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  • Strange problem with vectors.

    - by Catalin Dumitru
    I have a really strange problem with stl vectors in which the wrong destructor is called for the right object when I call the erase method if that makes any sense. My code looks something like this: for(vector<Category>::iterator iter = this->children.begin(); iter != this->children.end(); iter++) { if((*iter).item == item) { this->children.erase(iter); return; } ------------------------- } It's just a simple function that finds the element in the vector which has some item to be searched, and removes said element from the vector. My problem is than when the erase function is called, and thus the object which the iterator is pointing at is being destroyed, the wrong destructor is being called. More specific the destructor of the last element in the vector is being called, and not of the actual object being removed. Thus the memory is being removed from the wrong object, which will still be an element in the vector, and the actual object which is removed from the vector, still has all of it's memory intact. The costructor of the object looks like this: Category::Category(const Category &from) { this->name = from.name; for(vector<Category>::const_iterator iter = from.children.begin(); iter != from.children.end(); iter++) this->children.push_back((*iter)); this->item = new QTreeWidgetItem; } And the destructor Category::~Category() { this->children.clear(); if(this->item != NULL) { QTreeWidgetItem* parent = this->item->parent(); if(parent != NULL) parent->removeChild(this->item); delete this->item; } }

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  • function objects versus function pointers

    - by kumar_m_kiran
    Hi All, I have two questions related to function objects and function pointers, Question : 1 When I read the different uses sort algorithm of STL, I see that the third parameter can be a function objects, below is an example class State { public: //... int population() const; float aveTempF() const; //... }; struct PopLess : public std::binary_function<State,State,bool> { bool operator ()( const State &a, const State &b ) const { return popLess( a, b ); } }; sort( union, union+50, PopLess() ); Question : Now, How does the statement, sort(union, union+50,PopLess()) work? PopLess() must be resolved into something like PopLess tempObject.operator() which would be same as executing the operator () function on a temporary object. I see this as, passing the return value of overloaded operation i.e bool (as in my example) to sort algorithm. So then, How does sort function resolve the third parameter in this case? Question : 2 Question Do we derive any particular advantage of using function objects versus function pointer? If we use below function pointer will it derive any disavantage? inline bool popLess( const State &a, const State &b ) { return a.population() < b.population(); } std::sort( union, union+50, popLess ); // sort by population PS : Both the above references(including example) are from book "C++ Common Knowledge: Essential Intermediate Programming" by "Stephen C. Dewhurst". I was unable to decode the topic content, thus have posted for help. Thanks in advance for your help.

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  • Crash generated during destruction of hash_map

    - by Alien01
    I am using hash_map in application as typedef hash_map<DWORD,CComPtr<IInterfaceXX>> MapDword2Interface; In main application I am using static instance of this map static MapDword2Interface m_mapDword2Interface; I have got one crash dump from one of the client machines which point to the crash in clearing this map I opened that crash dump and here is assembly during debugging > call std::list<std::pair<unsigned long const ,ATL::CComPtr<IInterfaceXX> >,std::allocator<std::pair<unsigned long const ,ATL::CComPtr<IInterfaceXX> > > >::clear > mov eax,dword ptr [CMainApp::m_mapDword2Interface+8 (49XXXXX)] Here is code where crash dump is pointing. Below code is from stl:list file void clear() { // erase all #if _HAS_ITERATOR_DEBUGGING this->_Orphan_ptr(*this, 0); #endif /* _HAS_ITERATOR_DEBUGGING */ _Nodeptr _Pnext; _Nodeptr _Pnode = _Nextnode(_Myhead); _Nextnode(_Myhead) = _Myhead; _Prevnode(_Myhead) = _Myhead; _Mysize = 0; for (; _Pnode != _Myhead; _Pnode = _Pnext) { // delete an element _Pnext = _Nextnode(_Pnode); this->_Alnod.destroy(_Pnode); this->_Alnod.deallocate(_Pnode, 1); } } Crash is pointing to the this->_Alnod.destroy(_Pnode); statement in above code. I am not able to guess it, what could be reason. Any ideas??? How can I make sure, even is there is something wrong with the map , it should not crash?

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  • std::string insert method has ambiguous overloads?

