Get a Reference to an Object's Monitor

[bearophile]

Timon Gehr:

> The vptr is used to implement dynamic method calls.
> Therefore it might not correspond to the static type of
> the reference and has to be an instance attribute.

Right. In that old enhancement request I was asking for __vptr to be both a class attribute and instance attribute.


> Why would you have to manipulate vptr?

To quickly know what's the class of a class instance that's on the heap, to avoid structs because I sometimes need virtual methods, and avoid initializing another field just for this purpose. It's for a special usage.


> You can use typeid to compare 
> instances for identity of their corresponding type.

I think I need something more light.


> Anyway, to get the vptr of a class C, do this:
> 
> void** vptr = typeid(C).vtbl.ptr;

I will compare this to the solution I have used to safe.
Creating a class instance of TypeInfo just to know the value of what it looks like a static field (the head of the virtual table) seems strange.

Bye,
bearophile