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• A cross between std::multimap and std::vector?

  - by Milan Babuškov

  I'm looking for a STL container that works like std::multimap, but has constant access time to random n-th element. I need this because I have such structure in memory that is std::multimap for many reasons, but items stored in it have to be presented to the user in a listbox. Since amount of data is huge, I'm using list box with virtual items (i.e. list control polls for value at line X). As a workaround I'm currently using additional std::vector to store "indexes" into std::map, and I fill it like this: std::vector<MMap::data_type&> vec; for (MMap::iterator it = mmap.begin(); it != mmap.end(); ++it) vec.push_back((*it).second); But this is not very elegant solution. Is there some such containter?

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• inserting std::strings in to a std::map

  - by PaulH

  I have a program that reads data from a file line-by-line. I would like to copy some substring of that line in to a map as below: std::map< DWORD, std::string > my_map; DWORD index; // populated with some data char buffer[ 1024 ]; // populated with some data char* element_begin; // points to some location in buffer char* element_end; // points to some location in buffer > element_begin my_map.insert( std::make_pair( index, std::string( element_begin, element_end ) ) ); This std::map<>::insert() operation takes a long time (It doubles the file parsing time). Is there a way to make this a less expensive operation? Thanks, PaulH

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• std::basic_stringstream<unsigned char> won't compile with MSVC 10

  - by Michael J

  I'm trying to get UTF-8 chars to co-exist with ANSI 8-bit chars. My strategy has been to represent utf-8 chars as unsigned char so that appropriate overloads of functions can be used for the two character types. e.g. namespace MyStuff { typedef uchar utf8_t; typedef std::basic_string<utf8_t> U8string; } void SomeFunc(std::string &s); void SomeFunc(std::wstring &s); void SomeFunc(MyStuff::U8string &s); This all works pretty well until I try to use a stringstream. std::basic_ostringstream<MyStuff::utf8_t> ostr; ostr << 1; MSVC Visual C++ Express V10 won't compile this: c:\program files\microsoft visual studio 10.0\vc\include\xlocmon(213): warning C4273: 'id' : inconsistent dll linkage c:\program files\microsoft visual studio 10.0\vc\include\xlocnum(65) : see previous definition of 'public: static std::locale::id std::numpunct<unsigned char>::id' c:\program files\microsoft visual studio 10.0\vc\include\xlocnum(65) : while compiling class template static data member 'std::locale::id std::numpunct<_Elem>::id' with [ _Elem=Tk::utf8_t ] c:\program files\microsoft visual studio 10.0\vc\include\xlocnum(1149) : see reference to function template instantiation 'const _Facet &std::use_facet<std::numpunct<_Elem>>(const std::locale &)' being compiled with [ _Facet=std::numpunct<Tk::utf8_t>, _Elem=Tk::utf8_t ] c:\program files\microsoft visual studio 10.0\vc\include\xlocnum(1143) : while compiling class template member function 'std::ostreambuf_iterator<_Elem,_Traits> std::num_put<_Elem,_OutIt>:: do_put(_OutIt,std::ios_base &,_Elem,std::_Bool) const' with [ _Elem=Tk::utf8_t, _Traits=std::char_traits<Tk::utf8_t>, _OutIt=std::ostreambuf_iterator<Tk::utf8_t,std::char_traits<Tk::utf8_t>> ] c:\program files\microsoft visual studio 10.0\vc\include\ostream(295) : see reference to class template instantiation 'std::num_put<_Elem,_OutIt>' being compiled with [ _Elem=Tk::utf8_t, _OutIt=std::ostreambuf_iterator<Tk::utf8_t,std::char_traits<Tk::utf8_t>> ] c:\program files\microsoft visual studio 10.0\vc\include\ostream(281) : while compiling class template member function 'std::basic_ostream<_Elem,_Traits> & std::basic_ostream<_Elem,_Traits>::operator <<(int)' with [ _Elem=Tk::utf8_t, _Traits=std::char_traits<Tk::utf8_t> ] c:\program files\microsoft visual studio 10.0\vc\include\sstream(526) : see reference to class template instantiation 'std::basic_ostream<_Elem,_Traits>' being compiled with [ _Elem=Tk::utf8_t, _Traits=std::char_traits<Tk::utf8_t> ] c:\users\michael\dvl\tmp\console\console.cpp(23) : see reference to class template instantiation 'std::basic_ostringstream<_Elem,_Traits,_Alloc>' being compiled with [ _Elem=Tk::utf8_t, _Traits=std::char_traits<Tk::utf8_t>, _Alloc=std::allocator<uchar> ] . c:\program files\microsoft visual studio 10.0\vc\include\xlocmon(213): error C2491: 'std::numpunct<_Elem>::id' : definition of dllimport static data member not allowed with [ _Elem=Tk::utf8_t ] Any ideas? ** Edited 19 June 2012 ** OK, I've gotten closer to understanding this, but not how to solve it. As we all know, static class variables get defined twice: once in the class definition and once outside the class definition which establishes storage space. e.g. // in .h file class CFoo { // ... static int x; }; // in .cpp file int CFoo::x = 42; Now in the VC10 headers we get something like this: template<class _Elem> class numpunct : public locale::facet { // ... _CRTIMP2_PURE static locale::id id; // ... } When the header is included in an application, _CRTIMP2_PURE is defined as __declspec(dllimport), which means that the variable is imported from a dll. Now the header also contains the following template<class _Elem> locale::id numpunct<_Elem>::id; Note the absence of the __declspec(dllimport) qualifier. i.e. The class declaration says that the static linkage of the id variable is in the dll, but for the general case, it gets declared outside the dll. For the known cases, there are specialisations. template locale::id numpunct<char>::id; template locale::id numpunct<wchar_t>::id; These are protected by #ifs so that they are only included when building the DLL. They are excluded otherwise. i.e. the char and wchar_t versions of numpunct ARE inside the dll So we have the class definition saying that id's storage is in the DLL, but that is only true for the char and wchar_t specialisations, meaning that my unsigned char version is doomed. :-( The only way forward that I can think of is to create my own specialisation: basically copying it from the header file and fixing it. This raises many issues. Anybody have a better idea?