    - by sdg
    Environment: VS2005 C++ using STLPort 5.1.4. Compiling the following code snippet: std::string copied = "asdf"; char ch = 's'; copied.insert(0,1,ch); I receive an error: Error 1 error C2668: 'stlpx_std::basic_string<_CharT,_Traits,_Alloc>::insert' : ambiguous call to overloaded function It appears that the problem is the insert method call on the string object. The two defined overloads are void insert ( iterator p, size_t n, char c ); string& insert ( size_t pos1, size_t n, char c ); But given that STLPort uses a simple char* as its iterator, the literal zero in the insert method in my code is ambiguous. So while I can easily overcome the problem by hinting such as copied.insert(size_t(0),1,ch); My question is: is this overloading and possible ambiguity intentional in the specification? Or more likely an unintended side-effect of the specific STLPort implementation? (Note that the Microsoft-supplied STL does not have this problem as it has a class for the iterator, instead of a naked pointer)

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  • Quicksort / vector / partition issue

    - by xxx
    Hi, I have an issue with the following code : class quicksort { private: void _sort(double_it begin, double_it end) { if ( begin == end ) { return ; } double_it it = partition(begin, end, bind2nd(less<double>(), *begin)) ; iter_swap(begin, it-1); _sort(begin, it-1); _sort(it, end); } public: quicksort (){} void operator()(vector<double> & data) { double_it begin = data.begin(); double_it end = data.end() ; _sort(begin, end); } }; However, this won't work for too large a number of elements (it works with 10 000 elements, but not with 100 000). Example code : int main() { vector<double>v ; for(int i = n-1; i >= 0 ; --i) v.push_back(rand()); quicksort f; f(v); return 0; } Doesn't the STL partition function works for such sizes ? Or am I missing something ? Many thanks for your help.

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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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  • Creating Binary Block from struct

    - by MOnsDaR
    I hope the title is describing the problem, i'll change it if anyone has a better idea. I'm storing information in a struct like this: struct AnyStruct { AnyStruct : testInt(20), testDouble(100.01), testBool1(true), testBool2(false), testBool3(true), testChar('x') {} int testInt; double testDouble; bool testBool1; bool testBool2; bool testBool3; char testChar; std::vector<char> getBinaryBlock() { //how to build that? } } The struct should be sent via network in a binary byte-buffer with the following structure: Bit 00- 31: testInt Bit 32- 61: testDouble most significant portion Bit 62- 93: testDouble least significant portion Bit 94: testBool1 Bit 95: testBool2 Bit 96: testBool3 Bit 97-104: testChar According to this definition the resulting std::vector should have a size of 13 bytes (char == byte) My question now is how I can form such a packet out of the different datatypes I've got. I've already read through a lot of pages and found datatypes like std::bitset or boost::dynamic_bitset, but neither seems to solve my problem. I think it is easy to see, that the above code is just an example, the original standard is far more complex and contains more different datatypes. Solving the above example should solve my problems with the complex structures too i think. One last point: The problem should be solved just by using standard, portable language-features of C++ like STL or Boost (

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  • C++ iterator and const_iterator problem for own container class

    - by BaCh
    Hi there, I'm writing an own container class and have run into a problem I can't get my head around. Here's the bare-bone sample that shows the problem. It consists of a container class and two test classes: one test class using a std:vector which compiles nicely and the second test class which tries to use my own container class in exact the same way but fails miserably to compile. #include <vector> #include <algorithm> #include <iterator> using namespace std; template <typename T> class MyContainer { public: class iterator { public: typedef iterator self_type; inline iterator() { } }; class const_iterator { public: typedef const_iterator self_type; inline const_iterator() { } }; iterator begin() { return iterator(); } const_iterator begin() const { return const_iterator(); } }; // This one compiles ok, using std::vector class TestClassVector { public: void test() { vector<int>::const_iterator I=myc.begin(); } private: vector<int> myc; }; // this one fails to compile. Why? class TestClassMyContainer { public: void test(){ MyContainer<int>::const_iterator I=myc.begin(); } private: MyContainer<int> myc; }; int main(int argc, char ** argv) { return 0; } gcc tells me: test2.C: In member function ‘void TestClassMyContainer::test()’: test2.C:51: error: conversion from ‘MyContainer::iterator’ to non-scalar type ‘MyContainer::const_iterator’ requested I'm not sure where and why the compiler wants to convert an iterator to a const_iterator for my own class but not for the STL vector class. What am I doing wrong?

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  • iterators to range of elements in a vector whose attributes have specific value

    - by user1801173
    I have a vector of objects and I want to return the range of elements whose attribute have a specific value. This is the structure: class A { public: std::vector<B*> vec_; pair<vector<B*>::iterator, vector<B*>::iterator> getElements(unsigned int attr_val); unsigned int name() { return name_; } private: unsigned int name_; }; class B { public: unsigned int attr() { return attr_; } A* source() { return source_; } B* dest() { return dest_; } private: A* source_; B* dest_; unsigned int attr_; }; The vector vec_; is already sorted by attr_ and dest_-name() (in that order). Now I want to return all elements, whose attr_ is equal to attr_val. What is the appropriate stl algorithm (or is there even a vector member function?) to implement getElements(unsigned int attr_val) ? Thanks for help.

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  • C++: Constructor/destructor unresolved when not inline?

