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  • Javascript Iterator Class

    - by Alsciende
    Do you know a js library that implements a generic Iterator class for collections (be it Arrays or some abstract Enumerable) with a full set of features, like the Google Common or the Apache Commons?

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  • Const references when dereferencing iterator on set, starting from Visual Studio 2010

    - by Patrick
    Starting from Visual Studio 2010, iterating over a set seems to return an iterator that dereferences the data as 'const data' instead of non-const. The following code is an example of something that does compile on Visual Studio 2005, but not on 2010 (this is an artificial example, but clearly illustrates the problem we found on our own code). In this example, I have a class that stores a position together with a temperature. I define comparison operators (not all them, just enough to illustrate the problem) that only use the position, not the temperature. The point is that for me two instances are identical if the position is identical; I don't care about the temperature. #include <set> class DataPoint { public: DataPoint (int x, int y) : m_x(x), m_y(y), m_temperature(0) {} void setTemperature(double t) {m_temperature = t;} bool operator<(const DataPoint& rhs) const { if (m_x==rhs.m_x) return m_y<rhs.m_y; else return m_x<rhs.m_x; } bool operator==(const DataPoint& rhs) const { if (m_x!=rhs.m_x) return false; if (m_y!=rhs.m_y) return false; return true; } private: int m_x; int m_y; double m_temperature; }; typedef std::set<DataPoint> DataPointCollection; void main(void) { DataPointCollection points; points.insert (DataPoint(1,1)); points.insert (DataPoint(1,1)); points.insert (DataPoint(1,2)); points.insert (DataPoint(1,3)); points.insert (DataPoint(1,1)); for (DataPointCollection::iterator it=points.begin();it!=points.end();++it) { DataPoint &point = *it; point.setTemperature(10); } } In the main routine I have a set to which I add some points. To check the correctness of the comparison operator, I add data points with the same position multiple times. When writing the contents of the set, I can clearly see there are only 3 points in the set. The for-loop loops over the set, and sets the temperature. Logically this is allowed, since the temperature is not used in the comparison operators. This code compiles correctly in Visual Studio 2005, but gives compilation errors in Visual Studio 2010 on the following line (in the for-loop): DataPoint &point = *it; The error given is that it can't assign a "const DataPoint" to a [non-const] "DataPoint &". It seems that you have no decent (= non-dirty) way of writing this code in VS2010 if you have a comparison operator that only compares parts of the data members. Possible solutions are: Adding a const-cast to the line where it gives an error Making temperature mutable and making setTemperature a const method But to me both solutions seem rather 'dirty'. It looks like the C++ standards committee overlooked this situation. Or not? What are clean solutions to solve this problem? Did some of you encounter this same problem and how did you solve it? Patrick

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  • C++: building iterator from bits

    - by gruszczy
    I have a bitmap and would like to return an iterator of positions of set bits. Right now I just walk the whole bitmap and if bit is set, then I provide next position. I believe this could be done more effectively: for example build statically array for each combination of bits in single byte and return vector of positions. This can't be done for a whole int, because array would be too big. But maybe there are some better solutions? Do you know any smart algorithms for this?

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  • Is there a standard Cyclic Iterator in C++

    - by Hippicoder
    Based on the following question: Check if one string is a rotation of other string I was thinking of making a cyclic iterator type that takes a range, and would be able to solve the above problem like so: std::string s1 = "abc" ; std::string s2 = "bca" ; std::size_t n = 2; // number of cycles cyclic_iterator it(s2.begin(),s2.end(),n); cyclic_iterator end; if (std::search(it, end, s1.begin(),s1.end()) != end) { std::cout << "s1 is a rotation of s2" << std::endl; } My question, Is there already something like this available? I've check Boost and STL doesn't have one. I've got a simple hand-written one but would rather use an already made/tested implementation.

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  • c++ std::map question about iterator order

    - by jbu
    Hi all, I am a C++ newbie trying to use a map so I can get constant time lookups for the find() method. The problem is that when I use an iterator to go over the elements in the map, elements do not appear in the same order that they were placed in the map. Without maintaining another data structure, is there a way to achieve in order iteration while still retaining the constant time lookup ability? Please let me know. Thanks, jbu edit: thanks for letting me know map::find() isn't constant time.

