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  • Anonymous iterator blocks in Clojure?

    - by Checkers
    I am using clojure.contrib.sql to fetch some records from an SQLite database. (defn read-all-foo [] (with-connection *db* (with-query-results res ["select * from foo"] (into [] res)))) Now, I don't really want to realize the whole sequence before returning from the function (i.e. I want to keep it lazy), but if I return res directly or wrap it some kind of lazy wrapper (for example I want to make a certain map transformation on result sequence), SQL-related bindings will be reset and connection will be closed after I return, so realizing the sequence will throw an exception. How can I enclose the whole function in a closure and return a kind of anonymous iterator block (like yield in C# or Python)? Or is there another way to return a lazy sequence from this function?

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  • Vector.erase(Iterator) causes bad memory access

    - by xon1c
    Hi, I am trying to do a Z-Index reordering of videoObjects stored in a vector. The plan is to identify the videoObject which is going to be put on the first position of the vector, erase it and then insert it at the first position. Unfortunately the erase() function always causes bad memory access. Here is my code: testApp.h: vector<videoObject> videoObjects; vector<videoObject>::iterator itVid; testApp.cpp: // Get the videoObject which relates to the user event for(itVid = videoObjects.begin(); itVid != videoObjects.end(); ++itVid){ if(videoObjects.at(itVid - videoObjects.begin()).isInside(ofPoint(tcur.getX(), tcur.getY()))){ videoObjects.erase(itVid); } } This should be so simple but I just don't see where I'm taking the wrong turn. Thx, xonic

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  • Iterator to last element in std::list

    - by Dave18
    #include <list> using std::list; int main() { list <int> n; n.push_back(1); n.push_back(2); n.push_back(3); list <int>::iterator iter = n.begin(); std::advance(iter, n.size() - 1); //iter is set to last element } is there any other way to have an iter to the last element in list?

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  • Input Iterator for a shared_ptr

    - by Baz
    I have an iterator which contains the following functions: ... T &operator*() { return *_i; } std::shared_ptr<T> operator->() { return _i; } private: std::shared_ptr<T> _i; ... How do I get a shared pointer to the internally stored _i? std::shared_ptr<Type> item = ??? Should I do: MyInterfaceIterator<Type> i; std::shared_ptr<Type> item = i.operator->(); Or should I rewrite operator*()?

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  • Trying to find USB device on iphone with IOKit.framework

