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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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  • list of polymorphic objects

    - by LivingThing
    I have a particular scenario below. The code below should print 'say()' function of B and C class and print 'B says..' and 'C says...' but it doesn't .Any ideas.. I am learning polymorphism so also have commented few questions related to it on the lines of code below. class A { public: // A() {} virtual void say() { std::cout << "Said IT ! " << std::endl; } virtual ~A(); //why virtual destructor ? }; void methodCall() // does it matters if the inherited class from A is in this method { class B : public A{ public: // virtual ~B(); //significance of virtual destructor in 'child' class virtual void say () // does the overrided method also has to be have the keyword 'virtual' { cout << "B Sayssss.... " << endl; } }; class C : public A{ public: //virtual ~C(); virtual void say () { cout << "C Says " << endl; } }; list<A> listOfAs; list<A>::iterator it; # 1st scenario B bObj; C cObj; A *aB = &bObj; A *aC = &cObj; # 2nd scenario // A aA; // B *Ba = &aA; // C *Ca = &aA; // I am declaring the objects as in 1st scenario but how about 2nd scenario, is this suppose to work too? listOfAs.insert(it,*aB); listOfAs.insert(it,*aC); for (it=listOfAs.begin(); it!=listOfAs.end(); it++) { cout << *it.say() << endl; } } int main() { methodCall(); retrun 0; }

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  • c# reflection - getting the first item out of a reflected collection without casting to specific col

    - by Andy Clarke
    Hi, I've got a Customer object with a Collection of CustomerContacts IEnumerable Contacts { get; set; } In some other code I'm using Reflection and have the PropertyInfo of Contacts property var contacts = propertyInfo.GetValue(customerObject, null); I know contacts has at least one object in it, but how do I get it out? I don't want to Cast it to IEnumerable because I want to keep my reflection method dynamic. I thought about calling FirstOrDefault() by reflection - but can't do that easily because its an extension method. Does anyone have any ideas? Thanks

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  • Is an "infinite" iterator bad design?

    - by Adamski
    Is it generally considered bad practice to provide Iterator implementations that are "infinite"; i.e. where calls to hasNext() always(*) return true? Typically I'd say "yes" because the calling code could behave erratically, but in the below implementation hasNext() will return true unless the caller removes all elements from the List that the iterator was initialised with; i.e. there is a termination condition. Do you think this is a legitimate use of Iterator? It doesn't seem to violate the contract although I suppose one could argue it's unintuitive. public class CyclicIterator<T> implements Iterator<T> { private final List<T> l; private Iterator it; public CyclicIterator<T>(List<T> l) { this.l = l; this.it = l.iterator(); } public boolean hasNext() { return !l.isEmpty(); } public T next() { T ret; if (!hasNext()) { throw new NoSuchElementException(); } else if (it.hasNext()) { ret = it.next(); } else { it = l.iterator(); ret = it.next(); } return ret; } public void remove() { it.remove(); } }

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  • Performance for myCollection.Add() vs. myCollection["key"]

    - by Atomiton
    When dealing with a collection of key/value pairs is there any difference between using its Add() method and directly assigning it? For example, a HtmlGenericControl will have an Attributes Collection: var anchor = new HtmlGenericControl("a"); // These both work: anchor.Attributes.Add("class", "xyz"); anchor.Attributes["class"] = "xyz"; Is it purely a matter of preference, or is there a reason for doing one or the other?

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  • Using boost::random as the RNG for std::random_shuffle

    - by Greg Rogers
    I have a program that uses the mt19937 random number generator from boost::random. I need to do a random_shuffle and want the random numbers generated for this to be from this shared state so that they can be deterministic with respect to the mersenne twister's previously generated numbers. I tried something like this: void foo(std::vector<unsigned> &vec, boost::mt19937 &state) { struct bar { boost::mt19937 &_state; unsigned operator()(unsigned i) { boost::uniform_int<> rng(0, i - 1); return rng(_state); } bar(boost::mt19937 &state) : _state(state) {} } rand(state); std::random_shuffle(vec.begin(), vec.end(), rand); } But i get a template error calling random_shuffle with rand. However this works: unsigned bar(unsigned i) { boost::mt19937 no_state; boost::uniform_int<> rng(0, i - 1); return rng(no_state); } void foo(std::vector<unsigned> &vec, boost::mt19937 &state) { std::random_shuffle(vec.begin(), vec.end(), bar); } Probably because it is an actual function call. But obviously this doesn't keep the state from the original mersenne twister. What gives? Is there any way to do what I'm trying to do without global variables?