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  • How to define a custom iterator in C++

    - by Robert Martin
    I've seen a number of posts on SO about how to define custom iterators, but nothing that seems to exactly answers my question, which is... How do I create an iterator that hides a nested for loop? For instance, I have a class Foo, inside of the Foo is a Bar, and inside of the Bar is a string. I could write for (const Foo& foo : foo_set) for (const Bar& bar : foo.bar_set) if (bar.my_string != "baz") cout << bar.my_string << endl; but instead I want to be able to do something like: for (const string& good : foo_set) cout << good << endl; How do I do something like this?

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  • Implementing an iterator over binary tree using C++ 11

    - by user1459339
    I would like to create an iterator over the binary tree so as to be able to use range-based for loop. I understand I ought to implement the begin() and end() function first. Begin should probably point to the root. According to the specification, however, the end() functions returns "the element following the last valid element". Which element (node) is that? Would it not be illegal to point to some "invalid" place? The other thing is the operator++. What is the best way to return "next" element in tree? I just need some advice to begin with this programming.

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  • Visual Studio C++ list iterator not decementable

    - by user69514
    I keep getting an error on visual studio that says list iterator not decrementable: line 256 My program works fine on Linux, but visual studio compiler throws this error. Dammit this is why I hate windows. Why can't the world run on Linux? Anyway, do you see what my problem is? #include <iostream> #include <fstream> #include <sstream> #include <list> using namespace std; int main(){ /** create the list **/ list<int> l; /** create input stream to read file **/ ifstream inputstream("numbers.txt"); /** read the numbers and add them to list **/ if( inputstream.is_open() ){ string line; istringstream instream; while( getline(inputstream, line) ){ instream.clear(); instream.str(line); /** get he five int's **/ int one, two, three, four, five; instream >> one >> two >> three >> four >> five; /** add them to the list **/ l.push_back(one); l.push_back(two); l.push_back(three); l.push_back(four); l.push_back(five); }//end while loop }//end if /** close the stream **/ inputstream.close(); /** display the list **/ cout << "List Read:" << endl; list<int>::iterator i; for( i=l.begin(); i != l.end(); ++i){ cout << *i << " "; } cout << endl << endl; /** now sort the list **/ l.sort(); /** display the list **/ cout << "Sorted List (head to tail):" << endl; for( i=l.begin(); i != l.end(); ++i){ cout << *i << " "; } cout << endl; list<int> lReversed; for(i=l.begin(); i != l.end(); ++i){ lReversed.push_front(*i); } cout << "Sorted List (tail to head):" << endl; for(i=lReversed.begin(); i!=lReversed.end(); ++i){ cout << *i << " "; } cout << endl << endl; /** remove first biggest element and display **/ l.pop_back(); cout << "List after removing first biggest element:" << endl; cout << "Sorted List (head to tail):" << endl; for( i=l.begin(); i != l.end(); ++i){ cout << *i << " "; } cout << endl; cout << "Sorted List (tail to head):" << endl; lReversed.pop_front(); for(i=lReversed.begin(); i!=lReversed.end(); ++i){ cout << *i << " "; } cout << endl << endl; /** remove second biggest element and display **/ l.pop_back(); cout << "List after removing second biggest element:" << endl; cout << "Sorted List (head to tail):" << endl; for( i=l.begin(); i != l.end(); ++i){ cout << *i << " "; } cout << endl; lReversed.pop_front(); cout << "Sorted List (tail to head):" << endl; for(i=lReversed.begin(); i!=lReversed.end(); ++i){ cout << *i << " "; } cout << endl << endl; /** remove third biggest element and display **/ l.pop_back(); cout << "List after removing third biggest element:" << endl; cout << "Sorted List (head to tail):" << endl; for( i=l.begin(); i != l.end(); ++i){ cout << *i << " "; } cout << endl; cout << "Sorted List (tail to head):" << endl; lReversed.pop_front(); for(i=lReversed.begin(); i!=lReversed.end(); ++i){ cout << *i << " "; } cout << endl << endl; /** create frequency table **/ const int biggest = 1000; //create array size of biggest element int arr[biggest]; //set everything to zero for(int j=0; j<biggest+1; j++){ arr[j] = 0; } //now update number of occurences for( i=l.begin(); i != l.end(); i++){ arr[*i]++; } //now print the frequency table. only print where occurences greater than zero cout << "Final list frequency table: " << endl; for(int j=0; j<biggest+1; j++){ if( arr[j] > 0 ){ cout << j << ": " << arr[j] << " occurences" << endl; } } return 0; }//end main

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  • Of C# Iterators and Performance