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• C++: Trouble with templates (C2064)

  - by Rosarch

  I'm having compiler errors, and I'm not sure why. What am I doing wrong here: Hangman.cpp: set<char> Hangman::incorrectGuesses() { // Hangman line 103 return Utils::findAll_if<char>(guesses.begin(), guesses.end(), &Hangman::isIncorrectGuess); } bool Hangman::isIncorrectGuess(char c) { return correctAnswer.find(c) == string::npos; } Utils.h: namespace Utils { void PrintLine(const string& line, int tabLevel = 0); string getTabs(int tabLevel); template<class result_t, class Predicate> std::set<result_t> findAll_if(typename std::set<result_t>::iterator begin, typename std::set<result_t>::iterator end, Predicate pred) { std::set<result_t> result; // utils line 16 return detail::findAll_if_rec<result_t>(begin, end, pred, result); } } namespace detail { template<class result_t, class Predicate> std::set<result_t> findAll_if_rec(typename std::set<result_t>::iterator begin, typename std::set<result_t>::iterator end, Predicate pred, std::set<result_t> result) { // utils line 25 typename std::set<result_t>::iterator nextResultElem = find_if(begin, end, pred); if (nextResultElem == end) { return result; } result.insert(*nextResultElem); return findAll_if_rec(++nextResultElem, end, pred, result); } } This produces the following compiler errors: algorithm(83): error C2064: term does not evaluate to a function taking 1 arguments algorithm(95) : see reference to function template instantiation '_InIt std::_Find_if<std::_Tree_unchecked_const_iterator<_Mytree>,_Pr>(_InIt,_InIt,_Pr)' being compiled 1> with 1> [ 1> _InIt=std::_Tree_unchecked_const_iterator<std::_Tree_val<std::_Tset_traits<char,std::less<char>,std::allocator<char>,false>>>, 1> _Mytree=std::_Tree_val<std::_Tset_traits<char,std::less<char>,std::allocator<char>,false>>, 1> _Pr=bool (__thiscall Hangman::* )(char) 1> ] utils.h(25) : see reference to function template instantiation '_InIt std::find_if<std::_Tree_const_iterator<_Mytree>,Predicate>(_InIt,_InIt,_Pr)' being compiled 1> with 1> [ 1> _InIt=std::_Tree_const_iterator<std::_Tree_val<std::_Tset_traits<char,std::less<char>,std::allocator<char>,false>>>, 1> _Mytree=std::_Tree_val<std::_Tset_traits<char,std::less<char>,std::allocator<char>,false>>, 1> Predicate=bool (__thiscall Hangman::* )(char), 1> _Pr=bool (__thiscall Hangman::* )(char) 1> ] utils.h(16) : see reference to function template instantiation 'std::set<_Kty> detail::findAll_if_rec<result_t,Predicate>(std::_Tree_const_iterator<_Mytree>,std::_Tree_const_iterator<_Mytree>,Predicate,std::set<_Kty>)' being compiled 1> with 1> [ 1> _Kty=char, 1> result_t=char, 1> Predicate=bool (__thiscall Hangman::* )(char), 1> _Mytree=std::_Tree_val<std::_Tset_traits<char,std::less<char>,std::allocator<char>,false>> 1> ] hangman.cpp(103) : see reference to function template instantiation 'std::set<_Kty> Utils::findAll_if<char,bool(__thiscall Hangman::* )(char)>(std::_Tree_const_iterator<_Mytree>,std::_Tree_const_iterator<_Mytree>,Predicate)' being compiled 1> with 1> [ 1> _Kty=char, 1> _Mytree=std::_Tree_val<std::_Tset_traits<char,std::less<char>,std::allocator<char>,false>>, 1> Predicate=bool (__thiscall Hangman::* )(char) 1> ]