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  • Higher order function « filter » in C++

    - by Red Hyena
    Hi all. I wanted to write a higher order function filter with C++. The code I have come up with so far is as follows: #include <iostream> #include <string> #include <functional> #include <algorithm> #include <vector> #include <list> #include <iterator> using namespace std; bool isOdd(int const i) { return i % 2 != 0; } template < template <class, class> class Container, class Predicate, class Allocator, class A > Container<A, Allocator> filter(Container<A, Allocator> const & container, Predicate const & pred) { Container<A, Allocator> filtered(container); container.erase(remove_if(filtered.begin(), filtered.end(), pred), filtered.end()); return filtered; } int main() { int const a[] = {23, 12, 78, 21, 97, 64}; vector<int const> const v(a, a + 6); vector<int const> const filtered = filter(v, isOdd); copy(filtered.begin(), filtered.end(), ostream_iterator<int const>(cout, " ")); } However on compiling this code, I get the following error messages that I am unable to understand and hence get rid of: /usr/include/c++/4.3/ext/new_allocator.h: In instantiation of ‘__gnu_cxx::new_allocator<const int>’: /usr/include/c++/4.3/bits/allocator.h:84: instantiated from ‘std::allocator<const int>’ /usr/include/c++/4.3/bits/stl_vector.h:75: instantiated from ‘std::_Vector_base<const int, std::allocator<const int> >’ /usr/include/c++/4.3/bits/stl_vector.h:176: instantiated from ‘std::vector<const int, std::allocator<const int> >’ Filter.cpp:29: instantiated from here /usr/include/c++/4.3/ext/new_allocator.h:82: error: ‘const _Tp* __gnu_cxx::new_allocator<_Tp>::address(const _Tp&) const [with _Tp = const int]’ cannot be overloaded /usr/include/c++/4.3/ext/new_allocator.h:79: error: with ‘_Tp* __gnu_cxx::new_allocator<_Tp>::address(_Tp&) const [with _Tp = const int]’ Filter.cpp: In function ‘Container<A, Allocator> filter(const Container<A, Allocator>&, const Predicate&) [with Container = std::vector, Predicate = bool ()(int), Allocator = std::allocator<const int>, A = const int]’: Filter.cpp:30: instantiated from here Filter.cpp:23: error: passing ‘const std::vector<const int, std::allocator<const int> >’ as ‘this’ argument of ‘__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> > std::vector<_Tp, _Alloc>::erase(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, __gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >) [with _Tp = const int, _Alloc = std::allocator<const int>]’ discards qualifiers /usr/include/c++/4.3/bits/stl_algo.h: In function ‘_FIter std::remove_if(_FIter, _FIter, _Predicate) [with _FIter = __gnu_cxx::__normal_iterator<const int*, std::vector<const int, std::allocator<const int> > >, _Predicate = bool (*)(int)]’: Filter.cpp:23: instantiated from ‘Container<A, Allocator> filter(const Container<A, Allocator>&, const Predicate&) [with Container = std::vector, Predicate = bool ()(int), Allocator = std::allocator<const int>, A = const int]’ Filter.cpp:30: instantiated from here /usr/include/c++/4.3/bits/stl_algo.h:821: error: assignment of read-only location ‘__result.