    - by James Michael Hare
    Some of you reading this will be wondering, "what is an iterator" and think I'm locked in the world of C++.  Nope, I'm talking C# iterators.  No, not enumerators, iterators.   So, for those of you who do not know what iterators are in C#, I will explain it in summary, and for those of you who know what iterators are but are curious of the performance impacts, I will explore that as well.   Iterators have been around for a bit now, and there are still a bunch of people who don't know what they are or what they do.  I don't know how many times at work I've had a code review on my code and have someone ask me, "what's that yield word do?"   Basically, this post came to me as I was writing some extension methods to extend IEnumerable<T> -- I'll post some of the fun ones in a later post.  Since I was filtering the resulting list down, I was using the standard C# iterator concept; but that got me wondering: what are the performance implications of using an iterator versus returning a new enumeration?   So, to begin, let's look at a couple of methods.  This is a new (albeit contrived) method called Every(...).  The goal of this method is to access and enumeration and return every nth item in the enumeration (including the first).  So Every(2) would return items 0, 2, 4, 6, etc.   Now, if you wanted to write this in the traditional way, you may come up with something like this:       public static IEnumerable<T> Every<T>(this IEnumerable<T> list, int interval)     {         List<T> newList = new List<T>();         int count = 0;           foreach (var i in list)         {             if ((count++ % interval) == 0)             {                 newList.Add(i);             }         }           return newList;     }     So basically this method takes any IEnumerable<T> and returns a new IEnumerable<T> that contains every nth item.  Pretty straight forward.   The problem?  Well, Every<T>(...) will construct a list containing every nth item whether or not you care.  What happens if you were searching this result for a certain item and find that item after five tries?  You would have generated the rest of the list for nothing.   Enter iterators.  This C# construct uses the yield keyword to effectively defer evaluation of the next item until it is asked for.  This can be very handy if the evaluation itself is expensive or if there's a fair chance you'll never want to fully evaluate a list.   We see this all the time in Linq, where many expressions are chained together to do complex processing on a list.  This would be very expensive if each of these expressions evaluated their entire possible result set on call.    Let's look at the same example function, this time using an iterator:       public static IEnumerable<T> Every<T>(this IEnumerable<T> list, int interval)     {         int count = 0;         foreach (var i in list)         {             if ((count++ % interval) == 0)             {                 yield return i;             }         }     }   Notice it does not create a new return value explicitly, the only evidence of a return is the "yield return" statement.  What this means is that when an item is requested from the enumeration, it will enter this method and evaluate until it either hits a yield return (in which case that item is returned) or until it exits the method or hits a yield break (in which case the iteration ends.   Behind the scenes, this is all done with a class that the CLR creates behind the scenes that keeps track of the state of the iteration, so that every time the next item is asked for, it finds that item and then updates the current position so it knows where to start at next time.   It doesn't seem like a big deal, does it?  But keep in mind the key point here: it only returns items as they are requested. Thus if there's a good chance you will only process a portion of the return list and/or if the evaluation of each item is expensive, an iterator may be of benefit.   This is especially true if you intend your methods to be chainable similar to the way Linq methods can be chained.    For example, perhaps you have a List<int> and you want to take every tenth one until you find one greater than 10.  We could write that as:       List<int> someList = new List<int>();         // fill list here         someList.Every(10).TakeWhile(i => i <= 10);     Now is the difference more apparent?  If we use the first form of Every that makes a copy of the list.  It's going to copy the entire list whether we will need those items or not, that can be costly!    With the iterator version, however, it will only take items from the list until it finds one that is > 10, at which point no further items in the list are evaluated.   So, sounds neat eh?  But what's the cost is what you're probably wondering.  So I ran some tests using the two forms of Every above on lists varying from 5 to 500,000 integers and tried various things.    Now, iteration isn't free.  If you are more likely than not to iterate the entire collection every time, iterator has some very slight overhead:   Copy vs Iterator on 100% of Collection (10,000 iterations) Collection Size Num Iterated Type Total ms 5 5 Copy 5 5 5 Iterator 5 50 50 Copy 28 50 50 Iterator 27 500 500 Copy 227 500 500 Iterator 247 5000 5000 Copy 2266 5000 5000 Iterator 2444 50,000 50,000 Copy 24,443 50,000 50,000 Iterator 24,719 500,000 500,000 Copy 250,024 500,000 500,000 Iterator 251,521   Notice that when iterating over the entire produced list, the times for the iterator are a little better for smaller lists, then getting just a slight bit worse for larger lists.  In reality, given the number of items and iterations, the result is near negligible, but just to show that iterators come at a price.  However, it should also be noted that the form of Every that returns a copy will have a left-over collection to garbage collect.   However, if we only partially evaluate less and less through the list, the savings start to show and make it well worth the overhead.  Let's look at what happens if you stop looking after 80% of the list:   Copy vs Iterator on 80% of Collection (10,000 iterations) Collection Size Num Iterated Type Total ms 5 4 Copy 5 5 4 Iterator 5 50 40 Copy 27 50 40 Iterator 23 500 400 Copy 215 500 400 Iterator 200 5000 4000 Copy 2099 5000 4000 Iterator 1962 50,000 40,000 Copy 22,385 50,000 40,000 Iterator 19,599 500,000 400,000 Copy 236,427 500,000 400,000 Iterator 196,010       Notice that the iterator form is now operating quite a bit faster.  But the savings really add up if you stop on average at 50% (which most searches would typically do):     Copy vs Iterator on 50% of Collection (10,000 iterations) Collection Size Num Iterated Type Total ms 5 2 Copy 5 5 2 Iterator 4 50 25 Copy 25 50 25 Iterator 16 500 250 Copy 188 500 250 Iterator 126 5000 2500 Copy 1854 5000 2500 Iterator 1226 50,000 25,000 Copy 19,839 50,000 25,000 Iterator 12,233 500,000 250,000 Copy 208,667 500,000 250,000 Iterator 122,336   Now we see that if we only expect to go on average 50% into the results, we tend to shave off around 40% of the time.  And this is only for one level deep.  If we are using this in a chain of query expressions it only adds to the savings.   So my recommendation?  If you have a resonable expectation that someone may only want to partially consume your enumerable result, I would always tend to favor an iterator.  The cost if they iterate the whole thing does not add much at all -- and if they consume only partially, you reap some really good performance gains.   Next time I'll discuss some of my favorite extensions I've created to make development life a little easier and maintainability a little better.