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• using BOOST_FOREACH with std::map

  - by kmote

  I'd like to iterate over a std::map using BOOST_FOREACH and edit the values. I can't quite get it. typedef std::pair<int, int> IdSizePair_t; std::map<int,int> mmap; mmap[1] = 1; mmap[2] = 2; mmap[3] = 3; BOOST_FOREACH( IdSizePair_t i, mmap ) i.second++; // mmap should contain {2,3,4} here Of course this doesn't change anything because I'm not iterating by reference. So I substitute this line instead (as per the example in the Boost docs): BOOST_FOREACH( IdSizePair_t &i, mmap ) and I get the compiler error: error C2440: 'initializing' : cannot convert from 'std::pair<_Ty1,_Ty2>' to 'IdSizePair_t &' with [ _Ty1=const int, _Ty2=int ] Any suggestions?

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• Ways std::stringstream can set fail/bad bit?

  - by Evan Teran

  A common piece of code I use for simple string splitting looks like this: inline std::vector<std::string> split(const std::string &s, char delim) { std::vector<std::string> elems; std::stringstream ss(s); std::string item; while(std::getline(ss, item, delim)) { elems.push_back(item); } return elems; } Someone mentioned that this will silently "swallow" errors occurring in std::getline. And of course I agree that's the case. But it occurred to me, what could possibly go wrong here in practice that I would need to worry about. basically it all boils down to this: inline std::vector<std::string> split(const std::string &s, char delim) { std::vector<std::string> elems; std::stringstream ss(s); std::string item; while(std::getline(ss, item, delim)) { elems.push_back(item); } if(ss.fail()) { // *** How did we get here!? *** } return elems; } A stringstream is backed by a string, so we don't have to worry about any of the issues associated with reading from a file. There is no type conversion going on here since getline simply reads until it sees a newline or EOF. So we can't get any of the errors that something like boost::lexical_cast has to worry about. I simply can't think of something besides failing to allocate enough memory that could go wrong, but that'll just throw a std::bad_alloc well before the std::getline even takes place. What am I missing?

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• std::list or std::multimap

  - by Tamir

  Hey, I right now have a list of a struct that I made, I sort this list everytime I add a new object, using the std::list sort method. I want to know what would be faster, using a std::multimap for this or std::list, since I'm iterating the whole list every frame (I am making a game). I would like to hear your opinion, for what should I use for this incident.

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• c++ std::ostringstream vs std::string::append

  - by NickSoft

  In all examples that use some kind of buffering I see they use stream instead of string. How is std::ostringstream and << operator different than using string.append. Which one is faster and which one uses less resourses (memory). One difference I know is that you can output different types into output stream (like integer) rather than the limited types that string::append accepts. Here is an example: std::ostringstream os; os << "Content-Type: " << contentType << ";charset=" << charset << "\r\n"; std::string header = os.str(); vs std::string header("Content-Type: "); header.append(contentType); header.append(";charset="); header.append(charset); header.append("\r\n"); Obviously using stream is shorter, but I think append returns reference to the string so it can be written like this: std::string header("Content-Type: "); header.append(contentType) .append(";charset=") .append(charset) .append("\r\n"); And with output stream you can do: std::string content; ... os << "Content-Length: " << content.length() << "\r\n"; But what about memory usage and speed? Especially when used in a big loop. Update: To be more clear the question is: Which one should I use and why? Is there situations when one is preferred or the other? For performance and memory ... well I think benchmark is the only way since every implementation could be different. Update 2: Well I don't get clear idea what should I use from the answers which means that any of them will do the job, plus vector. Cubbi did nice benchmark with the addition of Dietmar Kühl that the biggest difference is construction of those objects. If you are looking for an answer you should check that too. I'll wait a bit more for other answers (look previous update) and if I don't get one I think I'll accept Tolga's answer because his suggestion to use vector is already done before which means vector should be less resource hungry.

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• Trouble assigning a tr1::shared_ptr

  - by Max

  I've got a class that has a tr1::shared_ptr as a member, like so: class Foo { std::tr1::shared_ptr<TCODBsp> bsp; void Bar(); } In member function Bar, I try to assign it like this: bsp = newTCODBsp(x,y,w,h); g++ then gives me this error no match for ‘operator=’ in ‘((yarl::mapGen::MapGenerator*)this)->yarl::mapGen::MapGenerator::bsp = (operator new(40u), (<statement>, ((TCODBsp*)<anonymous>)))’ /usr/include/c++/4.4/tr1/shared_ptr.h:834: note: candidates are: std::tr1::shared_ptr<TCODBsp>& std::tr1::shared_ptr<TCODBsp>::operator=(const std::tr1::shared_ptr<TCODBsp>&) in my code, Foo is actually yarl::mapGen::MapGenerator. What am I doing wrong?