    - by Anamon
    In a plugin-based C++ project, I have a TmpClass that is used to exchange data between the main application and the plugins. Therefore the respective TmpClass.h is included in the abstract plugin interface class that is included by the main application project, and implemented by each plugin. As the plugins work on STL vectors of TmpClass instances, there needs to be a default constructor and destructor for the TmpClass. I had declared these in TmpClass.h: class TmpClass { TmpClass(); ~TmpClass(); } and implemented them in TmpClass.cpp. TmpClass::~TmpClass() {} TmpClass::TmpClass() {} However, when compiling plugins this leads to the linker complaining about two unresolved externals - the default constructor and destructor of TmpClass as required by the std::vector<TmpClass> template instantiation - even though all other functions I declare in TmpClass.h and implement in TmpClass.cpp work. As soon as I remove the (empty) default constructor and destructor from the .cpp file and inline them into the class declaration in the .h file, the plugins compile and work. Why is it that the default constructor and destructor have to be inline for this code to compile? Why does it even maatter? (I'm using MSVC++8).

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  • Visual Studio 2010 compile error with std::string?

    - by AJG85
    So this is possibly the strangest thing I've seen recently and was curious how this could happen. The compiler gave me an error saying that std::string is undefined when used as a return type but not when used as a parameter in methods of a class! #pragma once #include <string> #include <vector> // forward declarations class CLocalReference; class CResultSetHandle; class MyClass { public: MyClass() {} ~MyClass {} void Retrieve(const CLocalReference& id, CResultSetHandle& rsh, std::string& item); // this is fine const std::string Retrieve(const CLocalReference& id, CResultSetHandle& rsh); // this fails with std::string is undefined?!?! }; Doing a Rebuild All it still happened I had to choose clean solution and then Rebuild All again after for the universe to realign. While it's resolved for the moment I'd still like to know what could have caused this because I'm at a loss as to why when there should be no conflicts especially when I always use fully qualified names for STL.

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  • Pointers into elements in a container

    - by Pillsy
    Say I have an object: struct Foo { int bar_; Foo(int bar) bar_(bar) {} }; and I have an STL container that contains Foos, perhaps a vector, and I take // Elsewhere... vector<Foo> vec; vec.push_back(Foo(4)); int *p = &(vec[0].bar_) This is a terrible idea, right? The reason is that vector is going to be storing its elements in a dynamically allocated array somewhere, and eventually, if you add enough elements, it will have to allocate another array, copy over all the elements of the original array, and delete the old array. After that happens, p points to garbage. This is why many operations on a vector will invalidate iterators. It seems like it would be reasonable to assume that an operation that would invalidate iterators from a container will also invalidate pointers to data members of container elements, and that if an operation doesn't invalidate iterators, those pointers will still be safe. However, many reasonable assumptions are false. Is this one of them?

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  • Is it possible to create ostream object, which outputs to multiple destinations?

    - by fiktor
    In 0-th approximation I have a class class MyClass{ public: ... std::ostream & getOStream(){return f;} private: ofstream f; ... }; Which is used sometimes in the following way: MyClass myclass; myclass.getOStream()<<some<<information<<printed<<here; But now I want to change the class MyClass, so that information will be printed both to f and to std::out, i.e. I want the above line to be equivalent to myclass.f<<some<<information<<printed<<here; std::cout<<some<<information<<printed<<here; I don't know any good way to do that. Do you? Is there any standard solution (for example in stl or in boost)? P.S. I tried to search on this, but it seems that I don't know good keywords. Words multiple, output, ostream, C++, boost seem to be too general.

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  • Containers of reference_wrappers (comparison operators required?)

    - by kloffy
    If you use stl containers together with reference_wrappers of POD types, the following code works just fine: int i = 3; std::vector< boost::reference_wrapper<int> > is; is.push_back(boost::ref(i)); std::cout << (std::find(is.begin(),is.end(),i)!=is.end()) << std::endl; However, if you use non-POD types such as (contrived example): struct Integer { int value; bool operator==(const Integer& rhs) const { return value==rhs.value; } bool operator!=(const Integer& rhs) const { return !(*this == rhs); } }; It doesn't suffice to declare those comparison operators, instead you have to declare: bool operator==(const boost::reference_wrapper<Integer>& lhs, const Integer& rhs) { return boost::unwrap_ref(lhs)==rhs; } And possibly also: bool operator==(const Integer& lhs, const boost::reference_wrapper<Integer>& rhs) { return lhs==boost::unwrap_ref(rhs); } In order to get the equivalent code to work: Integer j = { 0 }; std::vector< boost::reference_wrapper<Integer> > js; js.push_back(boost::ref(j)); std::cout << (std::find(js.begin(),js.end(),j)!=js.end()) << std::endl; Now, I'm wondering if this is really the way it's meant to be done, since it seems impractical. It just seems there should be a simpler solution, e.g. templates: template<class T> bool operator==(const boost::reference_wrapper<T>& lhs, const T& rhs) { return boost::unwrap_ref(lhs)==rhs; } template<class T> bool operator==(const T& lhs, const boost::reference_wrapper<T>& rhs) { return lhs==boost::unwrap_ref(rhs); } There's probably a good reason why reference_wrapper behaves the way it does (possibly to accomodate non-POD types without comparison operators?). Maybe there already is an elegant solution and I just haven't found it.