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  • Anybody know why the Output of this program is like this?(using iterator in c#)

    - by Babu
    using System; using System.Collections; namespace Iterator_test { class Day { int days_idx = -1; private String[] days = { "mon", "tue", "wed","thu","fri","sat","sun" }; public IEnumerable getdays() { days_idx++; yield return days[days_idx]; } } class Program { static void Main(string[] args) { Day d = new Day(); foreach (string day in d.getdays()) { Console.WriteLine(day); } } } } Actually the output should be, mon tue wed thu fri sat sun but its printing only "mon" as, mon What will be the reason?

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  • C++ STL vector iterator... but got runtime error

    - by nzer0
    I'm studying STL and made win32 project.. But I got stuck in runtime error.. I tried to debug it but.. please click to see picture this is very strange because in watch table, n1,p1,it are defined but n2 isn't and tmp is not either.. I can't find what is wrong... please help..

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  • Is there a linear-time performance guarantee with using an Iterator?

    - by polygenelubricants
    If all that you're doing is a simple one-pass iteration (i.e. only hasNext() and next(), no remove()), are you guaranteed linear time performance and/or amortized constant cost per operation? Is this specified in the Iterator contract anywhere? Are there data structures/Java Collection which cannot be iterated in linear time? java.util.Scanner implements Iterator<String>. A Scanner is hardly a data structure (e.g. remove() makes absolutely no sense). Is this considered a design blunder? Is something like PrimeGenerator implements Iterator<Integer> considered bad design, or is this exactly what Iterator is for? (hasNext() always returns true, next() computes the next number on demand, remove() makes no sense). Similarly, would it have made sense for java.util.Random implements Iterator<Double>?

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  • How to remove an element from set using Iterator?

    - by ankit
    I have a scenario that I am iterating over a set using iterator. Now I want to remove 1st element while my iterator is on 2nd element. How can I do it. I dont want to convert this set to list and using listIterator. I dont want to collect all objects to be removed in other set and call remove all sample code. Set<MyObject> mySet = new HashSet<MyObject>(); mySet.add(MyObject1); mySet.add(MyObject2); ... Iterator itr = mySet.iterator(); while(itr.hasNext()) { // Now iterator is at second element and I want to remove first element }

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  • Const-correctness semantics in C++

