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  • How to correctly inherit std::iterator.

    - by Knowing me knowing you
    Guys if I have class like below: template<class T> class X { T** myData_; public: class iterator : public iterator<random_access_iterator_tag,/*WHAT SHALL I PUT HERE? T OR T** AND WHY?*/> { T** itData_;//HERE I'M HAVING THE SAME TYPE AS MAIN CLASS ON WHICH ITERATOR WILL OPERATE }; }; Questions are in code next to appropriate lines. Thank you.

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  • Java LinkedList iterator being exhausted prematurely

    - by Sujeet
    I am using LinkedList and retrieving an Iterator object by using list.iterator(). After that, I am checking it.hasNext(), real issue is while checking it.hasNext(), sometimes it returns false. I need help why this is happening, though I have elements in the list. Some code: public synchronized void check(Object obj) throws Exception { Iterator itr = list.iterator(); while(itr.hasNext()) { //This Line I get false.. though i have list size is 1 Item p = (Item)itr.next(); if(p.getId() == null) {continue;} if(p.getId().getElemntId() == obj.getId() || obj.getId() == 0 ) { p.setResponse(obj); notifyAll(); return; } } Log.Error("validate failed obj.getId="+obj.getId()+" **list.size="+list.size()*This shows 1*); throw new Exception("InvalidData"); }

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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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  • Clean solution to this ruby iterator trickiness?

    - by mstksg
    k = [1,2,3,4,5] for n in k puts n if n == 2 k.delete(n) end end puts k.join(",") # Result: # 1 # 2 # 4 # 5 # [1,3,4,5] # Desired: # 1 # 2 # 3 # 4 # 5 # [1,3,4,5] This same effect happens with the other array iterator, k.each: k = [1,2,3,4,5] k.each do |n| puts n if n == 2 k.delete(n) end end puts k.join(",") has the same output. The reason this is happening is pretty clear...Ruby doesn't actually iterate through the objects stored in the array, but rather just turns it into a pretty array index iterator, starting at index 0 and each time increasing the index until it's over. But when you delete an item, it still increments the index, so it doesn't evaluate the same index twice, which I want it to. This might not be what's happening, but it's the best I can think of. Is there a clean way to do this? Is there already a built-in iterator that can do this? Or will I have to dirty it up and do an array index iterator, and not increment when the item is deleted?

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  • How to implement iterator as an attribute of a class in Java

    - by de3
    Hi, let's say I have this simple MyArray class, with two simple methods: add, delete and an iterator. In the main method we can see how it is supposed to be used: public class MyArray { int start; int end; int[] arr; myIterator it; public MyArray(){ this.start=0; this.end=0; this.arr=new int[500]; it=new myIterator(); } public void add(int el){ this.arr[this.end]=el; this.end++; } public void delete(){ this.arr[this.start]=0; this.start++; } public static void main(String[] args){ MyArray m=new MyArray(); m.add(3); m.add(299); m.add(19); m.add(27); while(m.it.hasNext()){ System.out.println(m.it.next()); } } And then MyIterator should be implemented somehow: import java.util.Iterator; public class myIterator implements Iterator{ @Override public boolean hasNext() { // TODO Auto-generated method stub return false; } @Override public Object next() { // TODO Auto-generated method stub return null; } @Override public void remove() { // TODO Auto-generated method stub } } MyIterator should iterate arr from MyArray class, from start to end values; both are also attributes of MyArray. So, as MyIterator should use MyArray attributes, how should MyIterator be implemented? Perhaps I can send the current object in the initialization: it=new myIterator(this); But I guess it's not the best soultion. Or maybe MyArray itself should implement Iterator interface? How is this solved?

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  • Using an iterator without its container

    - by User1
    I am mixing some C and C++ libraries and have only a single pointer available to do some work in a callback function. All I need to do is iterate through a vector. Here's a simplified, untested example: bool call_back(void* data){ done=... if (!done) cout << *data++ << endl; return done; } Note that this function is in an extern "C" block in C++. call_back will be called until true is returned. I want it to cout the next element each time it's called. data is a pointer to something that I can pass from elsewhere in the code (an iterator in the above example, but can be anything). Something from data will likely be used to calculate done. I see two obvious options to give to data: Have data point to my vector. Have data point to an iterator of my vector. I can't use an iterator without having the .end() method available, right? I can't use a vector alone (unless maybe I start removing its data). I could make a struct with both vector and iterator, but is there a better way? What would you do?

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  • Java: why can't iterate over an iterator?

