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using yield in C# like I would in Ruby

- by Sarah Vessels

Besides just using yield for iterators in Ruby, I also use it to pass control briefly back to the caller before resuming control in the called method. What I want to do in C# is similar. In a test class, I want to get a connection instance, create another variable instance that uses that connection, then pass the variable to the calling method so it can be fiddled with. I then want control to return to the called method so that the connection can be disposed. I guess I'm wanting a block/closure like in Ruby. Here's the general idea: private static MyThing getThing() { using (var connection = new Connection()) { yield return new MyThing(connection); } } [TestMethod] public void MyTest1() { // call getThing(), use yielded MyThing, control returns to getThing() // for disposal } [TestMethod] public void MyTest2() { // call getThing(), use yielded MyThing, control returns to getThing() // for disposal } ... This doesn't work in C#; ReSharper tells me that the body of getThing cannot be an iterator block because MyThing is not an iterator interface type. That's definitely true, but I don't want to iterate through some list. I'm guessing I shouldn't use yield if I'm not working with iterators. Any idea how I can achieve this block/closure thing in C# so I don't have to wrap my code in MyTest1, MyTest2, ... with the code in getThing()'s body?

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Writing my own implementation of stl-like Iterator in C++.

- by Negai

Good evening everybody, I'm currently trying to understand the intrinsics of iterators in various languages i.e. the way they are implemented. For example, there is the following class exposing the list interface. template<class T> class List { public: virtual void Insert( int beforeIndex, const T item ) throw( ListException ) =0 ; virtual void Append( const T item ) =0; virtual T Get( int position ) const throw( ListException ) =0; virtual int GetLength() const =0; virtual void Remove( int position ) throw( ListException ) =0; virtual ~List() =0 {}; }; According to GoF, the best way to implement an iterator that can support different kinds of traversal is to create the base Iterator class (friend of List) with protected methods that can access List's members. The concrete implementations of Iterator will handle the job in different ways and access List's private and protected data through the base interface. From here forth things are getting confusing. Say, I have class LinkedList and ArrayList, both derived from List, and there are also corresponding iterators, each of the classes returns. How can I implement LinkedListIterator? I'm absolutely out of ideas. And what kind of data can the base iterator class retrieve from the List (which is a mere interface, while the implementations of all the derived classes differ significantly) ? Sorry for so much clutter. Thanks.

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new[n] and delete every location with delete instead the whole chunk with delete[]

- by pmr

Is this valid C++ (e.g. not invoking UB) and does it achieve what I want without leaking memory? valgrinds complains about mismatching free and delete but says "no leaks are possible" in the end. int main() { int* a = new int[5]; for(int i = 0; i < 5; ++i) a[i] = i; for(int i = 0; i < 5; ++i) delete &a[i]; } The reason I'm asking: I have a class that uses boost::intrusive::list and I new every object that is added to that list. Sometimes I know how many objects I want to add to the list and was thinking about using new[] to allocate a chunk and still be able to delete every object on its own with the Disposer-style of boost::intrusive.

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How to read verbose VC++ linker output