    - by HuGeek
    Hi all, i'm working on a project were i need the usb port to communicate with a external device. I have been looking for exemple on the net (Apple and /developer/IOKit/usb exemple) and trying some other but i can't even find the device. In my code i blocking at the place where the fucntion looks for a next iterator (pointer in fact) with the function getNextIterator but never returns a good value so the code is blocking. By the way i am using toolchain and added IOKit.framework in my project. All i what right now is the communicate or do like a ping to someone on the USB bus!! I blocking in the 'FindDevice'....i can't manage to enter in the while because the variable usbDevice is always = to 0....i have tested my code in a small mac program and it works... Thanks Here is my code : IOReturn ConfigureDevice(IOUSBDeviceInterface **dev) { UInt8 numConfig; IOReturn result; IOUSBConfigurationDescriptorPtr configDesc; //Get the number of configurations result = (*dev)->GetNumberOfConfigurations(dev, &numConfig); if (!numConfig) { return -1; } // Get the configuration descriptor result = (*dev)->GetConfigurationDescriptorPtr(dev, 0, &configDesc); if (result) { NSLog(@"Couldn't get configuration descriptior for index %d (err=%08x)\n", 0, result); return -1; } ifdef OSX_DEBUG NSLog(@"Number of Configurations: %d\n", numConfig); endif // Configure the device result = (*dev)->SetConfiguration(dev, configDesc->bConfigurationValue); if (result) { NSLog(@"Unable to set configuration to value %d (err=%08x)\n", 0, result); return -1; } return kIOReturnSuccess; } IOReturn FindInterfaces(IOUSBDeviceInterface *dev, IOUSBInterfaceInterface **itf) { IOReturn kr; IOUSBFindInterfaceRequest request; io_iterator_t iterator; io_service_t usbInterface; IOUSBInterfaceInterface **intf = NULL; IOCFPlugInInterface **plugInInterface = NULL; HRESULT res; SInt32 score; UInt8 intfClass; UInt8 intfSubClass; UInt8 intfNumEndpoints; int pipeRef; CFRunLoopSourceRef runLoopSource; NSLog(@"Debut FindInterfaces \n"); request.bInterfaceClass = kIOUSBFindInterfaceDontCare; request.bInterfaceSubClass = kIOUSBFindInterfaceDontCare; request.bInterfaceProtocol = kIOUSBFindInterfaceDontCare; request.bAlternateSetting = kIOUSBFindInterfaceDontCare; kr = (*dev)->CreateInterfaceIterator(dev, &request, &iterator); usbInterface = IOIteratorNext(iterator); IOObjectRelease(iterator); NSLog(@"Interface found.\n"); kr = IOCreatePlugInInterfaceForService(usbInterface, kIOUSBInterfaceUserClientTypeID, kIOCFPlugInInterfaceID, &plugInInterface, &score); kr = IOObjectRelease(usbInterface); // done with the usbInterface object now that I have the plugin if ((kIOReturnSuccess != kr) || !plugInInterface) { NSLog(@"unable to create a plugin (%08x)\n", kr); return -1; } // I have the interface plugin. I need the interface interface res = (*plugInInterface)->QueryInterface(plugInInterface, CFUUIDGetUUIDBytes(kIOUSBInterfaceInterfaceID), (LPVOID*) &intf); (*plugInInterface)->Release(plugInInterface); // done with this if (res || !intf) { NSLog(@"couldn't create an IOUSBInterfaceInterface (%08x)\n", (int) res); return -1; } // Now open the interface. This will cause the pipes to be instantiated that are // associated with the endpoints defined in the interface descriptor. kr = (*intf)->USBInterfaceOpen(intf); if (kIOReturnSuccess != kr) { NSLog(@"unable to open interface (%08x)\n", kr); (void) (*intf)->Release(intf); return -1; } kr = (*intf)->CreateInterfaceAsyncEventSource(intf, &runLoopSource); if (kIOReturnSuccess != kr) { NSLog(@"unable to create async event source (%08x)\n", kr); (void) (*intf)->USBInterfaceClose(intf); (void) (*intf)->Release(intf); return -1; } CFRunLoopAddSource(CFRunLoopGetCurrent(), runLoopSource, kCFRunLoopDefaultMode); if (!intf) { NSLog(@"Interface is NULL!\n"); } else { *itf = intf; } NSLog(@"End of FindInterface \n \n"); return kr; } unsigned int FindDevice(void *refCon, io_iterator_t iterator) { kern_return_t kr; io_service_t usbDevice; IOCFPlugInInterface **plugInInterface = NULL; HRESULT result; SInt32 score; UInt16 vendor; UInt16 product; UInt16 release; unsigned int count = 0; NSLog(@"Searching Device....\n"); while (usbDevice = IOIteratorNext(iterator)) { // create intermediate plug-in NSLog(@"Found a device!\n"); kr = IOCreatePlugInInterfaceForService(usbDevice, kIOUSBDeviceUserClientTypeID, kIOCFPlugInInterfaceID, &plugInInterface, &score); kr = IOObjectRelease(usbDevice); if ((kIOReturnSuccess != kr) || !plugInInterface) { NSLog(@"Unable to create a plug-in (%08x)\n", kr); continue; } // Now create the device interface result = (*plugInInterface)->QueryInterface(plugInInterface, CFUUIDGetUUIDBytes(kIOUSBDeviceInterfaceID), (LPVOID)&dev); // Don't need intermediate Plug-In Interface (*plugInInterface)->Release(plugInInterface); if (result || !dev) { NSLog(@"Couldn't create a device interface (%08x)\n", (int)result); continue; } // check these values for confirmation kr = (*dev)->GetDeviceVendor(dev, &vendor); kr = (*dev)->GetDeviceProduct(dev, &product); //kr = (*dev)->GetDeviceReleaseNumber(dev, &release); //if ((vendor != LegoUSBVendorID) || (product != LegoUSBProductID) || (release != LegoUSBRelease)) { if ((vendor != LegoUSBVendorID) || (product != LegoUSBProductID)) { NSLog(@"Found unwanted device (vendor = %d != %d, product = %d != %d, release = %d)\n", vendor, kUSBVendorID, product, LegoUSBProductID, release); (void) (*dev)-Release(dev); continue; } // Open the device to change its state kr = (*dev)->USBDeviceOpen(dev); if (kr == kIOReturnSuccess) { count++; } else { NSLog(@"Unable to open device: %08x\n", kr); (void) (*dev)->Release(dev); continue; } // Configure device kr = ConfigureDevice(dev); if (kr != kIOReturnSuccess) { NSLog(@"Unable to configure device: %08x\n", kr); (void) (*dev)->USBDeviceClose(dev); (void) (*dev)->Release(dev); continue; } break; } return count; } // USB rcx Init IOUSBInterfaceInterface** osx_usb_rcx_init (void) { CFMutableDictionaryRef matchingDict; kern_return_t result; IOUSBInterfaceInterface **intf = NULL; unsigned int device_count = 0; // Create master handler result = IOMasterPort(MACH_PORT_NULL, &gMasterPort); if (result || !gMasterPort) { NSLog(@"ERR: Couldn't create master I/O Kit port(%08x)\n", result); return NULL; } else { NSLog(@"Created Master Port.\n"); NSLog(@"Master port 0x:08X \n \n", gMasterPort); } // Set up the matching dictionary for class IOUSBDevice and its subclasses matchingDict = IOServiceMatching(kIOUSBDeviceClassName); if (!matchingDict) { NSLog(@"Couldn't create a USB matching dictionary \n"); mach_port_deallocate(mach_task_self(), gMasterPort); return NULL; } else { NSLog(@"USB matching dictionary : %08X \n", matchingDict); } CFDictionarySetValue(matchingDict, CFSTR(kUSBVendorID), CFNumberCreate(kCFAllocatorDefault, kCFNumberShortType, &LegoUSBVendorID)); CFDictionarySetValue(matchingDict, CFSTR(kUSBProductID), CFNumberCreate(kCFAllocatorDefault, kCFNumberShortType, &LegoUSBProductID)); result = IOServiceGetMatchingServices(gMasterPort, matchingDict, &gRawAddedIter); matchingDict = 0; // this was consumed by the above call // Iterate over matching devices to access already present devices NSLog(@"RawAddedIter : 0x:%08X \n", &gRawAddedIter); device_count = FindDevice(NULL, gRawAddedIter); if (device_count == 1) { result = FindInterfaces(dev, &intf); if (kIOReturnSuccess != result) { NSLog(@"unable to find interfaces on device: %08x\n", result); (*dev)-USBDeviceClose(dev); (*dev)-Release(dev); return NULL; } // osx_usb_rcx_wakeup(intf); return intf; } else if (device_count 1) { NSLog(@"too many matching devices (%d) !\n", device_count); } else { NSLog(@"no matching devices found\n"); } return NULL; } int main(int argc, char *argv[]) { int returnCode; NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; NSLog(@"Debut du programme \n \n"); osx_usb_rcx_init(); NSLog(@"Fin du programme \n \n"); return 0; // returnCode = UIApplicationMain(argc, argv, @"Untitled1App", @"Untitled1App"); // [pool release]; // return returnCode; }

