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  • STL in C++ how does it work

    - by helloWorld
    I have very technical question, I was working with C, and now I'm studying C++, if I have for example this class class Team { private: list<Player> listOfPlayers; public: void addPlayer(string firstName, string lastName, int id) { Player newPlayer(string firstName, string lastName, int id); listOfPlayers.push_back(Player(string firstName, string lastName, int id)); } } this is a declaration of the Player: class Player{ private: string strLastName; string strFirstName; int nID; public: Player(string firstName, string lastName, int id); } and this is my constructor of Player: Player::Player(string firstName, string lastName, int id){ nId = id; string strFirstName = firstName; string strLastName = lastName; } so my question is when I call function addPlayer what exactly is going on with program, in my constructor of Account do I need to allocate new memory for new Account(cause in C I always use malloc) for strFirstName and strLastName, or constructor of string of Account and STL do it without me, thanks in advance (if you don't want to answer my question please at least give me some link with information) thanks in advance

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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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  • STLifying C++ classes

    - by shambulator
    I'm trying to write a class which contains several std::vectors as data members, and provides a subset of vector's interface to access them: class Mesh { public: private: std::vector<Vector3> positions; std::vector<Vector3> normals; // Several other members along the same lines }; The main thing you can do with a mesh is add positions, normals and other stuff to it. In order to allow an STL-like way of accessing a Mesh (add from arrays, other containers, etc.), I'm toying with the idea of adding methods like this: public: template<class InIter> void AddNormals(InIter first, InIter last); Problem is, from what I understand of templates, these methods will have to be defined in the header file (seems to make sense; without a concrete iterator type, the compiler doesn't know how to generate object code for the obvious implementation of this method). Is this actually a problem? My gut reaction is not to go around sticking huge chunks of code in header files, but my C++ is a little rusty with not much STL experience outside toy examples, and I'm not sure what "acceptable" C++ coding practice is on this. Is there a better way to expose this functionality while retaining an STL-like generic programming flavour? One way would be something like this: (end list) class RestrictedVector<T> { public: RestrictedVector(std::vector<T> wrapped) : wrapped(wrapped) {} template <class InIter> void Add(InIter first, InIter last) { std::copy(first, last, std::back_insert_iterator(wrapped)); } private: std::vector<T> wrapped; }; and then expose instances of these on Mesh instead, but that's starting to reek a little of overengineering :P Any advice is greatly appreciated!

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  • Getting meaningful error messages from fstream's in C++

    - by Hassan Syed
    What is the best way to get meaningful file access error messages, in a portable way from std::fstreams ? The primitiveness of badbits and failbits is getting to be bit annoying. I have written my own exception hierarchies against win32 and POSIX before, and that was far more flexible than the way the STL does it. I am getting "basic::ios_clear" as an error message from the what method of a downcasted catch (std::exception) of a fstream which has exceptions enabled. This doesn't mean much to me, although I do know what the problem is I'd like my program to be a tad more informative so that when I start deployment a few months later my life will be easier. Is there anything in Boost to extract meaningful messages out of the ofstream's implementation cross platform and cross STL implementation ?

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  • How to maintain 2 lists of object

    - by michael
    Hi, My c++ program needs to maintain 2 list of objects. list inuse; list free; So objects A can even in 'inuse' list or in 'free' list, but not both. http://www.cplusplus.com/reference/stl/list/ I am think of using 'list' as the data structure for my lists. My questions are 1. why i can't randomly access an elmenet in the list, I look at the above api, I don't see a way to get inuse[2]; 2. How can I remove an element in the list? There is an erase(), but how can I use it to remove element #2? And after I remove element 2? will STL list fill the erased spot automatically? e.g. #3 will become #2, #4 will become #3 and so on? Thank you.

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  • STL Static-Const Member Definitions

    - by javery
    How does the following work? #include <limits> int main() { const int* const foo = &std::numeric_limits<int> ::digits; } I was under the impression that in order to take an address of a static const-ant member we had to physically define it in some translation unit in order to please the linker. That said, after looking at the preprocessed code for this TU, I couldn't find an external definition for the digits member (or any other relevant members). I tested this on two compilers (VC++ 10 and g++ 4.2.4) and got identical results (i.e., it works). Does the linker auto-magically link against an object file where this stuff is defined, or am I missing something obvious here?