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  • Bad_alloc exception when using new for a struct c++

    - by bsg
    Hi, I am writing a query processor which allocates large amounts of memory and tries to find matching documents. Whenever I find a match, I create a structure to hold two variables describing the document and add it to a priority queue. Since there is no way of knowing how many times I will do this, I tried creating my structs dynamically using new. When I pop a struct off the priority queue, the queue (STL priority queue implementation) is supposed to call the object's destructor. My struct code has no destructor, so I assume a default destructor is called in that case. However, the very first time that I try to create a DOC struct, I get the following error: Unhandled exception at 0x7c812afb in QueryProcessor.exe: Microsoft C++ exception: std::bad_alloc at memory location 0x0012f5dc.. I don't understand what's happening - have I used up so much memory that the heap is full? It doesn't seem likely. And it's not as if I've even used that pointer before. So: first of all, what am I doing that's causing the error, and secondly, will the following code work more than once? Do I need to have a separate pointer for each struct created, or can I re-use the same temporary pointer and assume that the queue will keep a pointer to each struct? Here is my code: struct DOC{ int docid; double rank; public: DOC() { docid = 0; rank = 0.0; } DOC(int num, double ranking) { docid = num; rank = ranking; } bool operator>( const DOC & d ) const { return rank > d.rank; } bool operator<( const DOC & d ) const { return rank < d.rank; } }; //a lot of processing goes on here; when a matching document is found, I do this: rank = calculateRanking(table, num); //if the heap is not full, create a DOC struct with the docid and rank and add it to the heap if(q.size() < 20) { doc = new DOC(num, rank); q.push(*doc); doc = NULL; } //if the heap is full, but the new rank is greater than the //smallest element in the min heap, remove the current smallest element //and add the new one to the heap else if(rank > q.top().rank) { q.pop(); cout << "pushing doc on to queue" << endl; doc = new DOC(num, rank); q.push(*doc); } Thank you very much, bsg.

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  • C++ linked list based tree structure. Sanely move nodes between lists.

    - by krunk
    The requirements: Each Node in the list must contain a reference to its previous sibling Each Node in the list must contain a reference to its next sibling Each Node may have a list of child nodes Each child Node must have a reference to its parent node Basically what we have is a tree structure of arbitrary depth and length. Something like: -root(NULL) --Node1 ----ChildNode1 ------ChildOfChild --------AnotherChild ----ChildNode2 --Node2 ----ChildNode1 ------ChildOfChild ----ChildNode2 ------ChildOfChild --Node3 ----ChildNode1 ----ChildNode2 Given any individual node, you need to be able to either traverse its siblings. the children, or up the tree to the root node. A Node ends up looking something like this: class Node { Node* previoius; Node* next; Node* child; Node* parent; } I have a container class that stores these and provides STL iterators. It performs your typical linked list accessors. So insertAfter looks like: void insertAfter(Node* after, Node* newNode) { Node* next = after->next; after->next = newNode; newNode->previous = after; next->previous = newNode; newNode->next = next; newNode->parent = after->parent; } That's the setup, now for the question. How would one move a node (and its children etc) to another list without leaving the previous list dangling? For example, if Node* myNode exists in ListOne and I want to append it to listTwo. Using pointers, listOne is left with a hole in its list since the next and previous pointers are changed. One solution is pass by value of the appended Node. So our insertAfter method would become: void insertAfter(Node* after, Node newNode); This seems like an awkward syntax. Another option is doing the copying internally, so you'd have: void insertAfter(Node* after, const Node* newNode) { Node *new_node = new Node(*newNode); Node* next = after->next; after->next = new_node; new_node->previous = after; next->previous = new_node; new_node->next = next; new_node->parent = after->parent; } Finally, you might create a moveNode method for moving and prevent raw insertion or appending of a node that already has been assigned siblings and parents. // default pointer value is 0 in constructor and a operator bool(..) // is defined for the Node bool isInList(const Node* node) const { return (node->previous || node->next || node->parent); } // then in insertAfter and friends if(isInList(newNode) // throw some error and bail I thought I'd toss this out there and see what folks came up with.