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = const int*, _Container = std::vector<const int, std::allocator<const int> >]()’ /usr/include/c++/4.3/ext/new_allocator.h: In member function ‘void __gnu_cxx::new_allocator<_Tp>::deallocate(_Tp*, size_t) [with _Tp = const int]’: /usr/include/c++/4.3/bits/stl_vector.h:150: instantiated from ‘void std::_Vector_base<_Tp, _Alloc>::_M_deallocate(_Tp*, size_t) [with _Tp = const int, _Alloc = std::allocator<const int>]’ /usr/include/c++/4.3/bits/stl_vector.h:136: instantiated from ‘std::_Vector_base<_Tp, _Alloc>::~_Vector_base() [with _Tp = const int, _Alloc = std::allocator<const int>]’ /usr/include/c++/4.3/bits/stl_vector.h:286: instantiated from ‘std::vector<_Tp, _Alloc>::vector(_InputIterator, _InputIterator, const _Alloc&) [with _InputIterator = const int*, _Tp = const int, _Alloc = std::allocator<const int>]’ Filter.cpp:29: instantiated from here /usr/include/c++/4.3/ext/new_allocator.h:98: error: invalid conversion from ‘const void*’ to ‘void*’ /usr/include/c++/4.3/ext/new_allocator.h:98: error: initializing argument 1 of ‘void operator delete(void*)’ /usr/include/c++/4.3/bits/stl_algobase.h: In function ‘_OI std::__copy_move_a(_II, _II, _OI) [with bool _IsMove = false, _II = const int*, _OI = const int*]’: /usr/include/c++/4.3/bits/stl_algobase.h:435: instantiated from ‘_OI std::__copy_move_a2(_II, _II, _OI) [with bool _IsMove = false, _II = __gnu_cxx::__normal_iterator<const int*, std::vector<const int, std::allocator<const int> > >, _OI = __gnu_cxx::__normal_iterator<const int*, std::vector<const int, std::allocator<const int> > >]’ /usr/include/c++/4.3/bits/stl_algobase.h:466: instantiated from ‘_OI std::copy(_II, _II, _OI) [with _II = __gnu_cxx::__normal_iterator<const int*, std::vector<const int, std::allocator<const int> > >, _OI = __gnu_cxx::__normal_iterator<const int*, std::vector<const int, std::allocator<const int> > >]’ /usr/include/c++/4.3/bits/vector.tcc:136: instantiated from ‘__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> > std::vector<_Tp, _Alloc>::erase(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, __gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >) [with _Tp = const int, _Alloc = std::allocator<const int>]’ Filter.cpp:23: instantiated from ‘Container<A, Allocator> filter(const Container<A, Allocator>&, const Predicate&) [with Container = std::vector, Predicate = bool ()(int), Allocator = std::allocator<const int>, A = const int]’ Filter.cpp:30: instantiated from here /usr/include/c++/4.3/bits/stl_algobase.h:396: error: no matching function for call to ‘std::__copy_move<false, true, std::random_access_iterator_tag>::__copy_m(const int*&, const int*&, const int*&)’ Please tell me what I am doing wrong here and what is the correct way to achieve the kind of higher order polymorphism I want. Thanks.