    - by thirtythreeforty
    For fun and profit™, I'm writing a trie class in C++ (using the C++11 standard.) My trie<T> has an iterator, trie<T>::iterator. (They're all actually functionally const_iterators, because you cannot modify a trie's value_type.) The iterator's class declaration looks partially like this: template<typename T> class trie<T>::iterator : public std::iterator<std::bidirectional_iterator_tag, T> { friend class trie<T>; struct state { state(const trie<T>* const node, const typename std::vector<std::pair<typename T::value_type, std::unique_ptr<trie<T>>>>::const_iterator& node_map_it ) : node{node}, node_map_it{node_map_it} {} // This pointer is to const data: const trie<T>* node; typename std::vector<std::pair<typename T::value_type, std::unique_ptr<trie<T>>>>::const_iterator node_map_it; }; public: typedef const T value_type; iterator() =default; iterator(const trie<T>* node) { parents.emplace(node, node->children.cbegin()); // ... } // ... private: std::stack<state> parents; // ... }; Notice that the node pointer is declared const. This is because (in my mind) the iterator should not be modifying the node that it points to; it is just an iterator. Now, elsewhere in my main trie<T> class, I have an erase function that has a common STL signature--it takes an iterator to data to erase (and returns an iterator to the next object). template<typename T> typename trie<T>::iterator trie<T>::erase(const_iterator it) { // ... // Cannot modify a const object! it.parents.top().node->is_leaf = false; // ... } The compiler complains because the node pointer is read-only! The erase function definitely should modify the trie that the iterator points to, even though the iterator shouldn't. So, I have two questions: Should iterator's constructors be public? trie<T> has the necessary begin() and end() members, and of course trie<T>::iterator and trie<T> are mutual friends, but I don't know what the convention is. Making them private would solve a lot of the angst I'm having about removing the const "promise" from the iterator's constructor. What are the correct const semantics/conventions regarding the iterator and its node pointer here? Nobody has ever explained this to me, and I can't find any tutorials or articles on the Web. This is probably the more important question, but it does require a good deal of planning and proper implementation. I suppose it could be circumvented by just implementing 1, but it's the principle of the thing!

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  • How might I wrap the FindXFile-style APIs to the STL-style Iterator Pattern in C++?

    - by BillyONeal
    Hello everyone :) I'm working on wrapping up the ugly innards of the FindFirstFile/FindNextFile loop (though my question applies to other similar APIs, such as RegEnumKeyEx or RegEnumValue, etc.) inside iterators that work in a manner similar to the Standard Template Library's istream_iterators. I have two problems here. The first is with the termination condition of most "foreach" style loops. STL style iterators typically use operator!= inside the exit condition of the for, i.e. std::vector<int> test; for(std::vector<int>::iterator it = test.begin(); it != test.end(); it++) { //Do stuff } My problem is I'm unsure how to implement operator!= with such a directory enumeration, because I do not know when the enumeration is complete until I've actually finished with it. I have sort of a hack together solution in place now that enumerates the entire directory at once, where each iterator simply tracks a reference counted vector, but this seems like a kludge which can be done a better way. The second problem I have is that there are multiple pieces of data returned by the FindXFile APIs. For that reason, there's no obvious way to overload operator* as required for iterator semantics. When I overload that item, do I return the file name? The size? The modified date? How might I convey the multiple pieces of data to which such an iterator must refer to later in an ideomatic way? I've tried ripping off the C# style MoveNext design but I'm concerned about not following the standard idioms here. class SomeIterator { public: bool next(); //Advances the iterator and returns true if successful, false if the iterator is at the end. std::wstring fileName() const; //other kinds of data.... }; EDIT: And the caller would look like: SomeIterator x = ??; //Construct somehow while(x.next()) { //Do stuff } Thanks! Billy3

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  • C++ Iterator lifetime and detecting invalidation

    - by DK.
    Based on what's considered idiomatic in C++11: should an iterator into a custom container survive the container itself being destroyed? should it be possible to detect when an iterator becomes invalidated? are the above conditional on "debug builds" in practice? Details: I've recently been brushing up on my C++ and learning my way around C++11. As part of that, I've been writing an idiomatic wrapper around the uriparser library. Part of this is wrapping the linked list representation of parsed path components. I'm looking for advice on what's idiomatic for containers. One thing that worries me, coming most recently from garbage-collected languages, is ensuring that random objects don't just go disappearing on users if they make a mistake regarding lifetimes. To account for this, both the PathList container and its iterators keep a shared_ptr to the actual internal state object. This ensures that as long as anything pointing into that data exists, so does the data. However, looking at the STL (and lots of searching), it doesn't look like C++ containers guarantee this. I have this horrible suspicion that the expectation is to just let containers be destroyed, invalidating any iterators along with it. std::vector certainly seems to let iterators get invalidated and still (incorrectly) function. What I want to know is: what is expected from "good"/idiomatic C++11 code? Given the shiny new smart pointers, it seems kind of strange that STL allows you to easily blow your legs off by accidentally leaking an iterator. Is using shared_ptr to the backing data an unnecessary inefficiency, a good idea for debugging or something expected that STL just doesn't do? (I'm hoping that grounding this to "idiomatic C++11" avoids charges of subjectivity...)