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• Are tr1 headers available for gcc v3.4.6?

  - by WilliamKF

  Are tr1 headers available for g++ v3.4.6? If so, how can I locate them at compile time. The following is failing to compile: #include <tr1/memory> With the following error: myModule.h:20:24: tr1/memory: No such file or directory Do I need to move to a later compiler or do I have the headers somewhere?

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• berkeley DB: can't compile c++ codes

  - by Brian

  When I compiled the sample codes of C++, I got following info: c++ excxx_example_database_read.cpp -o dbApp -I /usr/local/BerkeleyDB.5.0/include/ Undefined symbols: "Dbt::Dbt(void*, unsigned int)", referenced from: show_vendor(MyDb&, char const*)in ccnaWItX.o show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o "Dbc::get(Dbt*, Dbt*, unsigned int)", referenced from: show_all_records(MyDb&, MyDb&) in ccnaWItX.o show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o "Dbc::close()", referenced from: show_all_records(MyDb&, MyDb&) in ccnaWItX.o show_all_records(MyDb&, MyDb&) in ccnaWItX.o show_all_records(MyDb&, MyDb&) in ccnaWItX.o show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o "Dbt::~Dbt()", referenced from: show_vendor(MyDb&, char const*)in ccnaWItX.o show_vendor(MyDb&, char const*)in ccnaWItX.o show_vendor(MyDb&, char const*)in ccnaWItX.o show_vendor(MyDb&, char const*)in ccnaWItX.o show_all_records(MyDb&, MyDb&) in ccnaWItX.o show_all_records(MyDb&, MyDb&) in ccnaWItX.o show_all_records(MyDb&, MyDb&) in ccnaWItX.o show_all_records(MyDb&, MyDb&) in ccnaWItX.o show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o "Db::~Db()", referenced from: MyDb::~MyDb() in ccnaWItX.o MyDb::~MyDb() in ccnaWItX.o "typeinfo for DbException", referenced from: GCC_except_table3 in ccnaWItX.o GCC_except_table4 in ccnaWItX.o GCC_except_table5 in ccnaWItX.o GCC_except_table6 in ccnaWItX.o __ZTI11DbException$non_lazy_ptr in ccnaWItX.o "DbException::~DbException()", referenced from: __ZN11DbExceptionD1Ev$non_lazy_ptr in ccnaWItX.o "MyDb::close()", referenced from: MyDb::~MyDb() in ccnaWItX.o "MyDb::MyDb(std::basic_string<char, std::char_traits<char>, std::allocator<char> >&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&, bool)", referenced from: _main in ccnaWItX.o _main in ccnaWItX.o _main in ccnaWItX.o "Dbt::Dbt()", referenced from: show_vendor(MyDb&, char const*)in ccnaWItX.o show_all_records(MyDb&, MyDb&) in ccnaWItX.o show_all_records(MyDb&, MyDb&) in ccnaWItX.o show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o "DbException::get_errno() const", referenced from: show_vendor(MyDb&, char const*)in ccnaWItX.o show_all_records(MyDb&, MyDb&) in ccnaWItX.o show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o _main in ccnaWItX.o "DbException::DbException(DbException const&)", referenced from: show_vendor(MyDb&, char const*)in ccnaWItX.o show_all_records(MyDb&, MyDb&) in ccnaWItX.o show_item(MyDb&, MyDb&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)in ccnaWItX.o ld: symbol(s) not found collect2: ld returned 1 exit status I have no idea what is the problem. Please help!

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• Design of std::ifstream class

  - by Nawaz

  Those of us who have seen the beauty of STL try to use it as much as possible, and also encourage others to use it wherever we see them using raw pointers and arrays. Scott Meyers have written a whole book on STL, with title Effective STL. Yet what happened to the developers of ifstream that they preferred char* over std::string. I wonder why the first parameter of ifstream::open() is of type const char*, instead of const std::string &. Please have a look at it's signature: void open(const char * filename, ios_base::openmode mode = ios_base::in ); Why this? Why not this: void open(const string & filename, ios_base::openmode mode = ios_base::in ); Is this a serious mistake with the design? Or this design is deliberate? What could be the reason? I don't see any reason why they have preferred char* over std::string. Note we could still pass char* to the latter function that takes std::string. That's not a problem! By the way, I'm aware that ifstream is a typedef, so no comment on my title.:P. It looks short that is why I used it. The actual class template is : template<class _Elem,class _Traits> class basic_ifstream;

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• std::bind overload resolution

  - by bpw1621

  The following code works fine #include <functional> using namespace std; using namespace std::placeholders; class A { int operator()( int i, int j ) { return i - j; } }; A a; auto aBind = bind( &A::operator(), ref(a), _2, _1 ); This does not #include <functional> using namespace std; using namespace std::placeholders; class A { int operator()( int i, int j ) { return i - j; } int operator()( int i ) { return -i; } }; A a; auto aBind = bind( &A::operator(), ref(a), _2, _1 ); I have tried playing around with the syntax to try and explicitly resolve which function I want in the code that does not work without luck so far. How do I write the bind line in order to choose the call that takes the two integer arguments?