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  • issue with std::advance on std::sets

    - by tim
    I've stumbled upon what I believe is a bug in the stl algorithm advance. When I'm advancing the iterator off of the end of the container, I get inconsistent results. Sometimes I get container.end(), sometimes I get the last element. I've illustrated this with the following code: #include <algorithm> #include <cstdio> #include <set> using namespace std; typedef set<int> tMap; int main(int argc, char** argv) { tMap::iterator i; tMap the_map; for (int i=0; i<10; i++) the_map.insert(i); #if EXPERIMENT==1 i = the_map.begin(); #elif EXPERIMENT==2 i = the_map.find(4); #elif EXPERIMENT==3 i = the_map.find(5); #elif EXPERIMENT==4 i = the_map.find(6); #elif EXPERIMENT==5 i = the_map.find(9); #elif EXPERIMENT==6 i = the_map.find(2000); #else i = the_map.end(); #endif advance(i, 100); if (i == the_map.end()) printf("the end\n"); else printf("wuh? %d\n", *i); return 0; } Which I get the following unexpected (according to me) behavior in experiment 3 and 5 where I get the last element instead of the_map.end(). [tim@saturn advance]$ uname -srvmpio Linux 2.6.18-1.2798.fc6 #1 SMP Mon Oct 16 14:37:32 EDT 2006 i686 athlon i386 GNU/Linux [tim@saturn advance]$ g++ --version g++ (GCC) 4.1.1 20061011 (Red Hat 4.1.1-30) Copyright (C) 2006 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. [tim@saturn advance]$ g++ -DEXPERIMENT=1 advance.cc [tim@saturn advance]$ ./a.out the end [tim@saturn advance]$ g++ -DEXPERIMENT=2 advance.cc [tim@saturn advance]$ ./a.out the end [tim@saturn advance]$ g++ -DEXPERIMENT=3 advance.cc [tim@saturn advance]$ ./a.out wuh? 9 [tim@saturn advance]$ g++ -DEXPERIMENT=4 advance.cc [tim@saturn advance]$ ./a.out the end [tim@saturn advance]$ g++ -DEXPERIMENT=5 advance.cc [tim@saturn advance]$ ./a.out wuh? 9 [tim@saturn advance]$ g++ -DEXPERIMENT=6 advance.cc [tim@saturn advance]$ ./a.out the end [tim@saturn advance]$ g++ -DEXPERIMENT=7 advance.cc [tim@saturn advance]$ ./a.out the end [tim@saturn advance]$ From the sgi website (see link at top), it has the following example: list<int> L; L.push_back(0); L.push_back(1); list<int>::iterator i = L.begin(); advance(i, 2); assert(i == L.end()); I would think that the assertion should apply to other container types, no? What am I missing? Thanks!

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  • simple C++ hash_set example

    - by celil
    I am new to C++ and STL. I am stuck with the following simple example of a hash set storing custom data structures: #include <iostream> #include <ext/hash_set> using namespace std; using namespace __gnu_cxx; struct trip { int trip_id; int delta_n; int delta_secs; trip(int trip_id, int delta_n, int delta_secs){ this->trip_id = trip_id; this->delta_n = delta_n; this->delta_secs = delta_secs; } }; struct hash_trip { size_t operator()(const trip t) { hash<int> H; return H(t.trip_id); } }; struct eq_trip { bool operator()(const trip t1, const trip t2) { return (t1.trip_id==t2.trip_id) && (t1.delta_n==t2.delta_n) && (t1.delta_secs==t2.delta_secs); } }; int main() { hash_set<trip, hash_trip, eq_trip> trips; trip t = trip(3,2,-1); trip t1 = trip(3,2,0); trips.insert(t); } when I try to compile it, I get the following error message: /usr/include/c++/4.2.1/ext/hashtable.h: In member function ‘size_t __gnu_cxx::hashtable<_Val, _Key, _HashFcn, _ExtractKey, _EqualKey, _Alloc>::_M_bkt_num_key(const _Key&, size_t) const [with _Val = trip, _Key = trip, _HashFcn = hash_trip, _ExtractKey = std::_Identity<trip>, _EqualKey = eq_trip, _Alloc = std::allocator<trip>]’: /usr/include/c++/4.2.1/ext/hashtable.h:599: instantiated from ‘size_t __gnu_cxx::hashtable<_Val, _Key, _HashFcn, _ExtractKey, _EqualKey, _Alloc>::_M_bkt_num(const _Val&, size_t) const [with _Val = trip, _Key = trip, _HashFcn = hash_trip, _ExtractKey = std::_Identity<trip>, _EqualKey = eq_trip, _Alloc = std::allocator<trip>]’ /usr/include/c++/4.2.1/ext/hashtable.h:1006: instantiated from ‘void __gnu_cxx::hashtable<_Val, _Key, _HashFcn, _ExtractKey, _EqualKey, _Alloc>::resize(size_t) [with _Val = trip, _Key = trip, _HashFcn = hash_trip, _ExtractKey = std::_Identity<trip>, _EqualKey = eq_trip, _Alloc = std::allocator<trip>]’ /usr/include/c++/4.2.1/ext/hashtable.h:437: instantiated from ‘std::pair<__gnu_cxx::_Hashtable_iterator<_Val, _Key, _HashFcn, _ExtractKey, _EqualKey, _Alloc>, bool> __gnu_cxx::hashtable<_Val, _Key, _HashFcn, _ExtractKey, _EqualKey, _Alloc>::insert_unique(const _Val&) [with _Val = trip, _Key = trip, _HashFcn = hash_trip, _ExtractKey = std::_Identity<trip>, _EqualKey = eq_trip, _Alloc = std::allocator<trip>]’ /usr/include/c++/4.2.1/ext/hash_set:197: instantiated from ‘std::pair<typename __gnu_cxx::hashtable<_Value, _Value, _HashFcn, std::_Identity<_Value>, _EqualKey, _Alloc>::const_iterator, bool> __gnu_cxx::hash_set<_Value, _HashFcn, _EqualKey, _Alloc>::insert(const typename __gnu_cxx::hashtable<_Value, _Value, _HashFcn, std::_Identity<_Value>, _EqualKey, _Alloc>::value_type&) [with _Value = trip, _HashFcn = hash_trip, _EqualKey = eq_trip, _Alloc = std::allocator<trip>]’ try.cpp:45: instantiated from here /usr/include/c++/4.2.1/ext/hashtable.h:595: error: passing ‘const hash_trip’ as ‘this’ argument of ‘size_t hash_trip::operator()(trip)’ discards qualifiers What am I doing wrong?

