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January 29 C++ overloading operator& ( Or Find the addess of a object)Recently a friend of mine ( name : rejeesh ) asked me "how to find the address of an object if the & operator is overloaded" ?
Example class is like this
class AddressBlocker
{
public :
AddressBlocker* operator &() { return 0; }
};
so if you try to execute a code like this
AddressBlocker op;
AddressBlocker* Pt = &op;
Pt will be NULL. Pt = &op will not pass the real address of op to Pt. Because the operator is overloaded.
So how to get the address ??
When he asked me it, i found two solutions with templates . One deriving a new class from the required class , and the second one is
more tricky. I will explain ( by showing the code) here both two methods. Method 1. template<typename T> class Addressfinder : public T { public: Addressfinder* operator&() { return this; } }; and you use it like this AddressBlocker blockMe; Addressfinder<AddressBlocker >& finder = static_cast<Addressfinder<AddressBlocker >&> ( blockMe ); and address can be retrieved by simple "AddressBlocker* pValid = &finder;" . This will work since i overloaded the &operator in Addressfinder class. Method 2. I think this is more good compared to the above. Since it is not creating any more relationships with the classes. and also no need for casting to use it. template <typename T> class AddressfinderII { T& tOb; public: AddressfinderII(T& t): tOb(t){} T * operator&() { return reinterpret_cast<T*> ( *reinterpret_cast<int *>( this ) ); } }; usage is like this AddressBlocker blocker; AddressfinderII<AddressBlocker > finderII(blocker); AddressBlocker * pAddress = &finderII; if you look the size of this class , it just 4 bytes. because storing reference is same as pointer. The class object's memory will have just the real address of object. And i extracted that value in operator& and returned. Ok.. There is a more convenient way , he told me . and it is used in boost libraries. anyway i could find some alternatives  Method 3 template<typename T> T* addessof(T& t) { return reinterpret_cast<T*>(& reinterpret_cast<int&> ( t ) ); } and can be use like addressof( blocker); it is more convenient. it has similarities with method 1. So now no more address hiding.. |
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