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• Concatenate boost::dynamic_bitset or std::bitset

  - by MOnsDaR

  Hey, what is the best way to concatenate 2 bitsets? For example i've got boost::dynamic_bitset<> test1( std::string("1111") ); boost::dynamic_bitset<> test2( std::string("00") ); they should be concatenated into a thrid Bitset test3 which then holds 111100 Solutions should use boost::dynamic_bitset. If the solution works with std::bitset, it would be nice too. There should be a focus on performance when concatenating the bits.

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• taglib link errors

  - by Vihaan Verma

  I m using taglib for one of my projects . The Debug/Release library is build using MSVC 10. On compiling the code with the library in taglib/taglib/Release some linker error are thrown . id3.cpp.1.o : error LNK2019: unresolved external symbol "__declspec(dllimport) public: class TagLib::AudioPropertie s * __cdecl TagLib::FileRef::audioProperties(void)const " (__imp_?audioProperties@FileRef@TagLib@@QEBAPEAVAudioProp erties@2@XZ) referenced in function "struct MetaData __cdecl ID3::getMetaDataOfFile(class std::basic_string<char,st ruct std::char_traits<char>,class std::allocator<char> >)" (?getMetaDataOfFile@ID3@@YA?AUMetaData@@V?$basic_string@ DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z) id3.cpp.1.o : error LNK2019: unresolved external symbol "__declspec(dllimport) public: virtual __cdecl TagLib::Stri ng::~String(void)" (__imp_??1String@TagLib@@UEAA@XZ) referenced in function "struct MetaData __cdecl ID3::getMetaDa taOfFile(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >)" (?getMetaDataOfF ile@ID3@@YA?AUMetaData@@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z) id3.cpp.1.o : error LNK2019: unresolved external symbol "__declspec(dllimport) public: class std::basic_string<char ,struct std::char_traits<char>,class std::allocator<char> > __cdecl TagLib::String::to8Bit(bool)const " (__imp_?to8 Bit@String@TagLib@@QEBA?AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@_N@Z) referenced in function "struct MetaData __cdecl ID3::getMetaDataOfFile(class std::basic_string<char,struct std::char_traits<char>,class s td::allocator<char> >)" (?getMetaDataOfFile@ID3@@YA?AUMetaData@@V?$basic_string@DU?$char_traits@D@std@@V?$allocator @D@2@@std@@@Z) id3.cpp.1.o : error LNK2019: unresolved external symbol "__declspec(dllimport) public: virtual __cdecl TagLib::File Ref::~FileRef(void)" (__imp_??1FileRef@TagLib@@UEAA@XZ) referenced in function "struct MetaData __cdecl ID3::getMet aDataOfFile(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >)" (?getMetaData OfFile@ID3@@YA?AUMetaData@@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z) id3.cpp.1.o : error LNK2019: unresolved external symbol "__declspec(dllimport) public: class TagLib::Tag * __cdecl TagLib::FileRef::tag(void)const " (__imp_?tag@FileRef@TagLib@@QEBAPEAVTag@2@XZ) referenced in function "struct Meta Data __cdecl ID3::getMetaDataOfFile(class std::basic_string<char,struct std::char_traits<char>,class std::allocator <char> >)" (?getMetaDataOfFile@ID3@@YA?AUMetaData@@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z ) id3.cpp.1.o : error LNK2019: unresolved external symbol "__declspec(dllimport) public: bool __cdecl TagLib::FileRef ::isNull(void)const " (__imp_?isNull@FileRef@TagLib@@QEBA_NXZ) referenced in function "struct MetaData __cdecl ID3: :getMetaDataOfFile(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >)" (?getM etaDataOfFile@ID3@@YA?AUMetaData@@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z) id3.cpp.1.o : error LNK2019: unresolved external symbol "__declspec(dllimport) public: __cdecl TagLib::FileRef::Fil eRef(class TagLib::FileName,bool,enum TagLib::AudioProperties::ReadStyle)" (__imp_??0FileRef@TagLib@@QEAA@VFileName @1@_NW4ReadStyle@AudioProperties@1@@Z) referenced in function "struct MetaData __cdecl ID3::getMetaDataOfFile(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >)" (?getMetaDataOfFile@ID3@@YA?AU MetaData@@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z) id3.cpp.1.o : error LNK2019: unresolved external symbol "__declspec(dllimport) public: __cdecl TagLib::FileName::Fi leName(char const *)" (__imp_??0FileName@TagLib@@QEAA@PEBD@Z) referenced in function "struct MetaData __cdecl ID3:: getMetaDataOfFile(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >)" (?getMe taDataOfFile@ID3@@YA?AUMetaData@@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z) I m only including tag.lib from taglib/taglib/Release folder . Is there some other library I m missing out?