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  • Accessing a vector<vector<int>> as a flat array

    - by user1762276
    For this array: vector<vector<int> > v; v.push_back(vector<int>(0)); v.back().push_back(1); v.back().push_back(2); v.back().push_back(3); v.back().push_back(4); I can output {1, 2, 3, 4} easily enough: cout << v[0][0] << endl; cout << v[0][1] << endl; cout << v[0][2] << endl; cout << v[0][3] << endl; To access it as a flat array I can do this: int* z = (int*)&v[0].front(); cout << z[0] << endl; cout << z[1] << endl; cout << z[2] << endl; cout << z[3] << endl; Now, how do I access the multidimensional vector as a flat multidimensional array? I cannot use the same format as accessing a single-dimensional vector: // This does not work (outputs garbage) int** n = (int**)&v.front(); cout << n[0][0] << endl; cout << n[0][1] << endl; cout << n[0][2] << endl; cout << n[0][3] << endl; The workaround I've found is to do this: int** n = new int* [v.size()]; for (size_t i = 0; i < v.size(); i++) { n[i] = &v.at(i).front(); } cout << n[0][0] << endl; cout << n[0][1] << endl; cout << n[0][2] << endl; cout << n[0][3] << endl; Is there a way to access the entire multidimensional vector like a flat c-style array without having to dynamically allocate each dimension above the data before accessing it? Speed is not critical in the implementation and clarity for maintenance is paramount. A multidimensional vector is just fine for storing the data. However, I want to also expose the data as a flat c-style array in the SDK so that it can be easily accessible by other languages. This means that exposing the vectors as an STL object is a no go. The solution I came up with works fine for my needs as I only evaluate the array once at the very end of processing to "flatten" it. However, is there a better way to go about this? Or am I already doing it the best way I possibly can without re-implementing my own data structure (overkill since my flatten code is only a few lines). Thank you for your advice, friends!

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  • C++ linked list based tree structure. Sanely copy nodes between lists.

