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• Feed char array into stdin

  - by Brian Lindsey

  I am writing a parser for a mini scripting language. Some of my grammar rules require jumping to a different location in the file to obtain information. There doesn't seem to be a straightforward way to accomplish this. So, I was thinking about loading my data files into a char array array and parsing line by line. This will allow me to jump all over the array with ease. My question is, is it possible to feed char arrays (i.e. char *) into stdin, so I can easily invoke the yyparse() function as needed.

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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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• Adapting Map Iterators Using STL/Boost/Lambdas

  - by John Dibling

  Consider the following non-working code: typedef map<int, unsigned> mymap; mymap m; for( int i = 1; i < 5; ++i ) m[i] = i; // 'remove' all elements from map where .second < 3 remove(m.begin(), m.end(), bind2nd(less<int>(), 3)); I'm trying to remove elements from this map where .second < 3. This obviously isn't written correctly. How do I write this correctly using: Standard STL function objects & techniques Boost.Bind C++0x Lambdas I know I'm not eraseing the elements. Don't worry about that; I'm just simplifying the problem to solve.

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• converting a timestring to a duration

  - by radman

  Hi, At the moment I am trying to read in a timestring formatted and create a duration from that. I am currently trying to use the boost date_time time_duration class to read and store the value. boost date_time provides a method time_duration duration_from_string(std::string) that allows a time_duration to be created from a time string and it accepts strings formatted appropriately ("[-]h[h][:mm][:ss][.fff]".). Now this method works fine if you use a correctly formatted time string. However if you submit something invalid like "ham_sandwich" or "100" then you will still be returned a time_duration that is not valid. Specifically if you try to pass it to a standard output stream then an assertion will occur. My question is: Does anyone know how to test the validity of the boost time_duration? and failing that can you suggest another method of reading a timestring and getting a duration from it? Note: I have tried the obvious testing methods that time_duration provides; is_not_a_date_time(), is_special() etc and they don't pick up that there is an issue. Using boost 1.38.0

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• How to write a custom predicate for multi_index_containder with composite_key?

  - by Titan

  I googled and searched in the boost's man, but didn't find any examples. May be it's a stupid question...anyway. So we have the famous phonebook from the man: typedef multi_index_container< phonebook_entry, indexed_by< ordered_non_unique< composite_key< phonebook_entry, member<phonebook_entry,std::string,&phonebook_entry::family_name>, member<phonebook_entry,std::string,&phonebook_entry::given_name> >, composite_key_compare< std::less<std::string>, // family names sorted as by default std::greater<std::string> // given names reversed > >, ordered_unique< member<phonebook_entry,std::string,&phonebook_entry::phone_number> > > > phonebook; phonebook pb; ... // look for all Whites std::pair<phonebook::iterator,phonebook::iterator> p= pb.equal_range(boost::make_tuple("White"), my_custom_comp()); How should my_custom_comp() look like? I mean it's clear for me then it takes boost::multi_index::composite_key_result<CompositeKey> as an argumen (due to compilation errors :) ), but what is CompositeKey in that particular case? struct my_custom_comp { bool operator()( ?? boost::multi_index::composite_key_result<CompositeKey> ?? ) const { return blah_blah_blah; } }; Thanks in advance.

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• Convert enumeration to string

  - by emptyheaded

  I am trying to build a function that converts an item from an enum to its corresponding string. The enums I use are fairly long, so I didn't want to use a switch-case. I found a method using boost::unordered_map very convenient, but I don't know how to make a default return (when there is no item matching the enum). const boost::unordered_map<enum_type, const std::string> enumToString = boost::assign::map_list_of (data_1, "data_1") (data_2, "data_2"); I tried to create an additional function: std::string convert(enum_type entry) { if (enumToString.find(entry)) // not sure what test to place here, return enumToString.at(entry); //because the find method returns an iter else return "invalid_value"; } I even tried something exceedingly wrong: std::string convert(enum_type entry) { try{ return enumToString.at(entry); } catch(...){ return "invalid_value"; } } Result: evil "Debug" runtime error. Can somebody give me a suggestion on how to either 1) find an easier method to convert enum to a string with the same name as the enum item 2) find a way to use already built boost methods to get a default value from a hash map (best option) 3) find what to place in the test to use a function that returns either the pair of the key-value, or a different string if the key is not found in the map. Thank you very much.

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• is there a simple timed lock algorithm avoiding deadlock on multiple mutexes?