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• error C2440: '=' : cannot convert from 'std::string []' to 'std::string []'

  - by Bach

  now what is wrong with this code! Header: #pragma once #include <string> using namespace std; class Menu { public: Menu(string []); ~Menu(void); }; Implementation: #include "Menu.h" string _choices[]; Menu::Menu(string items[]) { _choices = items; } Menu::~Menu(void) { } compiler is complaining: error C2440: '=' : cannot convert from 'std::string []' to 'std::string []' There are no conversions to array types, although there are conversions to references or pointers to arrays there is no conversion! so what is it on about? please help, just need to pass a bloody array of strings and set it to Menu class _choices[] attribute. thanks

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• what's the job of std::unique_lock when used with std::conditional_variable::wait()

  - by Mike

  I'm quite confused with the need of a std::unique_lock when wait a std::conditional_variable. So I look into the library code in VS 2013 and get more confused. This is how std::conditional_variable::wait() implemented: void wait(unique_lock<mutex>& _Lck) { // wait for signal _Cnd_waitX(&_Cnd, &_Lck.mutex()->_Mtx); } Is this some kind of joke? Wrap a mutex in a unique_lock and do nothing but get it back latter? Why not just use mutex in the parameter list?

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• How to pronounce "std" (C & C++)? [closed]

  - by Matt Blaine

  How do you pronounce "std"? As in: __stdcall stdlib.h stdio.h stdin stdout stderr the namespace std Thank you. Please don't take this as being rude, but if you'd like to close this question, there are many others like it that were allowed to survive. So, if you decide to close any of them, would you kindly close all of them? Thanks.

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• Seeking STL-aware c++filt

  - by Don Wakefield

  In my development environment, I'm compiling a code base using GNU C++ 3.4.6. Code is under development, and unfortunately crashes now and then. It's nice to be able to run the traceback through a demangler, and I use c++filt 3.4. The problem comes when functions have a number of STL parameters. Consider My_callback::operator()( Status&, std::set<std::string> const&, std::vector<My_parameter*> const&, My_attribute_set const&, std::vector<My_parameter_base*> const&, std::vector<My_parameter> const&, std::set<std::string> const& ) { // ... } When this function is in the traceback, the mangled output on my platform is: (_ZN30My_callbackclER11StatusRKSt3setISsSt4lessISsESaISsEERKSt6vectorIP13My_parameterSaISB_EERK17My_attribute_setRKS9_IP18My_parameter_baseSaISK_EERKS9_ISA_SaISA_EES8_+0x76a) [0x13ffdaa] c++filt kindly demangles it to (My_callback::operator()(Status&, std::set<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&, std::vector<My_parameter*, std::allocator<My_parameter*> > const&, My_attribute_set const&, std::vector<My_parameter_base*, std::allocator<My_parameter_base*> > const&, std::vector<My_parameter, std::allocator<My_parameter> > const&, std::set<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&)+0x76a) [0x13ffdaa] This is the same problem as compiler errors encountered when using templates. However, the STL is a fairly regular and recognizable package of templates. So what I'm hoping is that someone out there has created an enhanced version of c++filt which would dump something closer to the original function signature. Any hints?

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• Initialization of std::vector<unsigned int> with a list of consecutive unsigned integers

  - by Thomas

  I want to use a special method to initialize a std::vector<unsigned int> which is described in a C++ book I use as a reference (the German book 'Der C++ Programmer' by Ulrich Breymann, in case that matters). In that book is a section on sequence types of the STL, referring in particular to list, vector and deque. In this section he writes that there are two special constructors of such sequence types, namely, if Xrefers to such a type, X(n, t) // creates a sequence with n copies of t X(i, j) // creates a sequence from the elements of the interval [i, j) I want to use the second one for an interval of unsigned int, that is std::vector<unsigned int> l(1U, 10U); to get a list initialized with {1,2,...,9}. What I get, however, is a vector with one unsigned int with value 10 :-| Does the second variant exist, and if yes, how do I force that it is called?

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• std::for_each on a member function with 1 argument

  - by Person

  I'm wondering how to implement what is stated in the title. I've tried something like... std::for_each( a.begin(), a.end(), std::mem_fun_ref( &myClass::someFunc ) ) but I get an error saying that the "term" (I"m assuming it means the 3rd argument) doesn't evaluate to a function with 1 argument, even though someFunc does take one argument - the type of the objects stored in a. I'm wondering if what I'm trying to do is possible using the standard library (I know I can do it easily using boost). P.S. Does using for_each and mem_fun_ref have any performance implications in comparison to just iterating through a manually and passing the object to someFunc?

