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Wednesday, 16 December 2015

Smart Pointers

The misuse of pointers is a major source of bugs: the constant allocation, deallocation and referencing that must be performed by a program written using pointers introduces the risk that memory leaks will occur. Smart pointers try to prevent memory leaks by making the resource deallocation automatic: when the pointer (or the last in a series of pointers) to an object is destroyed, for example because it goes out of scope, the referenced object is destroyed too.
Smart Pointer Implementation:
template
class SmartPointer
{
public:
SmartPointer(T * ptr)
{
ref = ptr;
ref_count = (unsigned*)malloc(sizeof(unsigned));
*ref_count = 1;
}
SmartPointer(SmartPointer & sptr)
{
ref = sptr.ref;
ref_count = sptr.ref_count;
++*ref_count;
}
SmartPointer & operator=(SmartPointer & sptr)
{
if (this != &sptr)
{
ref = sptr.ref;
ref_count = sptr.ref_count;
++*ref_count;
}
return *this;
}
~SmartPointer()
{
--*ref_count;
if (*ref_count == 0) {
delete ref;
free(ref_count);
ref = NULL;
ref_count = NULL;
}
}
T getValue()
{
return *ref;
}
protected:
T * ref;
unsigned * ref_count;
};
How to use smart pointer:
class Widget
{
public:
void Fun();
};
SmartPointer sp(new Widget);
sp->Fun();
(*sp).Fun();

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