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derek7

IUnknown::AddRef

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it's only a reference counter, AddRef increase by one a 32 bit internal member, Release decrease by one. When no reference from outside the object is deleted from memory

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Take a look at the DirectX SDK documentation at:

The DirectX Software Development Kit ->
DirectX Programming Guide ->
Using COM


IUnknown is the base class for all COM objects. All COM objects are "reference counted".

AddRef adds 1 to the reference count for an object. When you call Release() on an object, 1 is subtracted from its reference count; the object is only destroyed when its reference count is at 0.

in pseudo-code:


class IUnknown
{
public:
virtual AddRef() = 0;
virtual Release() = 0;
...
}

class IDirect3DBlah : public IUnknown
{
public:
AddRef();
Release();
...
private:
int m_refCount;
}

IDirect3DBlah::AddRef()
{
m_refCount++;
}

IDirect3DBlah::Release()
{
m_refCount--;
if (m_refCount == 0)
{
delete this object
}
}



Calling AddRef on an object directly can be useful to prevent it from being destroyed unexpectedly when you don't have control over the code which created the interface.

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