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  • Error of iterator in mys JSP

    - by Mercer
    Hello, in my jsp i do this <table> <tr> <th>TITLLE</th> </tr> <tr class="row0"> <logic:iterate id="listClient" name="Client"> <td> [...] </td> </logic:iterate> </tr> </table> <logic:iterate id="listClient" name="Client"> <table> <tr> <td> [...] </td> </tr> </table> </logic:iterate> But i have this error for my second iterate javax.servlet.jsp.JspException: Cannot create iterator for this collection

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  • std::list iterator: get next element

    - by sheepsimulator
    I'm trying to build a string using data elements stored in a std::list, where I want commas placed only between the elements (ie, if elements are {A,B,C,D} in list, result string should be "A,B,C,D". This code does not work: typedef std::list< shared_ptr<EventDataItem> > DataItemList; // ... std::string Compose(DataItemList& dilList) { std::stringstream ssDataSegment; for(iterItems = dilList.begin(); iterItems != dilList.end(); iterItems++) { // Lookahead in list to see if next element is end if((iterItems + 1) == dilList.end()) { ssDataSegment << (*iterItems)->ToString(); } else { ssDataSegment << (*iterItems)->ToString() << ","; } } return ssDataSegment.str(); } How do I get at "the-next-item" in a std::list using an iterator? I would expect that it's a linked-list, why can't I get at the next item?