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  • std::map operator[] and automatically created new objects

    - by thomas-gies
    I'm a little bit scared about something like this: std::map<DWORD, DWORD> tmap; tmap[0]+=1; tmap[0]+=1; tmap[0]+=1; Since DWORD's are not automatically initialized, I'm always afraid of tmap[0] being a random number that is incremented. How does the map know hot to initialize a DWORD if the runtime does not know how to do it? Is it guaranteed, that the result is always tmap[0] == 3?

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  • Load binary file using fstream

    - by Kirill V. Lyadvinsky
    I'm trying to load binary file using fstream in the following way: #include <iostream #include <fstream #include <iterator #include <vector using namespace std; int main() { basic_fstream<uint32_t file( "somefile.dat", ios::in|ios::binary ); vector<uint32_t buffer; buffer.assign( istream_iterator<uint32_t, uint32_t( file ), istream_iterator<uint32_t, uint32_t() ); cout << buffer.size() << endl; return 0; } But it doesn't work. In Ubuntu it crashed with std::bad_cast exception. In MSVC++ 2008 it just prints 0. I know that I could use file.read to load file, but I want to use iterator and operator>> to load parts of the file. Is that possible? Why the code above doesn't work?

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  • Method in ICollection in C# that adds all elements of another ICollection to it

    - by drasto
    Is there some method in ICollection in C# that would add all elements of another collection? Right now I have to always write foreach cycle for this: ICollection<Letter> allLetters = ... //some initalization ICollection<Letter> justWrittenLetters = ... //some initalization ... //some code, adding to elements to those ICollections foreach(Letter newLetter in justWrittenLetters){ allLetters.add(newLetter); } My question is, is there method that can replace that cycle? Like for example the method addAll(Collection c) in Java ? So I would write only something like: allLetters.addAll(justWrittenLetters);

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  • What is the big deal with IQueryable?

    - by jjr2527
    I've seen a lot of people talking about IQueryable and I haven't quite picked up on what all the buzz is about. I always work with generic List's and find they are very rich in the way you can "query" them and work with them, even run LINQ queries against them. So I'm wondering if there is a good reason to start considering a different default collection in my projects.

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  • How to traverse the item in the collection in a List or Observable collection?

    - by Ashish Ashu
    I have a collection that is binded to my Listview. I have provided options to user to "move up" "move down" the selected item in the list view. I have binded the selected item of the listview to my viewmodel, hence I get the item in the collection on which user want to do the operation. I have attached "move up" "move down" commands in my viewmodel. I want what is the best way to move up and down in the collection in the collection which is reflected in the list view. Please suggest.

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  • Getting a char array from a vector<int>?

    - by Legend
    I am trying to pass a value from C++ to TCL. As I cannot pass pointers without the use of some complicated modules, I was thinking of converting a vector to a char array and then passing this as a null terminated string (which is relatively easy). I have a vector as follows: 12, 32, 42, 84 which I want to convert into something like: "12 32 42 48" The approach I am thinking of is to use an iterator to iterate through the vector and then convert each integer into its string representation and then add it into a char array (which is dynamically created initially by passing the size of the vector). Is this the right way or is there a function that already does this?

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  • jquery-sortable using behavior of a linkedlist

    - by BabaBooey
    I suspect I'm not looking at this issue in the right way so here goes. I have essentially a LinkedList of data on a web page (http://en.wikipedia.org/wiki/Linked_list) that I'd like to manipulate using traditional Linked List behavior (i.e. just updating the reference/id of the "next" object) for performance reasons. Where this gets a bit tricky is I'd ideally like to use Jquery's sortable to do this. Like the user would drag something up/down and I could just do an Ajax call to the server with the id of the object that moved and the new parent id of that object (and then behind the scenes I could figure out how to reconnect things..maybe need more data than that...). But every example I've seen where sortable is used they were sending the whole re-indexed list to the database to update which seems unnecessary to me. With a linked list to change an element's "index" I only need to make 3 updates which depending on the size of the list could be a big performance savings. Anyone have an example of what I'm trying to do...am I too far in left field?

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  • operator<< cannot output std::endl -- Fix?

    - by dehmann
    The following code gives an error when it's supposed to output just std::endl: #include <iostream> #include <sstream> struct MyStream { std::ostream* out_; MyStream(std::ostream* out) : out_(out) {} std::ostream& operator<<(const std::string& s) { (*out_) << s; return *out_; } }; template<class OutputStream> struct Foo { OutputStream* out_; Foo(OutputStream* out) : out_(out) {} void test() { (*out_) << "OK" << std::endl; (*out_) << std::endl; // ERROR } }; int main(int argc, char** argv){ MyStream out(&std::cout); Foo<MyStream> foo(&out); foo.test(); return EXIT_SUCCESS; } The error is: stream1.cpp:19: error: no match for 'operator<<' in '*((Foo<MyStream>*)this)->Foo<MyStream>::out_ << std::endl' stream1.cpp:7: note: candidates are: std::ostream& MyStream::operator<<(const std::string&) So it can output a string (see line above the error), but not just the std::endl, presumably because std::endl is not a string, but the operator<< definition asks for a string. Templating the operator<< didn't help: template<class T> std::ostream& operator<<(const T& s) { ... } How can I make the code work? Thanks!