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  • Declaring STL Data Structures such as Vector in the .h

    - by sc_ray
    I am trying to declare a private Data Structure such as the Vector in my C++ header file which I want to eventually use within the method implementation of my .cpp. An example would be my header "SomeClass.h" where I have: class SomeClass { private: Vector<T> myVector; public: void AddTtoMyVector(T add); } And in my .cpp which is "SomeClass.cpp", I have the following: #include "SomeClass.h" SomeClass::AddTtoMyVector(T add) { myVector.Push_back(add); } Would the syntax here work? Or is there a different way of declaring and populating such structures?

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  • [C++][OpenMP] Proper use of "atomic directive" to lock STL container

    - by conradlee
    I have a large number of sets of integers, which I have, in turn, put into a vector of pointers. I need to be able to update these sets of integers in parallel without causing a race condition. More specifically. I am using OpenMP's "parallel for" construct. For dealing with shared resources, OpenMP offers a handy "atomic directive," which allows one to avoid a race condition on a specific piece of memory without using locks. It would be convenient if I could use the "atomic directive" to prevent simultaneous updating to my integer sets, however, I'm not sure whether this is possible. Basically, I want to know whether the following code could lead to a race condition vector< set<int>* > membershipDirectory(numSets, new set<int>); #pragma omp for schedule(guided,expandChunksize) for(int i=0; i<100; i++) { set<int>* sp = membershipDirectory[5]; #pragma omp atomic sp->insert(45); } (Apologies for any syntax errors in the code---I hope you get the point) I have seen a similar example of this for incrementing an integer, but I'm not sure whether it works when working with a pointer to a container as in my case.

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  • Performing time consuming operation on STL container within a lock

    - by Ashley
    I have an unordered_map of an unordered_map which stores a pointer of objects. The unordered map is being shared by multiple threads. I need to iterate through each object and perform some time consuming operation (like sending it through network etc) . How could I lock the multiple unordered_map so that it won't blocked for too long? typedef std::unordered_map<string, classA*>MAP1; typedef std::unordered_map<int, MAP1*>MAP2; MAP2 map2; pthread_mutex_lock(&mutexA) //how could I lock the maps? Could I reduce the lock granularity? for(MAP2::iterator it2 = map2.begin; it2 != map2.end; it2++) { for(MAP1::iterator it1 = *(it2->second).begin(); it1 != *(it2->second).end(); it1++) { //perform some time consuming operation on it1->second eg sendToNetwork(*(it1->second)); } } pthread_mutex_unlock(&mutexA)

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  • pointer delegate in STL set.

    - by ananth
    hi. Im kinda stuck with using a set with a pointer delegate. my code is as follows: void Graph::addNodes (NodeSet& nodes) { for (NodeSet::iterator pos = nodes.begin(); pos != nodes.end(); ++pos) { addNode(*pos); } } Here NodeSet is defined as: typedef std::set NodeSet; The above piece of code works perfectly on my windows machine, but when i run the same piece of code on a MAC, it gives me the following error: no matching function for call to 'Graph::addNode(const boost::shared_ptr&)' FYI, Node_ptr is of type: typedef boost::shared_ptr Node_ptr; can somebody plz tell me why this is happening?

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  • Does acos, atan functions in stl uses lots of cpu cycles

    - by jan
    Hi all, I wanted to calculate the angle between two vectors but I have seen these inverse trig operations such as acos and atan uses lots of cpu cycles. Is there a way where I can get this calculation done without using these functions? Also, does these really hit you when you in your optimization?

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  • Multithreading with STL container

    - by Steven
    I have an unordered map which stores a pointer of objects. I am not sure whether I am doing the correct thing to maintain the thread safety. typedef std::unordered_map<string, classA*>MAP1; MAP1 map1; pthread_mutex_lock(&mutexA) if(map1.find(id) != map1.end()) { pthread_mutex_unlock(&mutexA); //already exist, not adding items } else { classA* obj1 = new classA; map1[id] = obj1; obj1->obtainMutex(); //Should I create a mutex for each object so that I could obtain mutex when I am going to update fields for obj1? pthread_mutex_unlock(&mutexA); //release mutex for unordered_map so that other threads could access other object obj1->field1 = 1; performOperation(obj1); //takes some time obj1->releaseMutex(); //release mutex after updating obj1 }

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  • C++ STL: Trouble with iterators

    - by Rosarch
    I'm having a beginner problem: bool _isPalindrome(const string& str) { return _isPalindrome(str.begin(), str.end()); // won't compile } bool _isPalindrome(string::iterator begin, string::iterator end) { return begin == end || *begin == *end && _isPalindrome(++begin, --end); } What am I doing wrong here? Why doesn't str.begin() get type checked to be a string::iterator?

