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• Daylight saving time of current tz

  - by spam2

  Hi, in my c++ software I've used Boost in some parts and also for the local time. OK, now my problem is to make a check if in my machine is active or not the DST. With the follow part of code I can know only the difference from the UTC time. In my case the difference is 2 hours because is active the DST ptime tLoc = second_clock::local_time(); ptime tUTC = second_clock::universal_time(); time_duration tDiff = tUTC - tLoc; local_time_zone = tDiff.hours(); I think that the boolean funcion has_dst() can help, right? My system is Debian GNU/Linux. Thanks

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• .NET Regular expressions on bytes instead of chars

  - by brickner

  Hi, I'm trying to do some parsing that will be easier using regular expressions. The input is an array (or enumeration) of bytes. I don't want to convert the bytes to chars for the following reasons: Computation efficiency Memory consumption efficiency Some non-printable bytes might be complex to convert to chars. Not all the bytes are printable. So I can't use Regex. The only solution I know, is using Boost.Regex (which works on bytes - C chars), but this is a C++ library that wrapping using C++/CLI will take considerable work. How can I use regular expressions on bytes in .NET directly, without working with .NET strings and chars? Thank you.

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• Referring to this pointer in a static assert?

  - by Tyson Jacobs

  Is it possible to write a static assert referring to the 'this' pointer? I do not have c++11 available, and BOOST_STATIC_ASSERT doesn't work. struct blah { void func() {BOOST_STATIC_ASSERT(sizeof(*this));} }; Produces: error C2355: 'this' : can only be referenced inside non-static member functions error C2027: use of undefined type 'boost::STATIC_ASSERTION_FAILURE' In MSVC 2008. Motivation: #define CLASS_USES_SMALL_POOL() \ void __small_pool_check() {BOOST_STATIC_ASSERT(sizeof(*this) < SMALL_MALLOC_SIZE;} \ void* operator new(size_t) {return SmallMalloc();} \ void operator delete(void* p) {SmallFree(p);}

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• Detect aborted connection during ASIO request

  - by Tim Sylvester

  Is there an established way to determine whether the other end of a TCP connection is closed in the asio framework without sending any data? Using Boost.asio for a server process, if the client times out or otherwise disconnects before the server has responded to a request, the server doesn't find this out until it has finished the request and generated a response to send, when the send immediately generates a connection-aborted error. For some long-running requests, this can lead to clients canceling and retrying over and over, piling up many instances of the same request running in parallel, making them take even longer and "snowballing" into an avalanche that makes the server unusable. Essentially hitting F5 over and over is a denial-of-service attack. Unfortunately I can't start sending a response until the request is complete, so "streaming" the result out is not an option, I need to be able to check at key points during the request processing and stop that processing if the client has given up.

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• When to use the Flyweight Pattern

  - by elmt

  So I've just gotten on the boost train and was checking out the flyweight pattern and was interested in implementing it in my project. Obviously, it doesn't make sense to use it on any class that has only has one instance of it. However, say I have 5 instances of an class. Should I be using the flyweight pattern or should it be only used for a class that has at least N instances. I realize that many factors will influence this answer (how many fields there are, the size of the fields, etc.).

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• Hidden Features and Dark Corners of STL?

  - by Andrei

  C++ developers, all know the basics of C++: Declarations, conditionals, loops, operators, etc. Some of us even mastered the stuff like templates, object model, complex I/O, etc. But what are the most hidden features or tricks or dark corners of C++/STL that even C++ fans, addicts, and experts barely know? I am talking about a seasoned C++ programmer (be she/he a developer, student, fan, all three, etc), who thinks (s)he knows something 99% of us never heard or dreamed about. Something that not only makes his/her work easier, but also cool and hackish. After all, C++ is one of the most used programming languages in the world, thus it should have intricacies that only a few privileged know about and want to share with us. Boost is welcome too! One per post with an example please P.S Examples are important for other developers to copy and paste!

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• Returning references while using shared_ptrs

  - by Goose Bumper

  Suppose I have a rather large class Matrix, and I've overloaded operator== to check for equality like so: bool operator==(Matrix &a, Matrix &b); Of course I'm passing the Matrix objects by reference because they are so large. Now i have a method Matrix::inverse() that returns a new Matrix object. Now I want to use the inverse directly in a comparison, like so: if (a.inverse()==b) { ... }` The problem is, this means the inverse method needs to return a reference to a Matrix object. Two questions: Since I'm just using that reference in this once comparison, is this a memory leak? What happens if the object-to-be-returned in the inverse() method belongs to a boost::shared_ptr? As soon as the method exits, the shared_ptr is destroyed and the object is no longer valid. Is there a way to return a reference to an object that belongs to a shared_ptr?