- by Assaf Lavie

Trying to debug some linker errors, I turned on /VERBOSE and I'm trying to make sense of the output. It occurs to me that I really don't know how to read it. For example: 1>Compiling version info 1>Linking... 1>Starting pass 1 1>Processed /DEFAULTLIB:mfc80.lib 1>Processed /DEFAULTLIB:mfcs80.lib 1>Processed /DEFAULTLIB:msvcrt.lib 1>Processed /DEFAULTLIB:kernel32.lib 1>Processed /DEFAULTLIB:user32.lib .... 1>Processed /DEFAULTLIB:libgslcblasMD.lib 1>Searching libraries 1> Searching V:\Src\Solutions\\..\..\\Common\Win32\Lib\PlxApi.lib: 1> Searching ..\..\..\..\out\win32\release\lib\camerageometry.lib: 1> Searching ..\..\..\..\out\win32\release\lib\geometry.lib: 1> Found "public: __thiscall VisionMap::Geometry::Box2d::operator class VisionMap::Geometry::Box2DInt(void)const " (??BBox2d@Geometry@VisionMap@@QBE?AVBox2DInt@12@XZ) 1> Referenced in FocusDlg.obj 1> Loaded geometry.lib(Box2d.obj) 1>Processed /DEFAULTLIB:CGAL-vc80-mt.lib 1>Processed /DEFAULTLIB:boost_thread-vc80-mt-1_33_1.lib What's going on here? I think I understand this bit: 1>Processed /DEFAULTLIB:libgslcblasMD.lib 1>Searching libraries 1> Searching V:\Src\Solutions\\..\..\\Common\Win32\Lib\PlxApi.lib: 1> Searching ..\..\..\..\out\win32\release\lib\camerageometry.lib: 1> Searching ..\..\..\..\out\win32\release\lib\geometry.lib: 1> Found "public: __thiscall VisionMap::Geometry::Box2d::operator class VisionMap::Geometry::Box2DInt(void)const " (??BBox2d@Geometry@VisionMap@@QBE?AVBox2DInt@12@XZ) 1> Referenced in FocusDlg.obj 1> Loaded geometry.lib(Box2d.obj) It's trying to find the implementation of the above operator, which is used somewhere in FocusDlg.cpp, and it finds it in geometry.lib. But what does 1>Processed /DEFAULTLIB:libgslcblasMD.lib mean? What determines the order of symbol resolution? Why is it loading this particular symbol while processing libgslcblasMD.lib which is a 3rd party library? Or am I reading it wrong? It seems that the linker is going through the symbols referenced in the project's various object files, but I have no idea in what order. It then searches the static libraries the project uses - by project reference, explicit import and automatic default library imports; but it does so in an order that, again, seems arbitrary to me. When it finds a symbol, for example in geometry.lib, it then continues to find a bunch of other symbols from the same lib: 1> Searching V:\Src\Solutions\\..\..\\Common\Win32\Lib\PlxApi.lib: 1> Searching ..\..\..\..\out\win32\release\lib\camerageometry.lib: 1> Searching ..\..\..\..\out\win32\release\lib\geometry.lib: 1> Found "public: __thiscall VisionMap::Geometry::Box2d::operator class VisionMap::Geometry::Box2DInt(void)const " (??BBox2d@Geometry@VisionMap@@QBE?AVBox2DInt@12@XZ) 1> Referenced in FocusDlg.obj 1> Loaded geometry.lib(Box2d.obj) 1>Processed /DEFAULTLIB:CGAL-vc80-mt.lib 1>Processed /DEFAULTLIB:boost_thread-vc80-mt-1_33_1.lib 1> Found "public: __thiscall VisionMap::Geometry::Box2DInt::Box2DInt(int,int,int,int)" (??0Box2DInt@Geometry@VisionMap@@QAE@HHHH@Z) 1> Referenced in FocusDlg.obj 1> Referenced in ImageView.obj 1> Referenced in geometry.lib(Box2d.obj) 1> Loaded geometry.lib(Box2DInt.obj) 1> Found "public: virtual __thiscall VisionMap::Geometry::Point3d::~Point3d(void)" (??1Point3d@Geometry@VisionMap@@UAE@XZ) 1> Referenced in GPSFrm.obj 1> Referenced in MainFrm.obj 1> Loaded geometry.lib(Point3d.obj) 1> Found "void __cdecl VisionMap::Geometry::serialize<class boost::archive::binary_oarchive>(class boost::archive::binary_oarchive &,class VisionMap::Geometry::Point3d &,unsigned int)" (??$serialize@Vbinary_oarchive@archive@boost@@@Geometry@VisionMap@@YAXAAVbinary_oarchive@archive@boost@@AAVPoint3d@01@I@Z) 1> Referenced in GPSFrm.obj 1> Referenced in MainFrm.obj 1> Loaded geometry.lib(GeometrySerializationImpl.obj) But then, for some reason, it goes on to find symbols that are defined in other libs, and returns to geometry later on (a bunch of times). So clearly it's not doing "look in geometry and load every symbol that's references in the project, and then continue to other libraries". But it's not clear to me what is the order of symbol lookup. And what's the deal with all those libraries being processed at the beginning of the linker's work, but not finding any symbols to load from them? Does this project really not use anything from msvcrt.lib, kernel32.lib? Seems unlikely. So basically I'm looking to decipher the underlying order in the linker's operation.