    - by noamtm
    I read http://stackoverflow.com/questions/839178/why-is-javas-iterator-not-an-iterable and http://stackoverflow.com/questions/27240/why-arent-enumerations-iterable, but I still don't understand why this: void foo(Iterator<X> it) { for (X x : it) { bar(x); baz(x); } } was not made possible. In other words, unless I'm missing something, the above could have been nice and valid syntactic sugar for: void foo(Iterator<X> it) { for (X x; it.hasNext();) { x = it.next(); bar(x); baz(x); } }

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  • Function template accepting nothing less than a bidirectional iterator or a pointer

    - by san
    I need a function template that accepts two iterators that could be pointers. If the two arguments are random_access iterators I want the return type to be an object of std::iterator<random_access_iterator_tag, ...> type else a std::iterator<bidirectional_iterator_tag, ...> type. I also want the code to refuse compilation if the arguments are neither a bidirectional iterator, nor a pointer. I cannot have dependency on third party libraries e.g. Boost Could you help me with the signature of this function so that it accepts bidirectional iterators as well as pointers, but not say input_iterator, output_iterator, forward_iterators. One partial solution I can think of is the following template<class T> T foo( T iter1, T iter2) { const T tmp1 = reverse_iterator<T>(iter1); const T tmp2 = reverse_iterator<T>(iter2); // do something } The idea is that if it is not bidirectional the compiler will not let me construct a reverse_iterator from it.

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  • How to convert c++ std::list element to multimap iterator

    - by user63898
    Hello all, I have std::list<multimap<std::string,std::string>::iterator> > Now i have new element: multimap<std::string,std::string>::value_type aNewMmapValue("foo1","test") I want to avoid the need to set temp multimap and do insert to the new element just to get its iterator back so i could to push it back to the: std::list<multimap<std::string,std::string>::iterator> > can i somehow avoid this creation of the temp multimap. Thanks

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  • How to crete a Java Iterator that throws IOException

    - by Antonio
    I'd like to implement an iterator that retrieves objects from disk/network. Iterator itr = getRemoteIterator(); while(itr.hasNext()) { Object element = itr.next(); System.out.print(element + " "); } However the problem is that hasNext() and next() methods of the Iterator object does not allow to throw IOException. Is there any other standard interface work around this issue? Desired code is: public interface RemoteIterator<E> { boolean hasNext() throws IOException; E next() throws IOException; void remove(); }

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  • Simple Introduction to using the Enterprise Manager SOA/BPM Facade API by Jaideep Ganguli

    - by JuergenKress
    There may be times when you need to expose just a small section of what is displayed in the Enterprise Manager console for SOA/BPM (EM console). A simple example can be where stakeholders on the systems integration or customer teams want to monitor a dashboard of statistics on how many instances of a composite have been created and how many have faulted. You can see this in the EM, as shown below Some of these stakeholders may not have knowledge of  EM console and they just want a quick view into the statistics, without having to navigate EM. This post describes how to use the Oracle Fusion Middleware Infrastructure Management Java API  for Oracle SOA Suite (also called the Facade API)  to build a custom ADF page to display this information. If you want a quick introduction in using the Facade API, this post is for you. Read the complete article here. SOA & BPM Partner Community For regular information on Oracle SOA Suite become a member in the SOA & BPM Partner Community for registration please visit www.oracle.com/goto/emea/soa (OPN account required) If you need support with your account please contact the Oracle Partner Business Center. Blog Twitter LinkedIn Facebook Wiki Technorati Tags: Enterprise Manager,SOA Community,Oracle SOA,Oracle BPM,Community,OPN,Jürgen Kress

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  • how to use iterator in c++?

    - by tsubasa
    I'm trying to calculate distance between 2 points. The 2 points I stored in a vector in c++: (0,0) and (1,1). I'm supposed to get results as 0 1.4 1.4 0 but the actual result that I got is 0 1 -1 0 I think there's something wrong with the way I use iterator in vector. Could somebody help? I posted the code below. typedef struct point { float x; float y; } point; float distance(point *p1, point *p2) { return sqrt((p1->x - p2->x)*(p1->x - p2->x) + (p1->y - p2->y)*(p1->y - p2->y)); } int main() { vector <point> po; point p1; p1.x=0; p1.y=0; point p2; p2.x=1; p2.y=1; po.push_back(p1); po.push_back(p2); vector <point>::iterator ii; vector <point>::iterator jj; for (ii=po.begin(); ii!=po.end(); ii++) { for (jj=po.begin(); jj!=po.end(); jj++) { cout<<distance(ii,jj)<<" "; } } return 0; }