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  • C# iterator is executed twice when composing two IEnumerable methods

    - by achristoph
    I just started learning about C# iterator but got confused with the flow of the program after reading the output of the program. The foreach with uniqueVals seems to be executed twice. My understanding is that the first few lines up to the line before "Nums in Square: 3" should not be there. Can anyone help to explain why this happens? The output is: Unique: 1 Adding to uniqueVals: 1 Unique: 2 Adding to uniqueVals: 2 Unique: 2 Unique: 3 Adding to uniqueVals: 3 Nums in Square: 3 Unique: 1 Adding to uniqueVals: 1 Square: 1 Number returned from Unique: 1 Unique: 2 Adding to uniqueVals: 2 Square: 2 Number returned from Unique: 4 Unique: 2 Unique: 3 Adding to uniqueVals: 3 Square: 3 Number returned from Unique: 9 static class Program { public static IEnumerable<T> Unique<T>(IEnumerable<T> sequence) { Dictionary<T, T> uniqueVals = new Dictionary<T, T>(); foreach (T item in sequence) { Console.WriteLine("Unique: {0}", item); if (!uniqueVals.ContainsKey(item)) { Console.WriteLine("Adding to uniqueVals: {0}", item); uniqueVals.Add(item, item); yield return item; Console.WriteLine("After Unique yield: {0}", item); } } } public static IEnumerable<int> Square(IEnumerable<int> nums) { Console.WriteLine("Nums in Square: {0}", nums.Count()); foreach (int num in nums) { Console.WriteLine("Square: {0}", num); yield return num * num; Console.WriteLine("After Square yield: {0}", num); } } static void Main(string[] args) { var nums = new int[] { 1, 2, 2, 3 }; foreach (int num in Square(Unique(nums))) Console.WriteLine("Number returned from Unique: {0}", num); Console.Read(); } }

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  • Boost ASIO async_write "Vector iterator not dereferencable"

    - by xeross
    Hey, I've been working on an async boost server program, and so far I've got it to connect. However I'm now getting a "Vector iterator not dereferencable" error. I suspect the vector gets destroyed or dereferenced before he packet gets sent thus causing the error. void start() { Packet packet; packet.setOpcode(SMSG_PING); send(packet); } void send(Packet packet) { cout << "DEBUG> Transferring packet with opcode " << packet.GetOpcode() << endl; async_write(m_socket, buffer(packet.write()), boost::bind(&Session::writeHandler, shared_from_this(), placeholders::error, placeholders::bytes_transferred)); } void writeHandler(const boost::system::error_code& errorCode, size_t bytesTransferred) { cout << "DEBUG> Transfered " << bytesTransferred << " bytes to " << m_socket.remote_endpoint().address().to_string() << endl; } Start gets called once a connection is made. packet.write() returns a uint8_t vector Would it matter if I'd change void send(Packet packet) to void send(Packet& packet) Not in relation to this problem but performance wise.

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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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  • stringstream problem - vector iterator not dereferencable

    - by andreas
    Hello I've got a problem with the following code snippet. It is related to the stringstream "stringstream css(cv.back())" bit. If it is commented out the program will run ok. It is really weird, as I keep getting it in some of my programs, but if I just create a console project the code will run fine. In some of my Win32 programs it will and in some it won't (then it will return "vector iterator not dereferencable" but it will compile just fine). Any ideas at all would be really appreciated. Thanks! vector<double> cRes(2); vector<double> pRes(2); int readTimeVects2(vector<double> &cRes, vector<double> &pRes){ string segments; vector<string> cv, pv, chv, phv; ifstream cin("cm.txt"); ifstream pin("pw.txt"); ifstream chin("hm.txt"); ifstream phin("hw.txt"); while (getline(cin,segments,'\t')) { cv.push_back(segments); } while (getline(pin,segments,'\t')) { pv.push_back(segments); } while (getline(chin,segments,'\t')) { chv.push_back(segments); } while (getline(phin,segments,'\t')) { phv.push_back(segments); } cin.close(); pin.close(); chin.close(); phin.close(); stringstream phss(phv.front()); phss >> pRes[0]; phss.clear(); stringstream chss(chv.front()); chss >> cRes[0]; chss.clear(); stringstream pss(pv.back()); pss >> pRes[1]; pss.clear(); stringstream css(cv.back()); css >> cRes[1]; css.clear(); return 0; }

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  • How are iterators and pointers related?