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  • Why can't I sort this container?

    - by Knowing me knowing you
    Please don't mind that there is no insert fnc and that data are hardcoded. The main purpouse of it is to correctly implement iterator for this container. //file Set.h #pragma once template<class T> class Set { template<class T> friend ostream& operator<<(ostream& out, const Set<T>& obj); private: T** myData_; std::size_t mySize_; std::size_t myIndex_; public: Set(); class iterator : public std::iterator<std::random_access_iterator_tag, T*> { private: T** itData_; public: iterator(T** obj) { itData_ = obj; } T operator*() const { return **itData_; } /*Comparing values of two iterators*/ bool operator<(const iterator& obj) { return **itData_ < **obj.itData_; } /*Substracting two iterators*/ difference_type operator-(const iterator& obj) { return itData_ - obj.itData_; } /*Moving iterator backward for value*/ iterator operator-(const int value) { return itData_ - value; } /*Adding two iterators*/ difference_type operator+(const iterator& obj) { return itData_ + obj.itData_; } /*Moving iterator forward for value*/ iterator operator+(const int value) { return itData_ + value; } bool operator!=(const iterator& obj) { return (itData_ != obj.itData_); } bool operator==(const iterator& obj) { return (itData_ == obj.itData_); } T** operator++() { return ++itData_; } T** operator--() { return --itData_; } }; iterator begin() const { return myData_; } iterator end() const { return myData_ + myIndex_; } }; template<class T> ostream& operator<<(ostream& out, const Set<T>& obj) { for (int i = 0;i < 3; ++i) { out << *obj.myData_[i] << "\n"; } return out; } //file Set_impl.h #pragma once #include "stdafx.h" #include "Set.h" template<class T> Set<T>::Set() { mySize_ = 3; myIndex_ = 3; myData_ = new T*[mySize_]; myData_[0] = new T(3); myData_[1] = new T(1); myData_[2] = new T(2); } //main include "stdafx.h" #include "Set_impl.h" int _tmain(int argc, _TCHAR* argv[]) { Set<int> a; Set<int>::iterator beg_ = a.begin(); Set<int>::iterator end_ = a.end(); std::sort(beg_,end_);//WONT SORT THIS RANGE cin.get(); return 0; } Why sort can't accept this iterators even though I've provided all operators needed for sort to work? I think the best way to check what's going on is to paste this code and run it first. Thanks

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  • How to read arbitrary number of values using std::copy?

    - by Miro Kropacek
    Hi, I'm trying to code opposite action to this: std::ostream outs; // properly initialized of course std::set<int> my_set; // ditto outs << my_set.size(); std::copy( my_set.begin(), my_set.end(), std::ostream_iterator<int>( outs ) ); it should be something like this: std::istream ins; std::set<int>::size_type size; ins >> size; std::copy( std::istream_iterator<int>( ins ), std::istream_iterator<int>( ins ) ???, std::inserter( my_set, my_set.end() ) ); But I'm stuck with the 'end' iterator -- input interators can't use std::advance and neither I can use two streams with the same source... Is there any elegant way how to solve this? Of course I can use for loop, but maybe there's something nicer :)

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  • std::deque: How do I get an iterator pointing to the element at a specified index?

    - by Ptah- Opener of the Mouth
    I have a std::deque, and I want to insert an element at a specified index (I'm aware that std::list would be better at this). The deque::insert() function takes an iterator to specify the location to insert. Given an index, how can I get an iterator pointing to that location, so that I can pass that iterator to insert()? For example: void insertThing ( deque<Thing> & things, Thing thing, size_t index ) { deque<Thing>::iterator it = /* what do I do here? */ things.insert ( it, thing ); } I'm sure this is a very basic question, and I apologize for it. It's been a long time since I've used the STL, and I don't see anything in std::deque's member list that obviously does what I want. Thanks.

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