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  • overloading new/delete problem

    - by hidayat
    This is my scenario, Im trying to overload new and delete globally. I have written my allocator class in a file called allocator.h. And what I am trying to achieve is that if a file is including this header file, my version of new and delete should be used. So in a header file "allocator.h" i have declared the two functions extern void* operator new(std::size_t size); extern void operator delete(void *p, std::size_t size); I the same header file I have a class that does all the allocator stuff, class SmallObjAllocator { ... }; I want to call this class from the new and delete functions and I would like the class to be static, so I have done this: template<unsigned dummy> struct My_SmallObjectAllocatorImpl { static SmallObjAllocator myAlloc; }; template<unsigned dummy> SmallObjAllocator My_SmallObjectAllocatorImpl<dummy>::myAlloc(DEFAULT_CHUNK_SIZE, MAX_OBJ_SIZE); typedef My_SmallObjectAllocatorImpl<0> My_SmallObjectAllocator; and in the cpp file it looks like this: allocator.cc void* operator new(std::size_t size) { std::cout << "using my new" << std::endl; if(size > MAX_OBJ_SIZE) return malloc(size); else return My_SmallObjectAllocator::myAlloc.allocate(size); } void operator delete(void *p, std::size_t size) { if(size > MAX_OBJ_SIZE) free(p); else My_SmallObjectAllocator::myAlloc.deallocate(p, size); } The problem is when I try to call the constructor for the class SmallObjAllocator which is a static object. For some reason the compiler are calling my overloaded function new when initializing it. So it then tries to use My_SmallObjectAllocator::myAlloc.deallocate(p, size); which is not defined so the program crashes. So why are the compiler calling new when I define a static object? and how can I solve it?

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  • Any way to allow classes implementing IEntity and downcast to have operator == comparisons?

    - by George Mauer
    Basically here's the issue. All entities in my system are identified by their type and their id. new Customer() { Id = 1} == new Customer() {Id = 1}; new Customer() { Id = 1} != new Customer() {Id = 2}; new Customer() { Id = 1} != new Product() {Id = 1}; Pretty standard scenario. Since all Entities have an Id I define an interface for all entities. public interface IEntity { int Id { get; set;} } And to simplify creation of entities I make public abstract class BaseEntity<T> : where T : IEntity { int Id { get; set;} public static bool operator ==(BaseEntity<T> e1, BaseEntity<T> e2) { if (object.ReferenceEquals(null, e1)) return false; return e1.Equals(e2); } public static bool operator !=(BaseEntity<T> e1, BaseEntity<T> e2) { return !(e1 == e2); } } where Customer and Product are something like public class Customer : BaseEntity<Customer>, IEntity {} public class Product : BaseEntity<Product>, IEntity {} I think this is hunky dory. I think all I have to do is override Equals in each entity (if I'm super clever, I can even override it only once in the BaseEntity) and everything with work. So now I'm expanding my test coverage and find that its not quite so simple! First of all , when downcasting to IEntity and using == the BaseEntity< override is not used. So what's the solution? Is there something else I can do? If not, this is seriously annoying. Upadate It would seem that there is something wrong with my tests - or rather with comparing on generics. Check this out [Test] public void when_created_manually_non_generic() { // PASSES! var e1 = new Terminal() {Id = 1}; var e2 = new Terminal() {Id = 1}; Assert.IsTrue(e1 == e2); } [Test] public void when_created_manually_generic() { // FAILS! GenericCompare(new Terminal() { Id = 1 }, new Terminal() { Id = 1 }); } private void GenericCompare<T>(T e1, T e2) where T : class, IEntity { Assert.IsTrue(e1 == e2); } Whats going on here? This is not as big a problem as I was afraid, but is still quite annoying and a completely unintuitive way for the language to behave. Update Update Ah I get it, the generic implicitly downcasts to IEntity for some reason. I stand by this being unintuitive and potentially problematic for my Domain's consumers as they need to remember that anything happening within a generic method or class needs to be compared with Equals()

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  • Calling all the 3 functions while using or operator even after returning true as a result.