  - by Vicente Botet Escriba

  C++0x thread library or Boost.thread define a non-member variadic template function that locks all mutex at once that helps to avoid deadlock. template <class L1, class L2, class... L3> void lock(L1&, L2&, L3&...); The same can be applied to a non-member variadic template function try_lock_until, which locks all the mutex until a given time is reached that helps to avoid deadlock like lock(...). template <class Clock, class Duration, class L1, class L2, class... L3> void try_lock_until( const chrono::time_point<Clock,Duration>& abs_time, L1&, L2&, L3&...); I have an implementation that follows the same design as the Boost function boost::lock(...). But this is quite complex. As I can be missing something evident I wanted to know if: is there a simple timed lock algorithm avoiding deadlock on multiple mutexes? If no simple implementation exists, can this justify a proposal to Boost? P.S. Please avoid posting complex solutions.

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• Work with function references

  - by Ockonal

  Hello, I have another one question about functions reference. For example, I have such definition: typedef boost::function<bool (Entity &handle)> behaviorRef; std::map< std::string, ptr_vector<behaviorRef> > eventAssociation; The first question is: how to insert values into such map object? I tried: eventAssociation.insert(std::pair< std::string, ptr_vector<behaviorRef> >(eventType, ptr_vector<behaviorRef>(callback))); But the error: no matching function for call to ‘boost::ptr_vector<boost::function<bool(Entity&)> >::push_back(Entity::behaviorRef&)’ And I undersatnd it, but can't make workable code. The second question is how to call such functions? For example, I have one object of behaviorRef, how to call it with boost::bind with passing my own values?

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• Boost::Mutex & Malloc

  - by M. Tibbits

  Hi all, I'm trying to use a faster memory allocator in C++. I can't use Hoard due to licensing / cost. I was using NEDMalloc in a single threaded setting and got excellent performance, but I'm wondering if I should switch to something else -- as I understand things, NEDMalloc is just a replacement for C-based malloc() & free(), not the C++-based new & delete operators (which I use extensively). The problem is that I now need to be thread-safe, so I'm trying to malloc an object which is reference counted (to prevent excess copying), but which also contains a mutex pointer. That way, if you're about to delete the last copy, you first need to lock the pointer, then free the object, and lastly unlock & free the mutex. However, using malloc to create a boost::mutex appears impossible because I can't initialize the private object as calling the constructor directly ist verboten. So I'm left with this odd situation, where I'm using new to allocate the lock and nedmalloc to allocate everything else. But when I allocate a large amount of memory, I run into allocation errors (which disappear when I switch to malloc instead of nedmalloc ~ but the performance is terrible). My guess is that this is due to fragmentation in the memory and an inability of nedmalloc and new to place nice side by side. There has to be a better solution. What would you suggest?

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• Why aren't these shared_ptrs pointing to the same container?

  - by BeeBand

  I have a class Model: class Model { ... boost::shared_ptr<Deck> _deck; boost::shared_ptr<CardStack> _stack[22]; }; Deck inherits from CardStack. I tried to make _stack[0] point to the same thing that _deck points to by going: { _deck = boost::shared_ptr<Deck>(new Deck()); _stack[0] = _deck; } It seems that the assignment to _deck of _stack[0] results in a copy of _deck being made. How can I get them to point to the same thing?

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• shared_ptr requires complete type; cannot use it with lua_State*

  - by topright

  Hello! I'm writing a C++/OOP wrapper for Lua. My code is: class LuaState { boost::shared_ptr<lua_State> L; LuaState(): L( luaL_newstate(), LuaState::CustomDeleter ) { } } The problem is lua_State is incomplete type and shared_ptr constructor requires complete type. And I need safe pointer sharing. (Funny thing boost docs say most functions do not require complete type, but constructor requires, so there is no way of using it. http://www.boost.org/doc/libs/1_42_0/libs/smart_ptr/smart_ptr.htm) Can can I solve this? Thank you.

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• Is there an easy way to make `boost::ptr_vector` more debugger friendly in Visual Studio?

  - by Billy ONeal

  I'm considering using boost::ptr_container as a result of the responses from this question. My biggest problem with the library is that I cannot view the contents of the collection in the debugger, because the MSVC debugger doesn't recognize it, and therefore I cannot see the contents of the containers. (All the data gets stored as void * internally) I've heard MSVC has a feature called "debugger visualizers" which would allow the user to make the debugger smarter about these kinds of things, but I've never written anything like this, and I'm not hugely firmiliar with such things. For example, compare the behavior of boost::shared_ptr with MSVC's own std::tr1::shared_ptr. In the debugger (i.e. in the Watch window), the boost version shows up as a big mess of internal variables used for implementing the shared pointer, but the MSVC version shows up as a plain pointer to the object (and the shared_ptr's innards are hidden). How can I get started either using or implementing such a thing?