    - by sharptooth
    Code with iterators looks pretty much like code with pointers. Iterators are of some obscure type (like std::vector<int>::iterator for example). What I don't get is how iterators and pointer are related to each other - is an iterator a wrapper around a pointer with overloaded operations to advance to adjacent elements or is it something else?

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  • multi_index composite_key replace with iterator

    - by Rohit
    Is there anyway to loop through an index in a boost::multi_index and perform a replace? #include <iostream> #include <string> #include <boost/multi_index_container.hpp> #include <boost/multi_index/composite_key.hpp> #include <boost/multi_index/member.hpp> #include <boost/multi_index/ordered_index.hpp> using namespace boost::multi_index; using namespace std; struct name_record { public: name_record(string given_name_,string family_name_,string other_name_) { given_name=given_name_; family_name=family_name_; other_name=other_name_; } string given_name; string family_name; string other_name; string get_name() const { return given_name + " " + family_name + " " + other_name; } void setnew(string chg) { given_name = given_name + chg; family_name = family_name + chg; } }; struct NameIndex{}; typedef multi_index_container< name_record, indexed_by< ordered_non_unique< tag<NameIndex>, composite_key < name_record, BOOST_MULTI_INDEX_MEMBER(name_record,string, name_record::given_name), BOOST_MULTI_INDEX_MEMBER(name_record,string, name_record::family_name) > > > > name_record_set; typedef boost::multi_index::index<name_record_set,NameIndex>::type::iterator IteratorType; typedef boost::multi_index::index<name_record_set,NameIndex>::type NameIndexType; void printContainer(name_record_set & ns) { cout << endl << "PrintContainer" << endl << "-------------" << endl; IteratorType it1 = ns.begin(); IteratorType it2 = ns.end (); while (it1 != it2) { cout<<it1->get_name()<<endl; it1++; } cout << "--------------" << endl << endl; } void modifyContainer(name_record_set & ns) { cout << endl << "ModifyContainer" << endl << "-------------" << endl; IteratorType it3; IteratorType it4; NameIndexType & idx1 = ns.get<NameIndex>(); IteratorType it1 = idx1.begin(); IteratorType it2 = idx1.end(); while (it1 != it2) { cout<<it1->get_name()<<endl; name_record nr = *it1; nr.setnew("_CHG"); bool res = idx1.replace(it1,nr); cout << "result is: " << res << endl; it1++; } cout << "--------------" << endl << endl; } int main() { name_record_set ns; ns.insert( name_record("Joe","Smith","ENTRY1") ); ns.insert( name_record("Robert","Brown","ENTRY2") ); ns.insert( name_record("Robert","Nightingale","ENTRY3") ); ns.insert( name_record("Marc","Tuxedo","ENTRY4") ); printContainer (ns); modifyContainer (ns); printContainer (ns); return 0; } PrintContainer ------------- Joe Smith ENTRY1 Marc Tuxedo ENTRY4 Robert Brown ENTRY2 Robert Nightingale ENTRY3 -------------- ModifyContainer ------------- Joe Smith ENTRY1 result is: 1 Marc Tuxedo ENTRY4 result is: 1 Robert Brown ENTRY2 result is: 1 -------------- PrintContainer ------------- Joe_CHG Smith_CHG ENTRY1 Marc_CHG Tuxedo_CHG ENTRY4 Robert Nightingale ENTRY3 Robert_CHG Brown_CHG ENTRY2 --------------

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  • private class calling a method from its outer class

    - by oxinabox.ucc.asn.au
    Ok, so I have a class for a "Advanced Data Structure" (in this case a kinda tree) SO I implimented a Iterator as a private class with in it. So the iterator needs to implement a remove function to remove the last retuirned element. now my ADT already impliments a remove function, and in this case there is very little (thinking about it, i think nothing) to be gain by implimenting a different remove function for the iterator. so how do I go about calling the remove from my ADT sketch of my struture: public class ADT { ... private class ADT_Iterator impliments java.util.Itorator{ ... public void remove(){ //where I want to call the ADT's remove function from } ... public void remove( Object paramFoo ) { ... } ... } So just calling remove(FooInstance) won't work (will it?) and this.remove(FooInstance) is the same thing. what do i call? (and changign the name of the ADT's remove function is not an option, as that AD T has to meet an Interace wich I am note at liberty to change) I could make both of them call a removeHelper functon, I guess...