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  • [c++/STL] Selective iterator

    - by rubenvb
    FYI: no boost, yes it has this, I want to reinvent the wheel ;) Is there some form of a selective iterator (possible) in C++? What I want is to seperate strings like this: some:word{or other to a form like this: some : word { or other I can do that with two loops and find_first_of(":") and ("{") but this seems (very) inefficient to me. I thought that maybe there would be a way to create/define/write an iterator that would iterate over all these values with for_each. I fear this will have me writing a full-fledged custom way-too-complex iterator class for a std::string. So I thought maybe this would do: std::vector<size_t> list; size_t index = mystring.find(":"); while( index != std::string::npos ) { list.push_back(index); index = mystring.find(":", list.back()); } std::for_each(list.begin(), list.end(), addSpaces(mystring)); This looks messy to me, and I'm quite sure a more elegant way of doing this exists. But I can't think of it. Anyone have a bright idea? Thanks PS: I did not test the code posted, just a quick write-up of what I would try

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  • parallel computation for an Iterator of elements in Java

    - by Brian Harris
    I've had the same need a few times now and wanted to get other thoughts on the right way to structure a solution. The need is to perform some operation on many elements on many threads without needing to have all elements in memory at once, just the ones under computation. As in, Iterables.partition is insufficient because it brings all elements into memory up front. Expressing it in code, I want to write a BulkCalc2 that does the same thing as BulkCalc1, just in parallel. Below is sample code that illustrates my best attempt. I'm not satisfied because it's big and ugly, but it does seem to accomplish my goals of keeping threads highly utilized until the work is done, propagating any exceptions during computation, and not having more than numThreads instances of BigThing necessarily in memory at once. I'll accept the answer which meets the stated goals in the most concise way, whether it's a way to improve my BulkCalc2 or a completely different solution. interface BigThing { int getId(); String getString(); } class Calc { // somewhat expensive computation double calc(BigThing bigThing) { Random r = new Random(bigThing.getString().hashCode()); double d = 0; for (int i = 0; i < 100000; i++) { d += r.nextDouble(); } return d; } } class BulkCalc1 { final Calc calc; public BulkCalc1(Calc calc) { this.calc = calc; } public TreeMap<Integer, Double> calc(Iterator<BigThing> in) { TreeMap<Integer, Double> results = Maps.newTreeMap(); while (in.hasNext()) { BigThing o = in.next(); results.put(o.getId(), calc.calc(o)); } return results; } } class SafeIterator<T> { final Iterator<T> in; SafeIterator(Iterator<T> in) { this.in = in; } synchronized T nextOrNull() { if (in.hasNext()) { return in.next(); } return null; } } class BulkCalc2 { final Calc calc; final int numThreads; public BulkCalc2(Calc calc, int numThreads) { this.calc = calc; this.numThreads = numThreads; } public TreeMap<Integer, Double> calc(Iterator<BigThing> in) { ExecutorService e = Executors.newFixedThreadPool(numThreads); List<Future<?>> futures = Lists.newLinkedList(); final Map<Integer, Double> results = new MapMaker().concurrencyLevel(numThreads).makeMap(); final SafeIterator<BigThing> it = new SafeIterator<BigThing>(in); for (int i = 0; i < numThreads; i++) { futures.add(e.submit(new Runnable() { @Override public void run() { while (true) { BigThing o = it.nextOrNull(); if (o == null) { return; } results.put(o.getId(), calc.calc(o)); } } })); } e.shutdown(); for (Future<?> future : futures) { try { future.get(); } catch (InterruptedException ex) { // swallowing is OK } catch (ExecutionException ex) { throw Throwables.propagate(ex.getCause()); } } return new TreeMap<Integer, Double>(results); } }

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  • Is there a writable iterator in Java?

    - by Lukasz Lew
    In C+ one can use iterators for writing to a sequence. Simplest example would be: vector<int> v; for (vector<int>::iterator it = v.begin(); it!=v.end(); ++it) { *it = 42; } I need something more complicated - keep iterator as a class member for a later use. But I don't know how to get this behavior from Java iterators. Are there writable iterators in Java at all? If not then what replaces them?

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  • Custom iterator for dictionary?

    - by aaginor
    Hi folks, in my C#-Application, I have a Dictionary object. When iterating over the object using foreach, I naturally get each element of the dictionary. But I want only certain elements to be iterated, depending on the value of a property of MyValue. class MyValue { public bool AmIIncludedInTheIteration { get; set; } ... } Whenever AmIIncludedInTheIteration is false, the item shall not be returned by foreach. I understand that I need to implement my own iterator and override the Dictionary-Iterator somewhere. Can anyone here give me a short HowTo? Thanks in advance, Frank

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  • Building a custom iterator.