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• Preparing for the next C++ standard

  - by Neil Butterworth

  The spate of questions regarding BOOST_FOREACH prompts me to ask users of the Boost library what (if anything) they are doing to prepare their code for portability to the proposed new C++ standard (aka C++0x). For example, do you write code like this if you use shared_ptr: #ifdef CPPOX #include <memory> #else #include "boost/shared_ptr.hpp" #endif There is also the namespace issue - in the future, shared_ptr will be part of the std, namespace - how do you deal with that? I'm interested in these questions because I've decided to bite the bullet and start learning boost seriously, and I'd like to use best practices in my code. Not exactly a flood of answers - does this mean it's a non-issue? Anyway, thanks to those that replied; I'm accepting jalfs answer because I like being advised to do nothing!

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• Released object crashes app

  - by John Smith

  I am using objective-C++ (+Boost) for iPhone development. I am in a rather tight loop and need to allocate and release a certain object. The code is something like this. for (int i=0;i<100;i++) { opt = [[FObj alloc] init]; //do stuff with opt [opt release]; } The FObj object is something like @interface FObj MyCPPObj * cppobj; @end In the implementation of FObj there is a dealloc method: -(void) dealloc { delete cppobj; //previously allocated with 'new' [super dealloc]; } I am afraid that if i don't release then the 'MyCPPObj's will just pile up. But releasing makes the app crash after the first loop. What am I doing wrong? Or perhaps should I make cppobj and boost::shared_ptr? (do boost shared pointers automatically release their objects when an objective-C++ object is deleted?)

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• Get result type of function

  - by Robert

  I want to specialize a template function declared as: template<typename Type> Type read(std::istream& is); I then have a lot of static implementations static int read_integer(std::istream& is); a.s.o. Now I'd like to do a macro so that specialization of read is as simple as: SPECIALIZE_READ(read_integer) So I figured I'd go the boost::function_traits way and declare SPECIALIZE_READ as: #define SPECIALIZE_READ(read_function) \ template<> boost::function_traits<read_function>::result_type read(std::istream& is) { \ return read_function(is); \ } but VC++ (2008) compiler complains with: 'boost::function_traits' : 'read_integer' is not a valid template type argument for parameter 'Function' Ideas ?

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• Learning low latency C++ and Java?

  - by user997112

  I'm currently in a role where I dont get to write any C++ or Java. However, the role is good because provides me with exposure to the business side (i'm interested in finance). Eventually I would like to get into high frequency trading infrastructure. Therefore, outside of work hours i'd like to maximise the knowledge I can gain about high performance Java and C++. I already have the Java Performance Tuning book, which is ok but not impressive. Can people recommend anymore latency blogs/books/websites for learning about making C++/C/Java or even Unix very fast? Or perhaps making the network parts of the OS (if re-writing Unix components) faster? EDIT: Or perhaps we could make this THE thread for advice on writing fast code

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• Unix as opposed to Windows (Java and C++)

  - by user997112

  Firstly I should explain the background. I am interested in high frequency trading programming roles. After looking at many job specs it is very clear that there is a big demand for programmers who have programmed Java and C++ on Unix as opposed to Windows. My question is what are the differences a High Freq programmer would come across? It cannot be something in the language itself because syntactically they do not differ over OS? Therefore I thought it must be something which the programming language has to interface, resources etc? Could anyone please help me out as I am trying to improve my C++/Java on Unix, in order to aim for this type of career? ps I'm guessing part of this answer lies with the socket infrastructure on Unix?

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• Help with infrequent segmentation fault in accessing boost::unordered_multimap or struct

  - by Sarah

  I'm having trouble debugging a segmentation fault. I'd appreciate tips on how to go about narrowing in on the problem. The error appears when an iterator tries to access an element of a struct Infection, defined as: struct Infection { public: explicit Infection( double it, double rt ) : infT( it ), recT( rt ) {} double infT; // infection start time double recT; // scheduled recovery time }; These structs are kept in a special structure, InfectionMap: typedef boost::unordered_multimap< int, Infection > InfectionMap; Every member of class Host has an InfectionMap carriage. Recovery times and associated host identifiers are kept in a priority queue. When a scheduled recovery event arises in the simulation for a particular strain s in a particular host, the program searches through carriage of that host to find the Infection whose recT matches the recovery time (double recoverTime). (For reasons that aren't worth going into, it's not as expedient for me to use recT as the key to InfectionMap; the strain s is more useful, and coinfections with the same strain are possible.) assert( carriage.size() > 0 ); pair<InfectionMap::iterator,InfectionMap::iterator> ret = carriage.equal_range( s ); InfectionMap::iterator it; for ( it = ret.first; it != ret.second; it++ ) { if ( ((*it).second).recT == recoverTime ) { // produces seg fault carriage.erase( it ); } } I get a "Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: KERN_INVALID_ADDRESS at address..." on the line specified above. The recoverTime is fine, and the assert(...) in the code is not tripped. As I said, this seg fault appears 'randomly' after thousands of successful recovery events. How would you go about figuring out what's going on? I'd love ideas about what could be wrong and how I can further investigate the problem. Update I added a new assert and a check just inside the for loop: assert( carriage.size() > 0 ); assert( carriage.count( s ) > 0 ); pair<InfectionMap::iterator,InfectionMap::iterator> ret = carriage.equal_range( s ); InfectionMap::iterator it; cout << "carriage.count(" << s << ")=" << carriage.count(s) << endl; for ( it = ret.first; it != ret.second; it++ ) { cout << "(*it).first=" << (*it).first << endl; // error here if ( ((*it).second).recT == recoverTime ) { carriage.erase( it ); } } The EXC_BAD_ACCESS error now appears at the (*it).first call, again after many thousands of successful recoveries. Can anyone give me tips on how to figure out how this problem arises? I'm trying to use gdb. Frame 0 from the backtrace reads "#0 0x0000000100001d50 in Host::recover (this=0x100530d80, s=0, recoverTime=635.91148029170529) at Host.cpp:317" I'm not sure what useful information I can extract here. Update 2 I added a break; after the carriage.erase(it). This works, but I have no idea why (e.g., why it would remove the seg fault at (*it).first.

