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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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• Casting a container of shared_ptr

  - by Jamie Cook

  Hi all, I have a method void foo(list<shared_ptr<Base>>& myList); Which I'm trying to call with a two different types of lists, one of DerivedClass1 and one of DerivedClass2 list<shared_ptr<DerivedClass1>> myList1; foo(myList1); list<shared_ptr<DerivedClass2>> myList2; foo(myList2); However this obviously generates a compiler error error: a reference of type "std::list<boost::shared_ptr<Base>, std::allocator<boost::shared_ptr<Base>>> &" (not const-qualified) cannot be initialized with a value of type "std::list<boost::shared_ptr<DerivedClass1>, std::allocator<boost::shared_ptr<DerivedClass1>>>" Is there any easy way to cast a container of shared_ptr? Of alternate containers that can accomplish this?

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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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• Which libraries use the "We Know Where You Live" optimization for std::make_shared?

  - by KnowItAllWannabe

  Over two years ago, Stephan T. Lavavej described a space-saving optimization he implemented in Microsoft's implementation of std::make_shared, and I know from speaking with him that Microsoft has nothing against other library implementations adopting this optimization. If you know for sure whether other libraries (e.g., for Gnu C++, Clang, Intel C++, plus Boost (for boost::make_shared)) have adopted this implementation, please contribute an answer. I don't have ready access to that many make_shared implementations, nor am I wild about digging into the bowels of the ones I have to see if they've implemented the WKWYL optimization, but I'm hoping that SO readers know the answers for some libraries off-hand. I know from looking at the code that as of Boost 1.52, the WKWYL optimization had not been implemented, but Boost is now up to version 1.55. Note that this optimization is different from std::make_shared's ability to avoid a dedicated heap allocation for the reference count used by std::shared_ptr. For a discussion of the difference between WKWYL and that optimication, consult this question.

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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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• why my C++ output executable is so big?

  - by Vincenzo

  I have a rather simple C++ project, which uses boost::regex library. The output I'm getting is 3.5Mb in size. As I understand I'm statically linking all boost .CPP files, including all functions/methods. Maybe it's possible somehow to instruct my linker to use only necessary elements from boost, not all of them? Thanks.

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• Memory fragmentation @ boost::asio ?

  - by Poni

  I'm pretty much stuck with a question I never got an answer for, a question which addresses an extremely important issue; memory fragmentation at boost::asio. Found nothing at the documentation nor here at SO. The functions at boost::asio, for example async_write() & async_read_some() always allocate something. (in my case it's 144 & 96 bytes respectively, in VC9 Debug build). How do I know about it? I connect a client to the "echo server" example provided with this library. I put a breakpoint at "new.cpp" at the code of "operator new(size_t size)". Then I send "123". Breakpoint is hit! Now using the stack trace I can clearly see that the root to the "new" call is coming from the async_write() & async_read_some() calls I make in the function handlers. So memory fragmentation will come sooner or later, thus I can't use ASIO, and I wish I could! Any idea? Any helpful code example?

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• Mobile Intel® GMA 4500MHD boost

  - by Andy Smith

  My machine has a Mobile Intel® GMA 4500MHD integrated graphics chipset. The machine is currently running 64 bit windows 7 premium with 3GB of ram (1x1gb and 1x2gb). I note that the Mobile Intel® GMA 4500MHD shares the physical memory to process the graphics. now, the total available graphics memory can be up to 1,340 MB with a 32-bit operating system and 3 GB system memory or 1,759 MB with a 64-bit operating system and 4 GB system memory. I am considering investing in a 4GB stick to replace the 1gb stick bringing the total up to 6gb, mainly for an increase in graphics processing ability. Can anyone let me know what sort of power (if any over the 4gb) I could expect by upgrading to 6GB?

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• Boost Audio Input on OS X?

  - by alanstorm

  I'm using my 13" Mac Book Pro's audio input functionality with an external microphone (recent vintage, bought around Thanksgiving). I've increased my input volume to the maximum in system preference, but the resulting recorded volume (using iShowU HD) is very low. Is there anyway to increase the input volume/sensitivity beyond Apple's default settings? I've found plenty on google about increasing the OUTPUT volume, but I want to increase the input volume.