    - by Isai
    I am making this class which is a custom Map based off a hash map. I have an add method where if you add an object the object will be the key, and its value will be 1 if the object is not currently in the list. However if you add object that is currently in the list its value will be bumped up by 1. So if I added 10 strings which were all the same, the key would be that string and the value will be 10. I understand in practice when I iterate through the map, there is actually only one object to iterate, however, I am trying to create a inner class that will define an iterator that will iterate the same object however many times its value is. I can do this by simply using for loops to construct an appropriate ArrayList and just create an iterator for that, but that is too inefficient. Is there an easy or more efficient way of doing this?

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  • Strange iterator's behaviour;

    - by A-ha
    #include "stdafx.h" int _tmain(int argc, _TCHAR* argv[]) { string s = "Haven't got an idea why."; auto beg = s.begin(); auto end = s.end(); while (beg < end) { cout << *beg << '\n'; if (*beg == 'a') {//whithout if construct it works perfectly beg = s.erase(beg); } ++beg; } return 0; } Why if I erase one or more chars from this string this code breaks? I suppose it has something to do with returned iterator after erase operation being created at higher address than end iterator but I'm not sure and it surely isn't right behaviour. Or is it?

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  • Strange iterator behaviour

    - by A-ha
    #include "stdafx.h" int _tmain(int argc, _TCHAR* argv[]) { string s = "Haven't got an idea why."; auto beg = s.begin(); auto end = s.end(); while (beg < end) { cout << *beg << '\n'; if (*beg == 'a') {//whithout if construct it works perfectly beg = s.erase(beg); } ++beg; } return 0; } Why if I erase one or more chars from this string this code breaks? I suppose it has something to do with returned iterator after erase operation being created at higher address than end iterator but I'm not sure and it surely isn't right behaviour. Or is it?

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  • std::vector iterator or index access speed question

    - by Simone Margaritelli
    Just a stupid question . I have a std::vector<SomeClass *> v; in my code and i need to access its elements very often in the program, looping them forward and backward . Which is the fastest access type between those two ? Iterator access std::vector<SomeClass *> v; std::vector<SomeClass *>::iterator i; std::vector<SomeClass *>::reverse_iterator j; // i loops forward, j loops backward for( i = v.begin(), j = v.rbegin(); i != v.end() && j != v.rend(); i++, j++ ){ // some operations on v items } Subscript access (by index) std::vector<SomeClass *> v; unsigned int i, j, size = v.size(); // i loops forward, j loops backward for( i = 0, j = size - 1; i < size && j >= 0; i++, j-- ){ // some operations on v items } And, does const_iterator offer a faster way to access vector elements in case i do not have to modify them? Thank you in advantage.

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  • "end()" iterator for back inserters?

    - by Thanatos
    For iterators such as those returned from std::back_inserter(), is there something that can be used as an "end" iterator? This seems a little nonsensical at first, but I have an API which is: template<typename InputIterator, typename OutputIterator> void foo( InputIterator input_begin, InputIterator input_end, OutputIterator output_begin, OutputIterator output_end ); foo performs some operation on the input sequence, generating an output sequence. (Who's length is known to foo but may or may not be equal to the input sequence's length.) The taking of the output_end parameter is the odd part: std::copy doesn't do this, for example, and assumes you're not going to pass it garbage. foo does it to provide range checking: if you pass a range too small, it throws an exception, in the name of defensive programming. (Instead of potentially overwriting random bits in memory.) Now, say I want to pass foo a back inserter, specifically one from a std::vector which has no limit outside of memory constraints. I still need a "end" iterator - in this case, something that will never compare equal. (Or, if I had a std::vector but with a restriction on length, perhaps it might sometimes compare equal?) How do I go about doing this? I do have the ability to change foo's API - is it better to not check the range, and instead provide an alternate means to get the required output range? (Which would be needed anyways for raw arrays, but not required for back inserters into a vector.) This would seem less robust, but I'm struggling to make the "robust" (above) work.

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  • Guidelines to an Iterator Class

    - by isurulucky
    Hi, I have a Red Black tree implemented in c++. It supports the functionality of a STL map. Tree nodes contain keys and the values mapped. I want to write an iterator class for this, but I'm stuck with how to do it. Should I make it an inner class of the Tree class? Can anyone give me some guidelines on how to write it + some resources?? Thank You!!

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