    - by Shantanu Gupta
    I am calling three functions in my code where i want to validate some of my fields. When I tries to work with the code given below. It checks only for first value until it gets false result. I want some thing like that if fisrt function returns true then it should also call next function and so on. What can be used instead of Or Operator to do this. if (IsFieldEmpty(ref txtFactoryName, true, "Required") || IsFieldEmpty(ref txtShortName, true, "Required") || IsFieldEmpty(ref cboGodown, true, "Required")) { }

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  • Visitor and templated virtual methods

    - by Thomas Matthews
    In a typical implementation of the Visitor pattern, the class must account for all variations (descendants) of the base class. There are many instances where the same method content in the visitor is applied to the different methods. A templated virtual method would be ideal in this case, but for now, this is not allowed. So, can templated methods be used to resolve virtual methods of the parent class? Given (the foundation): struct Visitor_Base; // Forward declaration. struct Base { virtual accept_visitor(Visitor_Base& visitor) = 0; }; // More forward declarations struct Base_Int; struct Base_Long; struct Base_Short; struct Base_UInt; struct Base_ULong; struct Base_UShort; struct Visitor_Base { virtual void operator()(Base_Int& b) = 0; virtual void operator()(Base_Long& b) = 0; virtual void operator()(Base_Short& b) = 0; virtual void operator()(Base_UInt& b) = 0; virtual void operator()(Base_ULong& b) = 0; virtual void operator()(Base_UShort& b) = 0; }; struct Base_Int : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_Long : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_Short : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_UInt : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_ULong : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_UShort : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; Now that the foundation is laid, here is where the kicker comes in (templated methods): struct Visitor_Cout : public Visitor { template <class Receiver> void operator() (Receiver& r) { std::cout << "Visitor_Cout method not implemented.\n"; } }; Intentionally, Visitor_Cout does not contain the keyword virtual in the method declaration. All the other attributes of the method signatures match the parent declaration (or perhaps specification). In the big picture, this design allows developers to implement common visitation functionality that differs only by the type of the target object (the object receiving the visit). The implementation above is my suggestion for alerts when the derived visitor implementation hasn't implement an optional method. Is this legal by the C++ specification? (I don't trust when some says that it works with compiler XXX. This is a question against the general language.)

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  • C++ Code Clarification Needed..

    - by ke3pup
    Hi guys I'm trying to understand what the code below says: struct compare_pq; struct compare_pq { bool operator() (Events *& a, Events *& b); }; std::priority_queue<Events *, std::vector<Events *>, compare_pq> eventList; i looked at what priority_queue is and how its declared but can't quit understand what compare_pq is doing in the priority_queue eventList. Also what does operator() do since i've never seen *& before and empty operator overloading operator()! any help would be appreciated. Thank you

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  • Polynomial operations using operator overloading

    - by Vlad
    I'm trying to use operator overloading to define the basic operations (+,-,*,/) for my polynomial class but when i run the program it crashes and my computer frozes. Update3 Ok i successfully done the first two operations(+,-). Now at multiplication, after multiplying each term of the first polynomial with each of the second i want to sort the poly list descending and then if there are more than one term with the same power to merge them in only one term, but for some reason it doesn't compile because of the sort function which doesn't work. Here's what I got: polinom operator*(const polinom& P) const { polinom Result; constIter i, j, lastItem = Result.poly.end(); Iter it1, it2; int nr_matches; for (i = poly.begin() ; i != poly.end(); i++) { for (j = P.poly.begin(); j != P.poly.end(); j++) Result.insert(i->coef * j->coef, i->pow + j->pow); } sort(Result.poly.begin(), Result.poly.end(), SortDescending()); lastItem--; while (true) { nr_matches = 0; for (it1 = Result.poly.begin(); it < lastItem; it1++) { for (it2 = it1 + 1;; it2 <= lastItem; it2++){ if (it2->pow == it1->pow) { it1->coef += it2->coef; nr_matches++; } } Result.poly.erase(it1 + 1, it1 + (nr_matches + 1)); } return Result; } Also here's SortDescending: struct SortDescending { bool operator()(const term& t1, const term& t2) { return t2.pow < t1.pow; } }; What did i do wrong? Thanks!

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  • c++ overloading delete, retrieve size

    - by user300713
    Hi, I am currently writing a small custom memory Allocator in c++, and want to use it together with operator overloading of new/delete. Anyways, my memory Allocator basicall checks if the requested memory is over a certain threshold, and if so uses malloc to allocate the requested memory chunk. Otherwise the memory will be provided by some fixedPool allocators. that generally works, but for my deallocation function looks like this: void MemoryManager::deallocate(void * _ptr, size_t _size){ if(_size heapThreshold) deallocHeap(_ptr); else deallocFixedPool(_ptr, _size); } so I need to provide the size of the chunk pointed to, to deallocate from the right place. No the problem is that the delete keyword does not provide any hint on the size of the deleted chunk, so I would need something like this: void operator delete(void * _ptr, size_t _size){ MemoryManager::deallocate(_ptr, _size); } But as far as I can see, there is no way to determine the size inside the delete operator.- If I want to keep things the way it is right now, would I have to save the size of the memory chunks myself? Any ideas on how to solve this are welcome! Thanks!