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  • What's correct way to remove a boost::shared_ptr from a list?

    - by Catskul
    I have a std::list of boost::shared_ptr<T> and I want to remove an item from it but I only have a pointer of type T* which matches one of the items in the list. However I cant use myList.remove( tPtr ) I'm guessing because shared_ptr does not implement == for its template argument type. My immediate thought was to try myList.remove( shared_ptr<T>(tPtr) ) which is syntactically correct but it will crash from a double delete since the temporary shared_ptr has a separate use_count. std::list< boost::shared_ptr<T> > myList; T* tThisPtr = new T(); // This is wrong; only done for example code. // stand-in for actual code in T using // T's actual "this" pointer from within T { boost::shared_ptr<T> toAdd( tThisPtr ); // typically would be new T() myList.push_back( toAdd ); } { //T has pointer to myList so that upon a certain action, // it will remove itself romt the list //myList.remove( tThisPtr); //doesn't compile myList.remove( boost::shared_ptr<T>(tThisPtr) ); // compiles, but causes // double delete } The only options I see remaining are to use std::find with a custom compare, or to loop through the list brute force and find it myself, but it seems there should be a better way. Am I missing something obvious, or is this just too non-standard a use to be doing a remove the clean/normal way?

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  • Basic question about std::vector instantiation

    - by recipriversexclusion
    This looks simple but I am confused: The way I create a vector of hundred, say, ints is std::vector<int> *pVect = new std::vector<int>(100); However, looking at std::vector's documentation I see that its constructor is of the form explicit vector ( size_type n, const T& value= T(), const Allocator& = Allocator() ); So, how does the previous one work? Does new call the constructor with an initialization value obtained from the default constructor? If that is the case, would std::vector<int, my_allocator> *pVect = new std::vector<int>(100, my_allocator); where I pass my own allocator, also work?

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  • Remove Duplicates from List of HashMap Entries

    - by HonorGod
    I have a List<HashMap<String,Object>> which represents a database where each list record is a database row. I have 10 columns in my database. There are several rows where the values of 2 particular columns are equals. I need to remove the duplicates from the list after the list is updated with all the rows from database. What is the efficient way? FYI - I am not able to do distinct while querying the database, because the GroupName is added at a later stage to the Map after the database is loaded. And since Id column is not primary key, once you add GroupName to the Map. You will have duplicates based on Id + GroupName combination! Hope my question makes sense. Let me know if we need more clarification.

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  • remove specific values from multi value dictionary

    - by Anthony
    I've seen posts here on how to make a dictionary that has multiple values per key, like one of the solutions presented in this link: Multi Value Dictionary it seems that I have to use a List< as the value for the keys, so that a key can store multiple values. the solution in the link is fine if you want to add values. But my problem now is how to remove specific values from a single key. I have this code for adding values to a dictionary: private Dictionary<TKey, List<TValue>> mEventDict; // this is for initializing the dictionary public void Subscribe(eVtEvtId inEvent, VtEvtDelegate inCallbackMethod) { if (mEventDict.ContainsKey(inEvent)) { mEventDict[inEvent].Add(inCallbackMethod); } else { mEventDict.Add(inEvent, new List<TValue>() { v }); } } // this is for adding values to the dictionary. // if the "key" (inEvent) is not yet present in the dictionary, // the key will be added first before the value my problem now is removing a specific value from a key. I have this code: public void Unsubscribe(eVtEvtId inEvent, VtEvtDelegate inCallbackMethod) { try { mEventDict[inEvent].Remove(inCallbackMethod); } catch (ArgumentNullException) { MessageBox.Show("The event is not yet present in the dictionary"); } } basically, what I did is just replace the Add() with Remove() . Will this work? Also, if you have any problems or questions with the code (initialization, etc.), feel free to ask. Thanks for the advice.