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  • A map and set which uses contiguous memory and has a reserve function

    - by edA-qa mort-ora-y
    I use several maps and sets. The lack of contiguous memory, and high number of (de)allocations, is a performance bottleneck. I need a mainly STL-compatbile map and set class which can use a contiguous block of memory for internal objects (or multiple blocks). It also needs to have a reserve function so that I can preallocate for expected sizes. Before I write my own I'd like to check what is available first. Is there something in Boost which does this? Does somebody know of an available implementation elsewhere? Intrusive collection types are not usable here as the same objects need to exist in several collections. As far as I know STL memory pools are per-type, not per instance. These global pools are not efficient with respect to memory locality in mutli-cpu/core processing. Object pools don't work as the types will be shared between instance but their pool should not. In many cases a hash map may be an option in some cases.

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  • Determining if an unordered vector<T> has all unique elements

    - by Hooked
    Profiling my cpu-bound code has suggested I that spend a long time checking to see if a container contains completely unique elements. Assuming that I have some large container of unsorted elements (with < and = defined), I have two ideas on how this might be done: The first using a set: template <class T> bool is_unique(vector<T> X) { set<T> Y(X.begin(), X.end()); return X.size() == Y.size(); } The second looping over the elements: template <class T> bool is_unique2(vector<T> X) { typename vector<T>::iterator i,j; for(i=X.begin();i!=X.end();++i) { for(j=i+1;j!=X.end();++j) { if(*i == *j) return 0; } } return 1; } I've tested them the best I can, and from what I can gather from reading the documentation about STL, the answer is (as usual), it depends. I think that in the first case, if all the elements are unique it is very quick, but if there is a large degeneracy the operation seems to take O(N^2) time. For the nested iterator approach the opposite seems to be true, it is lighting fast if X[0]==X[1] but takes (understandably) O(N^2) time if all the elements are unique. Is there a better way to do this, perhaps a STL algorithm built for this very purpose? If not, are there any suggestions eek out a bit more efficiency?

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  • Determing if an unordered vector<T> has all unique elements

    - by Hooked
    Profiling my cpu-bound code has suggested I that spend a long time checking to see if a container contains completely unique elements. Assuming that I have some large container of unsorted elements (with < and = defined), I have two ideas on how this might be done: The first using a set: template <class T> bool is_unique(vector<T> X) { set<T> Y(X.begin(), X.end()); return X.size() == Y.size(); } The second looping over the elements: template <class T> bool is_unique2(vector<T> X) { typename vector<T>::iterator i,j; for(i=X.begin();i!=X.end();++i) { for(j=i+1;j!=X.end();++j) { if(*i == *j) return 0; } } return 1; } I've tested them the best I can, and from what I can gather from reading the documentation about STL, the answer is (as usual), it depends. I think that in the first case, if all the elements are unique it is very quick, but if there is a large degeneracy the operation seems to take O(N^2) time. For the nested iterator approach the opposite seems to be true, it is lighting fast if X[0]==X[1] but takes (understandably) O(N^2) time if all the elements are unique. Is there a better way to do this, perhaps a STL algorithm built for this very purpose? If not, are there any suggestions eek out a bit more efficiency?

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  • C++: Appending a vector to a vector

    - by sub
    Assuming I have 2 STL vectors: vector<int> a; vector<int> b; Let's also say the both have around 30 elements. How do I add the vector b to the end of vector a? The dirty way would be iterating through b and adding each element via push_back, though I wouldn't like to do that!

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  • What C++ pitfalls should I avoid ?

    - by Craig H
    I remember first learning about vectors in the STL and after some time, I wanted to use a vector of bools for one of my projects. After seeing some strange behavior and doing some research, I learned that a vector of bools is not really a vector of bools. Anyone out there have any other common pitfalls to avoid in C++?

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  • Do I need to check capacity before adding an element to a vector in c++ ?

    - by Cassie
    Hi dear all, I am a newbie to c++ STL vectors so sorry for silly questions in advence. :) In my program, I have a vector which needs to store unknown number of elements. Do I have to check if the vector has achieved its max_size before adding an new element to it ? Will a c++ compiler throw an exception automatically when a program tries to add elements to a full vector ? Thank you very much, Cassie

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  • Array performance question

    - by Konrad
    I am very familiar with STL vector (and other container) performance guarantees, however I can't seem to find anything concrete about plain arrays. Are pointer arithmetic and [] methods constant or linear time?

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