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How do I set scons system include path

- by Michael Anderson

Using scons I can easily set my include paths: env.Append( CPPPATH=['foo'] ) This passes the flag -Ifoo to gcc However I'm trying to compile with a lot of warnings enabled. In particular with env.Append( CPPFLAGS=['-Werror', '-Wall', '-Wextra'] ) which dies horribly on certain boost includes ... I can fix this by adding the boost includes to the system include path rather than the include path as gcc treats system includes differently. So what I need to get passed to gcc instead of -Ifoo is -isystem foo I guess I could do this with the CPPFLAGS variable, but was wondering if there was a better solution built into scons.

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Compiling and installing pyactivemq on osx

- by muanis

I'm having a hardtime trying to install pyactivemq (link) on my osx leopard. Following a tutorial (in portuguese) on compiling it ends up ok, but when I run the tests i receive only a crypt message: "Fatal Python error: Interpreter not initialized (version mismatch?)" There is not much information on the web about using pyactivemq on osx, but what I could find is that is something related to wrong linking when boost compiles. I'm running: Mac OS 10.5.8 MacPorts 1.8.2 APR 1.3.9 Xcode 3.1.4 Boost 1.41.0 (installing for python 2.5) Activemq-cpp 2.2.6 pyactivemq 0.1.0 If someone has any info on this it would be helpful

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Links to official style guides

- by User1

C++ has several types of styles: MFC, Boost, Google, etc. I would like to examine these styles and determine which one is best for my projects, but I want to read from the official style guidebook. Does anyone have an official guide that they typically use? Here are two that I found. I bet there are more: http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml http://www.boost.org/development/requirements.html Note: This is NOT a discussion about which styleis best..only a call for official style guides that people currently use. Please refrain from bashing other style guides that you don't like. Side question: Is there a good tool that can examine source code and tell if it matches a given style guide?

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A quick design question about C++ container classes in shared memory

- by recipriversexclusion

I am writing a simple wrapper around boost::interprocess's vector container to implement a ring buffer in shared memory (shm) for IPC. Assume that buf is an instance of RingBuffer created in shm. Now, in its ctor, buf itself allocates a private boost::interprocess::vector data member to store values, e.g. m_data. My question is: I think m_data should also be created in shared memory. But it this a necessity? What happens if buf that was created in shm itself, allocates standard memory, i.e. using new. Does this get allocated on the calling process's heap? I don't think buf is allocated there so how come a data member that is private to an object not on a process's heap gets allocated there. I'm confused.

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C++: what regex library should I use?

- by Stéphane

I'm working on a commercial (not open source) C++ project that runs on a linux-based system. I need to do some regex within the C++ code. (I know: I now have 2 problems.) QUESTION: What libraries do people who regularly do regex from C/C++ recommend I look into? A quick search has brought the following to my attention: 1) Boost.Regex (I need to go read the Boost Software License, but this question is not about software licenses) 2) C (not C++) POSIX regex (#include <regex.h>, regcomp, regexec, etc.) 3) http://freshmeat.net/projects/cpp_regex/ (I know nothing about this one; seems to be GPL, therefore not usable on this project) Thanks.

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Link error (LNK2019) when including other projects in Visual Studio 2005

- by jules

I am trying to work with several projects on visual studio 2005. I have one project that depends on two others. I have included those two project in the first project solution, and set the dependencies correctly. I get this error when linking the project: 1>server_controller.obj : error LNK2019: unresolved external symbol "public: __thiscall server_communication::TcpServer::TcpServer(class boost::asio::io_service &,struct server_communication::ServerParameters &)" (??0TcpServer@server_communication@@QAE@AAVio_service@asio@boost@@AAUServerParameters@1@@Z) referenced in function "public: __thiscall server_controller::ServerController::ServerController(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >)" (??0ServerController@server_controller@@QAE@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@0@Z) I seems that the symbols can not be found in the other projects, even though there are defined in those projects.