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  • C++ min heap with user-defined type.

    - by bsg
    Hi, I am trying to implement a min heap in c++ for a struct type that I created. I created a vector of the type, but it crashed when I used make_heap on it, which is understandable because it doesn't know how to compare the items in the heap. How do I create a min-heap (that is, the top element is always the smallest one in the heap) for a struct type? The struct is below: struct DOC{ int docid; double rank; }; I want to compare the DOC structures using the rank member. How would I do this? I tried using a priority queue with a comparator class, but that also crashed, and it also seems silly to use a data structure which uses a heap as its underlying basis when what I really need is a heap anyway. Thank you very much, bsg

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  • Problem with std::map and std::pair

    - by Tom
    Hi everyone. I have a small program I want to execute to test something #include <map> #include <iostream> using namespace std; struct _pos{ float xi; float xf; bool operator<(_pos& other){ return this->xi < other.xi; } }; struct _val{ float f; }; int main() { map<_pos,_val> m; struct _pos k1 = {0,10}; struct _pos k2 = {10,15}; struct _val v1 = {5.5}; struct _val v2 = {12.3}; m.insert(std::pair<_pos,_val>(k1,v1)); m.insert(std::pair<_pos,_val>(k2,v2)); return 0; } The problem is that when I try to compile it, I get the following error $ g++ m2.cpp -o mtest In file included from /usr/include/c++/4.4/bits/stl_tree.h:64, from /usr/include/c++/4.4/map:60, from m2.cpp:1: /usr/include/c++/4.4/bits/stl_function.h: In member function ‘bool std::less<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = _pos]’: /usr/include/c++/4.4/bits/stl_tree.h:1170: instantiated from ‘std::pair<typename std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::iterator, bool> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_unique(const _Val&) [with _Key = _pos, _Val = std::pair<const _pos, _val>, _KeyOfValue = std::_Select1st<std::pair<const _pos, _val> >, _Compare = std::less<_pos>, _Alloc = std::allocator<std::pair<const _pos, _val> >]’ /usr/include/c++/4.4/bits/stl_map.h:500: instantiated from ‘std::pair<typename std::_Rb_tree<_Key, std::pair<const _Key, _Tp>, std::_Select1st<std::pair<const _Key, _Tp> >, _Compare, typename _Alloc::rebind<std::pair<const _Key, _Tp> >::other>::iterator, bool> std::map<_Key, _Tp, _Compare, _Alloc>::insert(const std::pair<const _Key, _Tp>&) [with _Key = _pos, _Tp = _val, _Compare = std::less<_pos>, _Alloc = std::allocator<std::pair<const _pos, _val> >]’ m2.cpp:30: instantiated from here /usr/include/c++/4.4/bits/stl_function.h:230: error: no match for ‘operator<’ in ‘__x < __y’ m2.cpp:9: note: candidates are: bool _pos::operator<(_pos&) $ I thought that declaring the operator< on the key would solve the problem, but its still there. What could be wrong? Thanks in advance.

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  • IList<Item> Collection Class accessing database

    - by Mike
    Hi, I have a database with Users. Users have Items. These Items can change actively. How do you access the items in a collection type format? For the user, I fill all the user properties at the time of instantiation. If I load the user's items at the time of the instantiation, and the items change, they will have old data. I was thinking, maybe I need an ItemCollection class and have that a field/property apart of the user class, that way to traverse all the user's items I could use a foreach loop. So, my question is, what is the best practice/best way of accessing the items from a database using some sort of collection? On accessing the particular Item, it needs to get the latest database information, and when the user does do a foreach loop, the latest item information must be available. I.e. What I'm trying to do Console.WriteLine(User.Items[3].ID); returns 5. //this updates the item information and saves it to the database. User.Items[3].ID = 13; //Add a new item to the database. User.Items.Add(new Item { id = 17}); foreach (Item item in User.Items) { //this would traverse all items in the database. //not some cached copy at the time of instantiation of the user. }

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