C++ Using the “this” pointer as a normal pointer

Question

I am currently trying to use the "this" pointer to pass a pointer to a function:

void GameObject::process_events()
{
    std::vector<ObjectEvent*>::iterator it;
    for (it = events.begin(); it != events.end(); it++)
        (*it)->process(this);
}

Class ObjectEvent
{
private:
    bool* trigger;
    void (*response)(GameObject*);
public:
    process(GameObject* obj)
    {
        if (*trigger)
            response(obj);
    }
};

But I get an error:

No matching function call to 'ObjectEvent::process(GameObject* const)'

What could be the problem?

Answer 1

Judging by your error message, process_events() appears to actually be a const function.

void GameObject::process_events() const
{
    process(this);
}

If so, then this is a const pointer and process() must take a const GameObject * . Otherwise process() could modify the point that gets passed to it, which violates process_events's promise not to modify this .

void process(const GameObject* obj);

Alternatively, remove the const modifier from process_events().

Answer 2

If the member function you're returning this from or using this in is const , then it will be a const pointer. If the member function is not declared const , the pointer won't be either.

void GameObject::process_events()
{
    // ...
    process(this); // 'this' is NOT a const pointer
}

void GameObject::process_events() const
{
    // ...
    process(this); // 'this' IS a const pointer
}