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  • On counting pairs of words that differ by one letter

    - by Quintofron
    Let us consider n words, each of length k. Those words consist of letters over an alphabet (whose cardinality is n) with defined order. The task is to derive an O(nk) algorithm to count the number of pairs of words that differ by one position (no matter which one exactly, as long as it's only a single position). For instance, in the following set of words (n = 5, k = 4): abcd, abdd, adcb, adcd, aecd there are 5 such pairs: (abcd, abdd), (abcd, adcd), (abcd, aecd), (adcb, adcd), (adcd, aecd). So far I've managed to find an algorithm that solves a slightly easier problem: counting the number of pairs of words that differ by one GIVEN position (i-th). In order to do this I swap the letter at the ith position with the last letter within each word, perform a Radix sort (ignoring the last position in each word - formerly the ith position), linearly detect words whose letters at the first 1 to k-1 positions are the same, eventually count the number of occurrences of each letter at the last (originally ith) position within each set of duplicates and calculate the desired pairs (the last part is simple). However, the algorithm above doesn't seem to be applicable to the main problem (under the O(nk) constraint) - at least not without some modifications. Any idea how to solve this?

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  • License key pattern detection?

    - by Ricket
    This is not a real situation; please ignore legal issues that you might think apply, because they don't. Let's say I have a set of 200 known valid license keys for a hypothetical piece of software's licensing algorithm, and a license key consists of 5 sets of 5 alphanumeric case-insensitive (all uppercase) characters. Example: HXDY6-R3DD7-Y8FRT-UNPVT-JSKON Is it possible (or likely) to extrapolate other possible keys for the system? What if the set was known to be consecutive; how do the methods change for this situation, and what kind of advantage does this give? I have heard of "keygens" before, but I believe they are probably made by decompiling the licensing software rather than examining known valid keys. In this case, I am only given the set of keys and I must determine the algorithm. I'm also told it is an industry standard algorithm, so it's probably not something basic, though the chance is always there I suppose. If you think this doesn't belong in Stack Overflow, please at least suggest an alternate place for me to look or ask the question. I honestly don't know where to begin with a problem like this. I don't even know the terminology for this kind of problem.

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  • Vacancy Tracking Algorithm implementation in C++

    - by Dave
    I'm trying to use the vacancy tracking algorithm to perform transposition of multidimensional arrays in C++. The arrays come as void pointers so I'm using address manipulation to perform the copies. Basically, there is an algorithm that starts with an offset and works its way through the whole 1-d representation of the array like swiss cheese, knocking out other offsets until it gets back to the original one. Then, you have to start at the next, untouched offset and do it again. You repeat until all offsets have been touched. Right now, I'm using a std::set to just fill up all possible offsets (0 up to the multiplicative fold of the dimensions of the array). Then, as I go through the algorithm, I erase from the set. I figure this would be fastest because I need to randomly access offsets in the tree/set and delete them. Then I need to quickly find the next untouched/undeleted offset. First of all, filling up the set is very slow and it seems like there must be a better way. It's individually calling new[] for every insert. So if I have 5 million offsets, there's 5 million news, plus re-balancing the tree constantly which as you know is not fast for a pre-sorted list. Second, deleting is slow as well. Third, assuming 4-byte data types like int and float, I'm using up actually the same amount of memory as the array itself to store this list of untouched offsets. Fourth, determining if there are any untouched offsets and getting one of them is fast -- a good thing. Does anyone have suggestions for any of these issues?

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  • Find existence of number in a sorted list in constant time? (Interview question)

    - by Rich
    I'm studying for upcoming interviews and have encountered this question several times (written verbatim) Find or determine non existence of a number in a sorted list of N numbers where the numbers range over M, M N and N large enough to span multiple disks. Algorithm to beat O(log n); bonus points for constant time algorithm. First of all, I'm not sure if this is a question with a real solution. My colleagues and I have mused over this problem for weeks and it seems ill formed (of course, just because we can't think of a solution doesn't mean there isn't one). A few questions I would have asked the interviewer are: Are there repeats in the sorted list? What's the relationship to the number of disks and N? One approach I considered was to binary search the min/max of each disk to determine the disk that should hold that number, if it exists, then binary search on the disk itself. Of course this is only an order of magnitude speedup if the number of disks is large and you also have a sorted list of disks. I think this would yield some sort of O(log log n) time. As for the M N hint, perhaps if you know how many numbers are on a disk and what the range is, you could use the pigeonhole principle to rule out some cases some of the time, but I can't figure out an order of magnitude improvement. Also, "bonus points for constant time algorithm" makes me a bit suspicious. Any thoughts, solutions, or relevant history of this problem?