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• Higher order function « filter » in C++

  - by Red Hyena

  Hi all. I wanted to write a higher order function filter with C++. The code I have come up with so far is as follows: #include <iostream> #include <string> #include <functional> #include <algorithm> #include <vector> #include <list> #include <iterator> using namespace std; bool isOdd(int const i) { return i % 2 != 0; } template < template <class, class> class Container, class Predicate, class Allocator, class A > Container<A, Allocator> filter(Container<A, Allocator> const & container, Predicate const & pred) { Container<A, Allocator> filtered(container); container.erase(remove_if(filtered.begin(), filtered.end(), pred), filtered.end()); return filtered; } int main() { int const a[] = {23, 12, 78, 21, 97, 64}; vector<int const> const v(a, a + 6); vector<int const> const filtered = filter(v, isOdd); copy(filtered.begin(), filtered.end(), ostream_iterator<int const>(cout, " ")); } However on compiling this code, I get the following error messages that I am unable to understand and hence get rid of: /usr/include/c++/4.3/ext/new_allocator.h: In instantiation of ‘__gnu_cxx::new_allocator<const int>’: /usr/include/c++/4.3/bits/allocator.h:84: instantiated from ‘std::allocator<const int>’ /usr/include/c++/4.3/bits/stl_vector.h:75: instantiated from ‘std::_Vector_base<const int, std::allocator<const int> >’ /usr/include/c++/4.3/bits/stl_vector.h:176: instantiated from ‘std::vector<const int, std::allocator<const int> >’ Filter.cpp:29: instantiated from here /usr/include/c++/4.3/ext/new_allocator.h:82: error: ‘const _Tp* __gnu_cxx::new_allocator<_Tp>::address(const _Tp&) const [with _Tp = const int]’ cannot be overloaded /usr/include/c++/4.3/ext/new_allocator.h:79: error: with ‘_Tp* __gnu_cxx::new_allocator<_Tp>::address(_Tp&) const [with _Tp = const int]’ Filter.cpp: In function ‘Container<A, Allocator> filter(const Container<A, Allocator>&, const Predicate&) [with Container = std::vector, Predicate = bool ()(int), Allocator = std::allocator<const int>, A = const int]’: Filter.cpp:30: instantiated from here Filter.cpp:23: error: passing ‘const std::vector<const int, std::allocator<const int> >’ as ‘this’ argument of ‘__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> > std::vector<_Tp, _Alloc>::erase(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, __gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >) [with _Tp = const int, _Alloc = std::allocator<const int>]’ discards qualifiers /usr/include/c++/4.3/bits/stl_algo.h: In function ‘_FIter std::remove_if(_FIter, _FIter, _Predicate) [with _FIter = __gnu_cxx::__normal_iterator<const int*, std::vector<const int, std::allocator<const int> > >, _Predicate = bool (*)(int)]’: Filter.cpp:23: instantiated from ‘Container<A, Allocator> filter(const Container<A, Allocator>&, const Predicate&) [with Container = std::vector, Predicate = bool ()(int), Allocator = std::allocator<const int>, A = const int]’ Filter.cpp:30: instantiated from here /usr/include/c++/4.3/bits/stl_algo.h:821: error: assignment of read-only location ‘__result.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = const int*, _Container = std::vector<const int, std::allocator<const int> >]()’ /usr/include/c++/4.3/ext/new_allocator.h: In member function ‘void __gnu_cxx::new_allocator<_Tp>::deallocate(_Tp*, size_t) [with _Tp = const int]’: /usr/include/c++/4.3/bits/stl_vector.h:150: instantiated from ‘void std::_Vector_base<_Tp, _Alloc>::_M_deallocate(_Tp*, size_t) [with _Tp = const int, _Alloc = std::allocator<const int>]’ /usr/include/c++/4.3/bits/stl_vector.h:136: instantiated from ‘std::_Vector_base<_Tp, _Alloc>::~_Vector_base() [with _Tp = const int, _Alloc = std::allocator<const int>]’ /usr/include/c++/4.3/bits/stl_vector.h:286: instantiated from ‘std::vector<_Tp, _Alloc>::vector(_InputIterator, _InputIterator, const _Alloc&) [with _InputIterator = const int*, _Tp = const int, _Alloc = std::allocator<const int>]’ Filter.cpp:29: instantiated from here /usr/include/c++/4.3/ext/new_allocator.h:98: error: invalid conversion from ‘const void*’ to ‘void*’ /usr/include/c++/4.3/ext/new_allocator.h:98: error: initializing argument 1 of ‘void operator delete(void*)’ /usr/include/c++/4.3/bits/stl_algobase.h: In function ‘_OI std::__copy_move_a(_II, _II, _OI) [with bool _IsMove = false, _II = const int*, _OI = const int*]’: /usr/include/c++/4.3/bits/stl_algobase.h:435: instantiated from ‘_OI std::__copy_move_a2(_II, _II, _OI) [with bool _IsMove = false, _II = __gnu_cxx::__normal_iterator<const int*, std::vector<const int, std::allocator<const int> > >, _OI = __gnu_cxx::__normal_iterator<const int*, std::vector<const int, std::allocator<const int> > >]’ /usr/include/c++/4.3/bits/stl_algobase.h:466: instantiated from ‘_OI std::copy(_II, _II, _OI) [with _II = __gnu_cxx::__normal_iterator<const int*, std::vector<const int, std::allocator<const int> > >, _OI = __gnu_cxx::__normal_iterator<const int*, std::vector<const int, std::allocator<const int> > >]’ /usr/include/c++/4.3/bits/vector.tcc:136: instantiated from ‘__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> > std::vector<_Tp, _Alloc>::erase(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, __gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >) [with _Tp = const int, _Alloc = std::allocator<const int>]’ Filter.cpp:23: instantiated from ‘Container<A, Allocator> filter(const Container<A, Allocator>&, const Predicate&) [with Container = std::vector, Predicate = bool ()(int), Allocator = std::allocator<const int>, A = const int]’ Filter.cpp:30: instantiated from here /usr/include/c++/4.3/bits/stl_algobase.h:396: error: no matching function for call to ‘std::__copy_move<false, true, std::random_access_iterator_tag>::__copy_m(const int*&, const int*&, const int*&)’ Please tell me what I am doing wrong here and what is the correct way to achieve the kind of higher order polymorphism I want. Thanks.

