I ask.

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• Linux install error " dracut Warning: Can't mount root filesystem. "

  - by NBB

  I am installing Fedora 16. I just insert CD to install Fedora 16 in my laptop however, I am getting this error like "dracut Warning: Can't mount root filesystem." http://cfile7.uf.tistory.com/image/176BAA3C4EBF9F89051FA7 <--- like this I am not really sure how to fix it. (this is the first time to install Fedora 16 in my laptop) In my laptop , I previously installed Windows 7 Professional. I have not install any kind of Linux before. Does anyone know how to fix this problem ?

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• A space-efficient filesystem for grow-as-needed virtual disks ?

  - by Steve Schnepp

  A common practice is to use non-preallocated virtual disks. Since they only grow as needed, it makes them perfect for fast backup, overallocation and creation speed. Since file systems are usually based on physical disks they have the tendency to use the whole area available1 in order to increase the speed2 or reliability3. I'm searching a filesystem that does the exact opposite : try to touch the minimum blocks need by an aggressive block reuse. I would happily trade some performance for space usage. There is already a similar question, but it is rather general. I have very specific goal : space-efficiency. 1. Like page caching uses all the free physical memory 2. Canonical example : online defragmentation 3. Canonical example : snapshotting

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• Is there a filesystem that is "friendly" to both windows and Linux?

  - by Somebody still uses you MS-DOS

  I'm planning to install Ubuntu 10.04 with Windows 7. (I'm new to Linux, have to use at work so I'm planning to install it at home to learn more) I plan to use a partition to my Windows system files (C:), a partition for my personal files that already exists (D:) and a new partition for Linux. What I want is to have a partition for my personal files that works across these systems - so, if I start with Windows or Linux, there's the same "Videos", "Pictures", "Projects" folders. Is it possible? Is there a hd filesystem capable of having writes from both systems without too much risk of corrupting or something?

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• Is there a filesystem that is "friendly" to both windows and Linux?

  - by Somebody still uses you MS-DOS

  I'm planning to install Ubuntu 10.04 with Windows 7. (I'm new to Linux, have to use at work so I'm planning to install it at home to learn more) I plan to use a partition to my Windows system files (C:), a partition for my personal files that already exists (D:) and a new partition for Linux. What I want is to have a partition for my personal files that works across these systems - so, if I start with Windows or Linux, there's the same "Videos", "Pictures", "Projects" folders. Is it possible? Is there a hd filesystem capable of having writes from both systems without too much risk of corrupting or something? (Can't be FAT32, I need to store 4gb files). I've read some horror stories of corruption, and would like to know from a sysadmin POV all the risks involved in such scenario.

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