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  • Pushing a vector into an vector

    - by Sunil
    I have a 2d vector typedef vector <double> record_t; typedef vector <record_t> data_t; data_t data; So my 2d vector is data here. It has elements like say, 1 1 1 1 1 2 2 2 2 2 3 3 3 3 3 4 4 4 4 4 5 5 5 5 5 Now I want to insert these elements into another 2d vector std::vector< vector<double> > window; So what I did was to create an iterator for traversing through the rows of data and pushing it into window like std::vector< std::vector<double> >::iterator data_it; for (data_it = data.begin() ; data_it != data.end() ; ++data_it){ window.push_back ( *data_it ); // Do something else } Can anybody tell me where I'm wrong or suggest a way to do this ? BTW I want to push it just element by element because I want to be able to do something else inside the loop too. i.e. I want to check for a condition and increment the value of the iterator inside. for example, if a condition satisfies then I'll do data_it+=3 or something like that inside the loop. Thanks P.S. I asked this question last night and didn't get any response and that's why I'm posting it again.

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  • Deleting elements from stl set while iterating through it does not invalidate the iterators.

    - by pedromanoel
    I need to go through a set and remove elements that meet a predefined criteria. This is the test code I wrote: #include <set> #include <algorithm> void printElement(int value) { std::cout << value << " "; } int main() { int initNum[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 }; std::set<int> numbers(initNum, initNum + 10); // print '0 1 2 3 4 5 6 7 8 9' std::for_each(numbers.begin(), numbers.end(), printElement); std::set<int>::iterator it = numbers.begin(); // iterate through the set and erase all even numbers for (; it != numbers.end(); ++it) { int n = *it; if (n % 2 == 0) { // wouldn't invalidate the iterator? numbers.erase(it); } } // print '1 3 5 7 9' std::for_each(numbers.begin(), numbers.end(), printElement); return 0; } At first, I thought that erasing an element from the set while iterating through it would invalidate the iterator, and the increment at the for loop would have undefined behavior. Even though, I executed this test code and all went well, and I can't explain why. My question: Is this the defined behavior for std sets or is this implementation specific? I am using gcc 4.3.3 on ubuntu 10.04 (32-bit version), by the way. Thanks!

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  • Recursive Iterators

    - by soandos
    I am having some trouble making an iterator that can traverse the following type of data structure. I have a class called Expression, which has one data member, a List<object>. This list can have any number of children, and some of those children might be other Expression objects. I want to traverse this structure, and print out every non-list object (but I do want to print out the elements of the list of course), but before entering a list, I want to return "begin nest" and after I just exited a list, I want to return "end nest". I was able to do this if I ignored the class wherever possible, and just had List<object> objects with List<object> items if I wanted a subExpression, but I would rather do away with this, and instead have an Expressions as the sublists (it would make it easier to do operations on the object. I am aware that I could use extension methods on the List<object> but it would not be appropriate (who wants an Evaluate method on their list that takes no arguments?). The code that I used to generate the origonal iterator (that works) is: public IEnumerator GetEnumerator(){ return theIterator(expr).GetEnumerator(); } private IEnumerable theIterator(object root) { if ((root is List<object>)){ yield return " begin nest "; foreach (var item in (List<object>)root){ foreach (var item2 in theIterator(item)){ yield return item2; } } yield return " end nest "; } else yield return root; } A type swap of List<object> for expression did not work, and lead to a stackOverflow error. How should the iterator be implemented? Update: Here is the swapped code: public IEnumerator GetEnumerator() { return this.GetEnumerator(); } private IEnumerable theIterator(object root) { if ((root is Expression)) { yield return " begin nest "; foreach (var item in (Expression)root) { foreach (var item2 in theIterator(item)) yield return item2; } yield return " end nest "; } else yield return root; }

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  • C++ -- typedef "inside" template arguments?

