Question

I don’t understand why I am getting compiler errors when trying to compile this:

void* MemoryManagedObject::operator new(size_t size, bool UseMemPool)
{
    Engine* engine = Engine::GetEngine();
    void* alloc;

    alloc = engine->GetMemoryManager()->Allocate(size, UseMemPool);

    if (alloc && UseMemPool)
        mAllocatedWithMemPool = true;

    return alloc;
}

It says “invalid use of member MemoryManagedObject::mAllocatedWithMemPool in static member function”.

Basically, I have a flag that states whether I used my memory pool or just malloc() when allocating the class instance, and I want to set it when I override ‘new’.

I guess the ‘new’ method must return before you can use the class instance? Is there any way around this?

EDIT: Just curious, ss this code a valid solution as well?

void* MemoryManagedObject::operator new(size_t size, bool UseMemPool)
{
    Engine* engine = Engine::GetEngine();
    MemoryManagedObject* alloc;

    alloc = (MemoryManagedObject*)engine->GetMemoryManager()->Allocate(size, UseMemPool);

    if (alloc && UseMemPool)
        alloc->mAllocatedWithMemPool = true;

    return alloc;
}

Answer 1

Every overload for operator new() (and operator delete()) is implicitly and automatically declared static. This is a special rule in C++.

Therefore, you should design your class such that the constructor can also remember how it was allocated, if you need to retain that information:

Foo * p = new (true) Foo(true);

That is, your class would look like this:

class Foo
{
    bool mAllocatedWithMemPool;
public:
    static void * operator new(std::size_t n, bool usePool);
    static void operator delete(bool) throw();
    explicit Foo(bool usePool);
    /* ... */
};

Note that you should always declare the matching delete operator, even though its use is very limited.