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• resort on a std::vector vs std::insert

  - by Abruzzo Forte e Gentile

  I have a sorted std::vector of relative small size ( from 5 to 20 elements ). I used std::vector since the data is continuous so I have speed because of cache. On a specific point I need to remove an element from this vector. I have now a doubt: which is the fastest way to remove this value between the 2 options below? setting that element to 0 and call sort to reorder: this has complexity but elements are on the same cache line. call erase that will copy ( or memcpy who knows?? ) all elements after it of 1 place ( I need to investigate the behind scense of erase ). Do you know which one is faster? I think that the same approach could be thought about inserting a new element without hitting the max capacity of the vector. Regards AFG

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• Allocation Target of std::aligned_storage (stack or heap?)

  - by Zenikoder

  I've been trying to get my head around the TR1 addition known as aligned_storage. Whilst reading the following documents N2165, N3190 and N2140 I can't for the life of me see a statement where it clearly describes stack or heap nature of the memory being used. I've had a look at the implementation provided by msvc2010, boost and gcc they all provide a stack based solution centered around the use of a union. In short: Is the memory type (stack or heap) used by aligned_storage implementation defined or is it always meant to be stack based? and, What the is the specific document that defines/determines that?

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• std::map for storing static const Objects

  - by Sean M.

  I am making a game similar to Minecraft, and I am trying to fine a way to keep a map of Block objects sorted by their id. This is almost identical to the way that Minecraft does it, in that they declare a bunch of static final Block objects and initialize them, and then the constructor of each block puts a reference of that block into whatever the Java equivalent of a std::map is, so there is a central place to get ids and the Blocks with those ids. The problem is, that I am making my game in C++, and trying to do the exact same thing. In Block.h, I am declaring the Blocks like so: //Block.h public: static const Block Vacuum; static const Block Test; And in Block.cpp I am initializing them like so: //Block.cpp const Block Block::Vacuum = Block("Vacuum", 0, 0); const Block Block::Test = Block("Test", 1, 0); The block constructor looks like this: Block::Block(std::string name, uint16 id, uint8 tex) { //Check for repeat ids if (IdInUse(id)) { fprintf(stderr, "Block id %u is already in use!", (uint32)id); throw std::runtime_error("You cannot reuse block ids!"); } _id = id; //Check for repeat names if (NameInUse(name)) { fprintf(stderr, "Block name %s is already in use!", name); throw std::runtime_error("You cannot reuse block names!"); } _name = name; _tex = tex; //fprintf(stdout, "Using texture %u\n", _tex); _transparent = false; _solidity = 1.0f; idMap[id] = this; nameMap[name] = this; } And finally, the maps that I'm using to store references of Blocks in relation to their names and ids are declared as such: std::map<uint16, Block*> Block::idMap = std::map<uint16, Block*>(); //The map of block ids std::map<std::string, Block*> Block::nameMap = std::map<std::string, Block*>(); //The map of block names The problem comes when I try to get the Blocks in the maps using a method called const Block* GetBlock(uint16 id), where the last line is return idMap.at(id);. This line returns a Block with completely random values like _visibility = 0xcccc and such like that, found out through debugging. So my question is, is there something wrong with the blocks being declared as const obejcts, and then stored at pointers and accessed later on? The reason I cant store them as Block& is because that makes a copy of the Block when it is entered, so the block wouldn't have any of the attributes that could be set afterwards in the constructor of any child class, so I think I need to store them as a pointer. Any help is greatly appreciated, as I don't fully understand pointers yet. Just ask if you need to see any other parts of the code.

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