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  • Longitudinal Redundancy Check fails

    - by PaulH
    I have an application that decodes data from a magnetic stripe reader. But, I'm having difficulty getting my calculated LRC check byte to match the one on the cards. If I were to grab 3 cards each with 3 tracks, I would guess the algorithm below would work on 4 of the 9 tracks in those cards. The algorithm I'm using looks like this (C#): private static char GetLRC(string s, int start, int end) { int result = 0; for (int i = start; i <= end; i++) { result ^= Convert.ToByte(s[i]); } return Convert.ToChar(result); } This is an example of track 3 data that fails the check. On this card, track 2 matched, but track 1 also failed. 0 1 2 3 4 5 6 7 8 9 A B C D E F 00 3 4 4 4 4 4 4 4 4 4 4 5 5 5 5 5 10 5 5 5 5 5 6 6 6 6 6 6 6 6 6 6 7 20 7 7 7 7 7 7 7 7 7 8 8 8 8 8 8 8 30 8 8 8 9 9 9 9 9 9 9 9 9 9 0 0 0 40 0 0 0 0 0 0 0 1 2 3 4 1 1 1 1 1 50 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 60 3 3 3 3 3 3 3 3 The sector delimiter is ';' and it ends with a '?'. The LRC byte from this track is 0x30. Unfortunately, the algorithm above computes an LRC of 0x00 per the following calculation (apologies for its length. I want to be thorough): 00 ^ 3b = 3b ';' 3b ^ 33 = 08 08 ^ 34 = 3c 3c ^ 34 = 08 08 ^ 34 = 3c 3c ^ 34 = 08 08 ^ 34 = 3c 3c ^ 34 = 08 08 ^ 34 = 3c 3c ^ 34 = 08 08 ^ 34 = 3c 3c ^ 34 = 08 08 ^ 35 = 3d 3d ^ 35 = 08 08 ^ 35 = 3d 3d ^ 35 = 08 08 ^ 35 = 3d 3d ^ 35 = 08 08 ^ 35 = 3d 3d ^ 35 = 08 08 ^ 35 = 3d 3d ^ 35 = 08 08 ^ 36 = 3e 3e ^ 36 = 08 08 ^ 36 = 3e 3e ^ 36 = 08 08 ^ 36 = 3e 3e ^ 36 = 08 08 ^ 36 = 3e 3e ^ 36 = 08 08 ^ 36 = 3e 3e ^ 36 = 08 08 ^ 37 = 3f 3f ^ 37 = 08 08 ^ 37 = 3f 3f ^ 37 = 08 08 ^ 37 = 3f 3f ^ 37 = 08 08 ^ 37 = 3f 3f ^ 37 = 08 08 ^ 37 = 3f 3f ^ 37 = 08 08 ^ 38 = 30 30 ^ 38 = 08 08 ^ 38 = 30 30 ^ 38 = 08 08 ^ 38 = 30 30 ^ 38 = 08 08 ^ 38 = 30 30 ^ 38 = 08 08 ^ 38 = 30 30 ^ 38 = 08 08 ^ 39 = 31 31 ^ 39 = 08 08 ^ 39 = 31 31 ^ 39 = 08 08 ^ 39 = 31 31 ^ 39 = 08 08 ^ 39 = 31 31 ^ 39 = 08 08 ^ 39 = 31 31 ^ 39 = 08 08 ^ 30 = 38 38 ^ 30 = 08 08 ^ 30 = 38 38 ^ 30 = 08 08 ^ 30 = 38 38 ^ 30 = 08 08 ^ 30 = 38 38 ^ 30 = 08 08 ^ 30 = 38 38 ^ 30 = 08 08 ^ 31 = 39 39 ^ 32 = 0b 0b ^ 33 = 38 38 ^ 34 = 0c 0c ^ 31 = 3d 3d ^ 31 = 0c 0c ^ 31 = 3d 3d ^ 31 = 0c 0c ^ 31 = 3d 3d ^ 31 = 0c 0c ^ 31 = 3d 3d ^ 31 = 0c 0c ^ 31 = 3d 3d ^ 31 = 0c 0c ^ 32 = 3e 3e ^ 32 = 0c 0c ^ 32 = 3e 3e ^ 32 = 0c 0c ^ 32 = 3e 3e ^ 32 = 0c 0c ^ 32 = 3e 3e ^ 32 = 0c 0c ^ 32 = 3e 3e ^ 32 = 0c 0c ^ 33 = 3f 3f ^ 33 = 0c 0c ^ 33 = 3f 3f ^ 33 = 0c 0c ^ 33 = 3f 3f ^ 33 = 0c 0c ^ 33 = 3f 3f ^ 33 = 0c 0c ^ 33 = 3f 3f ^ 3f = 00 '?' If anybody can point out how to fix my algorithm, I would appreciate it. Thanks, PaulH

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  • Merge Sort issue when removing the array copy step

