How to avoid successive deallocations/allocations in C++?

Question

Consider the following code:

class A
{
    B* b; // an A object owns a B object

    A() : b(NULL) { } // we don\'t know what b will be when constructing A

             


        

Answer 1

I'd go with boost::scoped_ptr here:

class A: boost::noncopyable
{
    typedef boost::scoped_ptr b_ptr;
    b_ptr pb_;

public:

    A() : pb_() {}

    void calledVeryOften( /*…*/ )
    {
        pb_.reset( new B( params )); // old instance deallocated
        // safely use *pb_ as reference to instance of B
    }
};

No need for hand-crafted destructor, A is non-copyable, as it should be in your original code, not to leak memory on copy/assignment.

I'd suggest to re-think the design though if you need to re-allocate some inner state object very often. Look into Flyweight and State patterns.