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How to initialize a static const map in c++?

- by Meloun

Hi, I need just dictionary or asociative array string = int. There is type map C++ for this case. But I need make one map in my class make for all instances(- static) and this map cannot be changed(- const); I have found this way with boost library std::map<int, char> example = boost::assign::map_list_of(1, 'a') (2, 'b') (3, 'c'); Is there other solution without this lib? I have tried something like this, but there are always some issues with map initialization. class myClass{ private: static map<int,int> create_map() { map<int,int> m; m[1] = 2; m[3] = 4; m[5] = 6; return m; } static map<int,int> myMap = create_map(); } thanks

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C++ -- typedef "inside" template arguments?

- by redmoskito

Imagine I have a template function like this: template<Iterator> void myfunc(Iterator a, Iterator::value_type b) { ... } Is there a way to declare a typedef for Iterator::valuetype that I can use in the function signature? For example: template< typename Iterator, typedef Iterator::value_type type> void myfunc(Iterator a, type b) { ... } Thus far, I've resorted to using default template arguments and Boost concept checking to ensure the default is always used: template< typename Iterator, typename type = Iterator::value_type > void myfunc(Iterator a, type b) { BOOST_STATIC_ASSERT(( boost::type_traits::is_same< typename Iterator::value_type, type >::value )); ... } ...but it would be nice if there was support in the language for this type of thing.

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Which C++ graphics library should I use?

- by mspoerr

Hello, I found the following graphics libraries, but I am not sure which one I should use. Maybe there are some more... Graphviz (http://www.graphviz.org/) Boost Graph Library (http://www.boost.org/doc/libs/1_42_0/libs/graph/doc/index.html) Lemon (http://lemon.cs.elte.hu/trac/lemon) igraph (http://igraph.sourceforge.net/introduction.html) What it should do: draw a undirected network map come as header only or static lib for Windows the output format should be user editable Graphviz is the only one I tried so far, but I found no static lib for it, I failed to build it by my own and the documentation could be better. Therefore I looked around and found these other three libs. I would be glad to get some recommendations which lib to choose. Thanks, /mspoerr

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Which C++ graph library should I use?

- by mspoerr

Hello, I found the following graph libraries, but I am not sure which one I should use. Maybe there are some more... Graphviz (http://www.graphviz.org/) Boost Graph Library (http://www.boost.org/doc/libs/1_42_0/libs/graph/doc/index.html) Lemon (http://lemon.cs.elte.hu/trac/lemon) igraph (http://igraph.sourceforge.net/introduction.html) What it should do: draw a undirected network map come as header only or static lib for Windows the output format should be user editable Graphviz is the only one I tried so far, but I found no static lib for it, I failed to build it by my own and the documentation could be better. Therefore I looked around and found these other three libs. I would be glad to get some recommendations which lib to choose. Thanks, /mspoerr

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Detect template presence at compilation time

- by doublep

GCC up to 4.5 doesn't have standard C++0x type trait template has_nothrow_move_constructor. I could use it in my package for optimization, but I don't want to rule out one of the common compilers and don't want to overload configuration with symbols like HAVE_STD_HAS_NOTHROW_MOVE_CONSTRUCTOR. Is it somehow possible to use that template if present and just fall back to copying if not present without using any predefined configuration symbols? I also don't want to depend on Boost, since my library is small and doesn't need Boost for any other reasons. In pseudocode, I need something like: template <typename type> struct has_nothrow_move_constructor_robust : public integral_constant <bool, /* if possible */ has_nothrow_move_constructor <type>::value /* otherwise */ false> { }; Since move constructors are only for C++0x anyway, I don't mind using other C++0x features for the above definition, if at all possible.

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Is this a correct implementation of singleton C++?