    - by Ime Prezime
    I've been having an issue that I couldn't debug for quite some time. I am trying to implement a MergeSort algorithm with no additional steps of array copying by following Robert Sedgewick's algorithm in "Algorithm's in C++" book. Short description of the algorithm: The recursive program is set up to sort b, leaving results in a. Thus, the recursive calls are written to leave their result in b, and we use the basic merge program to merge those files from b into a. In this way, all the data movement is done during the course of the merges. The problem is that I cannot find any logical errors but the sorting isn't done properly. Data gets overwritten somewhere and I cannot determine what logical error causes this. The data is sorted when the program is finished but it is not the same data any more. For example, Input array: { A, Z, W, B, G, C } produces the array: { A, G, W, W, Z, Z }. I can obviously see that it must be a logical error somewhere, but I have been trying to debug this for a pretty long time and I think a fresh set of eyes could maybe see what I'm missing cause I really can't find anything wrong. My code: static const int M = 5; void insertion(char** a, int l, int r) { int i,j; char * temp; for (i = 1; i < r + 1; i++) { temp = a[i]; j = i; while (j > 0 && strcmp(a[j-1], temp) > 0) { a[j] = a[j-1]; j = j - 1; } a[j] = temp; } } //merging a and b into c void merge(char ** c,char ** a, int N, char ** b, int M) { for (int i = 0, j = 0, k = 0; k < N+M; k++) { if (i == N) { c[k] = b[j++]; continue; } if (j == M) { c[k] = a[i++]; continue; } c[k] = strcmp(a[i], b[j]) < 0 ? a[i++] : b[j++]; } } void mergesortAux(char ** a, char ** b, int l, int r) { if(r - l <= M) { insertion(a, l, r); return; } int m = (l + r)/2; mergesortAux(b, a, l, m); //merge sort left mergesortAux(b, a, m+1, r); //merge sort right merge(a+l, b+l, m-l+1, b+m+1, r-m); //merge } void mergesort(char ** a,int l, int r, int size) { static char ** aux = (char**)malloc(size * sizeof(char*)); for(int i = l; i < size; i++) aux[i] = a[i]; mergesortAux(a, aux, l, r); free(aux); }

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  • Output iterator's value_type

    - by wilhelmtell
    The STL commonly defines an output iterator like so: template<class Cont> class insert_iterator : public iterator<output_iterator_tag,void,void,void,void> { // ... Why do output iterators define value_type as void? It would be useful for an algorithm to know what type of value it is supposed to output. For example, a function that translates a URL query "key1=value1&key2=value2&key3=value3" into any container that holds key-value strings elements. template<typename Ch,typename Tr,typename Out> void parse(const std::basic_string<Ch,Tr>& str, Out result) { std::basic_string<Ch,Tr> key, value; // loop over str, parse into p ... *result = typename iterator_traits<Out>::value_type(key, value); } The SGI reference page of value_type hints this is because it's not possible to dereference an output iterator. But that's not the only use of value_type: I might want to instantiate one in order to assign it to the iterator.

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  • should std::auto_ptr<>::operator = reset / deallocate its existing pointee ?

    - by afriza
    I read here about std::auto_ptr<::operator= Notice however that the left-hand side object is not automatically deallocated when it already points to some object. You can explicitly do this by calling member function reset before assigning it a new value. However, when I read the source code for header file C:\Program Files\Microsoft Visual Studio 8\VC\ce\include\memory template<class _Other> auto_ptr<_Ty>& operator=(auto_ptr<_Other>& _Right) _THROW0() { // assign compatible _Right (assume pointer) reset(_Right.release()); return (*this); } auto_ptr<_Ty>& operator=(auto_ptr<_Ty>& _Right) _THROW0() { // assign compatible _Right (assume pointer) reset(_Right.release()); return (*this); } auto_ptr<_Ty>& operator=(auto_ptr_ref<_Ty> _Right) _THROW0() { // assign compatible _Right._Ref (assume pointer) _Ty **_Pptr = (_Ty **)_Right._Ref; _Ty *_Ptr = *_Pptr; *_Pptr = 0; // release old reset(_Ptr); // set new return (*this); } What is the correct/standard behavior? How do other STL implementations behave?

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  • Why an auto_ptr can "seal" a container

    - by icephere
    auto_ptr on wikipedia said that "an auto_ptr containing an STL container may be used to prevent further modification of the container.". It used the following example: auto_ptr<vector<ContainedType> > open_vec(new vector<ContainedType>); open_vec->push_back(5); open_vec->push_back(3); // Transfers control, but now the vector cannot be changed: auto_ptr<const vector<ContainedType> > closed_vec(open_vec); // closed_vec->push_back(8); // Can no longer modify If I uncomment the last line, g++ will report an error as t05.cpp:24: error: passing ‘const std::vector<int, std::allocator<int> >’ as ‘this’ argument of ‘void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = int, _Alloc = std::allocator<int>]’ discards qualifiers I am curious why after transferring the ownership of this vector, it can no longer be modified? Thanks a lot!

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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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  • 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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  • 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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  • 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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  • 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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  • C++ priority queue structure used ?

    - by John Retallack
    While searching for some functions in C++ STL documentation I read that push and pop for priority queues needs constant time. "Constant (in the priority_queue). Although notice that push_heap operates in logarithmic time." My question is what kind of data structure is used to mantain a priority queue with O(1) for push and pop ?

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  • C++ priority queue structure userd ?

    - by John Retallack
    While searching for some functions in C++ STL documentation I read that push and pop for priority queues needs constant time. "Constant (in the priority_queue). Although notice that push_heap operates in logarithmic time." My question is what kind of data structure is used to mantain a priority queue with O(1) for push and pop ?

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