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  • Friends, templates, overloading <<

    - by Crystal
    I'm trying to use friend functions to overload << and templates to get familiar with templates. I do not know what these compile errors are: Point.cpp:11: error: shadows template parm 'class T' Point.cpp:12: error: declaration of 'const Point<T>& T' for this file #include "Point.h" template <class T> Point<T>::Point() : xCoordinate(0), yCoordinate(0) {} template <class T> Point<T>::Point(T xCoordinate, T yCoordinate) : xCoordinate(xCoordinate), yCoordinate(yCoordinate) {} template <class T> std::ostream &operator<<(std::ostream &out, const Point<T> &T) { std::cout << "(" << T.xCoordinate << ", " << T.yCoordinate << ")"; return out; } My header looks like: #ifndef POINT_H #define POINT_H #include <iostream> template <class T> class Point { public: Point(); Point(T xCoordinate, T yCoordinate); friend std::ostream &operator<<(std::ostream &out, const Point<T> &T); private: T xCoordinate; T yCoordinate; }; #endif My header also gives the warning: Point.h:12: warning: friend declaration 'std::ostream& operator<<(std::ostream&, const Point<T>&)' declares a non-template function Which I was also unsure why. Any thoughts? Thanks.

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  • Conditional Operator Example

    - by mbcrump
    If you haven’t taken the time to learn conditional operators, then now is the time. I’ve added a quick and dirty example for those on the forums.   Code Snippet using System; using System.Net.Mail; using System.Net; using System.Globalization; using System.Windows.Forms;   class Demo {     //Please use conditional statements in your code. See example below.       public static void Main()     {         int dollars = 10;           //Bad Coder Bad !!! Don't do this         if (dollars == 1)         {             Console.WriteLine("Please deposit {0} dollar.", dollars);         }         else         {             Console.WriteLine("Please deposit {0} dollars.", dollars);         }             //Good Coder Good !!! Do this         Console.WriteLine("Please deposit {0} dollar{1}.", dollars, dollars == 1 ? ' ' : 's');         //                                                          expression   ? true : false           Console.ReadLine();          } }

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  • Showplan Operator of the Week – BookMark/Key Lookup

    Fabiano continues in his mission to describe the major Showplan Operators used by SQL Server's Query Optimiser. This week he meets a star, the Key Lookup, a stalwart performer, but most famous for its role in ill-performing queries where an index does not 'cover' the data required to execute the query. If you understand why, and in what circumstances, key lookups are slow, it helps greatly with optimising query performance.

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  • LINQ and the use of Repeat and Range operator

    - by vik20000in
    LINQ is also very useful when it comes to generation of range or repetition of data.  We can generate a range of data with the help of the range method.     var numbers =         from n in Enumerable.Range(100, 50)         select new {Number = n, OddEven = n % 2 == 1 ? "odd" : "even"}; The above query will generate 50 records where the record will start from 100 till 149. The query also determines if the number is odd or even. But if we want to generate the same number for multiple times then we can use the Repeat method.     var numbers = Enumerable.Repeat(7, 10); The above query will produce a list with 10 items having the value 7. Vikram

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  • Operator of the Week - Spools, Eager Spool

    For the fifth part of Fabiano's mission to describe the major Showplan Operators used by SQL Server's Query Optimiser, he introduces the spool operators and particularly the Eager Spool, explains blocking and non-blocking and then describes how the Halloween Problem is avoided.

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  • Showplan Operator of the week - Assert

    As part of his mission to explain the Query Optimiser in practical terms, Fabiano attempts the feat of describing, one week at a time, all the major Showplan Operators used by SQL Server's Query Optimiser to build the Query Plan. He starts with Assert

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  • Ruby: if statement using regexp and boolean operator [migrated]

    - by bev
    I'm learning Ruby and have failed to make a compound 'if' statement work. Here's my code (hopefully self explanatory) commentline = Regexp.new('^;;') blankline = Regexp.new('^(\s*)$') if (line !~ commentline || line !~ blankline) puts line end the variable 'line' is gotten from reading the following file: ;; alias filename backupDir Prog_i Prog_i.rb ./store Prog_ii Prog_ii.rb ./store This fails and I'm not sure why. Basically I want the comment lines and blank lines to be ignored during the processing of the lines in the file. Thanks for your help.