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• Boost Up My Old Laptop Using a SSD

  - by Sina Bizbone

  I have an old laptop Lenovo SL400 (Core2Due T9550 2.66GHz / 4GB DDR2 Ram). Since I can't afford to buy a new laptop, I thought maybe I could throw an ADATA SP600 64GB SSD as primary drive and move my current HDD to DVD-ROM space by using HDDCADDY. I know that 64gb will come short after installing Visual Studio, SQL Server, etc. So is there anyway to just install the kernel part of windows on SSD and the rest on HDD. Doesn't windows have built-in support to do this? (ReadyBoost is out of picture since it's just simple caching)

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• syntax help required on templated static member function

  - by omatai

  I have a bunch of containers of object pointers that I want to iterate through in different contexts to produce diagnostics for them. I'm struggling with the syntax required to define the functions... which, on account of these objects filtering through diverse parts of my application, seem best encapsulated in a dedicated diagnostics class thus: // Code sketch only - detail fleshed out below... class ObjectListDiagnoser { public: static void GenerateDiagnostics( /* help required here! */ ); }; ... // Elsewhere in the system... ObjectListDiagnoser::GenerateDiagnostics( /* help required here! */ ); What I'd like to be able to do (in places across my application) is at least this: std::vector<MyObject *> objGroup1; std::list<MyObject *> objGroup2; ObjectListDiagnoser::GenerateDiagnostics( objGroup1.begin(), objGroup1.end() ); ObjectListDiagnoser::GenerateDiagnostics( objGroup2.begin(), objGroup2.end() ); ObjectListDiagnoser::GenerateDiagnostics( objGroup1.rbegin(), objGroup1.rend() ); I have tried to template my function in two ways, with no success: class ObjectListDiagnoser { public: // 1 - nope. template <class ObjIter> static void GenerateDiagnostics( ObjIter first, ObjIter last ); // 2. - nope. template <class Container, class ObjIter> static void GenerateDiagnostics( Container<MyObject *>::ObjIter first, Container<MyObject *>::ObjIter last ); }; Can someone provide the correct syntax for this? The container type will vary, and the direction of iteration will vary, but always for the same type of object.

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• Iterating backward

  - by MBennett

  Suppose I have a vector<int> myvec and I want to loop through all of the elements in reverse. I can think of a few ways of doing this: for (vector<int>::iterator it = myvec.end() - 1; it >= myvec.begin(); --it) { // do stuff here } for (vector<int>::reverse_iterator rit = myvec.rbegin(); rit != myvec.rend(); ++rit) { // do stuff here } for (int i = myvec.size() - 1; i >= 0; --i) { // do stuff here } So my question is when should I use each? Is there a difference? I know that the first one is dangerous because if I pass in an empty vector, then myvec.end() - 1 is undefined, but are there any other hazards or inefficiencies with this?

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• Is there a simple way to make lists behave as files (with ftplib)

  - by Brent.Longborough

  I'd like to use ftplib to upload program-generated data as lists. The nearest method I can see for doing this is ftp.storlines, but this requires a file object with a readlines() method. Obviously I could create a file, but this seems like overkill as the data isn't persistent. Is there anything that could do this?: session = ftp.new(...) upload = convertListToFileObject(mylist) session.storlines("STOR SOMETHING",upload) session.quit

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• std::list iterator: get next element

  - by sheepsimulator

  I'm trying to build a string using data elements stored in a std::list, where I want commas placed only between the elements (ie, if elements are {A,B,C,D} in list, result string should be "A,B,C,D". This code does not work: typedef std::list< shared_ptr<EventDataItem> > DataItemList; // ... std::string Compose(DataItemList& dilList) { std::stringstream ssDataSegment; for(iterItems = dilList.begin(); iterItems != dilList.end(); iterItems++) { // Lookahead in list to see if next element is end if((iterItems + 1) == dilList.end()) { ssDataSegment << (*iterItems)->ToString(); } else { ssDataSegment << (*iterItems)->ToString() << ","; } } return ssDataSegment.str(); } How do I get at "the-next-item" in a std::list using an iterator? I would expect that it's a linked-list, why can't I get at the next item?

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• Python Beginner: Selective Printing in loops

  - by Jonathan Straus

  Hi there. I'm a very new python user (had only a little prior experience with html/javascript as far as programming goes), and was trying to find some ways to output only intermittent numbers in my loop for a basic bicycle racing simulation (10,000 lines of biker positions would be pretty excessive :P). I tried in this loop several 'reasonable' ways to communicate a condition where a floating point number equals its integer floor (int, floor division) to print out every 100 iterations or so: for i in range (0,10000): i = i + 1 t = t + t_step #t is initialized at 0 while t_step is set at .01 acceleration_rider1 = (power_rider1 / (70 * velocity_rider1)) - (force_drag1 / 70) velocity_rider1 = velocity_rider1 + (acceleration_rider1 * t_step) position_rider1 = position_rider1 + (velocity_rider1 * t_step) force_drag1 = area_rider1 * (velocity_rider1 ** 2) acceleration_rider2 = (power_rider2 / (70 * velocity_rider1)) - (force_drag2 / 70) velocity_rider2 = velocity_rider2 + (acceleration_rider2 * t_step) position_rider2 = position_rider2 + (velocity_rider2 * t_step) force_drag2 = area_rider1 * (velocity_rider2 ** 2) if t == int(t): #TRIED t == t // 1 AND OTHER VARIANTS THAT DON'T WORK HERE:( print t, "biker 1", position_rider1, "m", "\t", "biker 2", position_rider2, "m"

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• std::list : get next element