    - by krunk
    edit Clafification: The intention is not to remove the node from the original list. But to create an identical node (data and children wise) to the original and insert that into the new list. In other words, a "move" does not imply a "remove" from the original. endedit The requirements: Each Node in the list must contain a reference to its previous sibling Each Node in the list must contain a reference to its next sibling Each Node may have a list of child nodes Each child Node must have a reference to its parent node Basically what we have is a tree structure of arbitrary depth and length. Something like: -root(NULL) --Node1 ----ChildNode1 ------ChildOfChild --------AnotherChild ----ChildNode2 --Node2 ----ChildNode1 ------ChildOfChild ----ChildNode2 ------ChildOfChild --Node3 ----ChildNode1 ----ChildNode2 Given any individual node, you need to be able to either traverse its siblings. the children, or up the tree to the root node. A Node ends up looking something like this: class Node { Node* previoius; Node* next; Node* child; Node* parent; } I have a container class that stores these and provides STL iterators. It performs your typical linked list accessors. So insertAfter looks like: void insertAfter(Node* after, Node* newNode) { Node* next = after->next; after->next = newNode; newNode->previous = after; next->previous = newNode; newNode->next = next; newNode->parent = after->parent; } That's the setup, now for the question. How would one move a node (and its children etc) to another list without leaving the previous list dangling? For example, if Node* myNode exists in ListOne and I want to append it to listTwo. Using pointers, listOne is left with a hole in its list since the next and previous pointers are changed. One solution is pass by value of the appended Node. So our insertAfter method would become: void insertAfter(Node* after, Node newNode); This seems like an awkward syntax. Another option is doing the copying internally, so you'd have: void insertAfter(Node* after, const Node* newNode) { Node *new_node = new Node(*newNode); Node* next = after->next; after->next = new_node; new_node->previous = after; next->previous = new_node; new_node->next = next; new_node->parent = after->parent; } Finally, you might create a moveNode method for moving and prevent raw insertion or appending of a node that already has been assigned siblings and parents. // default pointer value is 0 in constructor and a operator bool(..) // is defined for the Node bool isInList(const Node* node) const { return (node->previous || node->next || node->parent); } // then in insertAfter and friends if(isInList(newNode) // throw some error and bail I thought I'd toss this out there and see what folks came up with.

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  • Different behavior of functors (copies, assignments) in VS2010 (compared with VS2005)

    - by Patrick
    When moving from VS2005 to VS2010 we noticed a performance decrease, which seemed to be caused by additional copies of a functor. The following code illustrates the problem. It is essential to have a map where the value itself is a set. On both the map and the set we defined a comparison functor (which is templated in the example). #include <iostream> #include <map> #include <set> class A { public: A(int i, char c) : m_i(i), m_c(c) { std::cout << "Construct object " << m_c << m_i << std::endl; } A(const A &a) : m_i(a.m_i), m_c(a.m_c) { std::cout << "Copy object " << m_c << m_i << std::endl; } ~A() { std::cout << "Destruct object " << m_c << m_i << std::endl; } void operator= (const A &a) { m_i = a.m_i; m_c = a.m_c; std::cout << "Assign object " << m_c << m_i << std::endl; } int m_i; char m_c; }; class B : public A { public: B(int i) : A(i, 'B') { } static const char s_c = 'B'; }; class C : public A { public: C(int i) : A(i, 'C') { } static const char s_c = 'C'; }; template <class X> class compareA { public: compareA() : m_i(999) { std::cout << "Construct functor " << X::s_c << m_i << std::endl; } compareA(const compareA &a) : m_i(a.m_i) { std::cout << "Copy functor " << X::s_c << m_i << std::endl; } ~compareA() { std::cout << "Destruct functor " << X::s_c << m_i << std::endl; } void operator= (const compareA &a) { m_i = a.m_i; std::cout << "Assign functor " << X::s_c << m_i << std::endl; } bool operator() (const X &x1, const X &x2) const { std::cout << "Comparing object " << x1.m_i << " with " << x2.m_i << std::endl; return x1.m_i < x2.m_i; } private: int m_i; }; typedef std::set<C, compareA<C> > SetTest; typedef std::map<B, SetTest, compareA<B> > MapTest; int main() { int i = 0; std::cout << "--- " << i++ << std::endl; MapTest mapTest; std::cout << "--- " << i++ << std::endl; SetTest &setTest = mapTest[0]; std::cout << "--- " << i++ << std::endl; } If I compile this code with VS2005 I get the following output: --- 0 Construct functor B999 Copy functor B999 Copy functor B999 Destruct functor B999 Destruct functor B999 --- 1 Construct object B0 Construct functor C999 Copy functor C999 Copy functor C999 Destruct functor C999 Destruct functor C999 Copy object B0 Copy functor C999 Copy functor C999 Copy functor C999 Destruct functor C999 Destruct functor C999 Copy object B0 Copy functor C999 Copy functor C999 Copy functor C999 Destruct functor C999 Destruct functor C999 Destruct functor C999 Destruct object B0 Destruct functor C999 Destruct object B0 --- 2 If I compile this with VS2010, I get the following output: --- 0 Construct functor B999 Copy functor B999 Copy functor B999 Destruct functor B999 Destruct functor B999 --- 1 Construct object B0 Construct functor C999 Copy functor C999 Copy functor C999 Destruct functor C999 Destruct functor C999 Copy object B0 Copy functor C999 Copy functor C999 Copy functor C999 Destruct functor C999 Destruct functor C999 Copy functor C999 Assign functor C999 Assign functor C999 Destruct functor C999 Copy object B0 Copy functor C999 Copy functor C999 Copy functor C999 Destruct functor C999 Destruct functor C999 Copy functor C999 Assign functor C999 Assign functor C999 Destruct functor C999 Destruct functor C999 Destruct object B0 Destruct functor C999 Destruct object B0 --- 2 The output for the first statement (constructing the map) is identical. The output for the second statement (creating the first element in the map and getting a reference to it), is much bigger in the VS2010 case: Copy constructor of functor: 10 times vs 8 times Assignment of functor: 2 times vs. 0 times Destructor of functor: 10 times vs 8 times My questions are: Why does the STL copy a functor? Isn't it enough to construct it once for every instantiation of the set? Why is the functor constructed more in the VS2010 case than in the VS2005 case? (didn't check VS2008) And why is it assigned two times in VS2010 and not in VS2005? Are there any tricks to avoid the copy of functors? I saw a similar question at http://stackoverflow.com/questions/2216041/prevent-unnecessary-copies-of-c-functor-objects but I'm not sure that's the same question. Thanks in advance, Patrick