- by Kamal

class A{ static boost::shared_ptr<A> getInstance(){ if(pA==NULL){ pA = new A(); } return boost::shared_ptr(pA); } //destructor ~A(){ delete pA; pA=NULL; } private: A(){ //some initialization code } //private assigment and copy constructors A(A const& copy); // Not Implemented A& operator=(A const& copy); // Not Implemented static A* pA; }; A* A::pA = NULL;

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Finding if all elements in a vector<string> are in a string

- by devin

I have a vector and I need to see if all the strings in that vector are substrings of another given string. eg vector<string> v; v.push_back("str1"); v.push_back("str2"); string s1 = "str1, str2, str3"; string s2 = "str1, str3"; Is there a way to get true from s1 and false from s2 without looping over the vector? Also, note that due to my environment, I can't use boost. I think if I had boost, I could do this.

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How to interrupt a waiting C++0x thread?

- by doublep

I'm considering to use C++0x threads in my application instead of Boost threads. However, I'm not sure how to reimplement what I have with standard C++0x threads since they don't seem to have an interrupt() method. My current setup is: a master thread that manages work; several worker threads that carry out master's commands. Workers call wait() on at least two different condition variables. Master has a "timed out" state: in this case it tells all workers to stop and give whatever result they got by then. With Boost threads master just uses interrupt_all() on a thread group, which causes workers to stop waiting. In case they are not waiting at the moment, master also sets a bool flag which workers check periodically. However, in C++0x std::thread I don't see any replacement for interrupt(). Do I miss something? If not, how can I implement the above scheme so that workers cannot just sleep forever?

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Multiset of shared_ptrs as a dynamic priority queue: Concept and practice

- by Sarah

I was using a vector-based priority queue typedef std::priority_queue< Event, vector< Event >, std::greater< Event > > EventPQ; to manage my Event objects. Now my simulation has to be able to find and delete certain Event objects not at the top of the queue. I'd like to know if my planned work-around can do what I need it to, and if I have the syntax right. I'd also like to know if dramatically better solutions exist. My plan is to make EventPQ a multiset of smart pointers to Event objects: typedef std::multi_set< boost::shared_ptr< Event > > EventPQ; I'm borrowing functions of the Event class from a related post on a multimap priority queue. // Event.h #include <cstdlib> using namespace std; #include <set> #include <boost/shared_ptr.hpp> class Event; typedef std::multi_set< boost::shared_ptr< Event > > EventPQ; class Event { public: Event( double t, int eid, int hid ); ~Event(); void add( EventPQ& q ); void remove(); bool operator < ( const Event & rhs ) const { return ( time < rhs.time ); } bool operator > ( const Event & rhs ) const { return ( time > rhs.time ); } double time; int eventID; int hostID; EventPQ* mq; EventPQ::iterator mIt; }; // Event.cpp Event::Event( double t, int eid, int hid ) { time = t; eventID = eid; hostID = hid; } Event::~Event() {} void Event::add( EventPQ& q ) { mq = &q; mIt = q.insert( boost::shared_ptr<Event>(this) ); } void Event::remove() { mq.erase( mIt ); mq = 0; mIt = EventPQ::iterator(); } I was hoping that by making EventPQ a container of pointers, I could avoid wasting time copying Events into the container and avoid accidentally editing the wrong copy. Would it be dramatically easier to store the Events themselves in EventPQ instead? Does it make more sense to remove the time keys from Event objects and use them instead as keys in a multimap? Assuming the current implementation seems okay, my questions are: Do I need to specify how to sort on the pointers, rather than the objects, or does the multiset automatically know to sort on the objects pointed to? If I have a shared_ptr ptr1 to an Event that also has a pointer in the EventPQ container, how do I find and delete the corresponding pointer in EventPQ? Is it enough to .find( ptr1 ), or do I instead have to find by the key (time)? Is the Event::remove() sufficient for removing the pointer in the EventPQ container? There's a small chance multiple events could be created with the same time (obviously implied in the use of multiset). If the find() works on event times, to avoid accidentally deleting the wrong event, I was planning to throw in a further check on eventID and hostID. Does this seem reasonable? (Dumb syntax question) In Event.h, is the declaration of dummy class Event;, then the EventPQ typedef, and then the real class Event declaration appropriate? I'm obviously an inexperienced programmer with very spotty background--this isn't for homework. Would love suggestions and explanations. Please let me know if any part of this is confusing. Thanks.