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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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• Dataflow Programming - Patterns and Frameworks

  - by Styrac

  I just came across the proposed Boost::Dataflow library. It seems like an interesting approach and I was wondering if there are other such alternative frameworks for C++, and if there are any related design patterns. I have not ruled out Boost::Dataflow, I am just looking into any available alternatives so I can understand the domain and my options better (or roll my own if necessary).

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• How does a portable Thread Specific Storage Mechanism's Naming Scheme Generate Thread Relative Uniqu

  - by Hassan Syed

  A portable thread specific storage reference/identity mechanism, of which boost/thread/tss.hpp is an instance, needs a way to generate a unique keys for itself. This key is unique in the scope of a thread, and is subsequently used to retrieve the object it references. This mechanism is used in code written in a thread neutral manner. Since boost is a portable example of this concept, how specifically does such a mechanism work ?

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• What's your convention for typedef'ing shared_ptr?

  - by Emile Cormier

  I'm flip-flopping between naming conventions for typedef'ing the boost::shared_ptr template. For example: typedef boost::shared_ptr<Foo> FooPtr; Before settling on a convention, I'd like to see what others use. What is your convention?

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• Apples new section 3.3.1

  - by ML

  With Apple making changes to section 3.3.1 on the iPhone dev agreement can one stillness libraries like boost in their apps? I want to use Boost in my iPad app...

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• python object to native c++ pointer

  - by Lodle

  Im toying around with the idea to use python as an embedded scripting language for a project im working on and have got most things working. However i cant seem to be able to convert a python extended object back into a native c++ pointer. So this is my class: class CGEGameModeBase { public: virtual void FunctionCall()=0; virtual const char* StringReturn()=0; }; class CGEPYGameMode : public CGEGameModeBase, public boost::python::wrapper<CGEPYGameMode> { public: virtual void FunctionCall() { if (override f = this->get_override("FunctionCall")) f(); } virtual const char* StringReturn() { if (override f = this->get_override("StringReturn")) return f(); return "FAILED TO CALL"; } }; Boost wrapping: BOOST_PYTHON_MODULE(GEGameMode) { class_<CGEGameModeBase, boost::noncopyable>("CGEGameModeBase", no_init); class_<CGEPYGameMode, bases<CGEGameModeBase> >("CGEPYGameMode", no_init) .def("FunctionCall", &CGEPYGameMode::FunctionCall) .def("StringReturn", &CGEPYGameMode::StringReturn); } and the python code: import GEGameMode def Ident(): return "Alpha" def NewGamePlay(): return "NewAlpha" def NewAlpha(): import GEGameMode import GEUtil class Alpha(GEGameMode.CGEPYGameMode): def __init__(self): print "Made new Alpha!" def FunctionCall(self): GEUtil.Msg("This is function test Alpha!") def StringReturn(self): return "This is return test Alpha!" return Alpha() Now i can call the first to functions fine by doing this: const char* ident = extract< const char* >( GetLocalDict()["Ident"]() ); const char* newgameplay = extract< const char* >( GetLocalDict()["NewGamePlay"]() ); printf("Loading Script: %s\n", ident); CGEPYGameMode* m_pGameMode = extract< CGEPYGameMode* >( GetLocalDict()[newgameplay]() ); However when i try and convert the Alpha class back to its base class (last line above) i get an boost error: TypeError: No registered converter was able to extract a C++ pointer to type class CGEPYGameMode from this Python object of type Alpha I have done alot of searching on the net but cant work out how to convert the Alpha object into its base class pointer. I could leave it as an object but rather have it as a pointer so some non python aware code can use it. Any ideas?

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