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  • Showplan Operator of the Week – BookMark/Key Lookup

    Fabiano continues in his mission to describe the major Showplan Operators used by SQL Server's Query Optimiser. This week he meets a star, the Key Lookup, a stalwart performer, but most famous for its role in ill-performing queries where an index does not 'cover' the data required to execute the query. If you understand why, and in what circumstances, key lookups are slow, it helps greatly with optimising query performance.

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  • Purpose of overloading operators in C++?

    - by Geo Drawkcab
    What is the main purpose of overloading operators in C++? In the code below, << and >> are overloaded; what is the advantage to doing so? #include <iostream> #include <string> using namespace std; class book { string name,gvari; double cost; int year; public: book(){}; book(string a, string b, double c, int d) { a=name;b=gvari;c=cost;d=year; } ~book() {} double setprice(double a) { return a=cost; } friend ostream& operator <<(ostream& , book&); void printbook(){ cout<<"wignis saxeli "<<name<<endl; cout<<"wignis avtori "<<gvari<<endl; cout<<"girebuleba "<<cost<<endl; cout<<"weli "<<year<<endl; } }; ostream& operator <<(ostream& out, book& a){ out<<"wignis saxeli "<<a.name<<endl; out<<"wignis avtori "<<a.gvari<<endl; out<<"girebuleba "<<a.cost<<endl; out<<"weli "<<a.year<<endl; return out; } class library_card : public book { string nomeri; int raod; public: library_card(){}; library_card( string a, int b){a=nomeri;b=raod;} ~library_card() {}; void printcard(){ cout<<"katalogis nomeri "<<nomeri<<endl; cout<<"gacemis raodenoba "<<raod<<endl; } friend ostream& operator <<(ostream& , library_card&); }; ostream& operator <<(ostream& out, library_card& b) { out<<"katalogis nomeri "<<b.nomeri<<endl; out<<"gacemis raodenoba "<<b.raod<<endl; return out; } int main() { book A("robizon kruno","giorgi",15,1992); library_card B("910CPP",123); A.printbook(); B.printbook(); A.setprice(15); B.printbook(); system("pause"); return 0; }

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  • How does delete deal with pointer constness?

    - by aJ
    I was reading this question Deleting a const pointer and wanted to know more about delete behavior. Now, as per my understanding: delete expression works in two steps: invoke destructor then releases the memory (often with a call to free()) by calling operator delete. operator delete accepts a void*. As part of a test program I overloaded operator delete and found that operator delete doesn't accept const pointer. Since operator delete does not accept const pointer and delete internally calls operator delete, how does Deleting a const pointer work ? Does delete uses const_cast internally?

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  • Why would the assignment operator ever do something different than its matching constructor?

    - by Neil G
    I was reading some boost code, and came across this: inline sparse_vector &assign_temporary(sparse_vector &v) { swap(v); return *this; } template<class AE> inline sparse_vector &operator=(const sparse_vector<AE> &ae) { self_type temporary(ae); return assign_temporary(temporary); } It seems to be mapping all of the constructors to assignment operators. Great. But why did C++ ever opt to make them do different things? All I can think of is scoped_ptr?

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  • Why does javascript's "in" operator return true when testing if 0 exists in an array that doesn't co

    - by Mariano Peterson
    For example, this returns true, and makes sense: var x = [1,2]; 1 in x; // true This returns false, and makes sense: var x = [1,2]; 3 in x; // false However this returns true, and I don't understand why: var x = [1,2]; 0 in x; You can quickly test it by putting this in your browser's address bar: javascript:var x=[1,2]; alert(0 in x); Why does the "in" operator in Javascript return true when testing if "0" exists in array, even when the array doesn't appear to contain "0"?

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  • subclassing QList and operator+ overloading

    - by Milen
    I would like to be able to add two QList objects. For example: QList<int> b; b.append(10); b.append(20); b.append(30); QList<int> c; c.append(1); c.append(2); c.append(3); QList<int> d; d = b + c; For this reason, I decided to subclass the QList and to overload the operator+. Here is my code: class List : public QList<int> { public: List() : QList<int>() {} // Add QList + QList friend List operator+(const List& a1, const List& a2); }; List operator+(const List& a1, const List& a2) { List myList; myList.append(a1[0] + a2[0]); myList.append(a1[1] + a2[1]); myList.append(a1[2] + a2[2]); return myList; } int main(int argc, char *argv[]) { QCoreApplication a(argc, argv); List b; b.append(10); b.append(20); b.append(30); List c; c.append(1); c.append(2); c.append(3); List d; d = b + c; List::iterator i; for(i = d.begin(); i != d.end(); ++i) qDebug() << *i; return a.exec(); } , the result is correct but I am not sure whether this is a good approach. I would like to ask whether there is better solution?

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