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pointer delegate in STL set.

- by ananth

hi. Im kinda stuck with using a set with a pointer delegate. my code is as follows: void Graph::addNodes (NodeSet& nodes) { for (NodeSet::iterator pos = nodes.begin(); pos != nodes.end(); ++pos) { addNode(*pos); } } Here NodeSet is defined as: typedef std::set NodeSet; The above piece of code works perfectly on my windows machine, but when i run the same piece of code on a MAC, it gives me the following error: no matching function for call to 'Graph::addNode(const boost::shared_ptr&)' FYI, Node_ptr is of type: typedef boost::shared_ptr Node_ptr; can somebody plz tell me why this is happening?

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Ubuntu makes noise and heat when AC charger is inserted

- by user2263752

I have an issue with heat and noise on my laptop with Ubuntu 14.04 installed. The thing is that when I have the AC charger plugged into the laptop, it automatically goes to "boost mode" or something. And when the laptop is on battery mode, the heat and noise is reduced shortly. I want the laptop to be on battery mode as general and "boost mode" as an option if more power is needed. Any solutions? I have installed tlp that doesn't seen to have any effect.

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Multiple key map in c++

- by Morgan

Hi, I'm wondering if any of you know of a c++ associative map container type which I can perform multiple key lookups on. The map needs to have constant time lookups but I don't care if it's ordered or unordered. It just needs to be fast. For example, I want to store a bunch of std::vector objects in a map with an integer and a void* as the lookup keys. Both the int and the void* must match for my vector to be retrieved. Does anything like this exist already? Or am I going to have to roll my own. If so, any suggestions? I've been trying to store a boost::unordered_map inside another boost::unordered_map, but I have not had any success with this method yet. Maybe I will continue Pershing this method if there is no simpler way. Thanks!

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How can I find out how much memory an object (rather the instance of an object) of a C++ class consu

- by Shadow

Hi, I am developing a Graph-class, based on boost-graph-library. A Graph-object contains a boost-graph, so to say an adjacency_list, and a map. When monitoring the total memory usage of my program, it consumes quite a lot (checked with pmap). Now, I would like to know, how much of the memory is exactly consumed by a filled object of this Graph-class? With filled I mean when the adjacency_list is full of vertices and edges. I found out, that using sizeof() doesn't bring me far. Using valgrind is also not an alternative as there is quite some memory allocation done previously and this makes the usage of valgrind impractical for this purpose. I'm also not interested in what other parts of the program cost in memory, I want to focus on one single object. Thank you.

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Creating TCP network errors for unit testing

- by Robert S. Barnes

I'd like to create various network errors during testing. I'm using the Berkely sockets API directly in C++ on Linux. I'm running a mock server in another thread from within Boost.Test which listens on localhost. For instance, I'd like to create a timeout during connect. So far I've tried not calling accept in my mock server and setting the backlog to 1, then making multiple connections, but all seem to successfully connect. I would think that if there wasn't room in the backlog queue I would at least get a connection refused error if not a timeout. I'd like to do this all programatically if possible, but I'd consider using something external like IPchains to intentionally drop certain packets to certain ports during testing, but I'd need to automate creating and removing rules so I could do it from within my Boost.Test unit tests. I suppose I could mock the various system calls involved, but I'd rather go through a real TCP stack if possible. Ideas?

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C++ obtaining milliseconds time on Linux -- clock() doesn't seem to work properly

- by hasen j

On Windows, clock() returns the time in milliseconds, but on this Linux box I'm working on, it rounds it to the nearest 1000 so the precision is only to the "second" level and not to the milliseconds level. I found a solution with Qt using the QTime class, instantiating an object and calling start() on it then calling elapsed() to get the number of milliseconds elapsed. I got kind of lucky because I'm working with Qt to begin with, but I'd like a solution that doesn't rely on third party libraries, Is there no standard way to do this? UPDATE Please don't recommend Boost .. If Boost and Qt can do it, surely it's not magic, there must be something standard that they're using!

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