  - by sheepsimulator

  I'm trying to build a string using data elements stored in a std::list, where I want commas placed only between the elements (ie, if elements are {A,B,C,D} in list, result string should be "A,B,C,D". This code does not work: typedef std::list< shared_ptr<EventDataItem> > DataItemList; // ... std::string Compose(DataItemList& dilList) { std::stringstream ssDataSegment; for(iterItems = dilList.begin(); iterItems = dilList.end(); iterItems++) { // Lookahead in list to see if next element is end if((iterItems + 1) == dilList.end()) { ssDataSegment << (*iterItems)->ToString(); } else { ssDataSegment << (*iterItems)->ToString() << ","; } } return ssDataSegment.str(); } How do I get at "the-next-item" in a std::list using an iterator? I would expect that it's a linked-list, why can't I get at the next item?

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• Display `pretty output` of directory content from array

  - by user275074

  Hi, I'm using the following code to get an array of directories and their sub-directories where each contain file type extension: png. It works great but I need to be able to output the results of the array in a list style format e.g. Test - test2.png - test1.png subfolder - test3.png sub sub folder - test4.png etc Code: $filter=".png"; $directory='../test'; $it=new RecursiveDirectoryIterator("$directory"); foreach(new RecursiveIteratorIterator($it) as $file){ if(!((strpos(strtolower($file),$filter))===false)||empty($filter)){ $items[]=preg_replace("#\\\#", "/", $file); } } Example array of results: array ( 0 => '../test/test2.png', 1 => '../test/subfolder/subsubfolder/test3.png', 2 => '../test/subfolder/test3.png', 3 => '../test/test1.png', ) What would be the best way of achieving the desired result?

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• List iterator not dereferencable?

  - by Roderick

  Hi All I get the error "list iterator not dereferencable" when using the following code: bool done = false; while (!_list_of_messages.empty() && !done) { // request the next message to create a frame // DEBUG ERROR WHEN NEXT LINE IS EXECUTED: Counted_message_reader reader = *(_list_of_messages.begin()); if (reader.has_more_data()) { _list_of_frames.push_back(new Dlp_data_frame(reader, _send_compressed_frames)); done = true; } else { _list_of_messages.pop_front(); } } (The line beginning with "Counted_message_reader..." is the one giving the problem) Note that the error doesn't always occur but seemingly at random times (usually when there's lots of buffered data). _list_of_messages is declared as follows: std::list<Counted_message_reader> _list_of_messages; In the surrounding code we could do pop_front, push_front and size, empty or end checks on _list_of_messages but no erase calls. I've studied the STL documentation and can't see any glaring problems. Is there something wrong with the above code or do I have a memory leak somewhere? Thanks! Appreciated!

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• Iterator blocks and inheritance.

  - by Dave Van den Eynde

  Given a base class with the following interface: public class Base { public virtual IEnumerable<string> GetListOfStuff() { yield return "First"; yield return "Second"; yield return "Third"; } } I want to make a derived class that overrides the method, and adds its own stuff, like so: public class Derived : Base { public override IEnumerable<string> GetListOfStuff() { foreach (string s in base.GetListOfStuff()) { yield return s; } yield return "Fourth"; yield return "Fifth"; } } However, I'm greeted with a warning that "access to a member through a base keyword from an iterator cannot be verified". What's the accepted solution to this problem then?

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• What does enabling STL iterator debugging really do?

  - by Roddy

  I've enabled iterator debugging in an application by defining _HAS_ITERATOR_DEBUGGING = 1 I was expecting this to really just check vector bounds, but I have a feeling it's doing a lot more than that. What checks, etc are actually being performed? Dinkumware STL, by the way.

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• Is there a neater way to get the first occurrence of something?

  - by Phil H

  I have a list which contains a number of things: lista = ['a', 'b', 'foo', 'c', 'd', 'e', 'bar'] I'd like to get the first item in the list that fulfils a predicate, say len(item) > 2. Is there a neater way to do it than itertools' dropwhile and next? first = next(itertools.dropwhile(lambda x: len(x) <= 2, lista)) I did use [item for item in lista if len(item)>2][0] at first, but that requires python to generate the entire list first.

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• Floating point comparison in STL, BOOST

  - by Paul

  Is there in the STL or in Boost a set of generic simple comparison functions? The one I found are always requiring template parameters, and/or instantiation of a struct template. I'm looking for something with a syntax like : if ( is_greater(x,y) ) { ... } Which could be implemented as : template <typename T> bool is_greater(const T& x, const T& y) { return x > y + Precision<T>::eps; }

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• compiling boost based application using cron

  - by user303544

  Hi All, I am building some boost based application for various embedded targets. I have developed a script which can build my application with different toolchain for several targets. This script works fine when I run it from command line but if it is invoked from cron it always fails to link the object files. My application has dependency on openssl. Can anyone please give some idea? What would be the root cause of this kind of behavior? Thanks in advance.

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