Question

I’m trying to (and have solved) a problem with 16 byte alignment issues with a class that contains SSE optimised members. But what is bugging me is a large portion of the examples I have found online contain a line of code that to me seems totally redundant yet is repeated in many places.

public:
void* operator new (size_t size)throw (std::bad_alloc)
{
    void * p = _aligned_malloc(size, 16);
    if (p == 0)  throw std::bad_alloc();
    return p; 
}

void operator delete (void *p)
{
    Camera* pC = static_cast<Camera*>(p);
    _aligned_free(p);
}

The line in question is

Camera* pC = static_cast<Camera*>(p);

As pC is never referenced and goes out of scope at the end of the function, what is the point of doing it? I have tried taking the line out and it appears to make no difference at all yet that line appears in lots of examples! Am I missing something really obvious or has an anomalous line of code been copied from example to example blindly and become prevalent across a lot of “tutorials”?

Answer 1

The object ends its lifetime as soon as the destructor is entered, so you cannot do much with this pointer. The line Camera* pC = static_cast<Camera*>(p); can be removed safely and the only reason it exists in tutorials is that many people just copy-n-paste the code here and there without actually thinking how it works.

The clean and correct code for your delete() will look as follows:

void operator delete (void *p)
{
    _aligned_free(p);
}