    - by redmoskito
    Imagine I have a template function like this: template<Iterator> void myfunc(Iterator a, Iterator::value_type b) { ... } Is there a way to declare a typedef for Iterator::valuetype that I can use in the function signature? For example: template< typename Iterator, typedef Iterator::value_type type> void myfunc(Iterator a, type b) { ... } Thus far, I've resorted to using default template arguments and Boost concept checking to ensure the default is always used: template< typename Iterator, typename type = Iterator::value_type > void myfunc(Iterator a, type b) { BOOST_STATIC_ASSERT(( boost::type_traits::is_same< typename Iterator::value_type, type >::value )); ... } ...but it would be nice if there was support in the language for this type of thing.

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  • C# iterator for async file copy

    - by uno
    Been running in circles to find the best solution for my client. We have a server that images are uploaded via ftp. I want to write an application that scans this server at frequent intervals and if it finds files it copies them to another,processing server. So if during a time cycle, my app finds that there are 100 files, i want to start copying as many files as i can across to the processing server i figured delegates would be the way to go but now i come across iterators...what do the experts say?

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  • Python iterator question

    - by hdx
    I have this list: names = ['john','Jonh','james','James','Jardel'] I want loop over the list and handle consecutive names with a case insensitive match in the same iteration. So in the first iteration I would do something with'john' and 'John' and I want the next iteration to start at 'james'. I can't think of a way to do this using Python's for loop, any suggestions?

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  • Is perl's each function worth using?

    - by eugene y
    From perldoc -f each we read: There is a single iterator for each hash, shared by all each, keys, and values function calls in the program; it can be reset by reading all the elements from the hash, or by evaluating keys HASH or values HASH. The iterator is not reset when you leave the scope containing the each(), and this can lead to bugs: my %h = map { $_, 1 } qw(1 2 3); while (my $k = each %h) { print "1: $k\n"; last } while (my $k = each %h) { print "2: $k\n" } Output: 1: 1 2: 3 2: 2 What are the common workarounds for this behavior? And is it worth using each in general?

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  • Is perl's each function worth using?

    - by eugene y
    From perldoc -f each we read: There is a single iterator for each hash, shared by all each, keys, and values function calls in the program; it can be reset by reading all the elements from the hash, or by evaluating keys HASH or values HASH. The iterator is not reset when you leave the scope containing the each(), and this can lead to bugs: my %h = map { $_, 1 } qw(1 2 3); while (my $k = each %h) { print "1: $k\n"; last } while (my $k = each %h) { print "2: $k\n" } Output: 1: 1 2: 3 2: 2 What are the common workarounds for this behavior? And is it worth using each in general?

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  • How to make a loop over all keys of a HashMap?

    - by Roman
    I try to do it in the following way: public String getValue(String service, String parameter) { String inputKey = service + ":" + parameter; Set keys = name2value.keySet(); Iterator itr = keys.iterator(); while (itr.hasNext()) { if (inputKey.equal(itr.next())) { return name2value.get(inputKey); } return ""; } } And I get an error message: cannot find symbol method.equal(java.lang.Object). I think it is because itr.next() is not considered as a string. How can I solve this problem? I tried to replace Set keys by Set<String> keys. It did not help.

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  • Container of shared_ptr's but iterate with raw pointers

    - by Sean Lynch
    I have a class that holds a list containing boost::shared_ptrs to objects of another class. The class member functions that give access to the elemets in the list return raw pointers. For consistency I'd also like to be able to iterate with raw pointers instead of shared_ptrs. So when I dereference the list iterator, I'd like to get raw pointer, not a shared_ptr. I assume I need to write a custom iterator for this. Is this correct? If so can someone point me in the right direction - I've never done this before.

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  • [struts 2] How do you iterate through a list of objects?

    - by Kevin
    I have a User class that has a String username in it. I have a list of users that I'm trying to display in a table using <s:iterator value="users" id="list"> <tr> <td><s:property value="#list.username" /></td> <td></td> <td></td> <td></td> </tr> </s:iterator> The rows are being displayed the right number of times, so it's iterating through my list properly. However, I don't know how to access the username property to display it. Obviously what I have above isn't correct... Any ideas?

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