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• killing a separate thread having a socket

  - by user311906

  Hi All I have a separate thread ListenerThread having a socket listening to info broadcasted by some remote server. This is created at the constructor of one class I need to develop. Because of requirements, once the separate thread is started I need to avoid any blocking function on the main thread. Once it comes to the point of calling the destructor of my class I cannot perform a join on the listener thread so the only thing I can do is to KILL it. My questions are: what happens to the network resoruces allocated by the function passed to the thead? Is the socket closed properly or there might be something pending? ( most worried about this ) is this procedure fast enough i.e. is the thread killed so that interrupt immediately ? I am working with Linux ...what command or what can I check to ensure that there is no networking resource left pending or that something went wrong for the Operating system I thank you very much for your help Regards MNSTN NOTE: I am using boost::thread in C++

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• C++ threaded class design from non-threaded class

  - by macs

  I'm working on a library doing audio encoding/decoding. The encoder shall be able to use multiple cores (i.e. multiple threads, using boost library), if available. What i have right now is a class that performs all encoding-relevant operations. The next step i want to take is to make that class threaded. So i'm wondering how to do this. I thought about writing a thread-class, creating n threads for n cores and then calling the encoder with the appropriate arguments. But maybe this is an overkill and there is no need for another class, so i'm going to make use of the "user interface" for thread-creation. I hope there are any suggestions.

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• How to accomplish covariant return types when returning a shared_ptr?

  - by Kyle

  using namespace boost; class A {}; class B : public A {}; class X { virtual shared_ptr<A> foo(); }; class Y : public X { virtual shared_ptr<B> foo(); }; The return types aren't covariant (nor are they, therefore, legal), but they would be if I was using raw pointers instead. What's the commonly accepted idiom to work around this, if there is one?

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• error: typedef name may not be a nested-name-specifier

  - by Autopulated

  I am trying to do something along the lines of this answer, and struggling: $ gcc --version gcc (GCC) 4.2.4 (Ubuntu 4.2.4-1ubuntu4) file.cpp:7: error: template argument 1 is invalid file.cpp:7: error: typedef name may not be a nested-name-specifier And the offending part of the file: template <class R, class C, class T0=void, class T1=void, class T2=void> struct MemberWrap; template <class R, class C, class T0> struct MemberWrap<R, C, T0>{ typedef R (C::*member_t)(T0); typedef typename boost::add_reference<typename T0>::type> TC0; // <---- offending line MemberWrap(member_t f) : m_wrapped(f){ } R operator()(C* p, TC0 p0){ GILRelease guard; return (p->*(this->m_wrapped))(p0); } member_t m_wrapped; };

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• Container for database-like searches

  - by Milan Babuškov

  I'm looking for some STL, boost, or similar container to use the same way indexes are used in databases to search for record using a query like this: select * from table1 where field1 starting with 'X'; or select * from table1 where field1 like 'X%'; I thought about using std::map, but I cannot because I need to search for fields that "start with" some text, and not those that are "equal to". I could create a sorted vector or list and use binary search (breaking the set in 2 in each step by reading the element in the middle and seeing if it's more or less than 'X'), but I wonder if there is some ready-made container I could use without reinventing the wheel?

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• How prevent anyone from stealing my shared_ptr?

  - by Kyle

  So, I use boost::shared_ptr for all the various reference-counting benefits it provides -- reference counting for starters, obviously, but also the ability to copy, assign, and therefore store in STL Containers. The problem is, if I pass it to just one "malicious" function or object, the object can save the ptr and then I'll never be able to de-allocate it without the foreign function or object nicely relinquishing its ownership. Ultimately, I try to keep object ownership explicit. I accomplish this by having the owner keep the only shared_ptr to the object, and "guest" objects only store weak_ptrs to the object. I really don't want the "shared" part of shared_ptr, but I'm required to use shared_ptr in order to make weak_ptrs. I want to use scoped_ptr, but it's extremely limited since you can't copy it. You can't store it in a container, you can't lend out weak_ptrs from it, and you can't transfer ownership to a new manager. What's the solution?

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• What strategies are efficient to handle concurrent reads on heterogeneous multi-core architectures?

  - by fabrizioM

  I am tackling the challenge of using both the capabilities of a 8 core machine and a high-end GPU (Tesla 10). I have one big input file, one thread for each core, and one for the the GPU handling. The Gpu thread, to be efficient, needs a big number of lines from the input, while the Cpu thread needs only one line to proceed (storing multiple lines in a temp buffer was slower). The file doesn't need to be read sequentially. I am using boost. My strategy is to have a mutex on the input stream and each thread locks - unlocks it. This is not optimal because the gpu thread should have a higher precedence when locking the mutex, being the fastest and the most demanding one. I can come up with different solutions but before rush into implementation I would like to have some guidelines. What approach do you use / recommend ?

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• How to pass a linc to class function and call it?

  - by Kabumbus

  So I have a class like class mySafeData { public: void Set( int i ) { myMutex.lock(); myData = i; myMutex.unlock(); } void Get( int& i) { myMutex.lock(); i = myData; myMutex.unlock(); } private: int myData; boost::mutex myMutex; }; its instance is running. Lets call instance A. I want to create a new class that would take as a start up argument some kind of link to Getter from A and would be capable to somehow save link to thet getter for calling it inside its private methods vhen needed. how to do such thing?