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  • Using custom std::set comparator

    - by Omry
    I am trying to change the default order of the items in a set of integers to be lexicographic instead of numeric, and I can't get the following to compile with g++: file.cpp: bool lex_compare(const int64_t &a, const int64_t &b) { stringstream s1,s2; s1 << a; s2 << b; return s1.str() < s2.str(); } void foo() { set<int64_t, lex_compare> > s; s.insert(1); ... } I get the following error: error: type/value mismatch at argument 2 in template parameter list for ‘template<class _Key, class _Compare, class _Alloc> class std::set’ error: expected a type, got ‘lex_compare’ what am I doing wrong?

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  • Iteration through std containers in openmp

    - by Sasun Hambardzumyan
    Hi, people. I try to use openmp for multithreading the loop through std::set. When I write the following code - #pragma omp parallel for for (std::set<A>::const_iterator i = s.begin(); i != s.end(); ++i) { const A a = *i; operate(a); } I get an error - error: invalid type for iteration variable 'i' error: invalid controlling predicate error: invalid increment expression. So is there an another way to correct iteration in std containers using openmp? There is a workaround to use int i and iterate from 0 to s.size() and using iterator inside a loop body, but this is not looks good.

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  • vector iterator not dereferencable at runtime on a vector<vector<vector<A*>*>*>

    - by marouanebj
    Hi, I have this destructor that create error at runtime "vector iterator not dereferencable". The gridMatrix is a std::vector<std::vector<std::vector<AtomsCell< Atom<T> * > * > * > * > I added the typename and also the typedef but I still have the error. I will move for this idea of vect of vect* of vect* to use boost::multi_array I think, but still I want to understand were this is wrong. /// @brief destructor ~AtomsGrid(void) { // free all the memory for all the pointers inside gridMatrix (all except the Atom<T>* ) //typedef typename ::value_type value_type; typedef std::vector<AtomsCell< Atom<T>* >*> std_vectorOfAtomsCell; typedef std::vector<std_vectorOfAtomsCell*> std_vectorOfVectorOfAtomsCell; std_vectorOfAtomsCell* vectorOfAtomsCell; std_vectorOfVectorOfAtomsCell* vectorOfVecOfAtomsCell; typename std_vectorOfVectorOfAtomsCell::iterator itSecond; typename std_vectorOfVectorOfAtomsCell::reverse_iterator reverseItSecond; typename std::vector<std_vectorOfVectorOfAtomsCell*>::iterator itFirst; //typename std::vector<AtomsCell< Atom<T>* >*>* vectorOfAtomsCell; //typename std::vector<std::vector<AtomsCell< Atom<T>* >*>*>* vectorOfVecOfAtomsCell; //typename std::vector<std::vector<AtomsCell< Atom<T>* >*>*>::iterator itSecond; //typename std::vector<std::vector<AtomsCell< Atom<T>* >*>*>::reverse_iterator reverseItSecond; //typename std::vector<std::vector<std::vector<AtomsCell< Atom<T>* >*>*>*>::iterator itFirst; for (itFirst = gridMatrix.begin(); itFirst != gridMatrix.end(); ++itFirst) { vectorOfVecOfAtomsCell = (*itFirst); while (!vectorOfVecOfAtomsCell->empty()) { reverseItSecond = vectorOfVecOfAtomsCell->rbegin(); itSecond = vectorOfVecOfAtomsCell->rbegin().base(); vectorOfAtomsCell = (*itSecond); // ERROR during run: "vector iterator not dereferencable" // I think the ERROR is because I need some typedef typename or template ???!!! // the error seems here event at itFirst //fr_Myit_Utils::vectorElementDeleter(*vectorOfAtomsCell); //vectorOfVecOfAtomsCell->pop_back(); } } fr_Myit_Utils::vectorElementDeleter(gridMatrix); } If someone want the full code that create the error I'm happy to give it but I do not think we can attach file in the forum. BUT still its is not very big so if you want it I can copy past it here. Thanks

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