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• Writing a filter for incoming connections

  - by Kornel Kisielewicz

  I'm using C++/boost::asio under Win7. I'm trying to "sniff" trafic over a given TCP/IP port. Hence, I'd like to listen on that port, receive messages, analyze them, but also immidately allow them to flow further, as if I never intercepted them. I want them to sink into the program that normally listens and connects on that port. Imagine a transparent proxy, but not for HTTP. I'd rather find a code-based solution, but barring that, maybe you would suggest a tool?

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• How do I create a set with std::pair thats sorted based on the ::second pair member using bind

  - by Stone Free

  I know I could use the following: template <typename Pair> struct ComparePairThroughSecond : public std::unary_function<Pair, bool> { bool operator ()(const Pair& p1, const Pair& p2) const { return p1.second < p2.second; } }; std::set<std::pair<int, long>, ComparePairThroughSecond> somevar; but wondered if it could be done with boost::bind

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• How to program a connection pool?

  - by the_drow

  Is there a known algorithm for implementing a connection pool? If not what are the known algorithms and what are their trade-offs? What design patterns are common when designing and programming a connection pool? Are there any code examples implement a connection pool using boost.asio? Is it a good idea to use a connection pool for presisting connections (not http)? How is threading related to connection pooling? When do you need a new thread?

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• Force an object to be allocated on the heap

  - by Warren Seine

  A C++ class I'm writing uses shared_from_this() to return a valid boost::shared_ptr<>. Besides, I don't want to manage memory for this kind of object. At the moment, I'm not restricting the way the user allocates the object, which causes an error if shared_from_this() is called on a stack-allocated object. I'd like to force the object to be allocated with new and managed by a smart pointer, no matter how the user declares it. I thought it could be done through a proxy or an overloaded new operator, but I can't find a proper way of doing that. Is there a common design pattern for such usage? If it's not possible, how can I test it at compile time?

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• How to get the next prefix in C++?

  - by Vicente Botet Escriba

  Given a sequence (for example a string "Xa"), I want to get the next prefix in order lexicographic (i.e "Xb"). As I don't want to reinvent the wheel, I'm wondering if there is any function in C++ STL or boost that can help to define this generic function easily? If not, do you think that this function can be useful? Notes The next of "aZ" should be "b". Even if the examples are strings, the function should work for any Sequence. The lexicographic order should be a template parameter of the function.

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• TCP 30 small packets per second polutes connection with server

  - by Denis Ermolin

  I'm testing connection with flash client and cloud server(boost::asio for software) over TCP connection. My connection with server already is really poor - 120 ms ping in average. I found when i start to send packets with 2 bytes size (without tcp header) with speed 30 packets/s ping grow to 170-200 average. I think that it's really bad and my bad connection and bad cloud provider is reason for this high ping without any load. What do you think? (I tested my software and can compute about 50k packets/s so software is not a problem).

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• How to know if the argument that is passed to the function is a class, union or enum in c++?

  - by Narek

  I want to define an operator<< for all enums, to cout the value and print that it is an enum like this: code: enum AnyEnum{A,B,C}; AnyEnum enm = A; cout << enm <<endl; output: This is an enum which has a value equal to 0 I know a way of doing this with Boost library by using is_enum struct. But I don’t understand how it works. So that's why, in general, I am interested how to identify if the veriable is a class type, union type or an enum (in compile time).

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• How to copy a structure with pointers to data inside (so to copy pointers and data they point to)?

  - by Kabumbus

  so I have a structure like struct GetResultStructure { int length; char* ptr; }; I need a way to make a full copy of it meaning I need a copy to have a structure with new ptr poinnting on to copy of data I had in original structure. Is It any how possible? I mean any structure I have which contains ptrs will have some fields with its lengths I need a function that would copy my structure coping all ptrs and data they point to by given array of lengthes... Any cool boost function for it? Or any way how to create such function?

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• Portable Socket programming in C/C++ possible?

  - by questions

  I am thinking of creating a multi-platform portable C++ server-client application. Is it even possible while using only standard libraries? If no, what other libraries are there? Are there any improvements in this direction in C++11x? Like for threads, now we have std::threads. To make it more clear.. I want something like boost::thread, which provides multiplatform portable multithreading, for networking. And why C++ doesn't have libraries(standard) for such basic things like networking?

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• Quickest way to compute the number of shared elements between two vectors

  - by shn

  Suppose I have two vectors of the same size vector< pair<float, NodeDataID> > v1, v2; I want to compute how many elements from both v1 and v2 have the same NodeDataID. For example if v1 = {<3.7, 22>, <2.22, 64>, <1.9, 29>, <0.8, 7>}, and v2 = {<1.66, 7>, <0.03, 9>, <5.65, 64>, <4.9, 11>}, then I want to return 2 because there are two elements from v1 and v2 that share the same NodeDataIDs: 7 and 64. What is the quickest way to do that in C++ ? Just for information, note that the type NodeDataIDs is defined as I use boost as: typedef adjacency_list<setS, setS, undirectedS, NodeData, EdgeData> myGraph; typedef myGraph::vertex_descriptor NodeDataID; But it is not important since we can compare two NodeDataID using the operator == (that is, possible to do v1[i].second == v2[j].second)

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